Re: [ATM]: What do they offer:

["David Harbour" <scarab2@cox.net>]

Re: [ATM]: What do they offer:Stan-

You are too generous! All I can tell you is that this little bulb, the one
that the hardward stores carry on their flashlight lamp charts (the only one
that is threaded, and for which radio shack has a socket and leads to a two
cell "D" cell battery holder), never caused me heat problems. In fact, I
cannot believe how good my experience with this tester was, over the years.
I built five testers. This one was ready when I destroyed my McIntosh tester
(#4) by failing to put counterweights on the extension to the platform of my
very long optical bench, to test a very long mirror. Glad I had it ready.
You can see it here:

http://www.atmsite.org/contrib/Harbour/Tester.html

My neat little (large, actually) McIntosh tester disintegrated in a shower
of flying parts when it fell to the concrete floor.. But I was ready with
#5!!! Someone kept it. (I expected this). It's okay; I was never going to
use it again. I hope he loans it to others, whoever he is (the guy who kept
it).

It is hard to believe that it was so bright that it caused me to have
SERIOUS difficulty reading shadows on coated mirrors, but it was. Maybe we
should form a club: "Not Happy with LED Illumination" club. On the other
had, everyone on the list would probably just get mad at us, and shun us,
forever.

Thanks,

Dave

P.S.- Late stuff, since my website, courtesy my dear friend, Master GORDON
TULLOCH:


 http://www.gordtulloch.com/harbour/index.html

Dave

All of you guys are the best club anyone could be a memeber of (ATM list)


----- Original Message ----- 
From: Stan Truitt
To: atm@atmlist.net
Cc: scarab2@cox.net
Sent: Saturday, June 18, 2005 6:35 PM
Subject: Re: [ATM]: What do they offer:


Aloha Dave,

<Will someone offer me an explanation for what the "advantages" of LEDs are,
<compared to VERY BRIGHT incandescent filament lamps? I just have never been
<able to figure this out. I'm sure it's not a fad;' it's just probably
<because I am stupid about these things.

While being a fan of incandescent Tungsten, and to a lesser extent Zirconium
arc lamps, I would like to share an experience relating to LED sources.  In
an ellipsoid being tested with the knife at it's long focus and the source
at the focus closer to the mirror, convection currents from the heat
dissipated within the light path seriously disturbed data repeatability.
Efforts in ducting away the heated air, and water cooling the lamp surround,
improved the setup; but not without blocking an unacceptably large area at
the mirror's center.  Switching to the vastly more efficient LED source
while retaining a bit of the water cooling resulted in excellent
repeatability of the data, even with the water flow turned off.

Perhaps you are not "stupid about these things", rather than highly
enthusiastic about those things that worked for you.  Patient forbearance of
others' curious investigation of alternate avenues seems, to me, a good way
to go!  Pontificating is, at least for me, not.

Tungsten ribbon lamps are a practical necessity in the double bounce from
uncoated Cass secondaries in Hindle sphere setups.  Not to mention providing
a fine place atop the lamp housing to set my pyroceram coffee cup!
Coherence effects in porting my HeNe beam to this setup make the filament
approach all the more desirable.

I enjoy many of your messages to the ATM list.  Some, for me, have been
valuable.  Your kindness and generosity garner my appreciation and sometimes
admiration.


Sincerely,

Stan Truitt


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