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Using an 85 filter ttl


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#1 Robert Lewis

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Posted 02 November 2009 - 04:02 AM

Hi.

I am confused about what should be simple and I would be grateful for advice.

I have Bolex REX5 which is fitted with a Kern Vario-Switar 18-86OE zoom lens. So, exposure is ttl.

Until now I have used only daylight film and the built in exposure meter takes care of everything. However, I have been given a number of rolls of 200T film and I would like to use them in daylight. I know I need to use a 85 filter, and I have two types of filter - a "drop in filter" which, when fitted, is taken into account by the exposure meter. The other filter is, of course, the Bolex "behind the lens" filter which is not taken into account by the exposure meter.

The normal speed of the 200T film is 200ASA, but with an 85 filter this is reduced to 125ASA.

Now, if I use the "drop in filter", do I set the exposure meter for 200ASA or 125ASA?

I understand that an 85 filter absorbs 2/3 of a stop. The difference between 200ASA and 125ASA is 2/3 of a stop. I have a feeling that I should set the exposure meter at 200ASA and the effect of the filter reduces the actual ASA to 125, because if I reduce the exposure meter setting to 125ASA and use the filter, I am doubling the required reduction. Am I correct or mistaken?

If, on the other hand, I use the the behind the lens filter which is then not taken into account by the exposure meter, do I set the set the exposure meter at 125ASA and simply use the filter or is this also doubling the reduction in ASA?

I really would appreciate advice on this.
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#2 Mark Dunn

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Posted 02 November 2009 - 02:43 PM

You'd leave the setting at 200 for the filter on the front and set 125 for the gate filter, because in that case the TTL meter can't take that into account itself.
But you'd be better off using an external meter in any case, set to 125, neglecting any deliberate over-exposure which is favoured by some for colour neg.
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#3 Robert Lewis

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Posted 03 November 2009 - 03:40 AM

You'd leave the setting at 200 for the filter on the front and set 125 for the gate filter, because in that case the TTL meter can't take that into account itself.
But you'd be better off using an external meter in any case, set to 125, neglecting any deliberate over-exposure which is favoured by some for colour neg.


Thank you Mark. I am most grateful for your help.
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