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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Circle of confusion for Red One

richard cook said:
I am trying to find out the CoC for the Red one at 4k and 2k, does anyone know where I can find this information?
Many thanks Richard
Click to expand...
This phenomena is 100% dependent on the lens you are using and the size of the final projection. In theory it has nothing to do with the imager.
 
I disagree- it has everything to do with the imager as the imager resolution determines the DOF. I wouldn't go higher than 10 microns.
Out of curiosity: what do you need it for?
 
OptiTek said:
I disagree- it has everything to do with the imager as the imager resolution determines the DOF. I wouldn't go higher than 10 microns.
Out of curiosity: what do you need it for?
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Wrong ... the DOF is 100% determined by the lens focal length and aperture. Your image sensor can be any size. The DOF on a RED ONE is determined by the lens, (focal length and aperture).
 
George Butterfield said:
Wrong ... the DOF is 100% determined by the lens focal length and aperture. Your image sensor can be any size. The DOF on a RED ONE is determined by the lens.
Click to expand...
How about the object distance? is it the same for any object distance? How about the circle of confusion? is it the same for different circle of confusion?
I would do a bit more research before you posts in such assertive way next time...
 
All of these factors play a role in DOF. Primarily DOF is determined by focal length, aperture and subject (focal) distance. DOF also varies in its perception or how the viewer "sees" it based on the imager size, resolving power or resolution, output size and resolution and viewing distance. CoC, which is a determinant of those resolutions and viewing distance, is a measure of the visual acuity within a given construct or imaging paradigm. You can't simply define a CoC for a given size or resolution of imager. Or you can, based on other pre-determined factors that I mention below. Some DOF calculator programs [erroneously] attempt to use CoC, but I find that of many of them out there the issue is not their CoC values on their own, but how they factor them into the DOF calcualations. If you're trying to estimate DOF for a given focal length and aperture combo, you're best to ignore arbitrary CoC calculations altogether and take a value that gives you an approximation of the widest acceptable focal zone you can work with. Then scale down from there. Or sample various CoC scenarios and apply them to see how they affect DOF. In most situations, you will probably get more meaningful results in a reasonable amount of time if you just test the optical path and delivery in question.

One of the most accepted means of calculating CoC is to use this method:
CoC (mm) = viewing distance (cm) / delivery resolution (lp/mm) / enlargement factor / viewing distance (cm)

Other common shortcuts to approximate CoC are to divide the imager diagonal by a pre-determined value. Zeiss has given us values that they recommend as starting points. The values are recommended for different film and digital formats, or imager resolutions in actuality. They primarily recommend d/1730. d/1500 is also commonly used for simplicity and often viewed as close enough for most practical purposes within the still photography realm.

RED ONE 4K 16:9 is 4096x2304 at 0.0054mm/pixel square. We have imager dimensions of 22.12mm x 12.44mm and a 25.38mm diagonal (coverage circle). We can assume for most practical working purposes using 25.38/1730 = 0.0147mm and 25.38/1500 = 0.0169mm could be acceptable values. I would lean toward the latter of 0.0169mm as it would compensate more for lower resolution delivery. But either should be viewed as a starting point and better values can be derived if you know more specifics of your chain of acquisition to delivery. I guess those simplistic numbers are differing from Jacek's recommendation of 10 microns as we're hovering closer to 15 microns. I would think anything in the 10 to 17 micron range would probably give you acceptable numbers to calculate more accurate DOF. And trying to discern this visually may be impossible in most cases.

Ultimately, you can't control aspects of delivery, so people don't tend to put much weight into all of this. If you absolutely must know a workable CoC value of some sort, then you should figure one for your intended delivery scenario and imager being used. If your sweet spot is RED One 4K delivered as 1080p digital projection for theatrical distribution, then calculate for that. When it gets shrunk down later for viewing on 42" LCD HDTV sets from a DVD, you would have a different CoC value for sure. But your viewing audience is most likely not going to ever notice or care.
 
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Jeff,
Thats all correect and fine, BUT I like to think of it this way. IF it were a 35mm frame of film we would be talking about the same numbers you quote. However; AND HERE I GO AGAIN>>>>>
It does not means a can of beans if the Focal Depth is not correct! This is the distance from the Lens seat to the Sensor. Now on film we always set that a little into the film, about 2 tenths of a gnats. On a RED and useing a Collimator I reckon the same applies. When you have the lens exactly right and not up to 005 thou out as many are, you are not going to get any CoC THATS MEANINGFUL. It will be blurred and not in focus. which is what is required.
"Definition" is what its all about and to get that you need top optics like Cooke Zeiss Angenieux Leica. SLR lenses unless selected and mounted in top engineering scrolls, will not cut the mustard on 2k 4k or even 5k.
Thats my twopennyworth from 45 years in the Optics and Camera biz.
Cheers people. Tony Covell.
 
Historically we used to test the entire workflow for the production in question to be sure. I think Jacek's recommendation of 10 microns is about right from tests I did with Cooke S4's.

