I bought a D7000 as a backup to my D700 and plan to trade that in on an 800. I appreciate the longer reach with the DX crop but am curious if I would get a better image using the 800 full frame and cropping on the computer or putting the 800 into DX (1.5) mode in the field as I am shooting. If the image would be essentially the same in both cases, wouldn;t using the 800 in DX mode in the filed at least help me focus a bit better? Is that a logical assumption?
Thanks for any input.
Best,
Dennis

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By my way of thinking, the disadvantage of DX crop mode is the tunnel-view in the viewfinder. The advantage is saving on storage space.

I don't generally find myself having problems with storage space, so I'd opt for cropping in post, unless I was on a week-long camping trip or something where I didn't have a daily opportunity to backup my images.

Larry - a Bay Area Nikonian
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I was going to try the 1.2 format with DX glass to see how much edge loss there is .With wildlife photos I'm always cropping the center 1/3 , perhaps a better view in the finder compared to DX 1.5 .
As always the DX format helps Telephoto work FX helps Super wide lenses . FX glass is always more in newer lenses .Newer glass beat 95% of older nikon " legacy Glass " just in
AF and sharpness .

Hans K.

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The image you get either way would be the same, however there is one difference: When you set any FX camera to DX mode, then it will meter only based on the DX frame. That may not make a difference in most cases, but in case you have, say, some bright highlights outside of the DX frame (but still within the FX frame), then the camera would expose for them in FX mode, and your DX post processing crop may be underexposed. By setting the camera to DX, the meter would consider only the DX frame and choose the best exposure based on that.

So this would lead one to believe that in-camera crop has the advantage, in addition to requiring less storage since the files are smaller. But there is also a significant downside: With in-camera crop you are forced to the crop of the exact central portion of the image. No way to adjust that later (except to crop further into the DX frame). If you shoot FX and crop later, you are free to crop any portion of the FX frame into a DX image, i.e. the left side, or right side, or top or bottom. I've had plenty of cases where my subject was small enough to fit into the DX frame (i.e. flying bird), but I did not manage to keep it centered perfectly in the frame. If I had set the camera to DX crop, some wing would usually be missing on one side or the other. By shooting FX, I can adjust the crop later.

Tom
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Thanks to all for the feedback. Here's a another angle - I like the reach of the D7000 with my long lenses. I will be giving that up if I get the D800 - is there any reason whatsoever to consider the D7000 a better camera in any situation anyone could think of?
Thanks,
Dennis

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I'm unwilling to commit to cropping on an FX camera as a strategy precisely since I spend a lot of time waiting for the light to hit a bird in just the right way. I don't want that image to be 25% smaller, which it will be in the D800's viewfinder.

Now, if you look at Bill Claff's DR chart regarding the D800 (DX) vs. D7000, there's only a marginal advantage to the D800. I'm quite confident that we'll soon see a DX camera from Nikon that will simply be better for supertelephoto work than the D800.

Jim

>I don't want that image to be 25% smaller, which it will
>be in the D800's viewfinder.

Engaging DX Crop Mode (while keeping the same focal length and subject distance) will not change the magnification of the bird in the viewfinder - it will simply fill a greater proportion of a smaller frame.

Brian
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The magnification will still be .70, as opposed to .93 in DX (same lens). 25% smaller.

Jim

>The magnification will still be .70, as opposed to .93 in DX
>(same lens). 25% smaller.

To make sure we are on the same page, let's look at the D3s, which I already own. Its viewfinder magnification is the same as the D800 at 0.7x, and it does not change when you engage DX Crop Mode. All that happens is that the outer area of the viewfinder outside the DX frame is greyed out. The part that's left in the centre still looks exactly the same - it doesn't get magnified.

I assume the D800 will work the same, but haven't tried it myself.

Compare that with the D7000 or D300s, both of which have 0.94x magnification viewfinders to compensate (partially) for the smaller size of the DX focusing screen.

Brian
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The peculiar thing about the measurement of viewfinder magnification is that they use a "normal" 50mm lens for both FX and DX. You can quickly calculate that an FX screen is about 11.7% larger (linearly). But the DX crop area of an FX viewfinder is 25% smaller (linearly) than a DX screen. Or to put it another way, the DX viewfinder is 133% of the DX crop view in an FX camera.

Jim

I know this is hard to believe, but cropping in post may cost you up to half of a stop (I'm going from memory here) of DR. The other thing to bear in mind is that if you know you're going to crop you need about 1 stop less DOF, which likely means 1 stop lower ISO (again increasing DR). Then there's the smaller file and better fps. Adding all of these advantages together, I'd suggest using the DX crop as a deliberate technique and strategy when you know you need the reach.

Jim

>I know this is hard to believe, but cropping in post may cost
>you up to half of a stop (I'm going from memory here) of DR.

I've never heard of that before. Why would the DR be different between in-camera crop and post processing crop? Can you provide some reference?


>The other thing to bear in mind is that if you know you're
>going to crop you need about 1 stop less DOF, which likely
>means 1 stop lower ISO (again increasing DR).

It is the other way around. The cropped image has less DOF than the uncropped image (at same f-stop, same focal length, same subject distance). If you want to maintain a given DOF, then you will need to stop down the aperture, which usually means higher ISO (if you want to maintain you shutter speed), so less DOF for the cropped image.

