Mark,
I bought a used Zone VI head and the prior owner had made a disk out of grey mat board (two or three inches in dia.), and inserted it behind the tube. Due to poor packing, the unit arrived with a broken tube and I replaced it with a V-54. I removed the mat board but kept it because I wasen't sure what it was for. Now I know and will check mine for light falloff / uneveness.
It just pays to read all these threads. You never know what you'll learn.
dee
I used an Aristo VCL 4500 head on a Beseler MXT enlarger and a Schneider Componon S 150mm lens for many years, always one or two stops down from wide open. I never noticed any consistent fall-off at the edges of my prints.
Brian Ellis
Before you criticize someone, walk a mile in their shoes. That way when you do criticize them you'll be
a mile away and you'll have their shoes.
Brian,
The Aristo VCL 4500 cold light head is a designed differently than the Aristo head that Mark is referring to. The 4500 has two tubes encased in a larger sized box, as well as a double diffusion screen on the bottom. It emits a more evenly diffused light pattern than Mark's single tube "snake in the flowerpot" type of Aristo cold light.
The problem is not your lens or the enlarger. It is the Aristo unit, which is smallish for a 4x5 negative because it was sized to be the same size as the Omega and Bessler condensors in order to fit those enlargers. I give a 15% burn to the edges of the print, which adds twice that to the corners. Edge burning is not needed with smaller negatives. It does help to use a longer lens. It will be about 30" from the lens to the paper to make a 16x20 with a 150mm lens. I use a 180mm, and it is about 36" from lens to the paper to make a 16x20 with it. Don't forget that this enlarger can be used for wall projection for really big enlargements. Someone above mentioned being able to see the shadow of the coils on a test print made without a negative in the carrier. I have the standard lamp and do not have that problem, but I have heard that can happen with the high intensity lamps. I believe Fred Picker used to solve that problem by using two sheets of opal glass separated by a small air space. That solution might reduce light falloff at the edges too.
On the other hand it might save you the bother of using a centre filter with wide angle lens on camera!
I am using the identical setup (Aristo head, V54 lamp, Beseler MCR enlarger) and have not experienced the problems you are having. Ctien, in his book "Post Exposure" has a section (page 61) addressing the problem of uniformity. He indicates testing for uniformity of illumination is better done using paper and making prints. He describes his method, stating that using a photometer it is". . . extremely difficult to align one to eliminate errors introduced by off axis measurements." Check out his book. I have found it very informative and have had some e-mail exchanges with him in which he has been very helpful.
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