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Cooke 25-250 filter slot


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#1 Jason Eitelbach

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Posted 06 February 2006 - 03:54 PM

Hello,

Our school has a Cooke 25-250 T3.7 I think that it is a MkII or a MkI. It has a filter slot in the back of the lens. What sort of drop-in filters does it take, 40.5mm or something else? How does that work, is there a special filter holder I need as well or do they just fit in?

It seems like this may be a better way to put 85's or ND's on as opposed to getting 6X6's for the matte box. Is this true or should I shy away from using filters behind the lens?


thanks,
je
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#2 Stephen Williams

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Posted 07 February 2006 - 10:57 AM

Hello,

Our school has a Cooke 25-250 T3.7 I think that it is a MkII or a MkI. It has a filter slot in the back of the lens. What sort of drop-in filters does it take, 40.5mm or something else? How does that work, is there a special filter holder I need as well or do they just fit in?

It seems like this may be a better way to put 85's or ND's on as opposed to getting 6X6's for the matte box. Is this true or should I shy away from using filters behind the lens?
thanks,
je


Hi,

Kodak gelatin filters. There should be a holder.

Stephen
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#3 Jason Eitelbach

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Posted 07 February 2006 - 01:07 PM

Thanks,

I went on the Cooke website but they only had specs for the MkIII lens and I didn't know if filter holding properties had changed b/w versions.

Several years ago when I was working in a camera shop I was told that wratten gels were the best filters because they had no glass element to introduce flare etc. is this true?


je
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#4 Hal Smith

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Posted 07 February 2006 - 07:14 PM

I'd like to add a question to this thread: are there any noticeable optical distortions created by using a gel filter over a lens that isn't absolutely flat? For instance: If rather than using a holder, I taped a piece of CTO over the front of a reasonably good quality prime lens would a discerning eye be able to see anything fishy? (Assuming I at least worked on getting the filter as flat as possible). I'm asking because I have a fair amount of experience with theatrical gels, mostly Rosco and Lee, and would like to leverage my knowledge of them onto my cinematography learning curve.

(Well maybe if that "good quality prime" was something like a Zeiss Super Speed more than a few DOP's would think that gaff taping something on a $6K lens in itself was rather fishy) :)

Edmond, OK
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#5 Stephen Williams

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Posted 08 February 2006 - 04:27 AM

I'd like to add a question to this thread: are there any noticeable optical distortions created by using a gel filter over a lens that isn't absolutely flat? For instance: If rather than using a holder, I taped a piece of CTO over the front of a reasonably good quality prime lens would a discerning eye be able to see anything fishy? (Assuming I at least worked on getting the filter as flat as possible). I'm asking because I have a fair amount of experience with theatrical gels, mostly Rosco and Lee, and would like to leverage my knowledge of them onto my cinematography learning curve.

(Well maybe if that "good quality prime" was something like a Zeiss Super Speed more than a few DOP's would think that gaff taping something on a $6K lens in itself was rather fishy) :)

Edmond, OK



Hi,

Its normal to place the gelatin filters behind the lens. The main effect is that the flange focal length is changed by the 1/3 thickness of the gel. The Kodak gels are very expensive relative to size, they are of very good optically, I don't think you will have any problems.

Some Cooke Zooms have 1 gel filter slot between some glass elements near the back. The flange focal length is not changed.

It's not unusual to tape nets on very expensive lenses!
Stephen
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#6 David Mullen ASC

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Posted 08 February 2006 - 11:01 AM

Theatrical lighting gels are optically poor, not meant for putting in front or behind the lens unless you're looking for a slightly blurred look.
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#7 Hal Smith

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Posted 08 February 2006 - 04:38 PM

Aha! Thanks David and Stephen. Use theatrical gels on lights, windows, etc. but not on lenses - not such a good idea. The theatrical dichroic filters are reportedly on optical glass - but they ain't cheap either!

Edmond, OK
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