Re: [ATM] New site

["Dream - Telescopes & Accessories, Inc." <shane@dreamscopes.com>]

Roman,

Unless your 3" telescope is a very slow focal ratio, f10-20+, a laser will 
help you get close but you should still be doing star collimation to get 
the most out of your telescope, no matter its aperture.  Once you get it 
roughed into place with a laser, put a bright star in the center of your 
field with a high power eyepiece and defocus that star.

Take a look at the out of focus images at the top of this page:
http://www.dreamscopes.com/pages/06/AstrographN-16-1st-lights-04.htm

Notice above how I collimated the optics so the secondary shadow went from 
being out of collimation (left images) to collimated (farthest right image).

Once that is accomplished, then I take images closer to focus.
http://www.dreamscopes.com/pages/06/AstrographN-16-1st-lights-06.htm

Closer to focus is much more sensitive to artifacts, which can be anything 
from coma correction of the corrector to collimation errors to pinched 
optics, etc..  Further out of focus stars, like the first link illustrates, 
can also be used to evaluate the primary mirror in a 
Newtonian.  Characteristics like surface ripple, cell-induced astigmatism, 
zones, etc., can be evaluated.

Rutten & Van Venrooij's book is an excellent resource for learning about 
optical aberrations:
http://www.wvi.com/~rberry/mybooks/bk-edto.htm

There are a great deal many formula's in the book but for basics, they do 
not need to be studied.  It goes over a great many telescope optical designs.

Thank you.

Sincerely,
Shane Santi - President
Dream - Telescopes & Accessories, Inc.
http://www.dreamscopes.com
610 - 365 - 2833



At 08:26 PM 7/17/2006, you wrote:
>          Vlad, very nice web site,  as a new user who's reading all I
>can find.
>  I found it very refreshing specially the pages on airy disk and
>defraction. I'm currently reading Texareau's book.
>
>         I beleive I now know what I did not like about a telescope I
>just sent back. (coma like crazy) Also not having the trained eye of
>the experts on this list, I know enough to say the 3" tele i have has
>quite good optics "all things being equal" after colimating it with a
>laser, and finally having a good night to see thru.
>
>       thank you for passing on the knowledge.
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