Birding on high MP - ISO vs focal length

Ruined

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Aug 22, 2013
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Just curious for those using either the RF 100-500 or EF 100-400 with 1.4 TC on a 45+ MP body

For very high shutter speed (ie fast moving birds) that will drive ISOs higher up, are the longer lenses with narrower aperture really any better than the 100-400 II @400mm 5.6 on a 45+ MP body? I would think with the loss of light between nearly a full stop to a full stop, the corresponding increase in ISO to compensate would not sufficiently improve detail when have a 45mp+ camera that is able to be heavily cropped.

In other words on high MP camera seems like cropping more @ 400mm f/5.6 might actually yield the same or more detail than 500-560mm at f/7.1-f/8 - at those high shutter speeds to fully stop action in flight. The extra noise from higher iso would reduce contrast and then detail when you have to more aggressively remove that noise in post.

Thoughts?
 

AlanF

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Short answer is that loss of detail is at best minimal and at worst the same for those cases. Long answer. The 100-500mm f/7.1 and 100-400 f/5.6 have the same diameter front element, ~72mm. And the extenders don’t change that. So, they all let in the same amount of light. The same number of photons hit the cropped image if you crop all the different images to the size of the same subject. The f-number gets larger as you increase the focal length with the same diameter front element and so you have to increase the iso if you keep the same shutter speed speed and aperture wide open. Doubling the focal length will need the iso to increase 4x but the area of the image of the subject will increase 4x. At the very worst, the loss of detail is compensated for by the increase in size.

In practical terms, pushing up the iso when using the 100-500mm at 7.1 compared with the 100-400 at f.5.6 should not result in loss of any detail after cropping and if the light is good will retain the advantages of extra focal length. If the light is bad, putting on an extender is a waste of time.
 

Ruined

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Aug 22, 2013
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Short answer is that loss of detail is at best minimal and at worst the same for those cases. Long answer. The 100-500mm f/7.1 and 100-400 f/5.6 have the same diameter front element, ~72mm. And the extenders don’t change that. So, they all let in the same amount of light. The same number of photons hit the cropped image if you crop all the different images to the size of the same subject. The f-number gets larger as you increase the focal length with the same diameter front element and so you have to increase the iso if you keep the same shutter speed speed and aperture wide open. Doubling the focal length will need the iso to increase 4x but the area of the image of the subject will increase 4x. At the very worst, the loss of detail is compensated for by the increase in size.

In practical terms, pushing up the iso when using the 100-500mm at 7.1 compared with the 100-400 at f.5.6 should not result in loss of any detail after cropping and if the light is good will retain the advantages of extra focal length. If the light is bad, putting on an extender is a waste of time.
I wish there was a more mathematical way of discerning which is better, or if they are about the same, but I don't think there is.

At 400mm 5.6 cropped to 500mm there will be significantly lower amount of ISO noise, higher contrast, but the ISO noise will be slightly chunkier since it will be digitally blown up a bit

At 500mm 7.1 native or 560mm f/8 there will be significantly more ISO noise, lower contrast, but the ISO noise will be finer (maybe)

In terms of fine detail on 45mp+ I am wondering if there will be little difference after more aggressive NR is needed to rid the ISO noise at f/7.1-f/8

This wouldn't be an issue if you could have a slower shutter to drop iso but that's not really an option for flying birds, especially the fast ones. I feel like I need to be at 1/3200 to get super sharp captures...
 
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AlanF

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I wish there was a more mathematical way of discerning which is better, or if they are about the same, but I don't think there is.

At 400mm 5.6 cropped to 500mm there will be significantly lower amount of ISO noise, higher contrast, but the ISO noise will be slightly chunkier since it will be digitally blown up a bit

At 500mm 7.1 native or 560mm f/8 there will be significantly more ISO noise, lower contrast, but the ISO noise will be finer (maybe)

In terms of fine detail on 45mp+ I am wondering if there will be little difference after more aggressive NR is needed to rid the ISO noise at f/7.1-f/8

This wouldn't be an issue if you could have a slower shutter to drop iso but that's not really an option for flying birds, especially the fast ones. I feel like I need to be at 1/3200 to get super sharp captures...
Why would there be more contrast cropping 400/5.6 to 500 than there would be at native 500mm and f/7.1?
 

