From: Jim Chung <jim_chung@sunshine.net>

Date: November 28, 2012 4:10:07 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Focussing issues .. need advice

Hi Rodolphe,

I've imaged with 3 and 4" refractors in the past with 5x Powermate and if the seeing is good you should be able to get better sharpness.  The 5X Powermate is a funny creature because it actually delivers more than 5x magnifcation .... more like 8x so the focal length is rather high and producing a dim image they may be hard to see on screen to discern best focus.  Plus you don't want to max out your gain in AstroIIDC and introduce unnecessary noise.

I would think about 2000mm focal length is best for a 3-4 inch refractor so maybe a true 3x barlow.

regards,

Jim

 Quoting Rodolphe Pineau <pineau@rti-zone.org>:

On Tue 11/27/12, at 21:47, Dave Goodyear wrote:

I think you approached the Dawes Limit of the scope... I see other pictures on the net using a 102 and 5x powermate and they look about the same..  How's your collimation?

Hi Dave.

I though about that too and when I read your previous email it made sense to me... I'll have to try with a 3x Barlow and see if there is an improvement.

The collimation is prefect on this scope.

I have an 8" f/4 refractor (812mm focal length) that I haven't try in a while so I'll do more test with that too.

But overall I think you're right and I've gone over the Dawes limit which explain the issue I see.

Thanks for the reply and clarification.

Regards, Rodolphe.

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