Fine tune 8" Newt

[satcomsta]

Hello everybody;

I have a Discovery 8" Newtonian that I can't seem to quiet collimate. I use an Orion Laser Mate collimator and according to it, my telescope is collimated. But for some reason when I look thru the eyepiece, can't seem to focus well enough. It will give an acceptable view but not a finely detail one. Noticed that I have to look really close to the edge of the eyepiece in order to get some kind of definition specially on bright stars. Have tried to adjust the travel(distance of secondary from the primary)of the secondary lense but have noticed no improvement. Any suggestions?

[magic612]

Is the telescope fully cooled down to outside ambient temperature? The primary mirror, as it releases stored heat, can ruin images at the eyepice for a good 30 to 90 minutes sometimes, depending on the temperature difference between storage and outside.

Point the scope at Polaris, and center the star in the eyepiece. Now rack out the focuser. If the star is centered, and the scope is collimated, you should see a black shadow of the secondary mirror in the center of the racked out image (or racked in, if that's the only way you can go).

Not seeing the scope, there are other options too - perhaps pinched optics? Are any of the primary mirror clips tightened down onto the primary mirror itself? I'm just throwing out a few ideas of what it could be.

[umadog]

It sounds to me as though your laser isn't collimated. Put it into the focuser. Look at the reflection of the beam on the primary mirror. Rotate the laser in the focuser. If the beam moves in an arc of some sort as you rotate then the laser needs to be collimated. If the laser isn't collimated then your axial alignment will be off and you'll get crappy views. You should also check the positioning of the secondary, for which you will need a sight-tube. The laser won't help you do that.

The procedure Magic is describing with Polaris will show you whether or not the secondary is positioned correctly. You can also do a star test, which will allow you to assess the axial alignment: A Star Test Primer Starizona's Telescope Basics Star Testing Astronomical Telescopes, A Manual for Optical Evaluation and Adjustment, Second Edition by Harold Richard Suiter Star-Test

[satcomsta]

Thank you for the fast response. I have not noticed anything out of the ordinary as far as the primary goes. But for the secondary I'm not too sure. The collimator is brand new but your statement makes lots of sense will check on it. I will try the Polaris method once the skies clear up and will post results.Also, the telescope stands out for at least a good hour before use.

It sounds to me as though your laser isn't collimated. Put it into the focuser. Look at the reflection of the beam on the primary mirror. Rotate the laser in the focuser. If the beam moves in an arc of some sort as you rotate then the laser needs to be collimated. If the laser isn't collimated then your axial alignment will be off and you'll get crappy views. You should also check the positioning of the secondary, for which you will need a sight-tube. The laser won't help you do that.

The procedure Magic is describing with Polaris will show you whether or not the secondary is positioned correctly. You can also do a star test, which will allow you to assess the axial alignment: A Star Test Primer Starizona's Telescope Basics Star Testing Astronomical Telescopes, A Manual for Optical Evaluation and Adjustment, Second Edition by Harold Richard Suiter Star-Test