Ruined

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Aug 22, 2013
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Why would there be more contrast cropping 400/5.6 to 500 than there would be at native 500mm and f/7.1?
Because if I have the camera in 1/3200 fixed shutter at widest aperture to freeze motion as best as possible, f/7.1 will require notably higher ISO setting than f/5.6 for similar brightness, and as iso goes up amount of noise increases and contrast goes down. Cropping will not reduce contrast or increase noise artifacts, it will just make the existing noise artifacts a bit larger in size.

I would think the main advantage of a 500mm-560mm f/7.1-f/8 would be when the sensor runs out of digital resolution to render a detailed picture when cropping 400mm f/5.6 . But on 45mp+ cameras this becomes a lot less of an issue than lower MP cameras, hence looking at ISO vs focal length becomes a lot more important in high shutter speed applications.

Also worth considering both the 100-400+TC and 100-500 are narrower aperture @ 400mm range than the 100-400 II , so it's not like you can just step back the zoom to 400 and get 5.6 in these cases - the 100-500 you have to drop to 364mm and the 100-400 you'd have to take off the TC
 
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AlanF

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Because if I have the camera in 1/3200 fixed shutter at widest aperture to freeze motion as best as possible, f/7.1 will require notably higher ISO setting than f/5.6 for similar brightness, and as iso goes up amount of noise increases and contrast goes down. Cropping will not reduce contrast or increase noise artifacts, it will just make the existing noise artifacts a bit larger in size.

I would think the main advantage of a 500mm-560mm f/7.1-f/8 would be when the sensor runs out of digital resolution to render a detailed picture when cropping 400mm f/5.6 . But on 45mp+ cameras this becomes a lot less of an issue than lower MP cameras, hence looking at ISO vs focal length becomes a lot more important
If you view at the same output size, then you have to magnify the crop from the 400mm by a factor of 1.25x1.25 and that magnifies noise, decreases DR etc etc. Viewing at the same size is the reason why APS-C has worse DR, worse S/N etc than FF. The maths is quite simple: if the signal is limited by light, then the crucial factor is the number of photons in the image, and the S/N in the final image varies as the square root of the number of photons.
 

Ruined

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Aug 22, 2013
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If you view at the same output size, then you have to magnify the crop from the 400mm by a factor of 1.25x1.25 and that magnifies noise, decreases DR etc etc. Viewing at the same size is the reason why APS-C has worse DR, worse S/N etc than FF. The maths is quite simple: if the signal is limited by light, then the crucial factor is the number of photons in the image, and the S/N in the final image varies as the square root of the number of photons.
I understand where you are coming from, but again dropping 5.6 to 7.1 is 2/3 of a stop of light. And f/8 a full stop of light.

So then it becomes a question on the higher MP bodies whether the ISO increase to make up for that difference in brightness is worth the extra optical reach vs cropping and magnifying the lesser artifacts in a lens with a bit less optical reach.

I think its not entirely doable by math because sensors respond differently to higher ISOs in terms of ugliness of artifacts and how easy to remove
 

AlanF

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I understand where you are coming from, but again dropping 5.6 to 7.1 is 2/3 of a stop of light. And f/8 a full stop of light.

So then it becomes a question on the higher MP bodies whether the ISO increase to make up for that difference in brightness is worth the extra optical reach vs cropping and magnifying the lesser artifacts in a lens with a bit less optical reach.

I think its not entirely doable by math because sensors respond differently to higher ISOs in terms of ugliness of artifacts and how easy to remove
If you drop 5.6 to to 7.1 then you do lose 2/3 of a stop of light, but if you do this by increasing the focal length from 400mm to 500mm and keeping the same diameter, you have gained 1.25x1.25 in area of the cropped image, which is 2/3 stop. So the changes cancel out. Similarly, with 5.6 to f/8 if it is done by increasing the focal length by a factor of 2 etc.
 

Czardoom

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Jan 27, 2020
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Rather than over-think this to death, why don't you just go out and take some photos with ISO's that are 2/3rds to a 1 stop apart. I doubt you'll see much noise difference, but actual photos will give you an answer.
 

