FS7: Sony FS7 purple fringing - any fix?

Martin.G said:
So i saw this image:

http://the-delivery-men.com/wp-content/uploads/2014/12/Screen-Shot-2014-11-22-at-3.18.56-PM.png

http://the-delivery-men.com/sony-fs7/

This purple fringing is completely destroying the image. Is this a common problem on the FS7?

I plan to shoot a lot of backlit, high contrast scenes much similar to the one in the photo here.

If this occurs often, how do one proceed to fix it?
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What's the glass you're using?

It's worth reading up on chromatic aberration. Fundamentally it's an optical principle where different wavelengths of light are focused at different positions. Practically, it can be compensated for both by composing to avoid it, and by improving optics. Higher end lenses tend to use glass with properties that help keep the wavelengths all focused correctly. Newer lens also frequently have electronic compensation, but the electronic compensation only works when the lens is used on it's native camera system that recognizes it's digital profile and makes processing adjustments in camera. Also, note that lenses made for 3-chip prism cameras intentionally separate the light wavelengths, which would be an issue if using them with an adapter on a single chip S35 system.

Short version: You'll need to either find better glass, compose the shots differently, or maximize your lens aperture to peak performance, and light to suit. Intentionally (for effect, or budget limitation) pushing the dynamic range will likely exacerbate the problem. Even if your desire is for a final image with a heavy backlight, you may need to use an increased amount of on set front fill to reduce the contrast and make it easier to expose.

Also, the High Frame Rate (over 60p) might make this issue worse.
 
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Purple fringing like that can (can not is) be due to axial chromatic aberration. If you can repeat the scene changing focus depth should reduce it then you'll know it was Axial chromatic aberration.

If there's any sharpening due to post processing or aliasing induced by the codec it can exacerbate the fringing.

Sam M-M mentioned to me he had seen it in high contrast high frequency parts of the image in 4K. I haven't seen any sign of it yet but we all use different lenses so it's difficult to absolutely pin down.

Whatever the cause it should be relatively easy to knock out of the image with a secondary correction.

I've been shooting in CineEI mode but if you're in Custom check the sharpening settings and turn them off although I'm not sure if this completely defeats sharpening so cameras it does others it doesn't. Doug will probably know. Both FS100 and 700 are susceptible to aliasing at the hot end especially when even tiny amounts of sharpening are used.
 
It does look like CA, but I've never seen such even distribution of CA across a frame before. So I'd by no means discount the possibility of it being shoddy highlight processing on the part of the camera.

Test it again, stopping the camera down further and further (while maintaining the same exposure). That should reveal whether it's CA that can be avoided with a better lens, or whether it's something inside the camera.
 
Paul schefz said:
it's CA, not an issue with the camera...
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Yes and no. I commented on it on Sony forum with no response, I'm glad it was brought up here. It's my unscientific observation but there is something about the way the FS7 handles those spherochromatic abberations, it greatly emphasizes the magenta fringes, often rendering them as primary red. I'm not an engineer but think it has something to do with a bayer pattern and demosaic process and the fact that the camera renders high detail images (as reported, the OLPF is optiized for high detail with a greater risk of aliasing being a trade of). I observe it in magnified view of the EVF, something about how sharpenned those magenta fringes become at specific focus setting. Since the OLPF does not deal with aliasing off primary colors uniformly in bayer type sensors, I think that what we see are aliases in red channel triggered by the spherochromatic abberations. Pretty much every lens has some degree of spherochromatism, especially at wide openings but FS7 makes it much more noticable.
 
The picture in the OP is not my photo. I cannot reshoot because i have only recently placed an order for an FS7, so i am waiting for that to arrive.

However, when reading up i see several posts about purple fringing. It looks like i may be doing a bad descision to sell my FS700+Odyssey7Q and go for a purple fringing box from Sony.

This is what the blogger says about their lenses:

We used both he Metabones Speedbooster IV and Metabones Adaptor II with Canon Cinema primes.
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That combo shouldnt exhibit that amount of CA, surely? And so purple too?

