Exposure variation between formats

[Robert Jaques]

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

Thanks

Robert

 

[Steve Hamley]

Robert,

Likely the difference is the shutter(s). It isn't unusual for LF shutters to be slow at the faster speeds. Try checking the shutter speeds. BTW, what kind(s) of LF shutter?

Steve

 

[David A. Goldfarb]

If you're accounting for reciprocity and bellows factor and still getting a difference in exposure, there could be a number of factors involved.

Your shutter speeds might not be accurate.

There could be inconsistencies at the lab in the processing of the film from one format to another.

The manufacturer's recommendation for reciprocity correction might be unrealistic.

Difference in transmissive light loss between your 35mm and LF lenses, though I would expect this to be within a half stop.

 

[Stan. L-B]

I'll put a cat among the pigeons..

I expose velvia 50 at 40ASA on my Seconic. and get constant good results. There are time when I do not have the meter with me so I use my Nikon F3 TTL meter to take a reading, but ensure that I have a corresponding focal length lens on the Nikon to the LF. (5X4).

Such as, if I have a 90mm lens on the LF and wish to take a reading, I put a 24mm lens on the Nikon, making sure the film speed is set correctly to 40ASA.

This system works for me also with the Hasselblad Meter viewer, which is also adjustable for focal length and max aperture, an adjustment is necessary each time to try and match the focal length of lenses.

The lenses on all my equipment is checked every two years, and certificated, so they should be in good nick. However, I do process all my film, and where necessary make alterations to suit but not very often.

 

[Flotsam]

I have always found that my 4x5s soak up at least a stop. I have always just rated my films to compensate.

 

[roteague]

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

I do something pretty similar; I use my Nikon N80 as a light meter if I am in a fast moving situation (fast for LF anyway), otherwise I use a handleld meter. I use the same film in both camera (Velvia 100F), same filters (usually a warm polarizer or 81 series). Exposures tend to be pretty close.