From: Milton Aupperle <milton@outcastsoft.com>

Date: January 29, 2011 9:08:55 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] OT: Astro-Tech 8" RC Astrograph

Hi Mark;

On 29-Jan-11, at 8:23 PM, Mark Gaffney wrote:

Milton,

Have you considered the AT6RC? They`re only $299 at present on sale..!

http://www.astronomics.com/main/product.asp/catalog_name/Astronomics/category_name/U5QNWB3RKWWL8N3EL99F9DX9A0/product_id/AT6RC

A 6" is too small. An 8" is just at the bottom edge of usability. I also want a carbon fiber tube, same as my C8 is as it's lighter and more thermally stable than Aluminum.

Also have you considered the Hyperstar route?

I've looked at it, but I want around around 1 arc second per pixel for doing Photometry or Astrometry. And I don't want a wider field of view either which is what you get with Fastar (F/2 is 400 mm focal length) as for photometry, you start getting stars overlapping. You can put any C-Mount type FireWire camera on a HyperStar as they use a T-Mount on it and a Tto C adapter are cheap. A Flea or Flea 2 would be an ideal for that, as you not going to go over a few minutes of exposure time anyhow, so cooling and exposure time won't matter.

I don`t know how your Grasshopper`d adapt to this but one of the new C9.25" scopes from Opt is only $1199 & because it`s Fastar compatible will adapt to the new Hyperstar lens..

My C8 is Fastar compatible, but that doesn't solve any of the issues I listed (like mirror flop, focus, collimating it etc.). It also doesn't solve the issue of guiding, as you can't go OAG either and would have to go with a guide scope. Then you have to fight Flexure issues between guide and imaging scope - which I have already been through and don't want to repeat again :)

Unless the C 9.25 is an EDGE HD scope, it has all the same issues as my current C8 does, so that solves nothing and it weights too much too. And a Edge C8 is about $1400 USD / CDN which is the same price as the AT8RC is, where as the Edge 9.25 are $1900 USD /CDN.

One of the issues with the Edge series is your stuck at F/10 for now. There are no Focal reducers available at all. So it's F/10 (or longer) or Hyperstar. You also have to be very precise with the camera spacing on the Edge HD too too or you get distortion on the corners.

Lastly a CGEM mount is rated for about 45 lbs (max) where as my HEQ5 is rated for about 35 lbs (max). For Astro photography you want to keep your total load (scope, cameras, filters, cables etc.) to about 50 to 75% of the rated capacity, which is about 18 to 20 lbs for my HEQ5 and is what I have now. So that's why I want an 8" Carbon Fibre scope, otherwise I need to buy a new mount. Your CGEM should just handle a C9.25" with some gear on it, but I would not push it beyond that for Astrophotography.

Thanks for the thoughts though..

Milton J. Aupperle