Jeff Kilgroe said:
All of these factors play a role in DOF. Primarily DOF is determined by focal length, aperture and subject (focal) distance. DOF also varies in its perception or how the viewer "sees" it based on the imager size, resolving power or resolution, output size and resolution and viewing distance. CoC, which is a determinant of those resolutions and viewing distance, is a measure of the visual acuity within a given construct or imaging paradigm. You can't simply define a CoC for a given size or resolution of imager. Or you can, based on other pre-determined factors that I mention below. Some DOF calculator programs [erroneously] attempt to use CoC, but I find that of many of them out there the issue is not their CoC values on their own, but how they factor them into the DOF calcualations. If you're trying to estimate DOF for a given focal length and aperture combo, you're best to ignore arbitrary CoC calculations altogether and take a value that gives you an approximation of the widest acceptable focal zone you can work with. Then scale down from there. Or sample various CoC scenarios and apply them to see how they affect DOF. In most situations, you will probably get more meaningful results in a reasonable amount of time if you just test the optical path and delivery in question.

One of the most accepted means of calculating CoC is to use this method:
CoC (mm) = viewing distance (cm) / delivery resolution (lp/mm) / enlargement factor / viewing distance (cm)

Other common shortcuts to approximate CoC are to divide the imager diagonal by a pre-determined value. Zeiss has given us values that they recommend as starting points. The values are recommended for different film and digital formats, or imager resolutions in actuality. They primarily recommend d/1730. d/1500 is also commonly used for simplicity and often viewed as close enough for most practical purposes within the still photography realm.

RED ONE 4K 16:9 is 4096x2304 at 0.0054mm/pixel square. We have imager dimensions of 22.12mm x 12.44mm and a 25.38mm diagonal (coverage circle). We can assume for most practical working purposes using 25.38/1730 = 0.0147mm and 25.38/1500 = 0.0169mm could be acceptable values. I would lean toward the latter of 0.0169mm as it would compensate more for lower resolution delivery. But either should be viewed as a starting point and better values can be derived if you know more specifics of your chain of acquisition to delivery. I guess those simplistic numbers are differing from Jacek's recommendation of 10 microns as we're hovering closer to 15 microns. I would think anything in the 10 to 17 micron range would probably give you acceptable numbers to calculate more accurate DOF. And trying to discern this visually may be impossible in most cases.

Ultimately, you can't control aspects of delivery, so people don't tend to put much weight into all of this. If you absolutely must know a workable CoC value of some sort, then you should figure one for your intended delivery scenario and imager being used. If your sweet spot is RED One 4K delivered as 1080p digital projection for theatrical distribution, then calculate for that. When it gets shrunk down later for viewing on 42" LCD HDTV sets from a DVD, you would have a different CoC value for sure. But your viewing audience is most likely not going to ever notice or care.
Click to expand...
 
Yes, Tony, you're right about that. If the lens in question is not properly tuned and collimated and the mount isn't properly shimmed or set with the right focal depth, then you're nowhere, CoC as a factor or not.

When all things are as they should be, CoC should not be meaningful to the final image. But it is still a value that can be, and often is, used to assist in DOF calculations. I'm thinking that's what the OP was looking for here. Personally I think most all DOF calculations fall into the realm of pedantic over-preparation and the spending of too much time on things that won't matter once production starts and all the uncontrollable aspects are in play -- actors hitting their marks, sagging tape measures and whatnot. There are ways to calculate an approximate DOF for a camera system without accounting for a minute CoC value and these are more than adequate for practical purposes.

Coming from an engineering and FX background myself. The only people I ever knew who actually NEEDED finite CoC calculations were the programmers writing rendering algorithms that attempted to simulate proper photon path mapping, lens and imager characteristics. And the math behind those algorithms is far more involved than the simplistic calculations I posted here, which are pretty much ripped from my own brain, which took them from the ASC book and/or wikipedia.

Stephen Williams said:
Historically we used to test the entire workflow for the production in question to be sure. I think Jacek's recommendation of 10 microns is about right from tests I did with Cooke S4's.
Click to expand...

Yes. And I can agree with 10 microns. I've been shooting RED for 3 years and have never specifically tested this aspect of the system. I don't put a whole lot of faith in the d/1730 over-simplified representation. Either way, a variance of a few microns on CoC diameter amounts to little in the grand scheme of things. Tony brings up a good point and that the acuity of the COC can be varied or even enlarged a bit by setting the FFD into the imager plane by a micron or two. Or to get very specific, unless someone breaks out the micrometer and measures their lenses and FFD, it's entirely possible to vary by a few microns on CoC calculations anyway. So what we're really doing here is an academic circle jerk of sorts. ;)
 
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I used Coc calculations quite often, and to great effect, in large format stills work for many years; but, just as Jeff says, once I got into the more chaotic world of motion, the practice fell apart fairly quickly. Still, if one is to completely familiarize themselves with the various workings and end results of calculating Coc, it greatly enhances one's "instincts" in these matters.
 
George Butterfield said:
Wrong ... the DOF is 100% determined by the lens focal length and aperture. Your image sensor can be any size. The DOF on a RED ONE is determined by the lens, (focal length and aperture).
Click to expand...

This is not, in fact true. For a given camera-to-subject distance, DOF is determined by the lens focal length, aperture, and viewing size.
 
Hi Jeff, Yes! I will go with that summation, But to sum up my thoughts on Focal Depth. If its not correct the CoC will NOT be in the right place and will be either in front or behind the point of focus which is where you could measure the CoC if that were possible. Too many guys turn up for focus checks with lenses they have just bought and 99% of the time the problem is a badly set Focal depth. Cheers. Tony Covell.
 
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