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Subject: RE: [M]: [M] Pictor216XT focusing hardware helpers
From: Herman Zwirn
Reply To: mapug@shore.net
Date: Fri Aug 01 06:26:34 1997

Yes; and Kendrick is marketing the commercial version for SCTs up to 16
inches.

-----Original Message-----
From: owner-mapug@shore.net On Behalf Of Ric L Ecker
Sent: Thursday, July 31, 1997 7:34 PM
To: mapug@shore.net
Subject: Re: [M]: [M] Pictor216XT focusing hardware helpers

The two hole (or more) aperature cover is called the Hartmann focuser.
The Hale Telescope uses one (a long time ago) to focus the 200" scope on
Palomar Mountain, and its displayed near the telescope. It has hundreds
of holes about 2" in diameter.........just some trivia...............


ric ecker co-pres. of OPTAS
OPTAS homepage and picture of Hale-Bopp
http://members.aol.com/rlecker/ric.html

On Thu, 31 Jul 97 02:24:36 UT "Herman Zwirn" <HAZ93@msn.com> writes:
>I have been using the commercial version of the offset focusing aid
>for about
>two years. It works just fine visually, photographically and with a
>CCD
>imager. The new one I just acquired for the 12" LX200 replaces the
>tube cover.
>You can also remove only one of the focusing aperature covers to
>convert it
>into an off axis mask.
>
>-----Original Message-----
>From: owner-mapug@shore.net On Behalf Of BJohns7764@aol.com
>Sent: Wednesday, July 30, 1997 3:59 PM
>To: mapug@shore.net
>Subject: Re: [M]: [M] Pictor216XT focusing hardware helpers
>
>In a message dated 97-07-30 15:52:09 EDT, you write:
>
><< Could someone give me some info on focusing methods for CCD imaging
>? >>
>
>I'm sure that by now, you've heard this response many times, but I'll
>just
>jump in and add, anyway. <G> This is certainly not a new idea; lots of
>people
>use this method.
>
>My method of focussing either my Cookbook camera or ST-7 is to get
>close with
>
>an eyepiece as you now do, then I flop a cardboard mask over the end
>of my
>10"
>LX-200, the mask having two round holes in it, each about 1" or so in
>diameter.
>
>Making the mask is easy and takes about 10 minutes. I just lopped off
>the end
>of a cardboard box that was more than 10" to a side.. leaving about 2"
>of the
> each side of the box intact. I then cut off two of these sides. So
>what I
>then had was a flat box end with two edges, of the original box.
>
>I flopped the box end, over the end of my scope so that the two
>"sides" were
>resting against the tube. A quick session of measuring showed me where
>to cut
>the two 1" holes so that they'd be on opposite sides of the central
>obstruction, and equal distances from it.
>
>>From then on, to make a very fast focus, I aim at a bright star,
>begin
>downloading
>and displaying the star, and I see two representations of the star.
>The
>further
>from focus, the further the stars are separated. Just tweak the focus
>a bit
>at a time ... I use a JIM Zero-image-shift focusser to keep the star
>from
>shifting during focus -- and presto, when only one clean star is
>visible...
>perfect focus!
>
>Takes maybe one or two minutes, max, to get focus bang-on. Quick and
>cheap!
>
>
>Bruce Johnston
>
>Bruce Johnston Computing
><http://members.aol.com/bjohns7764/>
>Internet home for "The SuperFix Package" of image processing software.
>
>