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Possible errata in ASC Film manual re: super-8 DoF?


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#1 George White

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Posted 14 March 2006 - 06:42 PM

If I've got this right, smaller formats have correspondingly smaller circles of confusion (key to calculating DoF). For example, the Wikipedia entry on circle of confusion gives the "Zeiss formula" as CoC = diagonal/1730 so its directly proportional to the film/imager size. The current (9th) edition of the ASC Cinematographers Handbook specifies .001 inches for "all formats", but allows that for 16mm you might use the more traditional (and smaller number) .0005 inches (p. 663). Thus a smaller format has a smaller CoC. Ok, on page 738 is the start of charts for DoF and angle of view for super-8. It indicates that the tables are based on a .002 inch CoC. This is obviously twice the recommended CoC for 35mm! I'm pretty sure that the correct CoC for Super-8 is more like .0002 inches (fits the Zeiss formula, for example, and is generally in a progression from .001 [35] to .0005 [16]) I thought this was a typo, leaving out a 0 is easy and I wouldn't be posting about that. However, I checked the tables against an online DoF calculator as well as using the equations to back-calculate what CoC is assumed by several of the table entries and it seems clear that the tables are actually based on a CoC of .002 which, unless I'm looking at something upside down, is 10x what it should be. It seems more likely that I've got something wrong than that the ASC Manual has this error, but if so, I can't see what.
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#2 S8 Booster

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Posted 14 March 2006 - 06:57 PM

this may be of interest for you: DOF calculators


s8hôôt
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#3 George White

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Posted 15 March 2006 - 10:09 PM

this may be of interest for you: DOF calculators
s8hôôt


thanks, it was quite helpful -- The calculator ref.'ed above seems great. It assumes .025 mm as the CoC for 35mm which is about the same (within 2%) as ASC manual's .001 inches -- great. It then uses .0007 for 16mm (the ASC manual says either stick with .001 or go to .0005, this calc is in the middle -- good) and uses .0004 for 8mm (ASC manual says .002 -- five times larger and even larger than the value used for 35mm - NOT good! My original contention was that they meant .0002 but used .002 by mistake). As this calc. shows, the CoC generally gets smaller as the format gets smaller. Bottom line -- this calc gives very close results for 35mm with the ASC manual (called "all formats in ASC manual), but different results than are found in the ASC 8mm tables (example: 13mm lens at f/4 has a hyperfocal distance of over 13 feet [calc] or less than 2 feet? [ASC manual]).
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#4 Andy_Alderslade

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Posted 16 March 2006 - 07:16 AM

Hmmmm' I wonder if the incosistency is because the grain is so comparitivly big in Super 8 that everything is slightly soft anyhow, but just a hypothisis.

This is really a question for David Mullen.

Personally I would trust the DOF tables in the Manual, they look logical to me. Though strangly in my book (9th) on a 13mm at f/4.0 the Hyperfocal Distance is 2' 9".
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#5 S8 Booster

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Posted 16 March 2006 - 07:59 AM

havent checked these data up against the calcs but they may give an indication on whos right or wrong.

s8hôôt

data for schneider/beaulieu 6-70.
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#6 George White

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Posted 16 March 2006 - 05:30 PM

re: [Though strangly in my book (9th) on a 13mm at f/4.0 the Hyperfocal Distance is 2' 9".]

Sorry Andy, after trying to be careful and precise with these numbers, I did accidentally slide a column over - it is 2' 9" in my 9th ed. also. Still a huge difference from the 13 feet of the calc.
______________

More to the point (thanks S8 Booster for the schneider info).

From the schneider/beaulieu 6-70 tables above:
12mm f/1.4 hyperfocal = 34' 2"
(chart shows 1/2 hyperfocal which is where near focus starts)
at 10' distance: near = 6' 6"; far = 22' 1"

ASC Manual:
13mm f/1.4 hyperfocal = 7' 10"
(no common foc. lgth between ASC and schneider tables)
at 10' distance: near = 4'5"; far = inf.

the calc. S8 Booster ref. to:
12mm f/1.4 hyperfocal = 33' 8"
13mm f/1.4 hyperfocal = 39' 7"

Hoping to get a DoF "expert" to double check this before I figure out how to bring this to the attention of someone involved with the manual.
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#7 David Mullen ASC

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Posted 16 March 2006 - 05:49 PM

Michael Goi, ASC is in charge of the next edition of the manual.
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