I am new to 4x5 (6 months) and I have been shooting Velvia 50 transparency film. I use my Olympus OM4Ti 35mm camera as a light meter with either 24mm or 50mm lenses. These focal lenghts are approximately equivalent to my 90mm and 150mm large format lenses. What I am finding is if I use the exposure taken with the OM4 I am consistantly getting underexposed results on 4x5 Velvia (but I get well exposed results on 35mm). Most of my Large Format exposures are 1 second or less. I have established from trial and error that if I add one stop to the exposure value I get from the OM4 plus add another stop for exposures over 1 sec to compensate for reciprocity I get a pleasing exposure.
The question I ask is why is there an exposure variation between formats in the first place.
I always thought that an exposure of say 1sec at F22 should give exact same result regardless of format. I'm aware of bellows factor compensation but the problem is the same wheather I use the 90mm with vertually no bellows extension or the 150mm with more.
I would appreaciate any thoughts you may have on this