View Full Version here: : 9mm Recticle EP

23-12-2006, 11:41 AM
Hi All

Could anyone shed some light on why i am not able to focus the 9mm Recticle Ep when it is used with the 12" SCT, it works fine in the ED80, but refuses to focus properly in the 12".

It wouldn't be that i'm using a Diagonal in the 12", would It ??

Cheers Leon

23-12-2006, 11:46 AM
I think either the 9mm is too much magnification for the 12" and the seeing's not good enough to take it...

or yeah, perhaps try focusing on a star without the diagonal?

Keep in mind the diagonal sort of acts like an extension tube increasing the distance the light has to be brought to a focus (fl) and that will be cranking the mag even higher with the already high-powered 9mm?

Try a longer focal length eyepiece in the diag... or use the 9mm and ditch the diag

23-12-2006, 12:33 PM
Thanks Matt, yea the seeing i have to admit at the time was poor, but i wasn't after good skies at that point as i was just going to train the RA and DEC drives, so i wasn't after quality.

There was heaps of diffraction, and the star looked quite colourful.
and there was some smoke in the atmosphere as well.

so i didn't really give it a chance, did i :P

Cheers Leon :thumbsup:

23-12-2006, 12:59 PM
Leon try adjusting the upper lens section of the eyepiece which should rotate for diopter adjustment to your eye. This should help.

Also, as you've stated about the seeing, wait for better conditions and let the SCT cool down before starting.

Good luck mate.


23-12-2006, 01:11 PM
Ah yes. Didn't know you had an adjustable diopter.

That could definitely be the culprit.

23-12-2006, 01:33 PM

That suggests you were perhaps trying to focus on a star a little too low above the horizon to be useful or easy to focus.

That rainbow appearance is diffraction that's usually caused by atmospheric dispersion close to the horizon.

Focus on a star higher up, mate:thumbsup:

23-12-2006, 04:22 PM
No Matt didnt think of the Diopter, how dumb :P

That would have to be the problem, as the star was quite high.

Thanks Guys

Cheers Leon :thumbsup: