From: Milton Aupperle <milton@outcastsoft.com>

Date: December 6, 2009 2:10:56 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] focal reducer for DMK

Hi Willie;

On 6-Dec-09, at 12:43 AM, Willie Strickland wrote:

Have any of you used a focal reducer with your DMK camera.  I have a DMK214AF and I have used it with a .5 focal reducer from Atik.  With the scope I am using, I really need something more along the lines of .63 I think.  Just wondering if anyone had hany recommendations.

A 0.63x will have a narrower FOV than a 0.5x reducer would, so I'm not sure how that would help with your needing a wider field?

I am attempting to capture the occultation of TYC 1252-803-1 by (423) Diotima this morning.  For occultations it would be nice to have the wider field.  I was able to get the targets and watch Diotima move closer to the star, but now I have nothing.

If you increase the distance from the Focal reducer to the CCD, you increase the amount of Focal reduction that you get. For a Celestron 0.63x reducer, the ideal distance from the Focal reducer to the CCD is 105 mm, however mine is a bit further back than that for the OAG, Filter Wheel and Hutech Idas LPR and I get 0.59x.

With some extender tubes, I've run it back as far as 0.45x.

However there are practical limits to this as stars on the edges of the field become distorted and you start getting severe vignetting on the edges of the field.

We are supposed to be in occultation right now.  It would be nice if the field was larger so I could watch a nearby star and know that I am still getting data and my tracking is still on target.  I really have no way of knowing until the occultation is supposed to be over.

It is quite cloudy here but I was getting some image through the clouds.  We will see how it goes.

It's been -10 to -21°C here, with 70+ kmph winds and 20+ cm of snow fall this weekend. It's supposed to clear up and drop to -27°C tomorrow night (-30 to -40°C with windchill). That will be 24°C (43.2°F) below normal day time high temperatures here monday,  so much for "global warming".

TTYL..

Milton J. Aupperle