From: Sandy King (sanking@hubcap.clemson.edu)
Date: 08/14/00-12:59:36 PM Z
Michael,
One of the interesting things about optics is that there is considerable
variation in the actual amount of coverage you get with specific lenses,
especially with lenses like Dagors that have been made for over 100 years.
Some of this is apparently caused by mechanical vignetting resulting from
remounting to specifications different from the original barrel mounting,
and there can also be considerable difference in performance. This will
explain, I believe, why my experiences with certain lenses are different
from those of Kerik.
Buy with caution and if possible get a return privelige if the lens is not
acceptable because you will really get some surprises with coverage. For
example, I have a 360mm F/5.6 Symmar in a #5 Compound (the old convertible
Symmar) that actually gives a greater circle of illumination than several
Dagors of equivalent focal length I tested. Now if you look at the
literature you will read that the coverage of a Symmar is only about 71 or
72 degrees, while that of Dagors is stated to be 88 or 89 degrees. Yet this
particular 360mm Symmar covers the 12X20 format (sharply) and even allows
some movement, indicating actual coverage of 81-82 degrees. The two shutter
mounted 14" Dagors I tried on the 12X20 actually covered *less* than the
Symmar. And a friend of mine got an even greater surprise when he
discovered that his shutter-mounted 16 1/2 Dagor did not come close to
covering 12X20!!
But back to your question regarding 7x17.
I use three wide angle lenses for 7x17.
1. 210mm f/6.8 Angulon.
My 210mm F/6.8 lens covers the 7x17 format but must be stopped down to f/45
or f/64 to cover the corners with acceptable sharpness. For contact
printing I find it gives ok performance even at the corners.
Advantages -- Very small, compact, nice contrasty image.
Disadvantages -- Has become rather pricely in the last few years, mediocre
performance at the corners but acceptable for contact printing.
2. 210mm f/8 Super Angulon.
This lens covers the format and allows considerable movements, with a
useful circle of over 510mm. (about 460mm needed for the 7x17 format).
Advantage -- Huge image circle, very good definition centrally, good at the
corners.
Disadvantage -- Expensive, very big (read *huge*), and subject to flare
because of huge front element and number of glass to air surfaces.
3. 240mm f/6.8 Dagor
This is a very old Goerz Berlin Dagor circa 1905-15 remounted in an Ilex #3
shutter. It has a circle of illumination of over 480mm and when stopped
down to f/45 or f/62 the definition at the corners is acceptable.
Advantage -- Very light, compact, not terribly pricely. Gives good
contrasty image.
Disadvantage -- Mediocre performance at the corners but quite acceptable
for contact printing.
Beyond 240mm there are quite of number of lens that work well for this
format and still are considered wide angle: 10 3/4" Dagors, 12" Dagors, 12"
G-Clarons, etc.
Sandy King
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