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Re: [ATM] Re: Star testing with a ronchi test to quantify a TDE
>You just look for little hooks going outwards at the very ends of the
>bands, where they meet the edge of the mirror
Exactly what I've seen.
>Using your measurments from the Ronchi is a good place to start and
probably
>all you need.
>I think he is just looking for a little confirmation.
Exactly Ken. Now I have it. Thanks a lot!
Raphaël
----- Original Message -----
From: "Ken Lowther" <hermit@outofoptions.org>
Cc: <atm@atmlist.net>
Sent: Friday, December 24, 2004 6:09 PM
Subject: Re: [ATM] Re: Star testing with a ronchi test to quantify a TDE
Well, the one thing I left out of the post, and probably the reason he
didn't
get a response the first time, is it sounds like he already knows what to
do.
I think he is just looking for a little confirmation.
Ken
Quoting Guy Brandenburg <gfbrandenburg@yahoo.com>:
> I find that using a ronchi grating while doing the
> star test is relatively insensitive to small defects.
> I find that the actual star test is difficult to
> interpret correctly - so much depends on the
> atmosphere, tube currents, and so forth. And you can
> only do them on clear nights. (I probably haven't done
> enough of them.) But then again, I also haven't made
> myself an artificial star to do the star test on. A
> ronchi test at the bench is very sensitive to turned
> edge, I find, especially if you look OUTSIDE of the
> point of the center of curvature. You just look for
> little hooks going outwards at the very ends of the
> bands, where they meet the edge of the mirror.
>
> Anybody beg to differ?
>
> Happy holidays
> Guy
>
> --- Ken Lowther <hermit@outofoptions.org> wrote:
>
>> The Ronchi has been pretty good in showing turned
>> edge for me. The true answer
>> is though that you see it in the star test. That is
>> the final test. Using
>> your measurments from the Ronchi is a good place to
>> start and probably all you
>> need.
>>
>> Ken
>>
>> Quoting Raphaël GUINAMARD <rguinamard@infonie.fr>:
>>
>> > It seems this message didn't reach the list.
>> > I send it again.
>> > ----- Original Message -----
>> > From: Raphaël GUINAMARD
>> > To: atm@atmlist.net
>> > Sent: Thursday, December 23, 2004 9:59 PM
>> > Subject: Star testing with a ronchi test to
>> quantify a TDE
>> >
>> >
>> > The star testing of my mirror shows a Turned
>> Down Edge.
>> > It doesn't seem very big but I think I 'm going
>> to put an annular > mask to avoid the image degradation.
>> > I've also seen this TDE using a ronchi grating,
>> and if I take a > picture of the image, I think I could mesure where
>> the TDE is > starting -at least on the picture itself-.
>> > My question is :
>> > I know the ronchi test is not very sensitive
>> with fast scope (mine > is a 24" f/3.3) so is the measure of the TDE on
>> the picture would be > a good approximation of the TDE on the real
>> mirror?
>> > I mean, if I measure for example on the image
>> that the 2% outer > part of the image has a TDE, does this mean I
>> could confidently make > a mask for the 2% outer part of the mirror?
>> > Maybe the low sensitivity of the ronchi test
>> could show a 2% outer > TDE with a 4 % outer TDE mirror? no?
>> > I know I could try different annular width and
>> star test with each, > but my question is to go as quickly as I could to
>> the solution
>> > Thanks in advance
>> > Raphaël
>> > _______________________________________________
>> > ATM mailing list http://www.atmlist.net/
>>
>>
>>
>> Hermit, holed up in Youngstown, Ohio
>> _______________________________________________
>> ATM mailing list http://www.atmlist.net/
>>
>
>
> =====
> Guy Brandenburg
> Washington, DC
> My home page:
> http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
Hermit, holed up in Youngstown, Ohio
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