From: Milton Aupperle <milton@outcastsoft.com>

Date: February 6, 2010 11:18:18 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] new filter wheel...!

Hi Alberto and Mark;

The other issue is your getting coma on the edges of the field as you use shorter focal lengths. For a small CCD (1/3") this wasn't a problem,  but with my 2/3" CCD it makes a big difference, lots of elongate stars on the edges. Vignetting became very apparent below F5 with a F6.3 reducer and you need to do flat frames to even things out.

And Mark, as I said in past conversations about this, using a MOOG per camera will never work with an OAG. You will likely never get both cameras into focus at the same time and will never maintain it easily. You want to put the F6.3 Antares on the SCT, attach the OAG to that, and then the cameras on the OAG.

Trust me, I have been down that road before and your just asking for a lot of frustration and fiddling without ever getting any images.

TTYL..

Milton Aupperle

On 6-Feb-10, at 2:40 AM, albe albo wrote:

Ok Mark,

the 6.3 is a lot more "forgiving" allowing longer extensions and experiments while the 3.3 is a wild beast LOL.

Now you make me curious to test the 6.3 in order to understand how much it can be "pushed" with acceptable results.

For example i pushed the 3.3. > to 2.8 and seems to work (the focus knob of the scope is almost completely turned CCW)  but the vignetting increased a lot. 

Unfortunately i have no clear sky since long time so i couldn't do a true session with dark frame, flat field etc.

It is almost one year that i don't do any DSO. (i'm lazy too i confess)

Regarding the focals i can check them on a building that is placed exactly at 1,5 km from my house.

By the way....I wanted to measure the exact point where the C11 gives the "nominal" focal length (2.800 mm).

Putting the visual back + nose i realized i had only 2.652 mm !

So i did some tests: did I published them already on this group?

http://dl.dropbox.com/u/1094920/ASTRO/100130-MisurazioneFocale.jpg

Cheers

Alberto