Should changing the aperture on my enlarger cause a dramatic change in contrast? I print 35mm negs on a Besseler condensor enlarger and it seems that increasing aperture causes a great lowering of contrast and vice-versa. This is not something that I recall happening on diffusion enlargers I've used elsewhere and the effect is far greater than what I can achieve using polycontrast filters. Is this something more inherent in the condensor enlargers? Or is it simply a by-product of the change in exposure time (i.e., long exposure:higher contrast & short exposure:lower contrast)?

-- Fred Schmidt (driko@ix.netcom.com), August 22, 1997

Answers

Aperature and contrast

Truly an unusual effect. I have been using multigraded papers for quite awhile but have never noticed this problem. What brand of paper do you see this with? Is your lens decent quality? If the lens had a major flaw then I can see some colour separation or shift happening at different aperatures but to get the effect you are desciribing you would probably see a colour change when projecting onto a white surface. For example as you close the aperature the light may become bluish.

-- Andy Laycock (pbrlab@unixg.ubc.ca), August 22, 1997.

Ikes! I think you had more questions than I Andy, but in the event you come back or it helps anyone else who doesn't instantly think I've lost it - I use Ilford Multigrade (IV is it?), both RC and FB. The lense came with the enlarger brand new, and is just your standard 50mm. I don't see any color shift with change in aperture, just brightness. But the contrast change is very evident.

Fred

-- anonymously answered, August 22, 1997

Aperature and contrast

I have been using Ilford multigrade for years and have never had this problem. However I have never really compared the contrast of the same photo at different aperatures because I usually make the change at the test strip stage. I can try a test this weekend. The only other thing I can think of would be the filters themselves. The Ilford filters fade (and lose contrast) over time with exposure to light so maybe that is the key. What filters are you using and how old are they?

-- Andy Laycock (pbrlab@unixg.ubc.ca), August 22, 1997.

I'm using Ilford's MG Filters as well, above the lens. They're about a year old, but I don't use them very much as I almost always get the results I want by changing aperture and, consequently, exposure time. Therefore, I don't really consider it problem, but was curious as to whether anyone else has experienced anything like it as I've not been able to find any information anywhere. And I didn't mean to ask you to test this, but if you really want to, feel free and let me know if I'm crazy (I won't take offense). Feel free to email me directly if you like, so we don't use up all of Mason's space with this one question. I'll go get a box of fresh paper and keep printing. Speaking of paper, have you crafted any yet?

-- anonymously answered, August 22, 1997

Which way does the contrast change? When you stop down do you get greater contrast? Or lower contrast? Run a few tests on it, also with a few different negs, low, med and high contrast & let us know the results. Once we know how the contrast increases( opened up or stopped down & if it is consistent from flat to contrasty negs) then we can give some constructive suggestions.

-- Dan Smith (shooter@brigham.net), August 24, 1997.

Contrast decreases as you open the aperture, right?

I would suspect lens flare as the most likely culprit. Enlarger lenses shouldn't normally be used at full aperture.

Try to beg, borrow or steal a known good lens, and see if you still have the problem.

Try sticking your lens on a camera, on a tripod. Take the photos, with the same exposures, at min aperture, mid-aperture and max aperture. Do the negatives look the same?

Here's a simpler test. Block half the negative carrier, with kitchen foil or something. Check the focusing. With no negative, print this "image" in the usual way. The print should be half black, and half white, with a sharp transition. Lens flare will show up as grey instead of white.

If you repeat that test with different apertures, using no filtration, it should be pretty definitive.

-- Alan Gibson (gibson.al@mail.dec.com), August 29, 1997.

I suppose it is possible to gain contrast at larger apertures(2.8, 5.6) because of more (highlights) light passing through your VC filters than shadows passing through.

either way, I use my lens ALWAYS at f/8 because(as you may know) most lenses(Camera, or Enalrger) have peak performance @ f/8. therfore I have not experiences any increased contrast @ larger apertures I let my filters handle the contrast, and my lens handle the quality of the image itself!

Adam

-- Adam Southerland (stitcher@iquest.net), September 01, 1997.

Actually, the contrast seemed to be lessening as the aperture opens, as noted in my initial post. I have (almost) gotten my hands on a new lens to try out (why is everyone "out" of good 50mm?!), but I'll be in and out of town for while and won't get much printing/testing done for a week or two. I'll also be able to work on a diffusion enlarger soon, so perhaps that will provide some more insight as well. I'll let you all know what comes of it and see if we have more to work with. For the time being, thank you all for your thoughts.

-Fred

-- anonymously answered, September 02, 1997

Contrast and Aperture

I can think of only one thing that would cause a loss of contrast in a lens, flare. But that occurs at very small apertures. Have you considered fogging? Is there any light leaking from your enlarger, say the condenser housing? the edges of the negative carrier? bellows? Have you painted the walls around your enlarger flat black to absorb reflections from light bouncing off the easel? Have you tested your safe lights? By the way, most lenses are sharpest at 2-3 stops below maximum. On a 5.6 this would be f8, but on a 2.8, it would be 5.6. On a high quality 6 element MULTI-COATED enlarging lens, just about any aperture below full will give exellent results. It's best to select a lens a little longer than "normal" for the negative, that way you're still using the center portion of the lens. 65mm for 35mm, rather than 50; 150mm for 4x5 instead of 135mm. This will give you more coverage of the negative as well.

-- Michael D Fraser (mdfraser@earthlink.net), September 10, 1997.

It appears that the answer to my question was indeed my lens. I thank you all for pointing me in the right direction.

-- Fred Schmidt (driko@ix.netcom.com), September 23, 1997.