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Subject: "DX cropping factor?" Previous topic | Next topic
dnf777 Registered since 08th Jan 2009Fri 01-Jan-10 05:10 PM
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"DX cropping factor?"


Franklin, US
          

If I may bare my ignorance again....
I understand the smaller imaging area of the DX format. When using a standard lens that projects an image larger than the sensor, you get an approximate 1.5x cropped magnification. So along comes lenses designed for DX format usage, that project a smaller image to match the sensor (as well as collomated to more parallel light to supposedly reduce distortion). Shouldn't a matched image and sensor when using a DX lens on a DX camera negate the magnification factor? (I did try to search for this answer, but came up empty...I know there's been numerous similar threads though)

Dave F
Franklin, Pa

"Always do right. You'll gratify some, and astound the rest." Mark Twain

  

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aolander Silver Member
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aolander Silver Member Nikonian since 15th Sep 2006Fri 01-Jan-10 07:38 PM
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#1. "RE: DX cropping factor?"
In response to Reply # 0
Fri 01-Jan-10 07:41 PM by aolander

Nevis, US
          

An FX lens projects an image circle much larger than a DX sensor needs. The DX lens projects an image circle just large enough to cover a DX sensor. The sensor is the same size in both cases, so same field of view for a given focal length whether the lens is DX or FX. But there is still the crop factor when comparing DX sensors to FX sensors. It's a sensor thing, not a lens thing.

Alan

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dnf777 Registered since 08th Jan 2009Sat 02-Jan-10 02:23 AM
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#3. "RE: DX cropping factor?"
In response to Reply # 1


Franklin, US
          

Ya got me confused on that one. The DX sensor is 16x24mm. The FX is 24x36mm. I thought that is where you got the cropping of the FX image by the smaller sensor, yielding an effective 1.5x image. When using a DX lens which projects a smaller image to match the smaller sensor size, it would seem the 1.5 crop is negated, as they are matched in size.

Dave F
Franklin, Pa

"Always do right. You'll gratify some, and astound the rest." Mark Twain

  

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dclarhorn Moderator In depth knowledge and high level skills in a variety of areas including landscape Nikonian since 31st Mar 2002Fri 01-Jan-10 11:31 PM
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#2. "RE: DX cropping factor?"
In response to Reply # 0


Berwyn Heights, US
          

There is no magnification, just a crop. DX lenses are constructed and optimized for that smaller size opening, but there is no magnification factor. It's more about FOV (field of view). Simply apply the math, x1.5, when using either DX or FX formatted lenses on your DX dslr.

Dan L.
http://www.danlarussophotography.com/

  

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wa_moses Registered since 07th Apr 2009Sat 02-Jan-10 03:51 AM
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#4. "RE: DX cropping factor?"
In response to Reply # 0


Houston, US
          

>Shouldn't a matched image and sensor when using a DX lens on a
>DX camera negate the magnification factor?

Dave, I think I understand where you are coming from.

The fact that the DX lens projects an image closely matched with the smaller DX sensor indeed means that there is no 'cropping' per se going on.

However, that does not mean that a 75 mm DX lens is now a true 75 mm lens, because there is no cropping. Since the standard is still the FX format, then the 75 mm lens is still viewed as being equivalent to a 50 mm 'standard' lens.

Regards
Wayne


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Socrates Silver Member Nikonian since 01st Apr 2008Sat 02-Jan-10 05:55 AM
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#5. "RE: DX cropping factor?"
In response to Reply # 4


US
          

>>Shouldn't a matched image and sensor when using a DX lens
>on a
>>DX camera negate the magnification factor?
>
>Dave, I think I understand where you are coming from.
>
>The fact that the DX lens projects an image closely matched
>with the smaller DX sensor indeed means that there is no
>'cropping' per se going on.
>
>However, that does not mean that a 75 mm DX lens is now a true
>75 mm lens, because there is no cropping. Since the standard
>is still the FX format, then the 75 mm lens is still viewed as
>being equivalent to a 50 mm 'standard' lens.

Absolutely untrue. 75mm is 75mm, period. With different sized sensors, the FoV will differ but that does not change the focal length of the lens.

  

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rbertalotto Registered since 25th Nov 2009Sat 02-Jan-10 12:06 PM
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#6. "RE: DX cropping factor?"
In response to Reply # 5
Sat 02-Jan-10 12:22 PM by rbertalotto

North Dartmouth, US
          

"Absolutely untrue. 75mm is 75mm, period. With different sized sensors, the FoV will differ but that does not change the focal length of the lens."


Wow! This is like saying "there is no Santa Clause". Everything I've read says there is a a telephoto advantage to a DX camera and it amounts to a 1.5X "DX Factor"

I was sold a 35mm lens for my D90 because it will perform like a 50mm on a 35mm film camera or a FX digital camera. (That 35mm sure does look like the 50mm on my wife's N90 film camera)

I'm told my 80-200mm is really a 120mm-300mm (Sure as heck looks like it to my eyes)


"Say it isn't so Virginia!"

RoyB
Dartmouth, MA
www.rvbprecision.com

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rbertalotto Registered since 25th Nov 2009Sat 02-Jan-10 12:16 PM
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#7. "RE: DX cropping factor?"
In response to Reply # 6
Sat 02-Jan-10 12:24 PM by rbertalotto

North Dartmouth, US
          

OK, just found this on Wikpedia.........

