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Old 08-05-2007, 06:58 PM
74tuc
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74tuc is offline
 
Join Date: Sep 2006
Location: Sandy Creek(Sth.Aust.)
Posts: 153
Hi Chaps,

Thanks for the good words and Marcus I've looked at your first pic on pbase and I think it is very impressive. I like the detail provided with your 'scope/camera. When the financial dust settles here I might consider getting a camera like yours. I told the financial controller here about the wonderful camera you had (she was cooking at the time), she sought of went stiff then started hurling vegies into the wok with more force than I thought was necessary. I walked away without saying a thing and surfed the web .

Re: Differential flexure.

I am sure the TGM gives negligible the plate flexing will cause more DF. DF can be managed in my case as I do not use focal lengths longer than 3000mm.

The problem I have is that I cannot prove to myself the minute blemishes are caused DF alone. Off axis the star image distortion is caused by spherical aberration (no field flatner), polar alignment inaccuracies, and DF.

I have made a counter weight for the guidescope/mount combination but not installed this weight as the system is still under test.

The main thing is to choose a guide scope matched to your system and choose one that is as light as possible. The optimum guidescope is smaller than one chosen by common rules of thumb. I use an achromatic refractor with a green filter and a B&W guide CCD. Chromatic aberration (and other distortions) has the effect of reducing the guiding accuracy. I am writing a note (partially complete) for the ASSA on the relation between the main 'scope/imaging CCD and the guidescope/guide CCD. I'll pass this on to you when it is completed.

Regards,

Jerry.
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