AlanF

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Rather than over-think this to death, why don't you just go out and take some photos with ISO's that are 2/3rds to a 1 stop apart. I doubt you'll see much noise difference, but actual photos will give you an answer.
This is not over thinking, it’s basic physics and optics.
 
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Joules

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Because if I have the camera in 1/3200 fixed shutter at widest aperture to freeze motion as best as possible, f/7.1 will require notably higher ISO setting than f/5.6 for similar brightness, and as iso goes up amount of noise increases and contrast goes down. Cropping will not reduce contrast or increase noise artifacts, it will just make the existing noise artifacts a bit larger in size.
I think that's the trouble here. You seem to understand that both 400 5.6 and 500 7.1 let in the same amount of total light (400/5.6 ~ 500/7.1) and the difference is just over what area that light is spread. As cropping to the same field of view negates the difference in area, the total amount of light that makes up both images is also the same.

What you seem to misunderstand is how noise works.

In particular the notion that increasing ISO increases noise while cropping an image just makes noise more apparent is problematic. Because these actually have the same impact: Making existing noise more apparent.

Especially with regards to high ISOs, increasing it does not actually add any noise to your image. It only amplifies the noise already in the source signal. The noise that dominates low light photography isn't a property of the sensor. It is a property of the very light itself, called shot noise.

Light is noisy. When light is the signal, the amount of noise is the square root of the signal. So with more light, there is more noise in the signal - but it is less apparent, as it grows slower than the light. The term signal to noise ratio (SNR or S/R) expresses how apparent the noise is and is calculated by the signal divided by the sum of the noise sources. As shot noise is by far the largest source for photography with low light and short exposure times, that's the only one that matters for your question.

ISO has no effect on shot noise. It is just amplifying it, but not adding to it. You can essentially ignore ISO when you want to optimize how little noise you can see in your images. More light is the only way to reduce the noise. As cropping the 400 5.6 image to the 500 7.1 field of view brings the amount of light in both images to the same level, the amount of noise is the same.

The difference in ISO is just there to cause the brightness to be the same, because that is of course necessary to make a meaningful comparison. But it is not degrading the 500 7.1 shot to be any worse than the 400 5.6 shot. In fact, as the 500 7.1 shot is uncropped, it has more detail and therefore more headroom for further cropping - more reach essentially.
I think its not entirely doable by math because sensors respond differently to higher ISOs in terms of ugliness of artifacts and how easy to remove
I don't quite understand what you mean by this. But if you argue that using only SNR to judge how noisy an image is simplifies the visual complexity of noise too much, that is in my opinion an intuitive reaction to the subject but nonetheless not correct. I originally felt the same way and investigated it myself through images. If you are skeptical of my claims, you can look deeper into what I am basing them off.

I have compiled the results in a fairly decent thread about equivalency here:

Post in thread 'Equivalency - Now with pictures!' https://www.canonrumors.com/forum/threads/equivalency-now-with-pictures.39787/post-874838

That's essentially covering the question you are asking here (focal length vs cropping). I still have to sit down and clean up (and finish!) those posts, which I haven't done yet. So excuse the rough edges, I just hope it might give you some impressions. It is not enough to just view the images, as they aren't fully self explaining. I am hoping to improve that eventually, but for now you should read at least the passage above each image that describes it.
 
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Ruined

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Aug 22, 2013
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What I meant re: ISO noise sensor differences was , to use a more extreme example, the 5d3 for instance to me at least appears to get a nasty patterning at higher ISOs that doesn't appear as prevalent as lower ISOs - while the 6D sensor released after it does not appear to have this issue at higher ISOs. I will review your post when I have more time but it's sounding like the answer to my original question is that it doesn't make too much of a difference if you don't run into a resolution wall at the sensor.
 

AlanF

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What I meant re: ISO noise sensor differences was , to use a more extreme example, the 5d3 for instance to me at least appears to get a nasty patterning at higher ISOs that doesn't appear as prevalent as lower ISOs - while the 6D sensor released after it does not appear to have this issue at higher ISOs. I will review your post when I have more time but it's sounding like the answer to my original question is that it doesn't make too much of a difference if you don't run into a resolution wall at the sensor.
The R5 is incredible at handling high iso. I am shooting at much higher isos than I dared previously, and DxO PL4 with DeepPRIME juts eats the noise. The answer to your original question is that the 100-500mm f/7.1 is at worst as good as the 100-400mm II f/5.6 and in the right conditions it outresolves it.
 