"The crop factor is sometimes referred to as "magnification factor",<2> "focal length factor" or "focal length multiplier".<3> This usage reflects the observation that lenses of a given focal length seem to produce greater magnification on crop-factor cameras than they do on full-frame cameras. This is an advantage in, for example, bird photography, where photographers often strive to get the maximum "reach". A camera with a smaller sensor can be preferable to using a teleconverter, because the latter affects the focal ratio of the lens, which can degrade the performance of the autofocus.

It should be noted that the lens casts the same image no matter what camera it is attached to. The extra "magnification" occurs when the image is enlarged more to produce output (print or screen) that matches the output size of a full-frame camera. That is, the magnification as usually defined, from subject to focal plane, is unchanged, but the system magnification from subject to final output is increased."

Read more here:
http://en.wikipedia.org/wiki/Crop_factor

SOOOO..... Mr. Socrates is correct in one way. The Focal Length of the lens DOES NOT CHANGE.....a 300mm lens is always a 300mm lens. But when used on a DX body, the magnification "factor" changes by about 1.5X........

RoyB
Dartmouth, MA
www.rvbprecision.com

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rbertalotto Registered since 25th Nov 2009Sat 02-Jan-10 12:21 PM
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#8. "RE: DX cropping factor?"
In response to Reply # 7
Sat 02-Jan-10 12:26 PM by rbertalotto

North Dartmouth, US
          

With regards to:

"However, that does not mean that a 75 mm DX lens is now a true 75 mm lens, because there is no cropping. Since the standard is still the FX format, then the 75 mm lens is still viewed as being equivalent to a 50 mm 'standard' lens."

I believe I NOW understand where Mr Socrates was coming from. His reference was to the above quote.

As I understand it and Mr Socrates stated, a 75mm lens on an FX format camera, is the same as a 75mm lens on a 35mm Film Camera. There is no "DX Crop Factor".

In this case, " a 75mm lens is a 75mm lens"......no math required.

Fhew!....Next thing they would be telling me is there is no Easter Bunny!

RoyB
Dartmouth, MA
www.rvbprecision.com

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elec164 Silver Member Nikonian since 15th Jan 2009Sat 02-Jan-10 01:24 PM
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#10. "RE: DX cropping factor?"
In response to Reply # 8
Sat 02-Jan-10 01:48 PM by elec164

US
          

Be careful what you read on the web for as Socrates says “75mm is 75mm”.

Think of it this way; within the FX image is the DX capture. If you crop about 50% of the center portion of the FX image frame and enlarge that you have the DX capture DOF and all. The difference between the two at that point would only be the spatial resolution. Being that the pixel density is greater on the DX camera it theoretically can capture finer detail.

Edited to add:
I need to clarify my statement about spatial resolution. For actually that may or may not be true for a given camera comparison. It would be true if both sensors are the same pixel count. Say for instance we take an enlarged crop of the D3s image and an image from the D300 then the spatial resolution of the D300 would be greater. But if we took an enlarged crop of the D3X and an image from the D300 then you would essentially have the same image.

So as you see there is really no reach advantage with the DX format.


Pete

Pete

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wa_moses Registered since 07th Apr 2009Sat 02-Jan-10 01:16 PM
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#9. "RE: DX cropping factor?"
In response to Reply # 5


Houston, US
          

>Absolutely untrue. 75mm is 75mm, period. With different
>sized sensors, the FoV will differ but that does not change
>the focal length of the lens.

While I agree with you that in the absolute and technical sense a 75 mm is a 75 mm (that is the focal length after all), I stand by my point.

The point that I was trying (unsuccessfully it appears) to get across is that according to convention (the convention being based on a view as presented by the 35mm / FX world) the 75 mm is 'really a 50 mm' from the 35 mm standpoint. You know, the same standpoint that the 35 mm film purists might use when they dismissively state that film is the only way to go.

That is what this whole notion about magnification and crop factor is all about, and that was my point. Without the basis as stated (say there was never any 35 mm / FX sensor sized camera) there would be no magnification or crop factor, would there?

Regards
Wayne


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dnf777 Registered since 08th Jan 2009Sat 02-Jan-10 01:27 PM
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#11. "RE: DX cropping factor?"
In response to Reply # 9


Franklin, US
          


>That is what this whole notion about magnification and crop
>factor is all about, and that was my point. Without the basis
>as stated (say there was never any 35 mm / FX sensor sized
>camera) there would be no magnification or crop factor, would
>there?


Right. So I'm back to my original thought. If a DX formatted lens is used on a DX sized sensor, there is no cropping, and therefore no effective magnification? The cropping occurs only when the larger FX image projected by and FX lens hits the smaller DX sensor, and is cropped. I agree, a 75mm lense is a 75mm lens....the two formats just collimate and project a different size image onto the sensor.

Dave F
Franklin, Pa

"Always do right. You'll gratify some, and astound the rest." Mark Twain

  

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briantilley Moderator Deep knowledge of bodies and lens; high level photography skills Nikonian since 26th Jan 2003Sat 02-Jan-10 01:43 PM
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#12. "RE: DX cropping factor?"
In response to Reply # 11


Paignton, GB
          

There seems to be some confusion in this thread.

>So I'm back to my original thought. If a DX formatted lens
>is used on a DX sized sensor, there is no cropping, and
>therefore no effective magnification?

The 1.5x "crop factor" depends on the camera format (DX or FX), and is not affected by the type of lens. When mounted on a DX camera, a 50mm DX lens and a 50mm FX lens will each have the same angle of view as a 75mm (FX) lens would have when mounted on an FX camera.

