# Understanding the Som Berthiot Cinor and Lytar

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### #1 Buddy Greenfield

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Posted 01 December 2007 - 10:32 AM

I'm a little... I am A LOT confused about the red center row of F stop numbers on my Som Berthiot Cinor and Lytar lenses.

If someone would be so kind as to please explain exactally what this indicates and/or how is it employed in conjunction with the F stop and DOF indications, I would be most greatful.

Thank you.
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### #2 Mike Rizos

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Posted 01 December 2007 - 12:22 PM

That's the depth of field scale. If your f-stop is 5.6 for example, look at the distance markings on the focus scale between the two red 5.6. Anything in between will be acceptably sharp in focus.
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### #3 Buddy Greenfield

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Posted 01 December 2007 - 01:05 PM

Mike, (Or anyone)

I appreciate the answer and I might understand it, but can you (Or someone) please confirm or deny my take on it?

So for example, if I need my F stop to be 5.6 and set it to 5.6, then determine that my subject is say 6 feet away and set the focus ring to 6 feet, then because roughly 5 feet to roughly 13 feet on the distance ring is what lines up/falls between the two red 5.6's, that depth (Between 5 and 13 feet) will be in focus?

Thanks.
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### #4 Hal Smith

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Posted 01 December 2007 - 01:23 PM

So for example, if I need my F stop to be 5.6 and set it to 5.6, then determine that my subject is say 6 feet away and set the focus ring to 6 feet, then because roughly 5 feet to roughly 13 feet on the distance ring is what lines up/falls between the two red 5.6's, that depth (Between 5 and 13 feet) will be in focus?

You've got the idea.

DOF is based on the len's Circle of Confusion, the smallest area on the film that will be recorded (resolved) by that lens. Therefore DOF scales are always based somewhat on someone's technical opinion. What that means is you shouldn't assume that the edges of the marked DOF zone are going to be in focus to your eye's preference - they will be close however on a professional lens.
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### #5 Buddy Greenfield

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Posted 01 December 2007 - 04:21 PM

Hal,

Thanks for your thoughts and confirmation on this.
Coincidentally, my whole interaction with Bolexdom has been based on a circle of confusion.

Seriously though, I have read some about that circle, but I appreciate your thoughts on it as well.
I suppose I can see why the depth of field process is part of the bigger picture, as obviously our eyes are a lot better than the lens, but where I still have a bit of confusion is... If by sight through the finder my subject is at least focused, then will it be in focus on film?

Thank you guys

Edited by Buddy Greenfield, 01 December 2007 - 04:23 PM.

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### #6 Hal Smith

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Posted 01 December 2007 - 04:37 PM

............ then will it be in focus on film?

In theory yes, in practice you're looking at a very small image that could easily be blown up to 20' wide or so (even with 16mm). It's always best to measure with a tape and set the distance on the lens whenever possible. Experienced AC's get pretty good at judging distances by eye but they trained their eye initially by taping everything.
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