Collimation issue or otherwise?

[sharkmelley]

13 hours ago, tooth_dr said:

I decided to go back to the smaller 8mp CCD sensor as I wanted to image around the full moon in Ha.  The scope is performing well at that size of sensor with current collimation, so I might stick with it for the time being. 

It's certainly true that a full frame sensor is more demanding on the collimation than a smaller sensor.

Mark

[tooth_dr]

2 hours ago, sharkmelley said:

It's certainly true that a full frame sensor is more demanding on the collimation than a smaller sensor.

Mark

How do you find the stock focuser?  I have to say I dont like it at all.  It's spongy to use, and it has some lateral image shift between in and outward focus adjustments.  I've tried adjusting the grub screws, and there isnt really a point where it's nice to use, with no lateral movement.  I can see why it was swapped out now.  Perhaps I have a poor version, but I have nothing to compare it to.

[sharkmelley]

I find there is some backlash in the standard focuser so I always make adjustments in the same direction - against gravity.  Always apply the focus lock after any adjustment.  I improved the accuracy of the adjustments by adding a makeshift pointer to the focusing knob with a focusing scale.  Combining these strategies allows me to make repeatable and very accurate focusing adjustments.

Mark

 

[tooth_dr]

1 hour ago, sharkmelley said:

I find there is some backlash in the standard focuser so I always make adjustments in the same direction - against gravity.  Always apply the focus lock after any adjustment.  I improved the accuracy of the adjustments by adding a makeshift pointer to the focusing knob with a focusing scale.  Combining these strategies allows me to make repeatable and very accurate focusing adjustments.

Mark

 

Thank you Mark.  I should have recorded the image shift between focusing, the stars actually move, because racking the focuser in or out causes a small degree of lateral movement of the drawtube - illustrated in my gif below.

 

I dont think I'll continue using the standard focuser, unless I can get it fixed, as there must be something wrong with it.  The lateral movement and general feel is really very poor.  If I dial out the lateral movement using the adjustment screws then the focuser is stiff.  Even if I dial it back to just a hint of lateral movement, if I try to use the fine control knob, it feels springy, and if I turn it 2-3mm, it will just spring back, not having actually moved the draw tube.  Thus it is incredible difficult to accurately move the drawtube.  I certainly cant focus it easily, nor could I focus it in one direction only.  I can say that this is the worst focuser I've owned (by a long shot) in my 10+ years of imaging.

 

I appreciate all your help on the matter.  I know you have advised against it, but if I cant improve the OEM focuser, I plan to remove it, and now that the scope is collimated to it, refit the Moonlite focuser, and try to get it fitted as close as possible to collimation without adjusting the telescope mirrors.  In my head this seems logical.

 

Adam

 

[sharkmelley]

It does sound like there is something wrong with the focuser - I don't have the problem you are describing.

Good luck with replacing it!

Mark