Basically, Alan's post (reply #1) is perfectly correct, and really says all there is to say.

Brian
Welsh Nikonian

  

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elec164 Silver Member Nikonian since 15th Jan 2009Sat 02-Jan-10 01:59 PM
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#15. "RE: DX cropping factor?"
In response to Reply # 12


US
          

>When
>mounted on a DX camera, a 50mm DX lens and a 50mm FX lens will
>each have the same angle of view as a 75mm (FX) lens would
>have when mounted on an FX camera.
>

I believe that is incorrect and where all the confusion comes in. The AOV of a focal length does not change with a given format, just the captured FOV.

So at a given subject distance a 50mm lens on a DX camera will capture the same FOV as a 75mm lens on a FX camera. But the AOV on the 75mm lens on the FX camera is narrower then the AOV of the 50mm lens on the DX camera.

Perhaps this is what you really meant but was a misuse of the term.

Pete

Pete

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briantilley Moderator Deep knowledge of bodies and lens; high level photography skills Nikonian since 26th Jan 2003Sat 02-Jan-10 02:53 PM
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#16. "RE: DX cropping factor?"
In response to Reply # 15


Paignton, GB
          

I'm afraid you are adding to the confusion...

What do you mean by the term "angle of view"? I think you may be confusing it with "angle of coverage", as explained at Wikipedia here.

The Wikipedia definition of "angle of view" is consistent with what I posted above.

You simply cannot define a lens' angle of view until you specify the format of the camera it is mounted upon.

Brian
Welsh Nikonian

  

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elec164 Silver Member Nikonian since 15th Jan 2009Sat 02-Jan-10 06:27 PM
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#26. "RE: DX cropping factor?"
In response to Reply # 16
Sat 02-Jan-10 08:02 PM by elec164

US
          

I was going by the way it is explained in John Hedgecoe’s ‘The new manual of PHOTOGRAPHY’.

There is a diagram of focal lengths and angle at which they extend outward. So perhaps I miss understood what it meant. Thanks for the clarification.

Pete

Edited to add: Ok it seems I remembered what I read in Hedgecoe’s book incorrectly for a small statement included with the diagram clearly states that those were the angle of view when the focal lengths were mounted to a 35mm body.

So let me restate the concepts with the proper terms as you have patiently been trying to explain to us to make sure I don’t make the same error in explanation.

While the angle of coverage of a lens of a particular focal length is fixed by its design, the angle of view is dependent on the size of the capture medium. So a 50mm FX lens will provide the same angle of coverage whether its mounted to an FX or DX body but the DX body will capture a much narrower angle of view. To achieve the same angle of view of the DX camera for a given subject distance you would need to use a 75mm lens on the FX camera which provides a narrower angle of coverage.

Did I get that correct or am I still confused!!

Pete

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briantilley Moderator Deep knowledge of bodies and lens; high level photography skills Nikonian since 26th Jan 2003Sat 02-Jan-10 08:52 PM
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#28. "RE: DX cropping factor?"
In response to Reply # 26


Paignton, GB
          

I think you've got it

Brian
Welsh Nikonian

  

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dnf777 Registered since 08th Jan 2009Sat 02-Jan-10 03:06 PM
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#17. "RE: DX cropping factor?"
In response to Reply # 12


Franklin, US
          

Brian,
I understand what you're saying, but let me put the question another way, to see if it clarifies my question.

Any two lenses of the same focal length are still the same focal length. I understand that. They just project a different sized image onto the sensor. But that difference in size is what creates both the vignetting (dx lense on fx camera) and cropping effect (fx lens on dx sesnor). So why does using a dx lens on a dx camera still result in the 1.5 cropping effect, if the image and sensor are the same size?

Figuring out the semantics and the optics/mechanics of this question is my quest for 2010!

Dave F
Franklin, Pa

"Always do right. You'll gratify some, and astound the rest." Mark Twain

  

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briantilley Moderator Deep knowledge of bodies and lens; high level photography skills Nikonian since 26th Jan 2003Sat 02-Jan-10 03:39 PM
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#21. "RE: DX cropping factor?"
In response to Reply # 17


Paignton, GB
          

>I understand what you're saying, but let me put the question
>another way, to see if it clarifies my question.

No problem - I know this can be a confusing subject, and there is sadly a lot of misinformation and misunderstanding about it out there on the web

>Any two lenses of the same focal length are still the same
>focal length. I understand that.

Yes, that's a given.

>They just project a different sized image onto the sensor.

The way you have phrased that may indicate where the misunderstanding lies. I'll try to clarify...

Take a 50mm FX lens on an FX camera. The "cone" of light emerging from the back of the lens covers the whole of the FX frame. If you mount the same lens on a DX camera, the angle of the cone of light produced does not change, but the outer parts of it don't hit the smaller sensor, so the image that is recorded is a smaller area of the scene. That is the cropping effect of the DX sensor.

Now take a 50mm DX lens. The cone of light emerging from this lens is narrower (typically) than that from the 50mm FX lens; it will be just wide enough to cover the DX frame. But the critical point is that the area of the scene that is recorded is exactly the same as the part you had with the 50mm FX lens on the DX camera, and both would be the same area as you would get from a 75mm lens on an FX camera.

>Figuring out the semantics and the optics/mechanics of this
>question is my quest for 2010!

