Re: ATM low cost secondarys

[Anthony Stillman <atmer@flash.net>]

>looking for a secondary...
>i was told i needed 2.8" secondary.
>why so big?

This seems to me to be small.  You can work with:

http://home.earthlink.net/~flyj/designns5.html

to understand how diagonal size effects field illumination.


>should it be elipticle?

An elliptical secondary is ideal, however a retangular works well also.


>can i get an inexpencive one?

That old adage, a chain is only as strong as its weakest link, comes to
mind.  A telescope is only as good as its worst component.  I've seen some
well made primaries put to shame by bad secondaries and oculars. These
componets should be as good as you can afford.

As has been threaded recently http://www.crbest.com/astronomy/ , you can
make your own eyepieces from surplus lenses.  Making a good flat is a
challange, and do-able.  However, even at McDonald wages, its less
expensive to buy.

Below are a few sites you can check for surplus and pre-owned components.

http://www.surplusshack.com/
http://www.bscoptics.com/
http://www.astronomy-mall.com/
http://www.astromart.com/


>thanks
>stan

Your welcome.

Anthony