The issue looks very much alike that of the FS700, where in high contrast areas would alias a heavy black fringe.
 
I have found in repeated testing that when the baked color space is wide (SGamut, SGamut3.Cine), there are chroma artifacts. When the baked color space is narrowed (709), the artifacts either disappear entirely or are substantially reduced.
Given a fixed bit rate, a wide gamut is more difficult to compress than a narrow gamut. So if you choose to compress a wide gamut, something else must suffer. This appears to be it.

For me, the best results with XAVC are consistently obtained by baking LC-709typeA.

Cheers.
Noel Sterrett

Admit One Pictures
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So i buy a wide gamut camera, but must shoot narrow gamut in order to get acceptable pictures?
 
Martin.G said:
The picture in the OP is not my photo. I cannot reshoot because i have only recently placed an order for an FS7, so i am waiting for that to arrive.

However, when reading up i see several posts about purple fringing. It looks like i may be doing a bad descision to sell my FS700+Odyssey7Q and go for a purple fringing box from Sony.

This is what the blogger says about their lenses:
**Quote from blogger mentioned Metabones Speedbooster


That combo shouldnt exhibit that amount of CA, surely? And so purple too?

The issue looks very much alike that of the FS700, where in high contrast areas would alias a heavy black fringe.
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Actually, the Metabones Speedbooster could definitely be causing problems. The Speedbooster works by employing an optical element to concentrate a full frame image into an S35 frame - the benefit here is greater light gathering capacity, wider framing, as well as shallower depth of field. However, there have been prior reports of the Metabones Speedbooster producing similar fringing issues. Essentially that Speedbooster optical element is throwing off the focusing distances of different wavelengths of light.

If the speedbooster was used in the sample frame you showed us, that was a poor choice on set - daylight outdoor medium and wide shots typically need neither shallow depth of field nor a light gathering boost. I stay away from Speedbooster unless the shot absolutely requires one.
 
Viddovation said:
Actually, the Metabones Speedbooster could definitely be causing problems. The Speedbooster works by employing an optical element to concentrate a full frame image into an S35 frame - the benefit here is greater light gathering capacity, wider framing, as well as shallower depth of field. However, there have been prior reports of the Metabones Speedbooster producing similar fringing issues. Essentially that Speedbooster optical element is throwing off the focusing distances of different wavelengths of light.

If the speedbooster was used in the sample frame you showed us, that was a poor choice on set - daylight outdoor medium and wide shots typically need neither shallow depth of field nor a light gathering boost. I stay away from Speedbooster unless the shot absolutely requires one.
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It is not a question whether the CA is there in the first place or not, no one argues whether the CA fringes (specifically spherochromatic ones) are there. The question is what happens with these color fringes later. Same lenses with same optical adapters create the same amount of aberrations optically on any system, it just that some systems make them more visible. It's like discussing the rolling shutter / jello artifacts - obviously it is the camera shake / fast horizontal motion that cause it to begin with BUT depending on the system it will or will not be noticeable at all. Something is definitely going on here, I suspect it is how compression and / debayering makes the fringes more pronounced. If the problem was purely optical then there would not be a significant difference between XAVC and RAW recording.
 
broughtonfilm said:
It is not a question whether the CA is there in the first place or not, no one argues whether the CA fringes (specifically spherochromatic ones) are there. The question is what happens with these color fringes later. Same lenses with same optical adapters create the same amount of aberrations optically on any system, it just that some systems make them more visible. It's like discussing the rolling shutter / jello artifacts - obviously it is the camera shake / fast horizontal motion that cause it to begin with BUT depending on the system it will or will not be noticeable at all. Something is definitely going on here, I suspect it is how compression and / debayering makes the fringes more pronounced. If the problem was purely optical then there would not be a significant difference between XAVC and RAW recording.
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Okay, you're right on a bunch of that, but I don't see how my comments aren't correct and on topic. I certainly wasn't under the impression the conversation was limited to discussing the limitations of the FS7 - my impression was that the OP was presenting a problems (purple fringing / CA ), and we were being asked to provide both explanations, as well as practical solutions. The OP never discusses RAW vs XAVC. nor does the OP claim the problem only occurs in the XAVC and not RAW. So just because you've experienced an issue that is specific to the digital implementation does not mean that the OP's issue is the same. Perhaps it is, but given the information the OP has provided, it remains valid to discuss this in terms of optical chromatic aberration, and therefore to discuss practical steps one can take to avoid it.

