VC Filter Holder for Beseler 45MXT w/Aristo cold litegreenspun.com : LUSENET : Large format photography : One Thread
I got into LF and built a darkroom at the same time. Probably should have given up my day job, too. Bought a venerable but very solid Beseler 45MXT enlarger with an Aristo cold light head. The enlarger has a very small filter holder below the lens that won't fit anything but the old Polycontrast filters, and is so small it vignettes the image if I'm using a 150mm lens and am not really careful. I just lay the filters on top of the holder. Anybody know of any better way to use the filters? I would prefer not to put the filter below the lens. If I have to leave it there, is there a way to support the filter without going to a machine shop?
-- John Sarsgard (Endive4U@aol.com), November 16, 1998
I had the same problem, only with an Omega enlarger. I have now solved it. What I finally did was build a filter drawer assembly that is a perfect slip fit over the Aristo. Mine is made of wood (walnut, as if it matters - but the unit is beautiful to look at as well as highly functional). It has a drawer with a clear bottom that takes 6 x 6" contrast filters. This accomplishes at least two things: First, it eliminates the problem you mention. Second, and more importantly, it eliminates a filter from the optical path that can reduce sharpness. I never did like the idea of putting a filter in the optical path.
One more fine point: Perphaps you read the articles by Ctein and the subsequent controversy over the possible loss of sharpness that might be experienced when using modern extended-range VC papers. Supposedly, these papers are sensitive to UV light that is emitted by some light sources. The reasoning goes that the UV light focuses on a different plane (true) which is not visible to the eye when focusing the image. Since theses papers "see" this UV, an out-of-focus image is also produced on the paper superimposed over the desired image, reducing the overall sharpness of the final print. Anyway, after this whole can of worms was opened (the enlarger lens manufacturers agreed with this assessment of the problem), it was dropped. All kinds of weird and compromising solutions were suggested by Ctein and others, most requiring extensive and ridiculous testing. All were a compromise solution to this supposed problem. But I wondered all along why, if the UV is the culprit, wouldn't it be better to simply eliminate the UV rather than going to extremes to try to reduce the claimed effect. Wanting to be safe, I decided to eliminate this possibility by making my filter drawer bottom out of Opar3 plexiglass (I may have that name slightly wrong). It is UV glass available from Light Impressions that is normally used for protecting displayed prints from UV exposure damage. (You could use any UV filter material, of course.) Having a little left, I cut a round disk of it and placed it above the diffuser in the Aristo for that little extra bit of peace of mind.
Oh yea, one more advantage of this drawer unit. My filter drawer allows me to add neutral density material ( it's not necessary to use optical grade - I use the stuff made for lighting - very inexpensive) into the drawer so that I can use my lense's at their sharpest F/stops without having to change to inconvenient (or impossible) printing times.
This whole arrangement works great and it actually takes less time to change filters than before. I don't have space to tell you exactly how I built the filter drawer, but it shouldn't be difficult to come up with a design that works for you. If you wish, I could give you a more precise description of my unit. In any case, I would recommend that you eliminate the use of below-the-lens contrast filters.
-- Tom Johnston (firstname.lastname@example.org), November 20, 1998.