Resolution comparison

[All about the glass]

I would like to compare a couple of different camera/lens combinations and establish what the resulting resolutions will be, but not confident I’ve got the maths right. Here’s the scenario.

Take an uncropped image from the APS-C Canon 90D. Using the 100-400 at 400mm and then take the same shot with the FF Canon R5 using the 100-500 at 500mm. Then in post, crop the R5 image to the same framing as the 90D image. What is the resulting R5 image resolution wise ?

My maths tells me 32.4mp with a larger than APS-C image size, due to the larger pixel size but I would appreciate opinions on whether this is correct ?

 

[chrisfisheye]

I would like to compare a couple of different camera/lens combinations and establish what the resulting resolutions will be, but not confident I’ve got the maths right. Here’s the scenario.

Take an uncropped image from the APS-C Canon 90D. Using the 100-400 at 400mm and then take the same shot with the FF Canon R5 using the 100-500 at 500mm. Then in post, crop the R5 image to the same framing as the 90D image. What is the resulting R5 image resolution wise ?
My maths tells me 32.4mp with a larger than APS-C image size, due to the larger pixel size but I would appreciate opinions on whether this is correct ?

The Canon R5 has 45Mp.

With the Canon 90D at 400mm et equivalent to 640mm FF (1.6 crop factor)

This means that to match the 640mm FF, the 500mm has to crop with a 1.28 factor.

Originally it had 45Mp pixels, it will have 45Mp/1.28 * 1.28) = 27.5 Mp

So this is 32.5Mp for Canon 90D vs 27.5Mp for Canon EOS R5

 

[gipper51]

I would like to compare a couple of different camera/lens combinations and establish what the resulting resolutions will be, but not confident I’ve got the maths right. Here’s the scenario.

Take an uncropped image from the APS-C Canon 90D. Using the 100-400 at 400mm and then take the same shot with the FF Canon R5 using the 100-500 at 500mm. Then in post, crop the R5 image to the same framing as the 90D image. What is the resulting R5 image resolution wise ?
My maths tells me 32.4mp with a larger than APS-C image size, due to the larger pixel size but I would appreciate opinions on whether this is correct ?

The Canon R5 has 45Mp.

With the Canon 90D at 400mm et equivalent to 640mm FF (1.6 crop factor)

This means that to match the 640mm FF, the 500mm has to crop with a 1.28 factor.

Originally it had 45Mp pixels, it will have 45Mp/1.28 * 1.28) = 27.5 Mp

So this is 32.5Mp for Canon 90D vs 27.5Mp for Canon EOS R5

+1

This is just the 'pixel math'. In the real world, you'll likely have a significantly higher keeper rate of well focused photos to exploit the pixels with the R5 and 100-500 combo due to superior autofocus (camera and lens) and more efficient image stabilization. The cost difference between the two combos is quite substantial though.

Actual detail capture of 27 vs 32 megapixels is practically identical.

 

[gary0319]

I would like to compare a couple of different camera/lens combinations and establish what the resulting resolutions will be, but not confident I’ve got the maths right. Here’s the scenario.

Take an uncropped image from the APS-C Canon 90D. Using the 100-400 at 400mm and then take the same shot with the FF Canon R5 using the 100-500 at 500mm. Then in post, crop the R5 image to the same framing as the 90D image. What is the resulting R5 image resolution wise ?
My maths tells me 32.4mp with a larger than APS-C image size, due to the larger pixel size but I would appreciate opinions on whether this is correct ?

The Canon R5 has 45Mp.

With the Canon 90D at 400mm et equivalent to 640mm FF (1.6 crop factor)

This means that to match the 640mm FF, the 500mm has to crop with a 1.28 factor.

