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Subject: Re: HELP: Beseler 23C II Lens won't screw in



jephey@gmail.com wrote:

> I had to take off the lens board and undo all the screws and hold the
> thread while I screwed the lens in.


How to make a simple task difficult and destroy your new enlarger all in one
easy step. Follow Scott's comment. Do not disassemble the enlarger
unnecessarily. Mosts tools are designed for easy operation. If you do not find
the easy way, keep looking.


Thanks for the help. Is there any
> real difference between the 75mm and the 50mm?
>


25 mm. Seriously, the lenses are sized to the negatives they are intended to
develop. (By the way, notice that the top rack and pinion bellows control has
markings for the locations that you should stop at for negatives from 35 mm to 2
1/4 x 3 1/4 inches. You have to adjust this for each lens that you use.) A 35
mm negative is 24 mm x 36 mm and the diagonal distance is about 43.5 mm. So a
50 mm lens is large enough with a little extra to "cover" the diameter of the
negative when projected. A 75 mm lens is about appropriate on the same basis
for a 2 1/4" x 2 1/4" negative, which is about 56 mm to a side. (SQRT [56^2 +
56^2] = 79 mm.) In fact, some people prefer a slightly larger lengs for the
job. I often use a 90 mm lens for a negative this size. To complete the
analysis for the lenses available for the Beseler 23C, (1) a 90 mm lens is
required for a 6 x 7 negative (nominally 60 mm x 70 mm or 2 1/4" x 2 3/4"), the
negative is about 56 mm x 65 mm, yielding a diagonal of 86 mm; (2) a 105 mm lens
is required for a 6 x 9 (aka 2 1/4" x 3 1/4") negative, with a diagonal of 102
mm (SQRT [56^2 + 85^2].


Francis A. Miniter

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