Archived posting to the Leica Users Group, 1999/08/19
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With regard to your use of matt screens on the SLR. Does it work out well
with focal lengths of 35mm or 50mm--and in dim light, such as an indoor
living room?
Thanks.......Julian
- ----- Original Message -----
From: Tom Bryant <tbryant@pars5.gsfc.nasa.gov>
Sent: Thursday, August 19, 1999 6:32 PM
Hi Luggers,
Some desultory comments for you.
On lens coatings:
I have heard that lens coating color may well be a function of the dyes
Having several colors in the MgF2 coating! (From Roland Christensen, who
makes astronomical refractor objectives). It also depends on its thickness.
Multiple colors in a lens do not, in general, indicate that a lens is
multicoated.
On matt screens for SLR:
Ted Grant is absolutely correct about matt screens being best for an
SLR.
I find them superior to microprisms or "rangefinder" wedges. It's all I've
used for years.
On Lens coverage:
Here is a table of some popular focal lengths with their horizontal x
vertical coverage, along with their diagonal coverage for the 35mm format:
The units are decimal degrees.
14mm: 104.250 x 81.203, 114.182d 55 mm: 36.244 x 24.616, 42.943d
15mm: 100.389 x 77.320, 110.527d 75 mm: 26.991 x 18.181, 32.180d
17mm: 93.273 x 70.435, 103.678d 90 mm: 22.620 x 15.189, 27.032d
20mm: 83.974 x 61.928, 94.493d 135 mm: 15.189 x 10.159, 18.208d
21mm: 81.203 x 59.490, 91.702d 180 mm: 11.421 x 7.628 , 13.706d
24mm: 73.740 x 53.130, 84.062d 200 mm: 10.286 x 6.867 , 12.347d
28mm: 65.470 x 46.397, 75.381d 300 mm: 6.867 x 4.581 , 8.249 d
35mm: 54.432 x 37.849, 63.440d 400 mm: 5.153 x 3.437 , 6.191 d
50mm: 39.598 x 26.991, 46.793d 1000mm: 2.062 x 1.375 , 2.479 d
On F stops:
Here is a table of full, third and half stops
full, + 1/3, + 1/2, + 2/3: full, + 1/3, + 1/2, + 2/3:
1.000 1.122 1.189 1.260 1.414 1.587 1.682 1.782
2.000 2.245 2.378 2.520 2.828 3.175 3.364 3.564
4.000 4.490 4.757 5.040 5.657 6.350 6.727 7.127
8.000 8.980 9.514 10.079 11.314 12.699 13.454 14.254
16.000 17.959 19.027 20.159 22.627 25.398 26.909 28.509
32.000 35.919 38.055 40.317 45.255 50.797 53.817 57.018
64.000 71.838 76.109 80.635 90.510 101.594 107.635 114.035
I have found these tables useful over the years. Enjoy!
On the Noctilux f/1:
Well, Erwin should get another spiff, as should Mitch. I have bitten
the
bullet, and bought a Noctilux. Yoikes! It's a big un. 2 cm shorter than
my
90mm Summilux, and larger in diameter. My old Summilux is 2.5 cm shorter
than
the Noct, and the diameter is about sqrt(2) smaller. It's a much more
portable lens, and it has the wonderful reversing, metal hood. The Noctilux
has a *plastic*, non reversing hood. The lens cap is awful. I've replaced
it
with a 69 cent plastic and elastic bowl cover. I won't be getting rid of
the
Summilux in any great hurry.
I'll be getting a roll through it presently, and will report on what
that
glorious extra stop is like. I have yet to stop the lens down. On the M3,
it
handles very well, as well as the Summilux. It's extra weight and inertia
make it a fairly steady lens to hand hold.
Overall, I'd say that for situations that don't require f/1, the
Summilux
is the better lens, as it's a mite sharper (see photodo.com for details) and
much more portable. If I always shot on a tripod or outside, a Summicron
would be the lens of choice, being even sharper and more portable. You
guessed it, I rarely do either, with the M3.
That's all for now!