I'm sure that between us all we'll get you there

Brian
Welsh Nikonian

  

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rbertalotto Registered since 25th Nov 2009Sat 02-Jan-10 03:44 PM
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#22. "RE: DX cropping factor?"
In response to Reply # 21


North Dartmouth, US
          

Sometimes a slide show is worth a 1000 words...

http://www.slideshare.net/lokerd/dx-crop-factor-presentation

RoyB
Dartmouth, MA
www.rvbprecision.com

Visit my Nikonians gallery.

  

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rbertalotto Registered since 25th Nov 2009Sat 02-Jan-10 03:47 PM
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#23. "RE: DX cropping factor?"
In response to Reply # 22


North Dartmouth, US
          

And this
http://www.slideshare.net/joelk/week-3-lens-and-focal-lenghts

RoyB
Dartmouth, MA
www.rvbprecision.com

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dnf777 Registered since 08th Jan 2009Sat 02-Jan-10 04:05 PM
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#24. "RE: DX cropping factor?"
In response to Reply # 21


Franklin, US
          


>Now take a 50mm DX lens. The cone of light emerging from this
>lens is narrower (typically) than that from the 50mm FX lens;
>it will be just wide enough to cover the DX frame. But the
>critical point is that the area of the scene that is recorded
>is exactly the same as the part you had with the 50mm
>FX lens on the DX camera, and both would be the same
>area as you would get from a 75mm lens on an FX camera.

Ok, THAT nailed it! Thank you.

I've really come full circle on this, as that is what I suspected in the first place, but the sematics tripped me up.

We have more snow pouring out of the clouds, on top of the 20 or so inches already on the ground. Now it's time to go shoot!

Thanks to Brain, and all who helped out.

Dave F
Franklin, Pa

"Always do right. You'll gratify some, and astound the rest." Mark Twain

  

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briantilley Moderator Deep knowledge of bodies and lens; high level photography skills Nikonian since 26th Jan 2003Sat 02-Jan-10 04:12 PM
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#25. "RE: DX cropping factor?"
In response to Reply # 24


Paignton, GB
          

>Ok, THAT nailed it! Thank you.

Great! Happy to be of service

Brian
Welsh Nikonian

  

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greenwing Gold Member Nikonian since 18th May 2006Sat 02-Jan-10 01:59 PM
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#14. "RE: DX cropping factor?"
In response to Reply # 9


Yorkshire, GB
          

>>Absolutely untrue. 75mm is 75mm, period. With
>different
>>sized sensors, the FoV will differ but that does not
>change
>>the focal length of the lens.
>
>While I agree with you that in the absolute and technical
>sense a 75 mm is a 75 mm (that is the focal length after all),
>I stand by my point.
>
>The point that I was trying (unsuccessfully it appears) to get
>across is that according to convention (the convention being
>based on a view as presented by the 35mm / FX world) the 75 mm
>is 'really a 50 mm' from the 35 mm standpoint. You know, the
>same standpoint that the 35 mm film purists might use when
>they dismissively state that film is the only way to go.

Wayne, I think you're wrong any way you try to phrase it, because I think you have it the wrong way around. 75mm focal length is just that. A 75mm DX lens will produce the same image as a 75mm FX lens when either is mounted on a DX camera. On a 35mm film camera, it will produce the same image as a 75mm FX lens, except that it will vignette due to the smaller image circle. It's a bit more complicated with the Nikon FX DSLRs, because unlike the 35mm camera they are able to compensate for the smaller image circle of the DX lens by using only a DX-sized portion of the FX sensor, thus effectively making them into DX cameras when a DX lens is attached. A 50mm DX lens when mounted on an FX DSLR will produce an image similar to that produced by a 75mm FX lens on the same camera, but you'll have less pixels in the image and will have to enlarge it more.

What I'm saying is that the best idea is to know what the lenses you have will perform like on the camera bodies that you have, and not to worry about crop factors and the like, as they probably don't affect you.

>That is what this whole notion about magnification and crop
>factor is all about, and that was my point. Without the basis
>as stated (say there was never any 35 mm / FX sensor sized
>camera) there would be no magnification or crop factor, would
>there?

I have to say that the vast majority of people would be better off without any notion of a magnification or crop factor, since that leads to unnecessary confusion.

Chris

  

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wa_moses Registered since 07th Apr 2009Sat 02-Jan-10 03:16 PM
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#19. "RE: DX cropping factor?"
In response to Reply # 14


Houston, US
          

Chris said:

>Wayne, I think you're wrong any way you try to phrase it,
>because I think you have it the wrong way around.

We are arguing two points, as far as I can see, and I will leave it at that.

>What I'm saying is that the best idea is to know what the
>lenses you have will perform like on the camera bodies that
>you have, and not to worry about crop factors and the like, as
>they probably don't affect you.

That I agree with 100%.

Regards
Wayne


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rbertalotto Registered since 25th Nov 2009Sat 02-Jan-10 03:23 PM
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#20. "RE: DX cropping factor?"
In response to Reply # 19


North Dartmouth, US
          

The birds are closer and bigger on my 24" monitor with my 300mmF4 on my D90 than they are when the same lens is mounted on a D700.......And shown on the same monitor.

