# FX (Crop) VS DX



## Timppa (Apr 14, 2020)

Hello,

I know the differences between FX and DX, I am also aware that when you use a FX camera in DX mode, you are cropping the image, resulting in less pixels.

But here is my question;
a FX sensor is known for better high ISO performance. According to what I found on the internet, it can result up to 3 stops of light (ISO 100 on DX = ISO 800 on FX in terms of amount of grain --> this formula is definitely not correct and also depends on type of sensor and many other things, but it's a rough comparison).
When cropping a FX down to a DX, does this benefit remain?

Would it be better to use a 46mp FX camera, cropped down to DX mode (resulting an image around 20mp), or would it be better to use a 20mp DX camera? Will I be able to use the FX camera at an ISO roughly 3 stops higher than the DX and remain the same amount of grain?
Or will the results be exactly the same?

Thanks in advance!

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.


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## Braineack (Apr 14, 2020)

Timppa said:


> Would it be better to use a 46mp FX camera, cropped down to DX mode (resulting an image around 20mp), or would it be better to use a 20mp DX camera? Will I be able to use the FX camera at an ISO roughly 3 stops higher than the DX and remain the same amount of grain?
> Or will the results be exactly the same?



Quite possibly on all accounts.  The D850 is a better imager than the D500 -- but the pixel pitch is almost the same size.


4.35 microns vs. 4.22 microns, whereas my d610 is 5.97 microns

However, if you look at the DXO mark results, somehow Nikon is able to keep the D850 on par with the D610 in terms of DR, color sensetivity, tonal range, and SNR.  That's what makes it somewhat magical -- like shooting between my D800 and D610.  Even though the pixel size is much smaller in the 36MP sensor, I achieve identical results in terms of image quality, but with the added bonus of extra resolution and image detail.  I've posted these results here once.


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## Ysarex (Apr 14, 2020)

Timppa said:


> Hello,
> 
> I know the differences between FX and DX, I am also aware that when you use a FX camera in DX mode, you are cropping the image, resulting in less pixels.
> 
> ...



Basically no. 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.

Because other factors (different sensor architectures, etc.) play secondary roles you can't just apply that evenly to any two FX/DX cameras. The best low-light performance crop camera these days will be very close to a medium performance FF camera. The best way to think about it is this: Crop an FX camera to DX size and the camera's low-light performance will be downgraded accordingly.

Joe


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## Braineack (Apr 14, 2020)

Ysarex said:


> Basically no. 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.



You're stuck in the past, and this is simply flawed logic.



> The best way to think about it is this: Crop an FX camera to DX size and the camera's low-light performance will be downgraded accordingly.



Again, this is not a good rule-of-thumb anymore.  Techonology has caught up to 1995.


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## Ysarex (Apr 14, 2020)

Braineack said:


> Ysarex said:
> 
> 
> > Basically no. 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.
> ...



Then the FX advantage comes from what?

Joe


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## Braineack (Apr 14, 2020)

4.35 microns ( expeed 5 ) vs. 4.22 microns ( expeed 5 ) vs. 5.97 microns ( expeed 3 ).  Image processors > pixel pitch.


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## Ysarex (Apr 14, 2020)

Braineack said:


> 4.35 microns ( expeed 5 ) vs. 4.22 microns ( expeed 5 ) vs. 5.97 microns ( expeed 3 ).  Image processors > pixel pitch.
> 
> View attachment 190050
> 
> ...



I said other factors like sensor architecture play a role. There's five years of tech advance between the D610 and the D850. You can't compare the two and control other variables. Compare a D850DX with a D500 (one year apart) -- here's Bill Claff's DR comparison chart:

Photographic Dynamic Range versus ISO Setting

And the D500 DR performance is slightly better.

 The D850's performance drops when you switch it from FX to DX. What causes that drop?

Joe


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## RVT1K (Apr 14, 2020)

Ysarex said:


> Braineack said:
> 
> 
> > Ysarex said:
> ...




It has more to due with the size of the individual elements on the sensor, not the size of the sensor itself. 
The larger sensor has, typically, allowed larger individual elements a.k.a. pixels. 

This comes up a lot and in reality it is an electronics/semiconductor question more than it is a camera question.


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## Ysarex (Apr 14, 2020)

RVT1K said:


> Ysarex said:
> 
> 
> > Braineack said:
> ...



No, it has more to do with the size of the sensor and not the size of the pixels/sensels on the sensor:
The effect of pixel size on noise
The effect of pixel size on noise

Joe


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## Braineack (Apr 14, 2020)

Ysarex said:


> The D850's performance drops when you switch it from FX to DX. What causes that drop?
> 
> Joe



you've zoomed in. which brings us back to the OP's question.


