[lister6520]

The D7100 has it's own 1.3x crop mode (just as the D800 has a 1.5x crop mode) which works out to be 1.3*1.5 (1.95) of a FF sensor. You end up with a 15MP file size and an effective 2x crop factor. A cheap $1200 300mm lens suddenly has the FOV (and a usefull file size) of an expensive 600mm lens. Obviously it would be much better to have a $10,000 f/4 600mm lens on a FF but that's another story as far as money and weight goes.

But you can achieve the exact same result in PP even without the special crop mode. When I mean exact same result I do mean exact same, as in pixel by pixel identical. All you need to do is to crop the images afterwards. All that's been said about DOF, aperture and so on is equally applicable (or not) when you crop in PP. The only thing that can be different is how many frames you can hold in the buffer when shooting at a fast frame rate.

The only thing the Nikon adds to that is that it shows you a frame in the viewfinder for reference. That may be useful to some but I'm not sure how. If you're going to shoot something and crop you might as well capture the full image and then crop as much or as little later rather than imposing a limit at the start.

[Barry Pearson]

The D7100 has it's own 1.3x crop mode (just as the D800 has a 1.5x crop mode) which works out to be 1.3*1.5 (1.95) of a FF sensor. You end up with a 15MP file size and an effective 2x crop factor. A cheap $1200 300mm lens suddenly has the FOV (and a usefull file size) of an expensive 600mm lens.

It is irrelevant that an Xmm lens can have the same field of view as a 2Xmm, if you've done that by throwing useful pixels away! If you don't do that extra 1.3x crop, the centre part of the recorded image has exactly the same field of view as the longer lens anyway - but in addition it is surrounded by extra pixels that might be useful.

(I assume no one would say "if we do an extra 10x crop we will get the same field of view as a lens of 10x the focal length, so let's do it"! Yet that appears to be the same logic as that extra 1.3x crop).

Once a lens's image circle has covered the sensor, you might as well use all the pixels, unless you have composed carefully in the camera. If just a 1.5x crop means that all the pixels on the sensor are used for image formed by the lens, why do an extra 1.3x crop? It won't improve image quality for anyone using all the captured pixels. (I shoot DNG).

[Rondec]

It is irrelevant that an Xmm lens can have the same field of view as a 2Xmm, if you've done that by throwing useful pixels away! If you don't do that extra 1.3x crop, the centre part of the recorded image has exactly the same field of view as the longer lens anyway - but in addition it is surrounded by extra pixels that might be useful.

(I assume no one would say "if we do an extra 10x crop we will get the same field of view as a lens of 10x the focal length, so let's do it"! Yet that appears to be the same logic as that extra 1.3x crop).

Once a lens's image circle has covered the sensor, you might as well use all the pixels, unless you have composed carefully in the camera. If just a 1.5x crop means that all the pixels on the sensor are used for image formed by the lens, why do an extra 1.3x crop? It won't improve image quality for anyone using all the captured pixels. (I shoot DNG).

Wildlife photography is hard, particularly birding and even photos that I take at the zoo usually end up needing to be cropped in post. Assuming that I will be doing that anyway, the camera could do it automatically. That said, I am convinced that the reason that Nikon stuck the crop mode on the D7100 was just because it isn't really built to deal with the 24 megapixel files it produces. Its raw buffer is, what, 6 files? That is not great and so if you get the file size down to 16 megapixel then it looks better.

[lister6520]

Wildlife photography is hard, particularly birding and even photos that I take at the zoo usually end up needing to be cropped in post. Assuming that I will be doing that anyway, the camera could do it automatically. That said, I am convinced that the reason that Nikon stuck the crop mode on the D7100 was just because it isn't really built to deal with the 24 megapixel files it produces. Its raw buffer is, what, 6 files? That is not great and so if you get the file size down to 16 megapixel then it looks better.

The camera can only do it automatically if you have managed to centre your subject within the smaller frame. What the crop mode does is remove your margin of error that you could have corrected for afterwards in PP. If you are shooting still subjects then it is no issue but if you're shooting birds in flight (or even insects or aeroplanes for that matter) the extra pixels are great to rescue what would have been a failure if you cropped in camera.

It seems the real purpose in the D7100 is simply because at 24MP it is limited to 6 FPS whereas the reduced amount of data from the cropped frame allows it to go a little over 7. (Maybe that's why it is D7100? 7.1 frames per second?)