To me, that's magnification. Has nothing to do with monitor size. My D90 and that 300mm looks the same size "magnification" as a 500mm on a D700

RoyB
Dartmouth, MA
www.rvbprecision.com

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simonsi Registered since 17th Apr 2003Thu 07-Jan-10 09:25 PM
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#30. "RE: DX cropping factor?"
In response to Reply # 20


Auckland, NZ
          

>The birds are closer and bigger on my 24" monitor with my 300mmF4 on my D90 than they are when the same lens is mounted on a D700.......And shown on the same monitor.
>
>To me, that's magnification. Has nothing to do with monitor size. My D90 and that 300mm looks the same size "magnification" as a 500mm on a D700

Yes, they are 150% bigger because you have enlarged both images to the same physical (not pixel) dimensions (ie the size of your monitor).

Cheers

Simon

A UK Nikonian

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blw Moderator Awarded for his high level of expertise in various areas Nikonian since 18th Jun 2004Sat 02-Jan-10 01:59 PM
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#13. "RE: DX cropping factor?"
In response to Reply # 0
Sat 02-Jan-10 02:03 PM by blw

Richmond, US
          

Here's one way of thinking of this problem.

Take a 35mm camera, say a Nikon F5, but it doesn't matter which one. Put a 50mm lens on it, and mount it on a tripod. Mark the "tripod holes." Take a picture, develop it and make an 8x12 print from it. Simple so far.

Now take a DX camera, say a D90. Put it on the tripod and put the tripod in the tripod holes from the F5. Mount a 50mm lens (ideally the same one you used on the F5). Take the same picture and make an 8x12 print from it.

Now put them side by side. The one from the DX camera will appear to be taken with a longer lens. If you literally crop the print from the film camera to 5x7.5, you will see that the cropped print will look EXACTLY like the print from the DX camera, only it is 5 x 7.5" rather than 8x12".

In fact what you saw here was that the DX camera literally cropped off the outside 60% of the area of the 35mm frame. That's why the cropped film print looks the same, content-wise.

If you repeat the experiment with an FX camera of the same density as the DX camera - let's pick a D700, which is 12mp just like the D90 - you will discover a "special feature." First, the same relationship holds as did between 35mm film and DX - the sizes are the same, since FX and 35mm are the same size, and of course the DX camera didn't change so it is the same too. But what you will find in this case is that the DX camera put all 12mp of its sensor into that central 40%, rather than just 5mp as happened on the FX camera. So if your subject is only within that central 40%, if you make equal size prints, you'll get much better results from the DX camera than the FX. This is hardly surprising given 12mp vs 5mp.

However, it's not something that's inherent to DX. If we compare a 12mp DX camera like the D90 to the DX crop of a camera like the D3x, a different result appears. The DX crop of the 24mp D3x is 10mp, not 5mp. And while I'm sure someone can show me the critical differences in 24x36 prints made from 10mp and 12mp files (for example from a D200 and a D2x), in practice there is very little difference.

DX tends to have "more reach" for a given level of technology, ie 12mp vs 12mp. As an exercise for the reader, consider what happens comparing a 4mp DX camera to a 12mp FX camera operating in DX crop mode.

_____
Brian... a bicoastal Nikonian and Team Member

My gallery is online. Comments and critique welcomed any time!

  

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dnf777 Registered since 08th Jan 2009Sat 02-Jan-10 03:12 PM
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#18. "RE: DX cropping factor?"
In response to Reply # 13
Sat 02-Jan-10 03:54 PM by dnf777

Franklin, US
          

>
>DX tends to have "more reach" for a given level
>of technology
, ie 12mp vs 12mp. As an exercise for the
>reader, consider what happens comparing a 4mp DX camera to a
>12mp FX camera operating in DX crop mode.


That's the way I've come to look at it. That's a really good explanation. I was thinking along similar lines, in that if two people took the same picture through the same camera and lens, but then one looked at the picture on a 27 inch monitor back home, and the other through a 17 inch, would you call that magnification? No.

Also, the Dx format collimates the light rays into a more parallel orientation, so they strike the sensor at a 90 degree angle over a larger area, increasing the efficiency of the sensor, from what I understand.

I think most have a working knowledge of the formats, but get lost in the semantics. That's better than the other way around, when it comes to taking pictures.

Happy New Year's to all,

Dave F
Franklin, Pa

"Always do right. You'll gratify some, and astound the rest." Mark Twain

  

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ZoneV Silver Member Nikonian since 08th Jan 2005Sat 02-Jan-10 07:10 PM
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#27. "RE: DX cropping factor?"
In response to Reply # 0


US
          

If the OP or anyone reading this is still in the dark, I posted an answer to a similar question recently. Since cross-posting was prohibited last time I checked, I will link to it:

http://www.nikonians.org/forums/dcboard.php?az=show_topic&forum=146&topic_id=172735&mesg_id=172735&page=#172752

I hope this is helpful and that it will end the debate over magnification versus no magnification once and for all.

An undeniable paradox: To think that there is any such thing as an absolute rule is at worst naïve, and at best, shortsighted. There is no such thing as an always-true, all context- or situation-salient, absolute rule that always holds true…including this one!

  

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OMMBoy Silver Member Nikonian since 22nd Feb 2007Tue 05-Jan-10 07:27 PM
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#29. "RE: DX cropping factor?"
In response to Reply # 0


San Diego, US
          

AAARGH! MY BRAIN HURTS!