So, as much as your comments about codec being a potential consideration are on point, so are my comments about practical solutions on set to reduce CA, including avoiding Speedboosters.
 
Viddovation said:
Okay, you're right on a bunch of that, but I don't see how my comments aren't correct and on topic. I certainly wasn't under the impression the conversation was limited to discussing the limitations of the FS7 - my impression was that the OP was presenting a problems (purple fringing / CA ), and we were being asked to provide both explanations, as well as practical solutions. The OP never discusses RAW vs XAVC. nor does the OP claim the problem only occurs in the XAVC and not RAW. So just because you've experienced an issue that is specific to the digital implementation does not mean that the OP's issue is the same. Perhaps it is, but given the information the OP has provided, it remains valid to discuss this in terms of optical chromatic aberration, and therefore to discuss practical steps one can take to avoid it.

So, as much as your comments about codec being a potential consideration are on point, so are my comments about practical solutions on set to reduce CA, including avoiding Speedboosters.
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Have you read the information in the other threads that OP provided? It is relevant. Those threads always tend to slide towards someone lecturing the other person whenever there is a chance (here a lecture about what speed boosters are and why it was such a bad idea to use it). It really muddies the water unnecessarily.
 
Is this suddenly news that just about every camera will struggle with wide open lesser lenses in high contrast areas?
 
broughtonfilm said:
Have you read the information in the other threads that OP provided? It is relevant. Those threads always tend to slide towards someone lecturing the other person whenever there is a chance (here a lecture about what speed boosters are and why it was such a bad idea to use it). It really muddies the water unnecessarily.
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Yes, I have. And even those threads have plenty of people arguing that users should address it optically as chromatic aberration. So again, I think I'm on point to discuss practical steps on set.
 
Ben Scott said:
Is this suddenly news that just about every camera will struggle with wide open lesser lenses in high contrast areas?
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You know, I think people have this impression that high dynamic range cameras have special little cinema leprechauns in them, and as long as you point the camera in the right direction and run the lens wide open, it doesn't matter what lens you use, what the lighting is, what the exposure is... you'll be able to grade wonderful images in post... just make sure you use 4k!!!

Then these wonderful, enlightened individuals posts camera tests and reviews, and scare other people who were considering investing in some magic cinema leprechauns instead of a nice Arri kit and a book or two about lighting and optics.
 
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It's simply absurd. Shooting objects with a ton of specular hotspots without a mattebox in incredibly bright and high contrast scene and you wonder why it might look shite and put it down to the camera? Take some responsibility for the bit you as an operator are supposed to bring to the party to solve or avoid scenes like that. Grrr...
 
Viddovation said:
Yes, I have. And even those threads have plenty of people arguing that users should address it optically as chromatic aberration. So again, I think I'm on point to discuss practical steps on set.
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Sure, some argue this should be addressed optically (just like some argue that rolling shutter / jello is not an issue - just use static shots and there is no issue...) but it is not always solution. That's the point. It is not only wide open. Many of my lenses (admittedly not Ultra or Master primes) even when stopped down seem to trigger this fringing (yes, slight amount of spherochromatic CA is there), same lenses which never were a problem on other systems. We are talking about the specific system - not about the camera and lenses individually. Sure, we all learn how to work around limitations of a given system but does it mean the issue does not exist and should not be discussed?
 
Ben Scott said:
It's simply absurd. Shooting objects with a ton of specular hotspots without a mattebox in incredibly bright and high contrast scene and you wonder why it might look s*%te and put it down to the camera? Take some responsibility for the bit you as an operator are supposed to bring to the party to solve or avoid scenes like that. Grrr...
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How does mattebox help in a situation where ton of specular hotspots and high contrast objects are in the frame?
 
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