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## Ysarex (Apr 14, 2020)

Braineack said:


> Ysarex said:
> 
> 
> > The D850's performance drops when you switch it from FX to DX. What causes that drop?
> ...



Zoomed in causes the drop in performance? In other words smaller sensor. Why is smaller sensor less performance?

Joe


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## Braineack (Apr 14, 2020)

no. sensor sizes dont change.


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## Ysarex (Apr 14, 2020)

Braineack said:


> no. sensor sizes dont change.



When you throw the switch in the D850 from FX to DX you use less of the sensor -- that = smaller. No question or argument the performance drops. What causes the performance drop? Zooming in causes the performance drop? How is that any different than using a smaller sensor?

Joe


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## Braineack (Apr 14, 2020)

persception.

Let's frame it this way:

Is there a differnece between using DX mode, or taking a full RAW image and cropping it to 20MP in post?


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## Ysarex (Apr 14, 2020)

Braineack said:


> persception.
> 
> Let's frame it this way:
> 
> Is there a differnece between using DX mode, or taking a full RAW image and cropping it to 20MP in post?



So if you crop in post the performance drop that happens when you switch FX to DX doesn't occur?

Joe


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## Braineack (Apr 14, 2020)

I dunno?  I'm assuming it's indentical.  it's a crop...


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## Ysarex (Apr 14, 2020)

Braineack said:


> I dunno?  I'm assuming it's indentical.  it's a crop...



You mean like what I originally said: "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."

Joe


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## JBPhotog (Apr 14, 2020)

In the 40+ years I have been shooting, much of it professionally, I have never come across a light meter that has a setting for different sized film or sensors.

Modern sensors are made up of clusters of photosites, photons do not spill over, they are either captured or not.

Think of it like pizza, two pies with the same ingredients, one 8” the other 12”, does the bigger one taste better!


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## Derrel (Apr 14, 2020)

Looking over the results at the site that Joe linked us to, I see that virtually every camera does worse in DX mode than it does when it is used in FX mode. Not by a large degree but by a measurable degree. In the past we had people who compared the Nikon D800 to the Nikon D7200 and in every case the D800 yielded slightly better results when its full frame images were cropped down to the DX equivalent image field of the Nikon D7200

Those comparisons were quite frequent about 6 years ago. The D800 was introduced in 2012, if I remember correctly. It is a particularly good sensor. Last summer I owned both the D800 and the Nikon D610 and in my non-scientific testing both cameras offered roughly equivalent dynamic range, but the D800 with its 36 million pixels offered incredible crop-in capability.

Instead of theory, I would urge you to actually rent a camera and conduct your own tests. I was at first not sold on the 36 million pixels of the D800. 24 million pixels is quite good but 36 million pixels offers incredible crop- in ability, as I said earlier. The difference is hard to put into words. In the field of portrait photography I found that it is possible at ISO 100 to crop from a half-body seated pose and into a Head and Shoulder portrait with no significant loss final image quality, even when using a relatively inexpensive lens. The idea that the D800 requires the highest level of glass is  in my opinion, over-stated.


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## Ysarex (Apr 14, 2020)

JBPhotog said:


> In the 40+ years I have been shooting, much of it professionally, I have never come across a light meter that has a setting for different sized film or sensors.



What has that to do with it? Did anyone say anything about different exposures? Larger sensors as a rule perform better in low light that smaller sensors. By that we mean less noise and more DR when used at high ISO values (low light). That's what I said. I'm correct about that.

What's that noise? Part one: Shedding some light on the sources of noise

Joe


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## Ysarex (Apr 14, 2020)

JBPhotog said:


> In the 40+ years I have been shooting, much of it professionally, I have never come across a light meter that has a setting for different sized film or sensors.
> 
> Modern sensors are made up of clusters of photosites, photons do not spill over, they are either captured or not.
> 
> Think of it like pizza, two pies with the same ingredients, one 8” the other 12”, does the bigger one taste better!



Let's have a look then.

I happen to have a Nikon camera. So I took two photos with the camera in a low light condition.

 FX at ISO 6400, 1/13th sec, f/8.

Same lens, I backed up the tripod so the scene was framed the same side to side.

DX at ISO 6400, 1/13th sec, f/8.

Both raw files default open in C1 with Luminance noise filtering off. Here's the central section of the two side by side at 100% for the DX camera.

Does the bigger one taste better? It sure does. Why? Larger sensor = less noise or if you prefer, a crop from a larger sensor = more noise.

Joe


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## Derrel (Apr 15, 2020)

I did not know you have a Z7@@@!


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## Ysarex (Apr 15, 2020)

Derrel said:


> I did not know you have a Z7@@@!



Long story, but yes.

