Re: [Leica] thambar questions

["Dan Post" <dwpost@email.msn.com>]

Henning!
YIKES! I was simply considering a simple miniscus lens, as an example.  Now
my 'Leetle gray cells' are totally discombobulated!
I actually am thinkingg of taking my old 1937 Elmar 90/4 and using the UV
filter, putting a dot, proportinal to the area covered by the Thambar, and
shooting that wide open....see what happens, maybe serendipity!  Anybody
familiar with the diameter or both the front element of the Thambar, and the
spot on the filter?
Dan ( having more fun than I really should have!)

- -----Original Message-----
From: Henning J. Wulff <henningw@archiphoto.com>
To: leica-users@mejac.palo-alto.ca.us <leica-users@mejac.palo-alto.ca.us>
Date: Monday, May 31, 1999 12:39 PM
Subject: Re: [Leica] thambar questions


>Dan P wrote:
>
>>Now- my next question- since I haven't had trig since college 30 years
ago,
>>but is the Sin 4th law the same principle as what I learned as the Cosine
>>law- that light falls off as a function of the cosine of the angle from
the
>>optical axis- as the angle increases, the light diminishes by a factor of
>>the cosine of that angle?
>
>Yes, of course. I was a bit too sloppy, and therefore it came out wrong. In
>a 'standard' construction lens the light intensity falling on any area of
>the image plane that is off axis is reduced by the factor of cosine theta
>to the fourth power, where theta is is angle between the light ray and the
>axis. Actually this holds for more complex lenses with no distortion as
>well, but then you get into rear nodal point location, which isn't simple
>anymore.
>
>
>   *            Henning J. Wulff
>  /|\      Wulff Photography & Design
> /###\   mailto:henningw@archiphoto.com
> |[ ]|     http://www.archiphoto.com