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T3D Re: Exposure at bbellows extension! (TECH-3D digest 361)

  • From: bobh@xxxxxxxxxxxxxxxxxx
  • Subject: T3D Re: Exposure at bbellows extension! (TECH-3D digest 361)
  • Date: Mon, 21 Sep 1998 15:24:57 -0700
RER: Tom wonders if he puts a 45mm lens on a 100mm bellows 
extension..if he had a 145mm lens? Well yes and no.  It is a 45mm 
lens at a bit more that 4X extension..meaning it is going to focus 
close and magnify. BUT he is right that the diaphragm is now about 
145mm from the film so the f/stop opening say it is 4mm becomes 
4/145mm or f/36, whereas on the 45mm lens alone 4mm was 
4/45mm or f/11. BobH


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