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Subject: "APS-C sensors" Previous topic | Next topic
simondyer Registered since 20th Jan 2011Thu 20-Jan-11 01:41 PM
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"APS-C sensors"


Banbury, Oxon, GB
          

I have had it confirmed by Nikon and Sigma that any lens attached to my D90 or D7000 will give a crop factor of 1.5x. Anyone else know this? Nikkor DX lenses apparently are smaller glass and lighter lenses for the benefit of small DSLR's?

Please enlighten me as I thought that by buying DX lenses, it would portray the correct focal distances?

The good side is that the lens zooms in greater distances!

Si

  

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Replies to this topic
Subject Author Message Date ID
Reply message RE: APS-C sensors
dm1dave Administrator
20th Jan 2011
1
Reply message RE: APS-C sensors
wingdo
20th Jan 2011
2
Reply message RE: APS-C sensors
gkaiseril Gold Member
20th Jan 2011
3
Reply message RE: APS-C sensors
kentak Silver Member
20th Jan 2011
4
Reply message RE: APS-C sensors
kentak Silver Member
20th Jan 2011
5
     Reply message RE: APS-C sensors
JohnE Nikon Silver Member
20th Jan 2011
6
Reply message RE: APS-C sensors
MstrBones Silver Member
20th Jan 2011
7
Reply message RE: APS-C sensors
simondyer
21st Jan 2011
8
     Reply message RE: APS-C sensors
Leonard62 Gold Member
21st Jan 2011
9
     Reply message RE: APS-C sensors
kentak Silver Member
22nd Jan 2011
12
          Reply message RE: APS-C sensors
WJMcIntosh
22nd Jan 2011
13
Reply message RE: APS-C sensors
blw Moderator
22nd Jan 2011
10
Reply message RE: APS-C sensors
kentak Silver Member
22nd Jan 2011
11

dm1dave Administrator Awarded for high level knowledge and skills in various areas, most notably in Wildlife and Landscape Writer Ribbon awarded for his excellent article contributions to the Nikonians community Nikonian since 12th Sep 2006Thu 20-Jan-11 03:49 PM
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#1. "RE: APS-C sensors"
In response to Reply # 0


Lowden, US
          

This is true. The crop factor is always a property of the image sensor. Nikon DX cameras always have a 1.5x crop factor.

The focal length is a physical property of the lens. All lenses are marked with the actual focal length.

Crop factor is only relevant when comparing the field of view between FX and DX.

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wingdo Registered since 26th Aug 2007Thu 20-Jan-11 04:16 PM
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#2. "RE: APS-C sensors"
In response to Reply # 0


Chicago, US
          

All ASP-C sensors no matter whom the manufacturer is (Nikon, Canon, Pentax, Sigma etc) have what is called a crop factor. Nikon and Pentax are usually in the 1.5x range, Canon in the 1.6x range and Sigma (not counting the brand new one coming out) the 1.7 range.

It can be rather confusing in the beginning to understand what this "crop factor" means. The focal length of a lens is ALWAYS the focal length. The focal length is a measurement from the rear element of the lens to the focal plane on the sensor. Therefore a 50mm lens on FX or DX is still a 50mm lens as when mounted on either camera the rear element is 50mm away from the focal plane. That said, because the DX sensor is smaller than an FX sensor (FX sensors are the same size as 35mm film), a crop factor comes into play and the FOV (field of view) changes. FOV meaning the angle of view one sees out of the lens. A DX sensor will have a narrower angle of view coming into the sensor so if you are used to shooting with film and liked say a 50mm lens on your film camera, due to the FOV changing on a DX sensor you want a 35mm lens (give or take) to replicate the FOV one had on film with a 50mm lens.

But back to the original point, a 70-200 lens is a 70-200 lens on both DX and FX, but the FOV changes between the two.

I assume that is as clear as mud.

Doug

  

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gkaiseril Gold Member Nikonian since 28th Oct 2005Thu 20-Jan-11 04:58 PM
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#3. "RE: APS-C sensors"
In response to Reply # 2


Chicago, US
          

There will also be a change in the DOF and hyperfocal distance between the FX sensor and DX sensor. The CoC, Circle of Confusion, for the FX sensor is 0.03mm while the CoC for the DX sensor is 0.02mm.

