This old Chestnut - Skywatcher 190MN collimation :)

[toc (Tim)]

So I know Collimation of the 190MN has been done to death, but I need some help in understanding what I am seeing. I have the moonlite focuser for the 190MN, and have not mucked around with the secondary.

I have the 'Howie Glatter' laser and Tubelug, and a Celestron Cheshire/sight tube.

I have used the Cheshire to centre the secondary spot under the crosshairs, and then used the laser and adjusted the secondary to ensure the laser hits the centre spot of the primary. I then put the laser in the tublug/barlow, with the intention of trying to align both dark circles from the primary and secondary.

I am able to do this and the Cheshire seems to be aligned, but then when I put the laser back in the focuser, the laser spot is no longer in the middle of the primary The star test shows the scope is out of collimation.

[glend (Glen)]

The number one mistake MN190 owners make is moving the secondary. The MN190 secondary is positioned at the factory and should never be moved fore or aft of its position on the corrector plate. In other words offset is fixed. There are many threads on the Cloudy Nights forum on this topic.
The correct way to install a Moonlite focuser, which requires the special MN190 adaptor, is to centre the focuser tube over the secondary in its original position. The adaptor is required to allow the Moonlite to be moved far enough forward on the tube to sit directly over the secondary ( which should sit in the factory set position.).
Did you buy this scope new, or second hand? Because , there are MN190s which are sold which have already been buggered up by a previous owner, and for that reason they should not be purchased from unknown sources who do not under stand the optical setup.

In my experience, and as the designer of the Moonlite MN190 Adaptor, when the Moonlite is centred correctly over the secondary, it is pretty much correct and usually only requires basic primary adjustment to get the collimation spot on. A laser in the focuser tube should be all you need to maintain perfect collimation, and they tend to stay in collimation.

[toc (Tim)]

Originally Posted by glend

The number one mistake MN190 owners make is moving the secondary. The MN190 secondary is positioned at the factory and should never be moved fore or aft of its position on the corrector plate. In other words offset is fixed. There are many threads on the Cloudy Nights forum on this topic.
The correct way to install a Moonlite focuser, which requires the special MN190 adaptor, is to centre the focuser tube over the secondary in its original position. The adaptor is required to allow the Moonlite to be moved far enough forward on the tube to sit directly over the secondary ( which should sit in the factory set position.).
Did you buy this scope new, or second hand? Because , there are MN190s which are sold which have already been buggered up by a previous owner, and for that reason they should not be purchased from unknown sources who do not under stand the optical setup.

In my experience, and as the designer of the Moonlite MN190 Adaptor, when the Moonlite is centred correctly over the secondary, it is pretty much correct and usually only requires basic primary adjustment to get the collimation spot on. A laser in the focuser tube should be all you need to maintain perfect collimation, and they tend to stay in collimation.

The scope was purchased new - got it from Andrews about 8 years ago. I havent touched the secondary other than the three adjustment screws.

Perhaps the marking on the secondary is off?