Re: ATM Baffled about baffles

["andy" <afmartyn@spin.net.au>]

Keir, here is my view on baffles.

1.    If you have a completely enclosed solid tube you do not need baffles.

2.    If you have an open tube, ie the typical truss tube design, you may
need the following baffles depending on your upper cage design and the
diameter of the open tube design:

a.    At the focuser end you may need a baffle with a hole in it between the
secondary and the focuser together with a solid baffle on the open tube side
opposite the focuser to prevent any stray light getting directly to the
focal plane.

b.    You may need a few baffles down the length of the tube towards the
primary to stop any stray light getting to the focal plane via the
secondary. Light can get to the focal plane this way as the field of the
secondary actually can see a certain distance outside the primary mirror
diameter. If this is outside the open tube diameter then you need the
baffles to prevent this. An easy way to determine if this is an issue place
a disk at the focal plane with a hole in it equal to the maximum focal plane
diameter you get with your lowest power eyepiece. Look through the hole and
if you can see outside the tube or the mirror box down the bottom you need
to do something to stop you seeing this.

As an alternative, I have a spreadsheet that does these calculations for you
if you would like me to send it to you (it is about 280k). The spreadsheet
also does the other usual stuff like calculate field of views and
illumination percentages etc.

Andy
Australia.

----- Original Message -----
From: "Keir Davis" <kbd@tpg.com.au>
To: <atm@shore.net>
Sent: Sunday, October 22, 2000 6:18 AM
Subject: ATM Baffled about baffles


>
> Hi all.
>
> Can someone enlighten me ;-) about the use of baffles in a tube?
> Are they essential for all/any particular aperture?
> Do they really work? If so, is there a suggested configuration?
> I recall years ago, seeing an article in one of the pop mags regarding
this
> topic, but for the life of me can't remember which one.
>
> Any ideas/advice/suggestions greatly appreciated.
>
> Keir
>
>
>