From: Alan Friedman <alan@greatarrow.com>

Date: December 24, 2007 12:14:41 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Mars Dec. 21

Hi Phil -

Thanks for the thoughts - the weather has been so bad here - my last opportunity to image mars was at 7 arc seconds!! I would be very bummed about it if I didn't have a bit of lunar data saved to keep me busy.

I always feel the need to tweak the focus between filters. If you image through IR, the focal shift is very noticeable, less so between green and blue. I also have a moving mirror focusing system, but I use an auxiliary feathertouch focuser for imaging. This works very well.

best wishes,

Alan

On Dec 23, 2007, at 11:36 AM, Phil Houston wrote:

Thanks Alan,

I have been watching the weather in your area in hopes of a nice clear night for you to capture Mars but, wow, the forecast looks really nasty there this coming week at least.

This is a little off topic but I would like your thoughts on the issue of refocusing for each filter change.  My scope has a movable primary mirror which causes a focal length change when refocusing.  This causes the captured size to change between images and I try to correct for this in processing.  I don't know if your AP operates the same way but if so, how do you deal with it?  Process then resize or resize first then process?  Any thoughts from the Master. ;-)

Phil

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