FX (Crop) VS DX

[Derrel]

The OP's question is, I think, actually three different questions. The answer to the question seems like it would most likely be partly theoretical, and partly based upon actual camera models.

Sensor Performance and Camera Tuning can play a part. For example, the Nikon D5 did not perform in exactly the same way as the D4 did... there was quite a bit of concern over the D5's Factory optimization in regard to dynamic range and noise performance. To Consumers and hobbyists, the D5 emphasis on Lower noise performance at the expense of dynamic range generated a lot of online comments from the peanut gallery.

 

[Ysarex]

The OP's question is, I think, actually three different questions. The answer to the question seems like it would most likely be partly theoretical, and partly based upon actual camera models.

Right. We know the theory -- all else equal the bigger sensor wins. But as soon as you move to specific camera brands and models all else is never equal so there's no good way to run a controlled test. I could test Nikon versus Fuji but there's so many complicating factors what real meaning do you ascribe to the results.

Joe

Sensor Performance and Camera Tuning can play a part. For example, the Nikon D5 did not perform in exactly the same way as the D4 did... there was quite a bit of concern over the D5's Factory optimization in regard to dynamic range and noise performance. To Consumers and hobbyists, the D5 emphasis on Lower noise performance at the expense of dynamic range generated a lot of online comments from the peanut gallery.

 

[Derrel]

I think the OP should rent a couple of cameras...

 

[zulu42]

I am just wondering in general if it would be better to get 2 cameras (a DX and FX around 20-24mp) or just 1 high mp fx camera.
I know there are many other factors in this decision, but I would just like an answer on the above question.

Just get one FX camera. The exception may be if you primarily need reach - for birds and such. IMO.

 

[Timppa]

Hmm, seems my question has brought up a big discussion.
I think my question has been answered tough.
Cropping down a FX to DX (in camera or in post) will also crop down the benefits of the FX camera. In some cases, it will still yield better results than a DX camera, but those are for pixelpeepers, the main benefit of FX, gaining more light, is almost completely lost.
If you are shooting wildlife, it is handy to maybe have a dedicated DX camera (like the D500) for all the other benefits that come with it.
... Al tough a high MP FX camera, when wildlife is close enough to shoot in FX, will results in amazing pictures surpassing anything a DX camera has to offer.
But buying a high MP FX camera only for that reasons, knowing that in 95% of the time even on DX you have to short reach is silly.
I think 2 cameras (a DX and FX, both around 20-25mp) is still the best option in most cases, also gives you a back up and more versatility.

 

[freixas]

Got it. You're thinking of the OP's original question. I answered that and no, cropping the FX sensor basically removes the low light advantage. In my post with the photos I was responding to JBPhotog who disagreed with my statement: "The fundamental reason an FX sensor provides better low-light performance is it's bigger. If you crop it so that it's no longer bigger then you're giving up the reason for the advantage."

I don't see how the sensor size matters at all. It seems that just the pixel size matters all else being equal. By all else being equal, I mean the electronics, the lens, the exposure, the shooting distance. While a bigger sensor often means bigger pixels, that is not always the case.

If I were magically given two cameras that were identical in every way except for the sensor size (same pixel pitch, though), shot the same scene from the same distance with the same exposure, cropped (not reduced) the FX to DX size and then compared the two images, they should be the identical (or close to it, if you allow for the randomness of noise). If you fill the frame with the same image on both, the FX image wins when reduced (not cropped) to DX size (this is what I think happened with your Superman samples).

It might seem like an arbitrary restriction, but for wildlife shooting where you might already be using your largest zoom lens, can't get any closer to your subject and find yourself often cropping even the DX image, the FX camera may not be much of an advantage (birds in flight would be one exception—you still crop, but you have a greater chance of having the bird in picture in the FX shot because of the wider field of view).

If you have two magically-equivalent cameras, but now the FX and DX have the same pixel count, the FX camera will have better low-light performance. For wildlife, if you have to crop, though, it may not matter. Cropped to the same field of view, the FX image will have less noise, but also less resolution (fewer pixels). However, when the DX image (which is now the larger one, pixel-wise) is reduced to the size of the FX image, it may look just as good.

I will add that since the two magically-equivalent cameras don't actually exist, comparisons like this are just interesting thought exercises. Real world comparisons are more useful and the results may vary depending on the types of images you take. FX would seem always superior to DX for landscapes (except maybe for your pocketbook), for example—well, as long as the technology is roughly equivalent. This should be true whether the two cameras have the same pixel pitch or have the same total pixels.

 

[Ysarex]

Got it. You're thinking of the OP's original question. I answered that and no, cropping the FX sensor basically removes the low light advantage. In my post with the photos I was responding to JBPhotog who disagreed with my statement: "The fundamental reason an FX sensor provides better low-light performance is it's bigger. If you crop it so that it's no longer bigger then you're giving up the reason for the advantage."

I don't see how the sensor size matters at all.

A larger sensor records more total light and that provides a low-light (less noise) advantage.

It seems that just the pixel size matters all else being equal. By all else being equal, I mean the electronics, the lens, the exposure, the shooting distance. While a bigger sensor often means bigger pixels, that is not always the case.