Originally it had 45Mp pixels, it will have 45Mp/1.28 * 1.28) = 27.5 Mp

So this is 32.5Mp for Canon 90D vs 27.5Mp for Canon EOS R5

+1

This is just the 'pixel math'. In the real world, you'll likely have a significantly higher keeper rate of well focused photos to exploit the pixels with the R5 and 100-500 combo due to superior autofocus (camera and lens) and more efficient image stabilization. The cost difference between the two combos is quite substantial though.

Actual detail capture of 27 vs 32 megapixels is practically identical.

Someone else can do the exact math but for “resolution” you can’t just use the crop factor. For instance, comparing a shot taken with a a 45mpx full frame to my 20 mpx MFT camera, the “field of view” crop factor is 2x, but the resolution (number of pixels) is 4x. So, if one crops the image of the 45 mpx to match the FOV image of the MFT, the resultant resolution of the ff image will be 1/4 of 45 mpx or just over 11 mpx. Field of view can be compared with the crop factor, but not resolution. I’m sure someone can provide the ratios for APS-C vs FF

 

[John Crowe]

I believe this is what Chrisfisheye did above. Looks right.

 

[gary0319]

I believe this is what Chrisfisheye did above. Looks right.

Could be, I got lost between the focal length difference and the sensor size difference. A lot easier with just comparing FF to MFT.

 

[John Crowe]

Math has been done.

If the 100-400 is Canon's IS II, it and the 90D will likely deliver a bit more detail. If it is a different 100-400, the R5 might beat it.

While the R5 combo may deliver more keepers to pick through, the 90D combo will certainly deliver excellent images as well.

 

[chrisfisheye]

I would like to compare a couple of different camera/lens combinations and establish what the resulting resolutions will be, but not confident I’ve got the maths right. Here’s the scenario.

Take an uncropped image from the APS-C Canon 90D. Using the 100-400 at 400mm and then take the same shot with the FF Canon R5 using the 100-500 at 500mm. Then in post, crop the R5 image to the same framing as the 90D image. What is the resulting R5 image resolution wise ?
My maths tells me 32.4mp with a larger than APS-C image size, due to the larger pixel size but I would appreciate opinions on whether this is correct ?

The Canon R5 has 45Mp.

With the Canon 90D at 400mm et equivalent to 640mm FF (1.6 crop factor)

This means that to match the 640mm FF, the 500mm has to crop with a 1.28 factor.

Originally it had 45Mp pixels, it will have 45Mp/1.28 * 1.28) = 27.5 Mp

So this is 32.5Mp for Canon 90D vs 27.5Mp for Canon EOS R5

To complete my answer, the crop factor that should be applied for dof comparisons, light diffraction in the op scenario is 1.6/1.28=1.25.

In fact, you are simply comparing aperture size.

So a 400mm f/4 lens with Canon APSC will be equivalent to a 500mm f/5 FF lens after cropping for the same angle of view.

No mystery, in optics the aperture size is really important, the bigger the better. Very true in astrophotography for instance.

 

[bastibe]

I find that telephoto lenses are typically resolution-limited by the lens, not the sensor. Normal focal lengths are more likely to be limited by the sensor resolution (depending on the lens and sensor in question, obviously).

But it all depends on the exact lenses tested, the subject distance... hard to tell from afar.

 

[All about the glass]

Thanks all, a very helpful set of answers.

 

[John Crowe]

While I know that the depth of field in the final image of a 400/4 on FF will be the same as the depth of field of a 500/5 on APS-C, I always compare FF to APS-C in terms of the exposure triangle.

I have used APS-C alongside FF for 9 of 16 digital years. I take advantage of APS-C to get more pixels on the subject with telephoto lenses. In this scenario I consider the 400/4 lens to act as a 500/4 on APS-C. The selected aperture, shutter speed, and ISO based on, available light, can be identical with the same lens used on both systems. So, one can get more pixels on the subject with APS-C without changing any exposure settings.

The alternative to using APS-C is to use a 1.4x on FF. However, in this scenario one actually loses a stop of light and hence one must either increase ISO which will degrade image quality, or use a slower shutter speed which will likely degrade IQ.