Welcome to our community

Be a part of something great, join today!

Log in
  • 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

Nice post Jorge. Adding to that...

The weaker the OLPF, the greater the less the apparent depth of field will be. I'm assuming that Jorge is referring to apparent as 'perceptual' so I'm using it the same way. By perceptual, I mean how quickly you start feel that something is out of focus with respect to what's in focus.

Grain size and distribution reduces edge sharpness a bit while at the same time the grain itself add perceptual sharpness because the eye locks on to the grain as 'sharp' features.

OLPF has the biggest impact on apparent depth of field and then the regularity of the sensor grid. I haven't seen fill factor have much of an influence on apparent depth of field.
 
Thanks Deanan!

I think that also having the photosites in a thin layer, as opposed to color film, which has three layers (I think they are a total of .0004 in [.01 mm] thick, has an effect of reducing apparent DoF.

Objects that are slightly out of the plane of ideal focus, will be focus slightly ahead or behind the image plane. On film, the slightly displaced well-focused aerial image may be captured by the blue or red layers, but on a sensor they will be just ahead or behind the photosite, so they would be captured out of focus.

I think this makes the fall-off of DoF "faster" with the sensor. This may also be another reason why older lenses with slightly less edge sharpness (less sudden DoF "fall-off") give very nice results on the RED ONE, perhaps better than they give with film.

Also, we should remember, there is no "35mm" Circle of Confusion. The CoC used to calculate DoF is always a choice based on the characteristics of the imaging medium. When .001 (or even .002 in) in was an accepted CoC for 35mm cinematography, lenses, filmstocks and projection were not as good as they are today. Back when I was working as a 1st AC, I noticed that the 1/500 (.002 in) CoC on the Samcine calculator was far from adequate. It was possible to see through the viewfinder that this CoC was not small enough.

If we put slow, high contrast B&W film (with modern emulsion technology, which isn't available in B&W motion picture film) in an ARRICAM with Master Primes, I'm sure you'll need to use a smaller CoC for that project.

NOTE: If you are using a "slide rule" DoF calculator, you can subtract 1, 1.5 or 2 stops to decrease the size of the CoC. Subtracting one stop divides the CoC by 1.4 and subtracting two stops divides by 2. I used to add 1.5 stops to the Samcine 1/1000 in to get 1/1667 in for Super 16mm capture.
 
Sorry is being a while with out posting: work and little holydays. grrr
Pawel "CoC for 4k, 3k and 2k are the same for the same sensor! It is about 7 micro meters" i think thats pretty incorrect because is the same case as in 35mm S16 and 16 mm s the same negative but it has o be amplified more time for the same final format. In red we have the same 3k is not using all the sensor and 2k the same.
I have found out that reds DoF to be far shorter than 35 mm. Jorge´s point is part of the reason, Mikes as well and i steel don´t know if the angle of the light and the sensor will be the 3th one.
Jon Corcuera
 
Corcuera said:
...Pawel "CoC for 4k, 3k and 2k are the same for the same sensor! It is about 7 micro meters" i think thats pretty incorrect because is the same case as in 35mm S16 and 16 mm s the same negative but it has o be amplified more time for the same final format....
Click to expand...

Jon, read Jorge's and my messages again. My message is correct. Jorge's is pretty correct :)
 
I want to use this DOF calculator:
http://www.dofmaster.com/dofjs.html

and want to know the circle of confusion use for calculate my DOF if:

I shoot 4K 2:1, 1.85 for 2K projection (film print)

and if

I shoot 4K 2:1, 16x9 for 1080 HDTV.


If i understand this thread, i have to use CoC: 0.010mm for film print and CoC: 0.012mm for HD1080 ? Can i use 35mm setting and open a stop (or 2) to fit the DOF have with Red at 4K ?

Thanks,

Etienne
 
Deanan said:
Nice post Jorge. Adding to that...

The weaker the OLPF, the greater the less the apparent depth of field will be. I'm assuming that Jorge is referring to apparent as 'perceptual' so I'm using it the same way. By perceptual, I mean how quickly you start feel that something is out of focus with respect to what's in focus.

Grain size and distribution reduces edge sharpness a bit while at the same time the grain itself add perceptual sharpness because the eye locks on to the grain as 'sharp' features.

OLPF has the biggest impact on apparent depth of field and then the regularity of the sensor grid. I haven't seen fill factor have much of an influence on apparent depth of field.
Click to expand...

I don't follow you on "the weaker the olpf the less apparent dof. I thought the olpf was a plano optical element therfore having no power beyond extending the backfocus appx. 1/3 it's thickness. Am I missing something here?
 
So to summarize it up:
For full 4K workflow and 4K filmout: 7μm (That's very little...)
For 2K filmout: 10μm
For 1080 HDTV: 12μm
For SD TV and DVD: 25μm.

PS: I think this thread is in the wrong sub-forum.
 
You must log in or register to reply here.
Back
Top