From: Mark Gaffney <markgaffney@me.com>

Date: January 30, 2011 12:51:01 AM MST

To: Astro_IIDC@yahoogroups.com

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

Hi Milton, 

One thing occurred to me reading your response & that`s the memory that my friend Brian Allan uses a 0.75x reducer on his Edge HD C8. 

I don`t know what kind exactly but I could ask if you like? 

I was under the impression that the Edge scopes had lockable mirrors which would eliminate mirror flop at least when you`ve arrived at your imaging parameters..

Brian does use a Q guider which has a guidescope of 50mm on ADM rails etc attached to the scope & an Antares Red dot finder (I have one of each of these too now myself & have used my Scorpion 20SOM on it, guiding with Astro IIDC-the problem was I think some stiction in Dec guiding with my CG-5). 

I have had the mount covers off  trying to deal with electrical problems since we last talked about this. I ran into problems with the self tapping screws inside the plastic covers incidentally..

Here`s one of Brian`s images with the 0.75 reducer & Canon 60D..

http://picasaweb.google.com/116260312230579398213/MVREmissionReflectionNebulas#5565670325686523986

I did look into the AT8RC`s a while ago & was assured by people at the time I think they could be also used visually..

I think you posted me a link to some custom curved spiders for them as you were concerned about the diffraction spikes they exhibit..

Interesting what you`re saying about C-mount camera`s being easily adapted to Hyperstar units which can cut imaging time on DSO`s up to 25x I believe with minimal guiding..

Each scope has it`s advantages of course but if one of your prime goal is Astrometry or Photometry..(?)

Brian does use a Moonlight SCT focuser also by the way..

Mark.      

On 30/01/2011, at 3:08 PM, Milton Aupperle wrote:

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