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16mm and 35mm depth of field


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#1 rob spence

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Posted 12 September 2005 - 04:00 PM

Hi
Does anyone know if depth of field is the same for 35mm lenses and S16 lenses when used on a S16 camera. I presume they are the same but not 100 per cent sure. Many thanks.
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#2 Chris Burke

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Posted 12 September 2005 - 04:34 PM

Hi
Does anyone know if depth of field is the same for 35mm lenses and S16 lenses when used on a S16 camera. I presume they are the same but not 100 per cent sure. Many thanks.

<{POST_SNAPBACK}>



No they are not. Because, the size of the imaging area, be it a film gate or a cmos chip or ccd or what have you, has a direct effect upon the depth of field. The smaller the imaging area, the deeper the depth of field. Take for instance a 1/3" chip video camera. At is wided focal length, pratically everything is in focus. With say a 35mm camera, your depth of field is a lot shallower. What focal length lens you use also effects the DoF. So Super 16 is a little bit shallower than say a 2/3 " chip camera. 35mm is even more so. they are not the same. If you shoot at longer focal lengths, like 35mm on up on a 16mm camera, you are going to get shallow DoF. Super 16 can and often does look exactly like 35mm, but if you use a 25mm on a S16 camera it is more like a 50mm on a 35mm camera. I hope I didn't completely confuse you and actually answered your question. Good luck


Chris

:D
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#3 Mike Lary

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Posted 12 September 2005 - 05:14 PM

Hi
Does anyone know if depth of field is the same for 35mm lenses and S16 lenses when used on a S16 camera. I presume they are the same but not 100 per cent sure. Many thanks.

<{POST_SNAPBACK}>

This is my understanding, based on the ASC manual's description of DOF problems when choosing a format (p. 156).

A given focal length lens at a given fstop has the same depth of field regardless of format. However, in order to get the same field of view on different formats, a different focal length is required. So, the DOF will change between formats if you are trying to achieve the same field of view (25mm lens on a 16mm camera, 50mm lens on a 35mm camera, etc.). The smaller the format, the larger the DOF when matching the same field of view.

Also, the DOF tables in the ASC manual are entitled 'all formats depth of field tables', which indicates the lens itself is the determining factor.
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#4 Dominic Case

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Posted 12 September 2005 - 10:36 PM

Let's read the question properly.

Does anyone know if depth of field is the same for 35mm lenses and S16 lenses when used on a S16 camera.

As Mike L says: A given focal length lens at a given fstop has the same depth of field regardless of format. So if you put a 50mm lens on a super 16 camera, then it will have the same depth of field at (say) f/4 as it would have on a 35mm camera.

But although a lens behaves the same in terms of focussing regardless of the size of the gate, most depth of field tables assume a crcle of confusion for 35mm of 0.001", but for 16mm it is 0.006". Circle of confusion is essentially the amount of blur that is still regarded as sharp. For the same projected image size (or viewing angle), the 16mm image has to be blown up more, so we see out-of-focus more critically.

One more factor: the same lens will have a far greater angle of view/coverage on the 35mm camera. You would use about a 85mm lens to get the same angle of view in a 35mm camera as a 50mm on 16mm, and that will have less depth of field.

Effectively, this overrules the other factor.

Take one set of figures from the charts in the AC manual:-

35mm camera (coc 0.001) - 85mm lens, f2 at 25ft 23'9" - 26'5"
16mm camera (coc 0.006) - 85mm lens, f2 at 25ft 24'2" - 25'10" (same lens)
16mm camera (coc 0.006) - 50mm lens, f2 at 25ft 22'7" - 27'7" (same field of view)

In summary, compared with a 35mm camera:
The same lens has the same depth of field on a 16mm camera, if the circle of confusion is considered the same.
The same lens has less depth of field if we consider the smaller circle of confusion for 16mm.
A different lens giving the same coverage on a 16mm camera has more depth of field.

Nothing is simple B)
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#5 andres victorero

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Posted 16 September 2005 - 02:29 AM

This is the panavision chart where you can experiment with various formats and lenses

http://www.panavisio...lenseqvform.asp
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#6 Glenn Hanns

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Posted 19 September 2005 - 06:35 PM

This is the panavision chart where you can experiment with various formats and lenses

http://www.panavisio...lenseqvform.asp

<{POST_SNAPBACK}>



Why aren't scope lenses included?
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#7 Doug Hart

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Posted 02 September 2006 - 09:02 PM

Why aren't scope lenses included?


If you are shooting 35mm anamorphic ("scope") then treat your lenses the same as 35mm spherical (non-scope), and use the same circle of confusion.
But understand that the focal lengths required for the same image height are almost doubled in anamorphic shooting - the full face closeup you might shoot with a 50mm lens in spherical 35mm, at the same distance, will require a 100mm lens in anamorphic shooting, reducing your depth-of-field greatly.
This is why pulling focus with anamorphic lenses is much more demanding.

Doug Hart
1AC, NYC
(My latest anamorphic production as 1AC, "Brooklyn Rules" opens in October.)
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#8 Doug Hart

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Posted 02 September 2006 - 09:27 PM

Hi
Does anyone know if depth of field is the same for 35mm lenses and S16 lenses when used on a S16 camera. I presume they are the same but not 100 per cent sure. Many thanks.


The lenses don't care whether you are shooting 16mm or 35mm (or IMAX).
Depth of Field and Circles of Confusion are concepts that deal with the negative size and the degree of magnification needed to get a sharp image up on the screen. It is a very subjective concept, and cannot be determined by using some mathematical formula.
Everyone has their own opinion, based on their own experience.
16mm negatives are smaller, so C-of-C also have to be small.
35mm negatives are larger, but if shooting for big screen theatres, so is the degree of magnification.
Shooting 35mm for TV gives you the large negative with a relatively smaller degree of magnification, so the C-of-C can be larger and still appear sharp on the small TV screen.
"Appear" is the key word here.
There is no precise definition of what is in focus and what is not.
Focus does not suddenly drop off at the limits of Depth of Field, it is a very gradual fall off, and it is often difficult to distinguish "sharp" from "soft."
There are many factors at play here - film negative stock used, lenses used, diffusion used, print stock used, projection lens used, distance to screen, size of screen, etc.
Change any one of these factors, and something that looked sharp is now soft.
Grainy films look softer than fine grain films.
Smaller screens look sharper than large screens.
Using diffusion filters reduced apparent sharpness (that's why we use them).
There are no hard and fast rules about C-of-C. Everyone does it differently.
Look at the charts printed in books, and in electronic calculators and plastic dial calculators, and you will see a wide range of C-of-C for the same formats, and it changes over the years.
The SamCine II calculator, still my favorite, gives the AC three choices for C-of-C, 1/500", 1/700" and 1/1000", without really making any recommendation which C-of-C to use for which format.
After many years of puilling focus, I have decided on my own, based on thousands of hours of film shot, that I should use 1/1000" for 16mm shooting, 1/700" for 35mm for theatres ("Big Screen"), and 1/500" for 35mm for TV ("Small Screen").
I also use 1/1000" for 35mm anamorphic shooting, because the anamorphic lenses are just not as sharp as spherical lenses, and the screens are often much larger.
These values work for me, and have done so for many years, but another 1AC might have a different opinion.
Whatever works for you is right.

Doug Hart
1AC, NYC

(Check out the chapter on Focus in my book (The Camera Assistant, Focal Press, 1996) for more on this subject.)
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