Why do mirrorless cameras struggle with red?

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sh1209

sh1209

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I don’t know if any of you have noticed, but every mirrorless camera I have had, which includes both generations of Nikon, Z6&7, Z9, Sony A1, and now a A7RV. If you’re trying to photograph a bird such as a summer Tanager or male cardinal for example, all of these cameras struggle to lock on for initial focus. It doesn’t matter what setting or mode you are in. Perhaps it’s something with sensor technology because on DSLR cameras, there was never any difference whatsoever in being able to acquire focus on red subjects. I have went as far as even setting up a red stuffed animal in the house and one of a neutral color, and every camera I have tried shows a substantial difference in the initial acquisition of focus on red. I’m just curious if any of you have experienced this, and if you have found a workaround. The A7RV seems to be the best of the bunch but still exhibits this issue. I have had male cardinals sitting on a branch with no obstructions 10 yards away, and my Sony A1, unless I grab the focus ring, will not acquire focus. It’s just really strange to me and I don’t understand why.
 
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Please share images.
I have not faced this issue -- is it the old complaint about mirrorless (typically) only using Phase Detect AF with only one orientation of Masks under the microlenses on the Phases Detect pixels and as a result there is a natural bias in favour of or against either horizontal or vertical lines -- depending on the sensor.
If your subject is small, low contrast AND has no favourable edges phase detect struggles.
If the number of Phase Detect Pixels are evenly spaced across all pixels then there would be naturally 2xG, 1xR, and 1xB BUT is the Phase detect mask is normally above the bayer filter immediately below the microlens. This would imply that a subject low in Green and Blue colours will deliver less light to the phase detect sensors. Similar issue could emerge with a predominantly Blue coloured subject. Hence why it is good to find the eyes or high contrast edges.
 
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Andy Miller Photo UK said:
Please share images.
I have not faced this issue -- is it the old complaint about mirrorless (typically) only using Phase Detect AF with only one orientation of Masks under the microlenses on the Phases Detect pixels and as a result there is a natural bias in favour of or against either horizontal or vertical lines -- depending on the sensor.
If your subject is small, low contrast AND has no favourable edges phase detect struggles.
If the number of Phase Detect Pixels are evenly spaced across all pixels then there would be naturally 2xG, 1xR, and 1xB BUT is the Phase detect mask is normally above the bayer filter immediately below the microlens. This would imply that a subject low in Green and Blue colours will deliver less light to the phase detect sensors. Similar issue could emerge with a predominantly Blue coloured subject. Hence why it is good to find the eyes or high contrast edges.
Click to expand...
Not sure the reason but I can assure you it happens. I photograph birds 6-7 days a week and have for many years and never experienced this until going to mirrorless. It’s only subjects that are dark red. It seems to be better if switching to afs which I hardly ever use as I prefer afc. I have not experienced this with darker blue birds at all. In my case it’s only dark red. For instance, I had a male cardinal no further than 10 yards for me on Friday with a green background and it took four or five actuations to acquire focus when it was completely clear of obstructions. I’m not sure where you live if you have many species that are that color that just humor me sometime and try it.
 
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This is one example I had to use manual focus to acquire focus and this was using the 600 prime on the A1
_DSC3177-ARW_DxO_DeepPRIME.jpeg
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Given the prominent eye and black feathers in the centre of the face I cannot see why your Af struggled. The shutter speed seems a little slow and so you may be suffering motion blur -- if you took the same shot at 1/2000th or faster wouldn't the results be sharper (yes at the cost of higher iso)
I would try using with EYE-subject tracking enabled and disabled -- given that at f/5.6 the face and branch would be in a similar focal plane and so both should be in the DOF -- but try other apertures as well. In other words if it does not work one way try other ways to see what works to enable you to take the image you want. Sure MF can works but only when there is no movement -- you, your camera, the subject -- and you provide enough DOF to compensate for minor movement.
The Leica rule is to time one's shot until you know the subject's eye is in focus. Me -- my eyes are shot so I have to rely on AF or zoom in to 100% to do this.
 