Chris

_________________________________
The camera doesn't make a bit of difference. All of them can record what you are seeing. But, you have to SEE.
Ernst Haas, 1985


Runfola Photography Gallery

  

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Bluewaterhooker0 Registered since 31st Jan 2009Sat 09-Jan-10 04:51 AM
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#31. "RE: DX cropping factor?"
In response to Reply # 0


Tampa, US
          

Two Cents.
Having shot many formats over the years, one realizes that a "normal" lens on one format is not "normal" on another. I have used 35mm, 6x6cm, and 4x5 formats. A normal lens is one that approximates the feild of view of human vision. Thus "normal". A 35mm format uses a 50mm lens as "normal". For 6x6cm, an 80mm lens was considered standard. On 4x5, approximately 150mm was considered standard. As can be seen, as the film format size (sensor size) was reduced, the "normal" lens size followed. Thus on the reduced DX sensor format, a 35mm lens would qualify as "normal", as it will produce approximately the same feild of view in terms of human vision as the 50mm/35mm, 80mm/6x6, and 150mm/4x5 lenses. I think the confusion comes from the fact that these "new fangled" SLR's look and feel like a 35mm film camera. However, they should have been sold as what, 27mm SLR's ?

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Alx Registered since 19th Nov 2005Sat 09-Jan-10 05:32 PM
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#32. "RE: DX cropping factor?"
In response to Reply # 31
Sat 09-Jan-10 05:45 PM by Alx

Nashville, US
          

I can't believe this is so hard for anybody to understand.

Without repeating any of the excellent replies and explanatons, it is just a matter of clear thinking, both about the technical realities and the terminology.

One other truth about lenses that is mainly misunderstood is that different focal length lenses do not provide different perspectives.
This is really an adjunct concept to the FX/DX differences.
Image perspective is only affected by distance, from the camera to the subject, NOT by the focal length of the lens used.

In other words, an image taken at 100 feet from the subject with a 24mm wide angle lens will have exactly the same perspective as if it was shot with a 400mm lens from that distance. If the wide angle image is cropped and enlarged to show the same image size as that of the telephoto, the only differences will be the grain, noise, sharpness and abberations produced by the respective lenses, camera's image recording qualities, and post-processes, but the perspective will be identical.
This holds true no matter whether the camera is a DX or FX.

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sidewinder Silver Member Nikonian since 05th Jan 2010Sat 09-Jan-10 06:21 PM
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#33. "RE: DX cropping factor?"
In response to Reply # 32
Sat 09-Jan-10 06:22 PM by sidewinder

US
          

> One other truth about lenses that is mainly misunderstood is that
> different focal length lenses do not provide different perspectives.
> This is really an adjunct concept to the FX/DX differences.
> Image perspective is only affected by distance, from the camera to
> the subject, NOT by the focal length of the lens used.

Sure. If I use a 20mm lens and a 200mm lens from the same spot, the relatives sizes of the objects in each frame do not change. A tree that appears to be twice as tall as another tree in the 20mm frame will still be twice as tall in the 200mm frame. Changing focal length only changes how much of the scene makes it the frame.

But we don't often takes photographs that way. We usually have a subject or a certain amount of landscape we want in the photograph. Changing focal length requires us to move closer or farther away which then causes the perspective change.

Scott

  

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dnf777 Registered since 08th Jan 2009Sat 09-Jan-10 09:09 PM
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#34. "RE: DX cropping factor?"
In response to Reply # 32
Sat 09-Jan-10 09:12 PM by dnf777

Franklin, US
          

That wasn't the issue at all.
I don't want to rekindle the topic either, as it has been explained by excellent posts, but I'm not sure what your definition of "perspective" is.
Anyway, its very easy to have a superficial working understanding of DX equipment. That's not what I was lacking. It has been explained simply as a cropping effect due to mismatched image/sensor sizes, which is NOT the complete story, as several explained. Post #21 by Brian explained a fine point which I don't think is widely understood, as gauged by other responses on this thread and others.

Dave F
Franklin, Pa

"Always do right. You'll gratify some, and astound the rest." Mark Twain

  

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Alx Registered since 19th Nov 2005Thu 14-Jan-10 06:49 AM
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#35. "RE: DX cropping factor?"
In response to Reply # 34
Sat 16-Jan-10 05:04 AM by Alx

Nashville, US
          

Perspectve is a property of photography and visual phenomena.
I can easily give an example better than an exact complete definition.

When you take a photo of a person's face, from a too-close distance, you see a larger nose than is preferred, but you also do not see the ears of the person, or not as much of them.
But if you back up, the nose is not as RELATIVELY large compared to the rest of the face, and you begin to see more of the ears, or all of them if far enough away. Portraits are generally preferred from a longer distance to give a better PERSPECTIVE to the face.

The camera can not change the perspective from what you see at the same distance, so the choice of a short or medium telephoto is preferred for the larger image size and frame-filling potential of the magnification, at that longer distance to preserve the preferred pleasing portrait perspective.

But if your 20mm wide angle photo is sharp enough and the grain or noise could be made acceptable for an extreme magnification, a wide angle lens at that preferred distance would give the same good perspective and be able to render the same portrait.

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Alx Registered since 19th Nov 2005Thu 14-Jan-10 07:37 AM
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#36. "RE: DX cropping factor?"
In response to Reply # 34
Thu 14-Jan-10 08:06 AM by Alx

Nashville, US
          

The DX crop issue is not compicated or obscure at all.

A 50mm lens has a certain defined image magnification in absolute terms. It's the same amount of magnification on any piece of film, PER SQUARE MM OR INCH OR WHATEVER, of film, OR digital sensor.(note that there is a difference of back focus distance - lens to film -that is being ignored here, admittedly, and would have to be adjusted for)

NOW, the reason 50mm is called standard on a 35mm camera, or FX "full-frame" digital, is because it has been agreed upon by the industry. 55mm, 45mm, 43mm, 40mm variations and sometimes even 36 mm has been considered standard by some 35mm camera manufacturers and photographers.

