Enlarger lenses: 135 mm vs 150 mm

[Chris Gittins]

I'm enlarging 4x5 negs to 8x10 on an Omega D3 with a 135 mm Rodagon. I find that I'm almost always burning the corners of my prints - an additional 20% to 30% of the base printing time is pretty typical. Does it make sense for me to go to a 150 if I want more even illumination?

Thanks, Chris

[Ed Eubanks]

I've noticed that my 4x5s all require burning around the corners, too-- but that is on the negative. The light source has nothing to do with it. Are you sure that your burning situation is based on the illumination?

[Ralph Barker]

Some 135s cover better than others. You might try measuring the light from center to the edge with no negative in the holder to determine how much fall-off you're getting with the Rodagon. A good 150mm lens will probably provide more even coverage, but will also limit the maximum enlargement possible on the baseboard, of course.

[Thilo Schmid]

Chris,

the 135mm Rodagon is meant to fit the continental european format 9x12cm (3.5x4.7"). However, at 2x magnification it should work well with 4x5. if your corners are burned (i.e. receive too much light), it is either your taking lens (you may need a center filter for it) or uneven illumination (which is unlikely brighter at corners). If the EL-lens has too less coverage or suffers from fall-off, than you would notice a dodging effect unless your are printing direct postives. An EL-lens with light fall-off might be able to compensate that of a taking lens. Try open aperture with your Rodagon 135mm. That should yield sharp prints as well at 2x magnification.

[Tadge Dryja]

If you're only printing 8x10, that's a 2X enlargement... you're not going to see any difference between the 135 and 150. It's sortof like with taking lenses -- at macro ranges, coverage goes up and you usually don't have to worry about it.

Set up your enlarger to make a 20x24, and notice how far the enlarging lens is from the film. Then set up & focus to make an 8x10. Just by looking at the angles involved, if it can cover the neg when making a 20x24, there will be lots of excess coverage at 8x10.

Maybe stop down another stop or two & see if that improves uniformity? But I imagine you might have already tried that. Certainly don't use it wide open, that definetly leaves the corners underexposed.

[phil sweeney]

Chris,

Typically you will get less falloff with the 150mm, but it still occurs. The character of uneven illumination is the combination of optics and lamp characteristics. I use a mask to compensate for my setup. This allows me to concentrate on my image. The mask was made per Alan Ross's mask techniques.

phil

[ronald moravec]

Make a contact print to detirmine if the problem is in the negative.

I use 135 and 150 comparons on a D2 and the results are indistinguishable.

Make sure you have the proper condensers in place. I think that is only the two large ones.

[Chris Gittins]

Thanks for comments so far. Masking sounds like a particularly interesting possibility. I'll look into that. Some addition information: I typically print with the lens stopped down to f/16 or f/22 to get the base exposure time in the range of 10-15 seconds. I checked the illumination on an 8x10 Kodak white card last night. There's 6% to 8% roll-off in intensity from the center to the corners. That's illuminating the card with no negative in the negative carrier but the film plane in focus, no filter in the condenser, and looking at the intensity of scattered off various points on the card with a 1 degree spot meter. I don't have an incident meter. (I did the test at f/5.6 because there wasn't enough change in the needle position at f/16 to get a good quantitative measure of roll-off.) In the past, I have noticed some roll-off with a 4x5 Stouffer step tablet enlarged to 8x10 - was doing a lot of paper testing a year ago. I checked tablet uniformity with a densitometer and I am definitely seeing an enlarger effect.

My two primary taking lenses are a 180 Nikkor W and a 150 Caltar S. The need to burn does not appear to be a function taking lens. It's pretty clear some of the motivation for burning the corners has to do with visual perception rather than physics - concentrates the image in an appealing way - but the less I have to compensate for physical effects, the better.

Chris

[Gem Singer]

Hi Chris,

Sounds like a condenser problem, not a lens problem, to me. Check the alignment and spacing of the condensers. Also, make sure the condenser lenses are not dirty or scratched. If it isn't already there, install a piece of round opal glass (or plastic) between the bottom of the condensers and the negative. If nothing else works, replace the condensers with an Aristo cold light unit.

[Brian Ellis]

I used a 150mm Schneider Componon S lens for 4x5 negatives. I never had to burn the corners that I recall unless I chose to do so for aesthetic reasons. And I didn't do that because to me it looks very obvious and phony ("oh look, he burned the corners so that our eyes would go to the center of the print") unless it's extremely subtle. Despite what others have said here, all other thing being equal a 150 lens will give you more even illumination than a 135 lens. That's the reason people buy them.