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We should also remember that the base sensor is more sensitive to red than to other colors. Specifically, there is a filter that blocks the infrared range to limit its impact on the photos. When converting to IR, that hot filter is removeed and replace with a filter that limits to a certain IR wavelength (my camera is 590nm while others may use 660nm or 720nm. So, your camera is more sensitive to red and, for more intense red colors, may overload the sensor and affect the sensor's ability to grab a clear focus. That hot filter also impacts UV rays on the other end of the visible spectrum. Some will remove the hot filter, then use specific frequency lens filters to pick the UV to IR range they wish to cover. All of this may impact the ability of the sensor to fouc properly.

Then there is the internal software manipulation the camera goes through to convert the Bayer array R, G and B sites into the photgraph you see. This too can influence how the photo is processed after capture and why things like red roses and cardinals can be more difficult to capture well. Just my thoughts. Others may have a more informed opinion.
 
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Here is another example as you can see there is absolutely no obstructions or anything to confuse the sensor yet the camera absolutely would not focus without acquiring focus manually first.
_DSC1540-ARW_DxO_DeepPRIME-Edit.jpeg
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Andy Miller Photo UK said:
Given the prominent eye and black feathers in the centre of the face I cannot see why your Af struggled. The shutter speed seems a little slow and so you may be suffering motion blur -- if you took the same shot at 1/2000th or faster wouldn't the results be sharper (yes at the cost of higher iso)
I would try using with EYE-subject tracking enabled and disabled -- given that at f/5.6 the face and branch would be in a similar focal plane and so both should be in the DOF -- but try other apertures as well. In other words if it does not work one way try other ways to see what works to enable you to take the image you want. Sure MF can works but only when there is no movement -- you, your camera, the subject -- and you provide enough DOF to compensate for minor movement.
The Leica rule is to time one's shot until you know the subject's eye is in focus. Me -- my eyes are shot so I have to rely on AF or zoom in to 100% to do this.
Click to expand...
It’s normally just a quick bump of the focus ring to correct it but other times even that’s a struggle.
 
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Are these images full frame or cropped in? The Alpha 1 is a great 50mp beast -- but a heavy crop will look soft.

I am not a sony shooter -- but perhaps you could say more about which AF mode you were using and whether or not eye-tracking was enabled etc..

If you were shooting with a Nikon I would ask you to indicate where the focus point was when AF was used - we use NX studio to do this. Can you do the same with your Sony?

I still "believe" 1/800th is too slow when shooting small birds -- any wind or movement and their tiny feathers move leading to what look like soft images. The image is too low resolution to see if anything is super sharp -- ie where the plane of focus is.

The image you posted on flickr (Cardinal Eating a praying mantis) seemed to work -- was that taken using AF or MF?
 
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Andy Miller Photo UK said:
Are these images full frame or cropped in? The Alpha 1 is a great 50mp beast -- but a heavy crop will look soft.

I am not a sony shooter -- but perhaps you could say more about which AF mode you were using and whether or not eye-tracking was enabled etc..

If you were shooting with a Nikon I would ask you to indicate where the focus point was when AF was used - we use NX studio to do this. Can you do the same with your Sony?

I still "believe" 1/800th is too slow when shooting small birds -- any wind or movement and their tiny feathers move leading to what look like soft images. The image is too low resolution to see if anything is super sharp -- ie where the plane of focus is.

The image you posted on flickr (Cardinal Eating a praying mantis) seemed to work -- was that taken using AF or MF?
Click to expand...
That image was with autofocus but still struggled to get focus initially. I would say it’s at least 85% of the time. No other color whatsoever has this issue.
 
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I haven't noticed it. I use both DSLR (Nikon D850 with lenses from wide up to 80-400) and mirrorless (Sony A74 with 200-600). We do have cardinals where I live and I have shot them with my Sony, though more often I take my Nikon. I guess If I see one again with my Sony in hand I will make a note of how it goes.

This may or may not be pertinent, but I worked at a photo lab for 20 years and I know in making developed photographic prints the reds would block up and have a hard time showing detail. Best example is a flower like a rose: it would print as solid red without the petal separation you would have with other colored flowers.
 
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These are two more examples with the tanager never being able to acquire focus automatically. The more red the worse the problem.
DSC08694_DxO-Edit-Edit.jpeg
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DSC07616-Edit.jpeg
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boviscopophobic said:
I believe the on-sensor PDAF pixels are all green or blue. So it might make sense that they have a harder time with a pure red subject.
Click to expand...
Do you have a source for that you can share — it would be surprising if confirmed.