For a 50mm lens at f16 focused to 10 feet:
FX sensor:
Near focus distance: 6.35 feet
Far focus distance: 23.6 feet
Total focus depth: 17.2 feet
Hyperfocal distance: 17.3 feet

DX sensor:
Near focus distance: 7.23 feet
Far focus distance: 16.2 feet
Total focus depth: 9 feet
Hyperfocal distance: 25.8 feet


George
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kentak Silver Member Nikonian since 03rd Jul 2010Thu 20-Jan-11 05:21 PM
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#4. "RE: APS-C sensors"
In response to Reply # 3
Thu 20-Jan-11 05:22 PM by kentak

US
          

Yes, this is probably one of the first things a person "getting into" digital SLR photography learns about when comparing various DSLR camera specs. As pointed out, the focal length of a lens is a property of the lens and is independent of the camera. What's different is the portion of the image projected onto the camera's focal plane that is captured by the sensor. The sensor "sees" a narrower angle of view, just as it would if a longer focal length lens was used. That's why we say a 50mm lens gives an image similar to a 75mm (50 x 1.5) lens on a full frame camera. As far as focal length goes, there is no difference between a 35mm full frame lens and a 35mm DX lens except that the latter can be designed such that the image projected onto the camera's focal plane only has to cover the smaller DX sensor and not a larger one. If used on a full frame (FX) camera, the image would likely show vignetting. I believe it's that different design requirement that allows a DX lens to be more compact and (maybe) less expensive than a comparable full frame lens.

  

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kentak Silver Member Nikonian since 03rd Jul 2010Thu 20-Jan-11 05:34 PM
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#5. "RE: APS-C sensors"
In response to Reply # 2


US
          

"The focal length is a measurement from the rear element of the lens to the focal plane on the sensor."

Well, it's a little more complicated than that theoretical explanation. Many 200mm lenses aren't even 200mm long to the front element. In fact, my 70-300 is about 200mm long at the 300mm zoom position, and the rear element is about 60mm from the lens mount.

It's some kind of lens design magic that allows us to have "long" lenses that aren't actually as long as our arms.

  

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JohnE Nikon Silver Member Nikonian since 15th Jun 2010Thu 20-Jan-11 05:59 PM
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#6. "RE: APS-C sensors"
In response to Reply # 5


New HArtford, US
          

>"The focal length is a measurement from the rear element
>of the lens to the focal plane on the sensor."
>
>Well, it's a little more complicated than that theoretical
>explanation. Many 200mm lenses aren't even 200mm long to the
>front element. In fact, my 70-300 is about 200mm long at the
>300mm zoom position, and the rear element is about 60mm from
>the lens mount.
>
>It's some kind of lens design magic that allows us to have
>"long" lenses that aren't actually as long as our
>arms.

I have found the following explanation online;
Very simply, it is the distance from the lens to the film, when focused on a subject at infinity. In other words, focal length equals image distance for a far subject. To focus on something closer than infinity, the lens is moved farther away from the film. This is why most lenses get longer when you turn the focusing ring. The distances follow this formula:

This means a 400mm lens should be 400mm long. If you get out your ruler and measure it, you will find it is less than 400mm. That is because a camera lens really has many individual glass lenses inside, and this makes it behave as if it is longer than it really is. This is called "telephoto."

http://www.paragon-press.com/lens/lenchart.htm

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MstrBones Silver Member Nikonian since 06th Dec 2005Thu 20-Jan-11 09:21 PM
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#7. "RE: APS-C sensors"
In response to Reply # 0


AW
          

>I have had it confirmed by Nikon and Sigma that any lens attached to my D90 or D7000 will give a crop factor of 1.5x.

Si,

What do you think crop factor actually means?

""

  

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simondyer Registered since 20th Jan 2011Fri 21-Jan-11 08:22 AM
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#8. "RE: APS-C sensors"
In response to Reply # 7


Banbury, Oxon, GB
          

Hi David,

I was just concerned that by using an FX lens, it would lie about the distance that I was photographing, that it would be longer than the lens stated?

e.g, If I wanted to purchase a wide angle lens around 16mm to 35mm, for landscape photo's, that an FX lens would be, say 1.5x would make the lens mm longer?

