|
Well, that fuzzy edge seems intermittent and moving about, now. Perhaps that was due to slight off-centering of the camera lens in the focuser tube....
Now the main issue is that your chesire and laser technique don’t agree, right?
You say the laser mark is off after collimating with the chesire….a cm or so…Can you describe your steps exactly in order?
The primary or first-out laser beam of the collimator, and the chesire, assess different things. The former for secondary adjustment, the latter for primary mirror adjustment. One can be on while the other is off, actually. However, the return-beam adjustment and the chesire should agree….assuming your laser is collimated, that is.
If the laser is not collimated, that return beam method won't work right. That's the vulnerability of laser collimators. If the laser beam isn’t drilling right down – and co-incident with – the central axis of the focuser (which should be the same as the central axis of the collimator chasis) – then it’s cactus. An un-collimated laser collimator is good for lecturing and exercising cats…and that’s about all. Unless you have a barlow attachment, in which case it'll still work for primary collimation...but that isn't relevant in your case....
When in doubt here about your primary mirror’s collimation, of all the tools you have as you describe, believe your Chesire.
You likely don't have a V-block for testing your laser's collimation, but a second-best method is to put the laser into the focuser tube, and, with the set screw loosened obviously, spin the collimator in the focuser and watch the beam on the mirror. If it describes a circle on the mirror as you spin the collimator, your laser is not collimated and you should either return it or collimate it if you can.
But, I’m pretty sure that correctly centering your secondary mirror under the drawtube (adjusting the center screw) will not correct the problem you describe: that the chesire and your laser merge-the return-beam-method do not agree. Centering the secondary under the focuser is still valuable, but will not fix this part.
Secondary position - under the focuser correctly or up or down or over a bit - is not really a "collimation" issue, but rather a way to avoid missing some of the light cone (vignetting). Assuming of course that you have already dialed in the secondary’s collimation (that is, it’s “tilt”) using a collimated laser, adjusting the screws so the laser beam hits the primary mirror center mark. That IS a true collimation issue. We can (and many will) argue about the practical definition of collimation, but IF a flat diagonal mirror's "tilt" is correctly reflecting the center of the focuser axis to the center of the primary mirror, but is "shifted" a bit to miss some of the light, your star test will still be correct, but your image will be less bright, so a purist could argue this isn't a collimation issue but rather vignetting.
The next step is checking your laser’s collimation. The other (less likely) explanation is that the collimator is not sitting flush straight in the drawtube and when you tighten the set screw, it tilts off-axis….but that’s unlikely, unless there is some flawed lip on the collimator’s rim….
My two cents...
Cheers,
Scott
|