Familiar with auto collimator need help

[pat]

Please solve this mystery. When looking through AC it is half dark & half bright (it should be all dark). For collimation I use an orion collimation cap,chishire (no cross hairs) and the auto collimator on my xt10" orion 4.7f. This can be ruled out: (1) any air temperature variance (2) movemont of scope up/down (3) loosness in eyepiece tube (4) movement of focuser tube travel (5) focuser not square (6) mirror float (7) spider vane missalignment (8) Same Lenght of primary clips in secondary mirror (9) dot off center in donut hole (10) center axies screw of secondary loose (11) three adjustment screws of secondary loose.

The annulus of the chishire is slightly off center. I have restrained from adjusting primary,thinking it might decenter the dot in the donut hole. I used to achive the darkness w/ minimal effect. Pat

Too many stars to little time **********

[Merlin66]

The AC test is very sensitive to the alignment of the focuser to the tube and the optical axis. Sounds like you've checked almost everthing....

Just release the AC slightly and see if you can tilt it into the black zone....

[pat]

Thanks, I wiil try this & leave the primary alone. Pat

[Jason D]

You need to fine tune you secondary mirror alignment using the 3 set screws until the background is darkened. Then realign the primary mirror using the collimation cap. You might have to go back-and-forth few times. Eventually all will converge.

Which brand of an autocollimator do you have?

Jason

[pat]

Thanks Jason, I use a one hole AC. It was bought at "Scopestuff". I believe that starting with the secondary is the right way to go. Tweaking it a bit. All I need now to do is center the chishire annulus, without disturbing the black dot in the donut hole. I'll have to ckeck if I already posted this. Sometimes I think I'm losing it. Thanks again, Pat