If it was done for any other reason they would have implemented it by simply lighting the reduced frame in the VF and storing the entire image anyway with crop information embedded in the file (RAW allows that). That way when you process you will automatically get the cropped jpeg but if you find that you need to reframe you can just re-crop off he original RAW file.

In any case by far the best I find is to simply shoot the full frame and crop afterwards. I still don;t see the advantage of placing a limitation on myself beyond that which is already dictated by the full sensor size - except of course for the frame rate issue, but that is just a workaround to a very specific problem in one particular camera (insufficient digital processing power).

[rawr]

The 'DX crop' feature in something like the D7100 may be quite useful, once you get used to it. I wouldn't write it off as a gimmick or a Nikon cop-out.

You can't always bring along a longer lens to a shoot, or a teleconvertor, or get closer, and thus shoot tight in 24MP mode all the time. And if you've got 300 24MP event shots to edit, and 200 of them had the action shot too far away, cropping them all selectively would be tedious. Better to have the cropping done by eye in-camera in 15MP mode at the time of shooting. So having a 'DX crop' mode at your disposal could certainly be handy sometimes, especially as you could just return to normal 'wider' 24MP mode at the flick of a switch.

[bossa]

But you can achieve the exact same result in PP even without the special crop mode. When I mean exact same result I do mean exact same, as in pixel by pixel identical. All you need to do is to crop the images afterwards. All that's been said about DOF, aperture and so on is equally applicable (or not) when you crop in PP. The only thing that can be different is how many frames you can hold in the buffer when shooting at a fast frame rate.

The only thing the Nikon adds to that is that it shows you a frame in the viewfinder for reference. That may be useful to some but I'm not sure how. If you're going to shoot something and crop you might as well capture the full image and then crop as much or as little later rather than imposing a limit at the start.

I am aware of that of course. This discussion seems to be going around in circles...

[bossa]

The 'DX crop' feature in something like the D7100 may be quite useful, once you get used to it. I wouldn't write it off as a gimmick or a Nikon cop-out.

You can't always bring along a longer lens to a shoot, or a teleconvertor, or get closer, and thus shoot tight in 24MP mode all the time. And if you've got 300 24MP event shots to edit, and 200 of them had the action shot too far away, cropping them all selectively would be tedious. Better to have the cropping done by eye in-camera in 15MP mode at the time of shooting. So having a 'DX crop' mode at your disposal could certainly be handy sometimes, especially as you could just return to normal 'wider' 24MP mode at the flick of a switch.

Exactly!

Also, a TC would be useless for recording more detail on a 24MP APS-C camera unless you were using a very fast lens which was super sharp wide open. Diffraction would be creeping in from f/5.6 on and you wouldn't be actually recording finer detail, just spreading a softer image across more pixels.

If I'm shooting birds high up in trees, I really don't want my computer chugging away rendering 1:1 previews for 200 shots which I then have to manually crop. My computer takes 23 seconds to render a 1:1 preview for a 36MP file and so shooting bird shots in my D800e's 1.5x crop mode saves a lot of time. But on the other hand, if I did own a 600mm lens I would certainly be using the full sensor for these kinds of shots.

[Serpiente]

So the 'DX-crop' is only useful for people who shoot JPG or who have slow computers? I would never use it on a APS-C camera. Lightroom is the way to go for me. More control and you make the full composition in the viewfinder. There is also more room for error.

[bossa]

I give up.. see ya guys.

[normhead]

Also, a TC would be useless for recording more detail on a 24MP APS-C camera unless you were using a very fast lens which was super sharp wide open. Diffraction would be creeping in from f/5.6 on and you wouldn't be actually recording finer detail, just spreading a softer image across more pixels.

That's simply wrong, I use a 1.7 TC on my A-400 5.6 all the time. The law of diminishing returns may set in, as in you probably get an actual 1.35 resolution boost instead of 1.7. but you do get more detail and a larger image. Close in to your subject (10 feet or less) you get a resolution boost right to F22, with a loss in resolution at perhaps f32 and beyond... diffraction sets in reasonably slowly across the f-stops, and for a lot of images, f-11 or F 8 are preferable to f-5.6, even without a TC. It's not just bang, you pass ƒ5.6 and you're finished. And you always have the trade off, more of your image in less sharp focus, or less of your image in very sharp focus. I'd say 10-15% of the time ƒ11 is the best image and by far F8 is the best compromise. You really have to watch what you say... newbies might believe you.