Tom
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>It is the other way around. The cropped image has less DOF
>than the uncropped image (at same f-stop, same focal length,
>same subject distance). If you want to maintain a given DOF,
>then you will need to stop down the aperture, which usually
>means higher ISO (if you want to maintain you shutter speed),
>so less DOF for the cropped image.

Well... no. At least not unless I misunderstand your point.

For a given FIELD OF VIEW a cropped sensor on the same f-stop and focal length will have a different DOF than an FX sensor.

But if it's the same distance, f-stop, focal length, the actual in-focus area is the same whether the light falls on the cropped portion of the sensor or the whole sensor. Just think about it in post processing -- if you crop you don't change DOF, you just change field of view.


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Shoot D800 w/ 500 f4 at f8 and 20' and DOF is .22' total. Crop to DX and DOF drops to .14'. However, shoot the same scene at 30' with a DX camera, and DOF increases to .33' at f8 and is .23' at f5.6. Per DOFMaster.

Jim

>
>For a given FIELD OF VIEW a cropped sensor on the same f-stop
>and focal length will have a different DOF than an FX sensor.
>
>But if it's the same distance, f-stop, focal length, the
>actual in-focus area is the same whether the light falls on
>the cropped portion of the sensor or the whole sensor. Just
>think about it in post processing -- if you crop you don't
>change DOF, you just change field of view.
>


No, if you crop, you change the DOF. This applies even to film - if you take a 35mm slide and cut out the APS frame from the center, the DOF goes down.

This concept is not well understood by many photographers, which is not surprising since it is not intuitive. You can go to an online DOF calculator to confirm it - dial in some scenario with a given f-stop, focal length and subject distance. Then change only the sensor/film frame (i.e. between FX and DX), and voila, the DOF changes. DX has less DOF than FX.

To understand what is going on, you can read up on wikipedia how DOF works. But here is a brief illustration: When you take a 35mm slide and make a print from it, say 8x12, and hang it on the wall, it will have a certain DOF. The DOF is determined from a certain viewing distance. Now cut out the center APS portion of that slide and make an 8x12 print from that. You would need to enlarge it more, so areas that just barely appeared in focus in the 35mm slide print will now appear out of focus, as tiny blur would have been enlarged more.

Tom
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"DX has less DOF than FX."

You were doing well, until you said this Tom. In fact, one of the key limitations of DX is that an f2.8 lens acts like an f4 lens on FX. You can never obtain the same shallow DOF you can with FX. The corollary to this is that with DX you get the same DOF for the same scene with an aperture one stop larger.

This is quite consistent, however, with a crop having less DOF than the file from which it is cropped.

Jim

>"DX has less DOF than FX."
>
>You were doing well, until you said this Tom. In fact, one of
>the key limitations of DX is that an f2.8 lens acts like an f4
>lens on FX. You can never obtain the same shallow DOF you can
>with FX. The corollary to this is that with DX you get the
>same DOF for the same scene with an aperture one stop larger.
>
>
>This is quite consistent, however, with a crop having less DOF
>than the file from which it is cropped.
>


You may want to read the post first. For the same focal length, subject distance and f-stop, indeed DX has less DOF than FX. It will be so much simpler if you simply go to a DOF calculator like this one and try it out yourself. This will save us endless arguments in this thread:

http://www.dofmaster.com/dofjs.html

Once you've done the homework , here is the reason for why what you said is also true: An f/2.8 lens on DX will act like a f/4 lens on FX, because, in order to achieve the same framing and composition, one will either need to shoot DX at a wider angle, or get farther away from the subject. Both will increase the DOF dramatically, and more than make up for the smaller CoC (Circle of Confusion) that the DX sensor has.

Alas, this is not the scenario discussed in this thread. The topic was cropping (in camera or in post), while not changing focal length or subject distance.

Tom
Bay Area Nikonian

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<An f/2.8 lens on DX will act like a f/4 lens on FX, because, in order to achieve the same framing and composition, one will either need to shoot DX at a wider angle, or get farther away from the subject. >

This is the main reason I see FX as being preferred for wildlife if you have enough reach. The subject isolation of shooting a longer focal length for the same framing is superior if you are looking for a smooth, blurred background.

Now the assumption is you have to have enough reach to fill the frame. If you lack reach and are simply cropping the image, you lose this benefit. Historically, the issue then shifts to pixels on the subject and other factors such as ISO.

We have had several threads talking about the relative benefit of the large image of the D800 reducing noise. That benefit is reduced and eliminated as you move to smaller crops - and at a DX crop mode is essentially the same as the D7000. But the relative comparison with cropping a D3 or D700 will be unchanged since those FX bodies require a crop as well.



Eric Bowles
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That's why the 300 f2.8 or 400 f2.8 come in so handy with DX cameras for closer or larger subjects.

Jim

Neil and I got crossed up on this a few days ago. When shooting wildlife I generally choose an aperture for a full-sized image. The distance depends on the size of the quarry, and what it does; to a lesser extent what I do. There's often little opportunity to adjust aperture "on the fly" (think BIF). Capturing the same scene allows you to open up by one stop with DX. A better way to put it would be to say that you're more likely to have the correct DOF if you use the DX crop as a deliberate strategy.

P.S. Sorry, I missed your first question: http://www.nikonians.org/forums/dcboard.php?az=show_topic&forum=226&topic_id=37513&mesg_id=37513&page=2
Bill is pretty careful with his facts.

Jim

;-)
Not sure where this all leaves me.. maybe I should hang on to the D7000 for now (my wife wants it as an upgrade from her 3100... and I was gonna get the new one)
Best,
DM

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