[none]

[Tom Bryant <tbryant@pars5.gsfc.nasa.gov>]

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!