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Switar 100 POE - manual exposure compensation on zoom?


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#1 Richard Ashrowan

Richard Ashrowan

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Posted 16 May 2012 - 04:51 AM

I'm shooting with a Vario Switar 100 POE with a Bolex RX5, but the built in exposure meter of the lens is dead (tried new batteries, but the contact seems to have been badly corroded away, so no joy), which means I'm working from a manual exposure meter. I wondered if any exposure compensation might be required when closely zoomed in? I would assume being zoomed in reduces the light entering the lens, so would have to open it up a little? Does anyone have any experience of this?

Sadly, I'm not right now in a position to develop any test footage.

I'm using a bolex lightmeter (which has built in compensation for the reflex viewfinder), taking incident lightreadings outdoors, mainly shooting high contrast light/dark subjects. Shooting on double-x 7222 b/w neg stock.

Many thanks,
Richard
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#2 Boris Belay

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Posted 23 May 2012 - 06:16 AM

Hi Richard, The Vario-Switar 100 POE has a constant aperture (max f : 1,9), which means there is no light loss whether zoomed in or out (one of the design features of a lot of cinema zoom lenses over cheaper photo lenses).

If anything, you may want to expose your film 1/2 of an f stop slower to compensate for light loss of the optical elements (for some reason Kern does not give T stops which account for that) and for the ageing of the lens. Film will be able to handle this very slight over exposure in any case.
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