[PhilfromOz]

Hi all,
First post! I would like to introduce myself to the IceInSpace community.

A bit of Background:
I go viewing with a few others in a “Horse Paddock” up at Kenthurst (Dural Pony Club) on reasonable Friday evenings. In the Bintel Monthly (NightSky), the group is listed as the Sydney Northwest Astronomical Society.

My current set-up is a Losmandy G8 Mount with Gemini. Scopes are on a Losmandy Dovetail Side by Side Plate. Guiding is via an Orion Starshoot Autoguider, on an Orion ShortTube 80 Guide Scope OTA. Viewing & astrophotography is either a Televue 76 or a Celestron 8”SCT (usually with 6.3 focal reducer). Connected to the viewing OTA, is a Meade 644 Flip Mirror, Eyepiece and Atik EFW (with Astronomik 1.25”LRGB filters), and Atik 314e CCD. On the laptop, I typically use The Sky (to see what is around), PHD (for guiding control), AstroArt (for imaging control) and EFW S/W (to change filters). As yet I do not drive the mount from the laptop, preferring to use the Hand-control & Gemini.

I assume that the learning never stops with this hobby, hence the fascination, but I am not sure if I am getting the most out of my gear, particularly on the imaging front, with stars appearing larger than I would expect.

In this Post there was suggestion for some light reading, and the following caught my eye

http://www.astro-imaging.com/Tutorial/MatchingCCD.html

Matching a CCD Camera to a Telescope
Using the formula:
Star Size = (Seeing * Focal Length)/206.3

So for the SCT, with a 6.3 Focal Reducer, the result is:
Star Size = (3 * 1,260)/206.3 = 18.32

For the TV76, the result is:
Star Size = (3 * 480)/206.3 = 6.98

Dividing these by the 3.3 FWHM gives me 5.6 and 2.1 respectively. So given the Atik 314e has a pixel size 4.65 uM x 4.65 uM (resolution of 1392 x 1040 pixels) it seems to be over-sampled or under-sampled.

Is this correct?

Regards Phil