Now, put it on a 6x9 cm format camera, that 50mm lens would make a wide angle, because the film extends farther to each side of the center of the image, making the image take in a WIDER view.

OK. Just reverse the idea for telephoto lenses.

Now the big issue, is that of image circle coverage, on the film or sensor. Full frame 35mm format lenses can project their image circle big enough to cover the entire piece of film in the camera they are designed for. But if you could mount that Nikon lens on a Hassleblad, the lens would not project to the edges of the film, instead it would leave a dark circle around the edge of the image, because the lens is not designed to cover the whole area of 6x6 film.

Then if you put that full-frame Nikon lens on a DX body, its circle would cover way past the edges of the DX sensor, which extra coverage would be lost, wasted off the edges of the captured image. The image would be "cropped" to show a smaller portion, as if it were a 75mm lens' image. But the image properties that are recorded would otherwise be the same optically. Well, thats what happens with a regular Nikkor on a DX body.

Now, a DX lens itself, a 50mm DX lens, is designed to only be able to project its 50mm image wide enough to cover the smaller DX sensor.
On a FX or film camera, it would only make its image large enough to show a circle image inside the full-frame of film or sensor. Its image would be ok within that circular covered area, and have IDENTICAL image properties of magnification and perspective, and the recorded image's edges could be cropped to not show the outer black surround, AND the image that would be cropped out in a fully exposed rectangle on the sensor or film would be a DX size image, showing the limits of view as if taken by a 75mm lens. Perspective is the same as a 50 mm lens on any format.

SO the only difference in the DX and FX lens is the extent of its image projected behind the lens, onto the sensor.

One great advantage of full-frame lenses used on DX bodies, is that the part of any lens' image at the edges of the frame are always less sharp and have less quality than the center, especially wide open. The better the lens, the less noticable, but still true.
IF cropped off, which the DX sensor does, this leaves only the sweeter inner part of the image.

SO, the use of the best full-frame Nikon lenses like the 17-35 f2.8. and the 24-70 f2.8 will give super-fine performance on DX cameras, with the best part of the best image possible.

Likewise, if you could take the inner part of a DX lens image and leave out the edges, its overall image performance would also be improved by not having the loss of quality at the edges being shown, but your actual image would now only cover the size of the Instamatic 110 film from the 1970's.


Noted, there are properties of digital lenses that have to do with the parallel or angular projection into the pixel wells, but that is another subject, and does not change the discussion above about the DX/FX crop.

Corrections, if any, to this explanation are welcomed.

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Alx Registered since 19th Nov 2005Thu 14-Jan-10 07:56 AM
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#37. "RE: DX cropping factor?"
In response to Reply # 36
Thu 14-Jan-10 08:10 AM by Alx

Nashville, US
          

Three traveling salesman go to a hotel to get a room for the night.
At the hotel, the clerk says the room is $30.
Each man takes out ten one dollar bills, and together they pay the $30 dollars for the room, (10x3=30)

An hour later, the clerk realizes he has overcharged by $5 for the room, and should only be for $25.00.

He sends the bell-boy to the room with the refund, five $1.00 bills.

When the bellboy tells the salesmen about the refund, they each are given back one dollar, and they let the bellboy keep two dollars for his tip. ... Refund $5 = (3x1) + $2 tip.

OK, now each salesman originally paid 10 dollars, but got one back, so he really ultimately paid only $9.00. Three salesmen, 9 dollars each, 3x9=27. Twenty-seven dollars they paid, and the bell-boy has two dollars .... $27 + $2 = $29 ..... Twenty-nine dollars .... ??
What happened to the other ONE DOLLAR ?

This problem or trick question has some similarity to the DX/FX confusion.

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latessa Silver Member Nikonian since 15th Nov 2009Thu 14-Jan-10 10:11 AM
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#38. "RE: DX cropping factor?"
In response to Reply # 36


GB
          

I have been following this thread, reading and re-reading the posts. While I have had no problem understanding the FX to DX crop it was the DX lens designation bit that had me stymied. But now thanks to Alx's clear explanation, for me, the penny has dropped.
So to make sure I have this correct... The image projected by a 50mm DX lens is the same as a 50mm FX lens, except the peripheral part of the image circle. As the DX camera doesn't use all of the image the FX lens produces, the part that isn't used, ie. the peripheral part, has been designed out of the lenses and they become designated as DX lenses.
That is how you would get a black circle using a DX lens on an FX camera , and why there is compensation on some, if not all, FX cameras to take account of this.
Would appreciate confirmation if I have got this right or wrong.

Eddie

http://www.flickr.com/photos/edzeditz/

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rodc14 Registered since 10th Feb 2009Thu 14-Jan-10 12:12 PM
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#39. "RE: DX cropping factor?"
In response to Reply # 38
Thu 14-Jan-10 12:22 PM by rodc14

Vienna, AT
          

It took me a while for the penny to drop too about crop factor/FOV when I recently changed from 35 film to DX format.

The reason I feel is causing the confusion is that lenses designed specifically for DX format are marketed in 35mm standard so one needs to apply the crop factor to know what one is buying, e.g. Tokina AT-X 12-24mm DX lens is in fact a 18-36mm lens in the DX world.

