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Re: [ATM] strange (collimation?) problem
Hi Jan,
Are you sure there is not a problem with the focuser, seems it is not
parallel to the optical axis.
Adrie Suijkerbuijk
----- Original Message -----
From: "Jan van Gastel" <jhm.vangastel@wanadoo.nl>
To: "ATM List" <atm@atmlist.net>
Sent: Monday, June 20, 2005 9:05 AM
Subject: [ATM] strange (collimation?) problem
> Yesterday I startested my selfmade, not yet aluminiumized 300 mm f/5 30 mm
> thickness (Pyrex) mirror (its my first mirror). To be able to do that I
> made
> an extra collimatable platform with a 6-pointcell on the mirrorbox of my
> 300
> mm f/6 telescope. Two round teflonpads at 90 degrees act as lateral
> supports
> (see: http://home.wanadoo.nl/jhm.vangastel/Astronomy/scope3.jpg ).
>
> What I saw inside of focus: nice round diffraction pattern with clear
> round
> diffraction rings. No sign of astigmatism. Nice outer ring. Secondary
> shadow
> well centered.
>
> And outside focus: more turbulence, nice round diffraction pattern as
> well,
> Rings a bit les clearly seen then inside focus. Secondary shadow breaks
> out
> a bit later (but clearly less later then in my other 1/8 lambda P-V
> mirror)
> as compared to inside focus (new mirror tested 1/13 lambda P-V; .98
> Strehl,
> using Figure XP; undercorrected edge).
>
> BIG DIFFERENCE as compared to inside focus: secondary shadow not centered
> but very clearly offset to one side. When I centered the secondary shadow
> during the startest in the outside focus pattern, it became decentered
> inside focus and was then also clearly off collimation as seen in the
> cheshire.
>
> I can't imagine I did the collimation wrong. Collimated the secondary with
> a
> laser and the primary with a cheshire as I always do.
>
> I have never expierienced this before and don't have a clue about the
> cause
> of the problem.
>
> Jan
> http://home.wanadoo.nl/jhm.vangastel/Astronomy/
>
>
> ----- Original Message -----
> From: "David Harbour" <scarab2@cox.net>
> To: "Stan Truitt" <s.truitt@verizon.net>; "ATM List" <atm@atmlist.net>
> Sent: Sunday, June 19, 2005 3:03 AM
> Subject: Re: [ATM]: What do they offer:
>
>
>> 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
>>
>>
>> _______________________________________________
>> ATM mailing list http://www.atmlist.net/
>
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