Joe


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## Designer (Apr 15, 2020)

Timppa said:


> 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.


You are getting caught up in the "megapixel" argument, which is useless as it goes. 

There are many side issues involved which all contribute to the final image quality.  I think you will not see two different size sensors produce the exact same image, as you seem to assume. 

Even if, by some strange coincidence, both sensors had the same pixel pitch, there would still be differences.  If the FX was manufactured by a different company using a different design, and at a different level of technology than the DX sensor, then simply using that FX sensor in "cropped mode" would probably not produce the same image as the DX sensor. 

As to the "high mp fx", keep in mind that the file size is huge!  You will need a fast computer with lots of RAM to do your editing. 

Make your decision based on your intended use, and get the system you need, and ignore the "mega-pixels".


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## PJM (Apr 15, 2020)

Ysarex said:


> JBPhotog said:
> 
> 
> > In the 40+ years I have been shooting, much of it professionally, I have never come across a light meter that has a setting for different sized film or sensors.
> ...



I would do your experiment differently.  Starting with the image framed the way you want it in DX mode, take both photos, FX and DX modes, without moving the camera.  I would then crop the FX down to DX size in post and then compare the photos.  When you move the camera you are changing how the light enters and falls on the sensor so I don't think you can make an apples to apples comparison.


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## Ysarex (Apr 15, 2020)

PJM said:


> Ysarex said:
> 
> 
> > JBPhotog said:
> ...



I made the only comparison that makes sense. What you're suggesting is to compare X with X -- the crop with the crop. I'll bet X will be the same as X.

What I did was use the two different formats to take the same photo. That's the logical comparison. We want to see if there's a performance difference in real usage. If you wanted to avoid moving the camera then it would be necessary to change lenses between the two photos, but the comparison should be: is there a difference when the two different formats are used to take the same photo.

Joe


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## PJM (Apr 15, 2020)

I also expect the two to be the same.  So, maybe I didn't understand the question.  I thought the question was would the image from an FX format cropped down to DX size be better than one from a DX format.  In order to do that I believe you have to take both images from the same spot.  My understanding is that assuming you used the same lens the target image would be the same size on each physical sensor.  The FX format would include more area around the target.  When you crop the FX down to DX they both show the same image area.  Then you can compare performance.  I think you can only do this with two different cameras, an FX and a DX.  Using the the FX and the same FX in DX mode produce the equivalent result.


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## Derrel (Apr 15, 2020)

My gut feeling is that the FX image when cropped down to DX will be slightly better than when the FX camera is used in DX mode....but there is only one way to find out...an actual test. LOOKING at the Photostophotons test result listing, it shows that image quality from a dynamic range standpoint declines when an FX Camera is shot at a smaller capture size, the example listed being DX (or aps-c).


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## Ysarex (Apr 15, 2020)

PJM said:


> I also expect the two to be the same.  So, maybe I didn't understand the question.  I thought the question was would the image from an FX format cropped down to DX size be better than one from a DX format.  In order to do that I believe you have to take both images from the same spot.  My understanding is that assuming you used the same lens the target image would be the same size on each physical sensor.  The FX format would include more area around the target.  When you crop the FX down to DX they both show the same image area.  Then you can compare performance.  I think you can only do this with two different cameras, an FX and a DX.  Using the the FX and the same FX in DX mode produce the equivalent result.



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."

Joe


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## Derrel (Apr 15, 2020)

I think the newest, best-performing full frame cameras perform so well that they would be more than adequate with the images cropped down to DX, either in-camera, or in post.

The Nikon D850 is amazing; the Nikon Z7 and Z6 are amazing, the Sony A7 RIII is amazing. The Sony A9 is amazing.


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## Derrel (Apr 15, 2020)

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.


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## Ysarex (Apr 15, 2020)

Derrel said:


> 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



Derrel said:


> 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.


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## Derrel (Apr 15, 2020)

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


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## zulu42 (Apr 15, 2020)

Timppa said:


> 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.


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## Timppa (Apr 16, 2020)

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.


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## freixas (Apr 21, 2020)

Ysarex said:


> 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.


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## Ysarex (Apr 21, 2020)

freixas said:


> Ysarex said:
> 
> 
> > 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."
> ...



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



freixas said:


> 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.



freixas said:


> 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.



freixas said:


> 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.



freixas 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



freixas said:


> 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.


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## freixas (Apr 22, 2020)

Ysarex said:


> 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.



Ysarex said:


> 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...


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## Ysarex (Apr 22, 2020)

freixas said:


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



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


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## freixas (Apr 23, 2020)

Ysarex said:


> 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:



Timppa said:


> 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.



Timppa said:


> 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).


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## greybeard (Oct 10, 2020)

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.


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