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Viewfinders for Film Cameras


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#1 John Mastrogiacomo

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Posted 15 March 2007 - 10:16 PM

I have an Eclair ACL S16 camera with an Angenieux optical viewfinder.

I have noticed that when looking through the VF, the DOF through the VF
is greater than the actual DOF on the film.

I know this has to do with the optics of the VF.

Can someone explain exactly what causes this difference?

Also, are there optical VF's for 16 or 35mm cameras that match the
actual DOF that is on the film?

Thanks for any information.
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#2 David Mullen ASC

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Posted 15 March 2007 - 10:20 PM

It should be the same depth of field -- you are seeing the same optical image from the lens being projected onto the film plane. The only difference is that it is usually a small image in your viewfinder, so areas may not look as out of focus as when you see the final, larger, sharper image.
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#3 Stephen Williams

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Posted 16 March 2007 - 02:58 AM

I have an Eclair ACL S16 camera with an Angenieux optical viewfinder.

I have noticed that when looking through the VF, the DOF through the VF
is greater than the actual DOF on the film.

I know this has to do with the optics of the VF.

Can someone explain exactly what causes this difference?

Also, are there optical VF's for 16 or 35mm cameras that match the
actual DOF that is on the film?

Thanks for any information.


Hi,

The thickness of the 'grinding' on the ground glass can have an effect. I remember their being a difference between an old Mitchell Rack over & an Arri III, can't remember which one showed more DOF!

I guess if the optics of the viewfinder were very slow (F 5.6 for example) then perhaps you could only judge the DOF when the taking lens was stopped down to 5.6. or smaller.

For an SD finish you will get more DOF than the ground glass as the resoloution of the video is lower than the ground glass. I find an HD image from a Spirit matches well what I see on most cameras.

Stephen
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#4 John Mastrogiacomo

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Posted 16 March 2007 - 12:08 PM

Hi,

The thickness of the 'grinding' on the ground glass can have an effect. I remember their being a difference between an old Mitchell Rack over & an Arri III, can't remember which one showed more DOF!

I guess if the optics of the viewfinder were very slow (F 5.6 for example) then perhaps you could only judge the DOF when the taking lens was stopped down to 5.6. or smaller.

For an SD finish you will get more DOF than the ground glass as the resoloution of the video is lower than the ground glass. I find an HD image from a Spirit matches well what I see on most cameras.

Stephen

I asked the original question because of some tests I did last year. I was filming some tests with the focus set at about 12'. The lens was pretty wide open. During the test, I held the slate in front of the lens with my hand (about 2' from the lens). Through the optical VF, the slate looked very in focus and I could read everything on it just fine.

When I got the film back, I could not even read the slate because it was so out of focus. I thought I read something a while back about the optics in the VF causing this. I have been searching for the information I previously read, but haven't been able to find it so far.

I will have to do some more tests and keep track of all the f-stops.
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