Why might this be true — red has the longer focal length of the 3 — blue having the shorter wave length and higher energy of the 3 colours as a result af with blue light could be more accurate — of course one is considering nm so one should add “relatively more accurate”
 
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Andy Miller Photo UK said:
Do you have a source for that you can share — it would be surprising if confirmed.

Why might this be true — red has the longer focal length of the 3 — blue having the shorter wave length and higher energy of the 3 colours as a result af with blue light could be more accurate — of course one is considering nm so one should add “relatively more accurate”
Click to expand...
One other thing I’ve noticed that amplifies the problem is whenever the surroundings are more green. This doesn’t make sense considering how much contrast there is between the two.
 
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Andy Miller Photo UK said:
Do you have a source for that you can share — it would be surprising if confirmed.

Why might this be true — red has the longer focal length of the 3 — blue having the shorter wave length and higher energy of the 3 colours as a result af with blue light could be more accurate — of course one is considering nm so one should add “relatively more accurate”
Click to expand...
It can be found in Thom Hogan's writings about Z system cameras. This is from the Z9 book:
"Note: I mentioned light wavelengths before. If you know anything
about spectral differences, you’re probably already
guessing that if the light is “too red” the camera might be
focusing to one direction, while if the light is “too blue” the
camera might be focusing to the other direction. The Z
Series cameras’ phase detect sensors live under blue and
green filters, so they’re not tuned to extremely red (and
near-IR) light. "
 
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sh1209 said:
I don’t know if any of you have noticed, but every mirrorless camera I have had, which includes both generations of Nikon, Z6&7, Z9, Sony A1, and now a A7RV. If you’re trying to photograph a bird such as a summer Tanager or male cardinal for example, all of these cameras struggle to lock on for initial focus. It doesn’t matter what setting or mode you are in. Perhaps it’s something with sensor technology because on DSLR cameras, there was never any difference whatsoever in being able to acquire focus on red subjects. I have went as far as even setting up a red stuffed animal in the house and one of a neutral color, and every camera I have tried shows a substantial difference in the initial acquisition of focus on red. I’m just curious if any of you have experienced this, and if you have found a workaround. The A7RV seems to be the best of the bunch but still exhibits this issue. I have had male cardinals sitting on a branch with no obstructions 10 yards away, and my Sony A1, unless I grab the focus ring, will not acquire focus. It’s just really strange to me and I don’t understand why.
Click to expand...
That’s very weird. I photograph a lot of cardinals and it locks onto the eye instantly. I have shot some summer tanager a few times and never noticed an issue with that bird either. Friend shoots an R5 and I’ve never heard or noticed him having any issues when we are out together.
 
pe1125 said:
It can be found in Thom Hogan's writings about Z system cameras. This is from the Z9 book:
"Note: I mentioned light wavelengths before. If you know anything
about spectral differences, you’re probably already
guessing that if the light is “too red” the camera might be
focusing to one direction, while if the light is “too blue” the
camera might be focusing to the other direction. The Z
Series cameras’ phase detect sensors live under blue and
green filters, so they’re not tuned to extremely red (and
near-IR) light. "
Click to expand...

Does he mention how he knows that about the phase detect being only under blur and green filters?
 
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DavidT said:
That’s very weird. I photograph a lot of cardinals and it locks onto the eye instantly. I have shot some summer tanager a few times and never noticed an issue with that bird either. Friend shoots an R5 and I’ve never heard or noticed him having any issues when we are out together.
Click to expand...
I can be twenty feet away with the A1 and 600GM and there are times I’ll have to engage for 4-5 times to lock on. Never ever happens with any other color. Also had the same issue with five different Nikon mirrorless bodies and various lenses. Again it’s not the end of the world but it’s puzzling.
 
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It’s just really hard for me to believe of the hundreds of thousands of bird images I’ve taken over the last 22 years and multiple bodies and lenses I’ve shot with and owned that I have suddenly developed an impediment for shooting red subjects lol. Like I also said earlier in the thread, it is more prominent when there is more green in the surroundings of the subject.
 
So if there was a lens filter that only allowed red light to pass, these cameras could not autofocus?
 
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