Joules

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What I meant re: ISO noise sensor differences was , to use a more extreme example, the 5d3 for instance to me at least appears to get a nasty patterning at higher ISOs that doesn't appear as prevalent as lower ISOs - while the 6D sensor released after it does not appear to have this issue at higher ISOs. I will review your post when I have more time but it's sounding like the answer to my original question is that it doesn't make too much of a difference if you don't run into a resolution wall at the sensor.
All older Canon sensors suffer from fixed pattern noise and nasty read noise in the shadows. That's why people loved Sony sensors so much for a while.

The only Canons that are truly free of that are the 90D, M6 II, 1DX III, R6 and R5. The R got a firmware update that mostly fixed the banding issues it inherited from the 5D IV. But only the newer sensors named above are clean enough to consider images as being totally dominated by shot noise.

If you want to talk about an old Canon sensor, that is different. But it seemed to me you were concerned with modern bodies, and the EOS R5 in particular. As no future Canon body is going to take a step backwards with regard to sensor technology, I think it was fair of me to address the current technology, not past one.
 

Ruined

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Aug 22, 2013
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All older Canon sensors suffer from fixed pattern noise and nasty read noise in the shadows. That's why people loved Sony sensors so much for a while.

The only Canons that are truly free of that are the 90D, M6 II, 1DX III, R6 and R5. The R got a firmware update that mostly fixed the banding issues it inherited from the 5D IV. But only the newer sensors named above are clean enough to consider images as being totally dominated by shot noise.

If you want to talk about an old Canon sensor, that is different. But it seemed to me you were concerned with modern bodies, and the EOS R5 in particular. As no future Canon body is going to take a step backwards with regard to sensor technology, I think it was fair of me to address the current technology, not past one.
I am using 5DsR personally , got a pair on clearance for $1499/ea , ISO performance at same viewing size is slightly better than the 6D but worse than the 5D4 at lower ISOs (similar to 5d4 at higher ISOs). Was looking at differences between cropping and higher aperture options (like 100-400 + 1.4TC) - but I figured many would have 100-500 f/7.1 which is relatively similar comparative to 140-560 f/8 - so that's why i included it in the topic

Am currently using 70-300L which is my go to travel lens and while I am getting spectacular results cropping, getting more into birds and deciding whether to jget 100-400 and crop, 100-400 + TC, or one of the other (sigma etc) longer + higher aperture lens options of which there are a few. For now I will probably keep what I have until the 100-400 II gets a rebate at the minimum as the 70-300L has offered spectacular results and I will be keeping it regardless for travel

Too bad there is no affordable canon 200-600 f/6.3 like sony has, that seemingly would be a better option than what Canon has now
 
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Ruined

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Aug 22, 2013
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The R5 is incredible at handling high iso. I am shooting at much higher isos than I dared previously, and DxO PL4 with DeepPRIME juts eats the noise. The answer to your original question is that the 100-500mm f/7.1 is at worst as good as the 100-400mm II f/5.6 and in the right conditions it outresolves it.
For me personally it would be the 400 II vs the 400 II + 1.4 TC since I am using 5DsR. But even in the case of the 100-500 f/7.1, theoretically from everything discussed here in this use case it seems it wouldn't be that great of a difference from the 100-400 ii f/5.6 in this case due to the aperture difference; and it seems the IS mechanism in the 100-500 is a bit controversial even if I could use it, plus the way TCs work is really odd, and its actually slower than the 100-400 II in many spots at 400mm and below. Maybe if you ran out of resolution on 45mp+ with an extreme crop on the 100-400 then the 100-500 would be noticably better in that case, but some of the competitors have lenses that are 200-600mm f/6.3 and cost less than either of the Canon options. It's a bigger lens, but I think a lot here wouldn't care because given everything we discussed theoretically 600mm f/6.3 should blow away 400mm f/5.6 or 500mm f/7.1 cropped to 600mm given similar quality optics used.
 
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