If I were magically given two cameras that were identical in every way except for the sensor size (same pixel pitch, though), shot the same scene from the same distance with the same exposure, cropped (not reduced) the FX to DX size and then compared the two images, they should be the identical (or close to it, if you allow for the randomness of noise).

Duh. Compare DX with DX and DX should be the same as DX.

If you fill the frame with the same image on both, the FX image wins when reduced (not cropped) to DX size (this is what I think happened with your Superman samples).

Let's rephrase that. When you print the FX and DX images to the same print size, the FX wins.

It might seem like an arbitrary restriction, but for wildlife shooting where you might already be using your largest zoom lens, can't get any closer to your subject and find yourself often cropping even the DX image, the FX camera may not be much of an advantage (birds in flight would be one exception—you still crop, but you have a greater chance of having the bird in picture in the FX shot because of the wider field of view).

I believe that's what I said.

If you have two magically-equivalent cameras, but now the FX and DX have the same pixel count, the FX camera will have better low-light performance. For wildlife, if you have to crop, though, it may not matter. Cropped to the same field of view, the FX image will have less noise,

No it won't. Duh. Compare DX with DX and DX should be the same as DX.

Joe

but also less resolution (fewer pixels). However, when the DX image (which is now the larger one, pixel-wise) is reduced to the size of the FX image, it may look just as good.

I will add that since the two magically-equivalent cameras don't actually exist, comparisons like this are just interesting thought exercises. Real world comparisons are more useful and the results may vary depending on the types of images you take. FX would seem always superior to DX for landscapes (except maybe for your pocketbook), for example—well, as long as the technology is roughly equivalent. This should be true whether the two cameras have the same pixel pitch or have the same total pixels.

 

[freixas]

A larger sensor records more total light and that provides a low-light (less noise) advantage.

Only if you equalize the field of view in the comparison.

Let's rephrase that. When you print the FX and DX images to the same print size, the FX wins.

Sure. And I realize this is how it works for most people, assuming comparable technology.

I spend a lot of time with bird photography, so maintaining the same field of view generally requires a larger lens—which I could then use on my DX camera to better effect. My perspective makes me focus more on the light-gathering powers of a pixel rather than a sensor. Printing an FX image to the same size as a DX image would just give me more of the landscape and less of the bird. And when I'm worried about low-light capability, I'm thinking of noise in the image of a bird and not all the stuff around it.

As I said, if we were talking about landscapes or portraits, it would be FX all the way...

 

[Ysarex]

A larger sensor records more total light and that provides a low-light (less noise) advantage.

Only if you equalize the field of view in the comparison.

No, as a general rule across the board. A larger sensor performs better in low-light -- less noise. You take a DX sensor camera wherever you are and set up a scene with X foot candles illumination and take a photo with the ISO set to 6400. I take an FX sensor camera here and set up a scene with the same X foot candles of illumination and take a photo with the ISO set to 6400. Baring make and model differences I get better low-light performance because my larger sensor captures more total light.

If anything is done to crop the FX sensor or crop the image from the FX sensor then it's no longer an FX sensor and Duh, not an FX sensor is not an FX sensor. In a comparison between FX sensor and DX sensor cameras with make model differences equal the FX sensor is less noisy. That's a period.

If you're not using the whole image from the whole FX sensor for any reason then you're not comparing FX and DX sensor cameras you're comparing something else.

I understand you're taking photos of small distant subjects and if you're ultimately lens-focal-length restricted you may not be able to even use the entire area of a DX sensor so you likewise can't take advantage of an FX sensor either. That was the OP's original question; does the advantage of an FX sensor remain when it's no longer being fully utilized -- no. So your topic isn't really comparing FX and DX sensor cameras. Your topic is you have to settle for X amount of noise in your photos relative to the lens focal length you can afford.

Joe

 

[freixas]

That was the OP's original question;

I went back to the OP and yes, I'll agree with you--when you crop an FX to DX size, all else being equal, there is no advantage to the FX. Since there was no more to the question, that's the only answer needed.

Looking at the OP's response later on, I can add a few notes:

In some cases, it will still yield better results than a DX camera, but those are for pixelpeepers, the main benefit of FX, gaining more light, is almost completely lost.

Assuming everything is equal except the sensor size (including pixel pitch, electronics, and cropping the FX image to DX size), there are no cases in which the FX camera will yield better results. Because there are no two cameras which differ only in sensor size, results could go any which way.

I think 2 cameras (a DX and FX, both around 20-25mp) is still the best option in most cases,

I'm not sure I'd agree that owning both a DX and FX, each at 20-25 MP would be the "best" option. Whether you need one camera or two, the sensor size(s) of the camera(s), and the ideal megapixels all depend on a lot of factors (including budget, of course).

 

[greybeard]

I use my D850 in crop mode from time to time. Smaller files, added reach. etc. I have also owned a D7500 which is roughly the same pixel pitch as the D850. I did use the D7500 with my Tamron 150-600. I compared the 2 using the D850 on the Tamron. I couldn't see much if any difference and that is why I sold the D7500.