From: Milton Aupperle <milton@outcastsoft.com>

Date: March 13, 2009 11:44:53 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] FOVs Celestron radial Guider..

Mark;

You missed the points where I said with 2 focal reducers your going to get extremely severe brightness drop off on the edges, known as vignetting:

http://benedict.isomedia.com/homes/cvedeler/scope/focal_reducers.htm

http://pws.prserv.net/testani/FR_Report.htm

Basically your going to get a bright central core that will probably fill up some central part of the CCD and your going to get a black halo around it. And the coma (elongation of stars) on the outside edges will also make you stars very none round.

If you really want to shoot M42 (which is a huge target), why not consider doing a mosaic of it, much the same as one does of the moon. With a C9.25, you should be able to use 2 to 4 minute exposures and pick up a lot of detail in it as it's very bright.

On a side note it finally warmed up here, so I shoveled the 6+ inches of snow off the balcony to the mount and then got my DSO rig (OAG,Filter wheel and cameras) attached back to my scope. Then I used a distant street light to get the guide camera and imaging cameras in focus at the same time and then took a quick image of stars around Procyon to measure the field of view. I now get a true focal length of 1186 mm and a focal reduction of 0.59x times. This means I get 1.16 arc second per pixel and my FOV is 26x20 arc minutes with the grasshopper.

PS:

Check out today's LPOD for February 13th:

http://the-moon.wikispaces.com/LPOD

Milton Aupperle

On 13-Mar-09, at 1:08 AM, Mark Gaffney wrote:

Hi Milton, The reason for using the 2 focal reducers in tandem was to get all of M42 (or pretty well all) into the picture. Look at my C9.25 set-up folder in Photos for The Sky 6`s graphic of this. As far as I can work it out it`s not possible otherwise. I have no idea of the practicalities of doing this & I guess your`re right that I`ll have problems. I am getting a subject 50 metres away in focus through the 2, 0.6 FRs & the Flea 2 through the visual back. I experimented with the OAG a little this morning managing to get this shipping container in focus with a 25 mm eyepiece & the f6.3 FR, through the prism on the OAG, whilst I had a small sign (on the container) centred in the finder. As to getting both cameras in focus I`ll have to wait probably another 2 & 1/2 weeks for the Mogg 1.25-T to come for further experiments. Mark.

On 13/03/2009, at 9:57 AM, Milton Aupperle wrote:

Milton J. Aupperle

President

ASC - Aupperle Services and Contracting

Mac Software (Drivers, Components and Application) Specialist

#916, 742 Kingsmere Crescent S.W.

Calgary Alberta T2V2H8

1-(403)-453-1624

milton@outcastsoft.com