I just picked up a Paterson/Philips PCS 2500 (seems to be identical to the Philips PCS 130) 6x7 enlarger which came with three sets of condensers--one for 35mm and smaller, one for 35mm-6x6, and one for 6x7. A quick check with a 6x6 neg reveals that I get the most even coverage with the 6x7 condenser set. Is there any good reason not to use the 6x7 condenser set for all formats?
By the way, if anyone is shopping for an enlarger (no, mine isn't for sale), these Philips and Paterson PCS enlargers from the 1980s are really nice and usually go for really cheap, because they aren't so well known. I paid $200 for this one with the three condenser sets, anti-newton glass neg carrier with adjustable masking blades, extra masks for 35mm, half-frame, 126, and mounted 35mm slides, and add-on fine focus control. The enlarger has a heavy single-column design, tilting lens stage and head for perspective correction, and the column is easily rotated for floor projection or the head can be rotated for wall projection. The color version uses an additive filtration system that has never really caught on, but was very advanced for its day and has its adherents.
The condenser "set" should match the lens. Theoretically, a 6 x 6 set should perform best with an 80mm lens- "standard" for 6 x 6, or a wide-angle lens (60mm or ?) designed for 6 x6 coverage. I don't think there is a great deal of distinction between 6 x 6 and 6 x 7, however.
Wildly mismatched sets, 35mm used for a 4" x 5" format, for example, can be expected to give unven illumination with a lot of edge fall-off; or, going the other way, reduced overall illumination.
Thanks for the response. Nothing too surprising then. I know of the coverage problem that comes from using a set (this enlarger uses a combination of two independent condenser lenses--I have five individual lenses to be used in three combinations) for a smaller format with a larger neg, but just was wondering whether there were any downsides other then reduced light output to going the other way. I'll experiment some more, but I suspect I'll be using the 6x7 combo for 6x6 and 6x7 and the 35mm combo for 35mm, and the 35mm-6x6 combo will stay in the desk drawer unless something inspires me to get a 645 camera (not a format I particularly like).
I had my first printing session with the new enlarger today, and I'm very pleased. Other features aside, a glass negative carrier really makes all the difference, and I like having a negative carrier with adjustable masking blades, which I've used in the past in school darkrooms, but have never had on my own enlarger.
I use an Opemus enlarger for 35mm and 6x5.4. Since I use a colour head, I keep the 6x6 mixing box on at all times. No need to change condensers unless you want to make ridiculously large prints from ridiculously small pieces of film.
But if someone has a spare pair of 240mm condensers for a Durst 138S, I'd be happy to give them a new home in Norway.
So I had a particularly dense 35mm neg to print yesterday and decided to compare the illumination level with the 6x7 cm condenser set to the 35mm set, and I found that the 35mm set gave me about a half stop more light--not a huge difference, but good to know.
The function of the "condensers" (actually collimating lenses) is to make the light "bundle" more coherent - to take a lot of random light rays and get them going in a parallel bundle of the right size and in the right direction. The reflector in a flashlight serves the same purpose.
The effect is to provide an acceptably even illumination over the "field", in this case the "negative stage" (although it COULD be a positive). The most efficient condensers will be the ones designed for the format: 35mm for 35mm, etc.
Using a condenser set for 35mm with a 4" x 5" negative and lens would, most probably, result in a *lot* of "light fall-off" toward the outer edges of the frame.
Going the other way, 4" x 5" condensers for 35mm, would be less noticable; the exposure would be less due to the expanded physical dimensions of the "light bundle" - and the "evenness of illumination" would be ( or should be) somewhat less than with the lenses designed specificaly for the 35mm format.
Oversimplification, I know - but I hope this conveys the idea.
My Omega D6XL condenser head has three lenses in the condenser. Two very large and heavy convex one side facing eachother and one convex facing down on top of the top lens that is on an adjustable bracket. The adjustment settings are for the focal length of the enlarging lens. There are settings for 50, 80, 105 and 150. It seems to work equally well at 16mm through 4x5.