Star Testing

[shaneaust]

i've been star testing my scope lately, but when i get to the "de-focusing" step, i see circle with the reflection of my secondary in the middle okay, but i dont see any "concentric" rings at all - does this mean it's badly out of collimation? the scope is a bintel bt-252. good sharp views using low powered ep's but a bit disappointing using high powered ones...

thanks!

[anthony2302749]

Hi Shane

Follow the link http://legault.club.fr/collim.html this will take you to a site entitled "The Collimation" it should help you answer some of your questions in regards to star testing.

Anthony

[ving]

whe defocusing dont go too far. just defocus a little :)

[Blue Skies]

The rings you are looking for are subtle, they don't jump out and hit you in the eye. I haven't done much star testing but a friend who has always advises to have Suiter's Star Testing book (the book from Willman-Bell) right next to you while you're learning how to do it.

[Dennis]

Hi Shane

Can you describe your equipment and procedure? Here is a brief description of my experiences in seeing the out-of-focus diffraction rings.

For my Vixen 4" f9 refractor, the rings become obvious when I plug in a 5mm eyepiece which is a magnification of x184.

For my Celestron C9.25 SCT, the rings become obvious when I plug in a 10mm eyepiece, which is a magnification of x235.

I can usually see rings even in bad seeing, although they are very messy and wobbly. I often find that the inside of focus rings are easier to see that the outside of focus rings. If you de-focus too much the rings can become quite faint.

Cheers

Dennis

[iceman]

As Ving said, when you see the shadow of the secondary you've defocused too far.

You only need to go inside/outside focus a little to get the rings.