I think I should stop writing now as I feel the onset of 'confusion' again.

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briantilley Moderator Deep knowledge of bodies and lens; high level photography skills Nikonian since 26th Jan 2003Thu 14-Jan-10 12:37 PM
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#40. "RE: DX cropping factor?"
In response to Reply # 39
Thu 14-Jan-10 12:39 PM by briantilley

Paignton, GB
          

>The reason I feel is causing the confusion is that lenses
>designed specifically for DX format are marketed in 35mm
>standard... e.g. Tokina AT-X 12-24mm DX lens is in fact a
>18-36mm lens in the DX world.

There is no such thing as a "35mm standard" for labelling lenses. A 12-24mm lens is a 12-24mm lens. Always. Whether it's a DX lens or a full-frame lens.

Focal length does not depend on the format the lens is designed for or the camera it is mounted on. It's only because many of us grew up with the 35mm format that we unconsciously associate a particular focal length with its angle of view on that format.

Labelling a Tokina 12-24mm DX lens as 18-36mm would be optically inaccurate and unhelpful. And it wouldn't be feasible anyway - the version for Canon cameras would have to be labelled 19.2-38.4mm, because their crop cameras have a different sensor size with a crop factor of 1.6x.

Brian
Welsh Nikonian

  

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rodc14 Registered since 10th Feb 2009Thu 14-Jan-10 12:44 PM
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#41. "RE: DX cropping factor?"
In response to Reply # 40


Vienna, AT
          

Just when I thought I got the hang of this crop factor thing.....
Back to square 1 !!

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dnf777 Registered since 08th Jan 2009Fri 15-Jan-10 11:20 PM
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#42. "RE: DX cropping factor?"
In response to Reply # 41


Franklin, US
          

Check reply #17 by Brian. That is what cleared the smoke for me. It's like an Apple computer....it's so easy, it's hard to figure out sometimes!

Maybe the FX/DX issue is simple (it really is) but it may not be intuitive, and add to that imprecise semantics, and you got a confused situation.

If it were simple, and everyone understood, there wouldn't be over 40 posts, many saying the correct thing differently, and some saying incorrect things. Not to point any fingers, except at myself, but from reading this thread and other related ones, it's clear that more than a few people don't understand this concept, other than to multiply by 1.5 when using a DX format camera. The latter posts, referring to the portraiture issues showed very nicely that there's more to it than "1.5x".

From the OP, thank you to all who responded. I hope others have learned or confirmed like I did.

Dave F
Franklin, Pa

"Always do right. You'll gratify some, and astound the rest." Mark Twain

  

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Alx Registered since 19th Nov 2005Sat 16-Jan-10 04:52 AM
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#43. "RE: DX cropping factor?"
In response to Reply # 42
Sat 16-Jan-10 05:26 AM by Alx

Nashville, US
          

In the past before digital cameras, there was still an issue of focal lengths vs. formats, but at least camera lenses were almost always used on their own particular format cameras, not crossed from one format to another.

I used to think it would be better to designate lenses according to the ANGLE OF VIEW they gave. Lenses could have been labeled 45 DEGREES, for roughly standard, or 90 DEGREES for a wide angle, and 10 DEGREES for a telephoto etc.

This would have been a great way to begin with lenses in the digital industry. No more confusion of focal lengths and what they meant as far as angle....

But now with Nikon lenses on both DX and FX cameras, it is obvious that the focal length designation is the best and only way to go, and it is for us to get "used to", familiar with, and comfortable with these format / angle conversions.

This is one more reason I like NIKON and dislike Canon .... The 1.5 factor of DX is so much easier to deal with. 24mm DX ? think focal length plus half again .... 24+12=36 ..... the 24mm lens on a DX camera acts like a 36mm lens(on a full-frame 35mm format camera) .... 12~24 equivalent 18~36 .... 50mm equivalent 75mm ... (50+25=75) ... pretty easy compared to Canon with their 1.3 and 1.6 factors. For them I would have to do the math with a calculator or pencil and paper every time until I memorized them.

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jrp Administrator JRP is one of the co-founders, has in-depth knowledge in various areas. Awarded for his contributions for the Resources Charter MemberSun 07-Feb-10 05:03 AM
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#45. "RE: DX cropping factor?"
In response to Reply # 43


San Pedro Garza García, MX
          

Just for fun

Let's just talk about horizontal sensor sizes to avoid further complications with height variations.

The horizontal width of a 135mm film frame is 36mm, like in our D700, D3 and D3s cameras' sensors. So they are 100% FX
(The D3X has 35.9, so it is 99.7% FX)

But our D200, D300, D300s sensors (like the D40x, D60, D70, D890 and D90, D5000 and D3000) are 23.6mm wide (not 24mm) or 65.56% FX; the inverse of it is 1.53X, not 1.50X

Previous DX cameras in the Pro series (D1, D1X, D1H, D2H, D2Hs, D2X, D2Xs), and the D40, D70, D70s, have 23.7mm width sensors, or 65.83% FX; its inverse is 1.525X, not 1.5X

More precise pixel, pixels size and pixel density counts of the effective area will reveal a factor closer to 1.5X but a bit under.

However, I really don't think it matters much

Have a great time
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Alx Registered since 19th Nov 2005Sat 16-Jan-10 05:00 AM
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#44. "RE: DX cropping factor?"
In response to Reply # 38


Nashville, US
          

RIght, now you have it, and even better said that I did, in a lot less words.

Visit my Nikonians gallery.

  

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