I've possibly got myself in a tiswas as an inexperienced Nikon Owner, lol!

regards,

Simon

  

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Leonard62 Gold Member Awarded for excellent contributions and sharing his in-depth knowledge and experience with the community, especially of Nikkor Lenses Nikonian since 15th Mar 2009Fri 21-Jan-11 11:36 AM
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#9. "RE: APS-C sensors"
In response to Reply # 8


Hatboro, Pa, US
          

As mentioned above, the focal length of a lens does not change regardless of what camera it's attached to. The 50mm lens is still 50mm if the lens is adapted to a 35mm camera, a medium format camera or a 4X5 camera. What's different is what portion of the projected image gets on the film or digital sensor. The FX 50mm lens on a full frame Nikon camera will give you the same photo as the older 35mm film cameras. The DX cameras only use the center of the projected image so the photo taken with the 50mm lens will appear to have been taken with a 75mm lens on a 35mm film camera. The outer edges of the image are cropped out by the small sensor.

Len

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kentak Silver Member Nikonian since 03rd Jul 2010Sat 22-Jan-11 10:53 AM
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#12. "RE: APS-C sensors"
In response to Reply # 8


US
          


>I was just concerned that by using an FX lens, it would lie
>about the distance that I was photographing, that it would be
>longer than the lens stated?
>
>e.g, If I wanted to purchase a wide angle lens around 16mm to
>35mm, for landscape photo's, that an FX lens would be, say
>1.5x would make the lens mm longer?

Simon,

No, the lens focal distance scale will not lie, if that your question. Both a DX and FX lens will show the correct focal distance when focused on a given object from the same camera position.

It sounds like you are coming from a film SLR background, is that right? If so, you have a notion of what a lens of a certain focal length will show when shooting scenes like landscapes.

Just remember you have to take into account the x1.5 factor when selecting lenses for a cropped sensor camera (DX). If you want a lens to show as much of a scene as a 35mm lens on a film camera or full frame digital, then you would need a lens of about 24mm. It doesn't matter if the 24mm lens is a FX or DX lens--the camera doesn't care and the distance scale will be accurate and the images will be the same.

Hope that helps.

Kent

  

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WJMcIntosh Registered since 22nd Jan 2011Sat 22-Jan-11 02:33 PM
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#13. "RE: APS-C sensors"
In response to Reply # 12


US
          

For myself, I didn't really care too much about the crop factor until I purchased my first wide angle lens. The Sigma 10-20 sounded like it was going to give me a huge range, but once you deal with the crop factor, it's really only 16x30, if I'm doing my math correctly.

On the other hand, I recently purchased the Pro Optic 8mm Fisheye which is purported to deal with the 1.5 and give you a "real" 8mm. Not sure how they did that, but that is one seriously wide lens.

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blw Moderator Awarded for his high level of expertise in various areas Nikonian since 18th Jun 2004Sat 22-Jan-11 06:33 AM
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#10. "RE: APS-C sensors"
In response to Reply # 0


Richmond, US
          

It's a crop factor. All an APS-C sensor is doing is taking the central portion of the frame. It is literally the same as taking the picture with a bigger sensor, making a print and then using a pair of scissors to cut out the central section. For all of the discussion and confusion about it, that's ALL it is.

_____
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kentak Silver Member Nikonian since 03rd Jul 2010Sat 22-Jan-11 10:30 AM
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#11. "RE: APS-C sensors"
In response to Reply # 10


US
          

>It's a crop factor. All an APS-C sensor is doing is taking
>the central portion of the frame. It is literally the same as
>taking the picture with a bigger sensor, making a print and
>then using a pair of scissors to cut out the central section.
>For all of the discussion and confusion about it, that's ALL
>it is.

Not a bad explanation, but don't you think it should be extended to say that you then take that clipped out portion of the image and enlarge it to the original size? What you then see, compared to the original, is what would look like an image taken of the same scene, but with the angle of view of a longer lens and the attendant "magnification." Again, you're absolutely right in your description of what's happening to the image in the camera, but we ultimately view the image "resized" in the viewfinder, or on our computer screen, or as a print of given dimensions.

  

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