Re: [ATM] ATM Digest, Vol 23, Issue 24

[Thomas A Simmons <tasimmons@raytheon.com>]

FWIW, besides the baffle on the bottom of the focuser
I've used 48MM filters, replacing the plastic insert
with various sized disks. I've used thin particle board
turned to fit (you can do it with a hand drill if you're
careful), then cut a variety of apertures. Construction
paper works just as well.

Tom
Tucson, AZ

Date: Mon, 21 Nov 2005 03:14:47 -0700
From: "Tom Krajci" <tom_krajci@tularosa.net>
Subject: Re: [ATM] New 16" telescope design
To: <atm@atmlist.net>,         <alanne1956@hotmail.com>
Message-ID: <ALEIKIMFDBDICIHJOPFEEENCCNAA.tom_krajci@tularosa.net>
Content-Type: text/plain; charset=us-ascii

>From: "Alan Scott" <alanne1956@hotmail.com>

>I have just finished the designs for an ultralight 16"....

>http://www.xmission.com/~alanne/DS4Main.html

Overall seems like a nice design!

You list as one requirement:

"This telescope will be able to carry a half height or full height shroud.
It will also be usable without a shroud for observing during windy nights."

Unfortunately you provide no diagrams/drawings, so I looked at:
http://www.xmission.com/~alanne/DS3-NightScope-1.jpg

Because you use a low profile focuser/focal plane position...you are forced
to use a large baffle disk opposite the secondary mirror.  That will
provide
a large wind profile.  Are you sure you want to do that?

See: http://overton2.tamu.edu/aset/krajci/dobsonian/dobsonian.htm
specifically:
http://overton2.tamu.edu/aset/krajci/dobsonian/baffle-train-67pct.JPG
for an example of a smaller baffle disk that's possible if you don't use a
low profile focal plane position.  This presents a smaller wind profile.
(And there are some other anti-wind measures covered on this page.)

Also, why use a shroud?

Tom Krajci
Cloudcroft, New Mexico

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