Date: Thu, 22 Oct 1998 17:44:35 +0100
Now I am wondering, as I shall be using a flip mirror, and will sometimes
want to use a focal reducer - would the best order be NGF-S : reducer : flip
mirror : CCD?

Dr Nigel Puttick
Great Broughton, North Yorkshire, UK
054.45N 001.15W
"Where observation is concerned, chance favours only the prepared mind"
(Louis Pasteur, in 1854)

------------------------------
Yes, that's a useable order.

Remember the following:

1. The NGF-S attaches to the rear of the telescope, the only thing that
could/should be ahead of it is a skylight 1A dust seal or "Hot Mirror"
IR filter.

2. If you use the Optec f/3.3 focal reducer you won't be able to use
a flip mirror because the reducer-ccd distance must be 29.5mm.

3. When using a flip mirror with another kind of focal reducer, such
as the Meade f/6.3 unit, the actual reduction will be somewhat more
than the rated value because of the increased distance between the
rear of the reducer and the CCD chip. My f/6.3 actually delivers
f/4.9 with my flip-mirror in the path. The same holds for planetary
photography using a Barlow. My 3X TeleView Barlow delivers 4.7X with
the flip-mirror in the path. I am sure that there is some quality
reduction due to using these components out of their designed range.

Chris Frye

Silver Spring, MD

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