Is it me or are the dev times and/or iso ratings for 35mm and 120 different. The density from 35mm is excellent whereas from 120 [both under studio flash] the density appear to need about half to three quarters of a stop more exposure.

Film used B&W. APX 25, APX100 and TMX100 Developers Rodinal, Ilfosol

It would appear to me that 100 asa 120 roll to get equivelant density needs about 64asa.

Cameras Olympus OM1 and Hasselblad.

Colour tranny both cameras identical.

Regards Steve Nicholls.

-- Steve Nicholls (gl1500@chariot.net.au), February 22, 1999

Answers

Steve, I agree with you.

I've only just got into 120 via a 645 Bronica using Delta 100 and Pan F. I've also had some negs on the thin side. I've not yet found the correct asa for me on either Pan F or Delta, but Pan F would seem to need about a stop more. I've also been using Rodinal and Ilfosol S.

-- Michael Chappell (mickyc@slhosiery.com.au), February 23, 1999.

Steve, the directions from the Great Yellow Father (Kodak) indicate the same processing times for their 120 as their 35mm films of the same specifications. However, 120 negatives seem to accept a slightly heavier exposure and still print well.

To determine actual film speeds, you would probably need to shoot a series of identically exposed films and them process each of the films at say, as recommended, 10% more, 20% more, and so on.And then use a densitometer and lots of scientific junk. You need not be that pickey to find settings that work well for you.

Regardless, actual film speed to give a set tonal range and reproduce a 18% grey accurately at its film speed are conditions of the film.

What might be happening here is that your Hasselblad shutter speeds at any number are not identical to your 35mm camera...that the 35mm is giving "longer" exposures at its settings than the 'Blad. Or the aperatures of your 35mm lenses are not stopping down to exactly the same settings (though the same numbers) as your 'blad lenses.

Have fun, experiment, test. Jim

-- Jim Ensign (jlensign@aol.com), March 01, 1999.

Since there's the same amount of emulsion, roughly, in 36 exposures of 35mm as in a roll of 120, could there be developer exhaustion to account for the differing processing times? I can develop 4 rolls of 35mm or 2 rolls of 120 in the same tank so there's twice as much emulsion to develop. (This is an academic consideration for me. I never use 35mm.)

-- Don Karon (karon@ibm.net), April 29, 1999.

It's not you Steve! Although Olympus is tough in contrast and Zeiss is a lot softer. Compare slides of an Olympus with Nikon or Hasselblad. You'll see the difference in contrast. But MF development is certainly a different story than 35mm.

-- Lot (lotw@wxs.nl), April 29, 1999.