[pure-silver] Re: bellows contraction factor
- From: "Rob C" <forum@xxxxxxxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sat, 21 Apr 2007 19:38:18 +0100
I would echo what has already been said but also add that when you calibrate
film speed, the ususal advice is to focus at infinty and then work out bellows
extension factor when you make an image. It may well be the case that you have
not been applying a bellows extension factor (I don't know) but if your film
speed tests were done at infinity and no bellows extension factor was used for
you 150 lens, then now you are using a shorter focal length lens you will
likely be focussing nearer to infinity and therefore your images may be a
little brighter.
Without knowing the above details its impossible to say exactly why your images
are lighter.
Personally I do film speed tests at about 6 feet distance and don't worry about
bellows extension. That means some of my images may be slightly overexposed but
that is better than underexposed.
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