|
[quote=Dujon As a matter of interest, I used the Cheshire and then checked with the laser unit. The laser unit indicated that I was out in my adjustments - but the slightest touch on the laser housing (for example turning it off/on) caused the 'red dot' on the primary mirror to move anywhere between the mirror centre mark and two-thirds of the way to the mirror's edge.[/quote]
Funny you should mention this, I was concerned with the "slop" with my laser when it was put into the focuser and so machined a piece of aluminium down to make a "snug" fit for it, basically a "tight 1 1/4 to 2 adaptor" (this took an amazing amount of work because the only scrap I had lying around was 80mm diameter, that's 30mm of turning...and another story, anyone want a bucket of swarf?). I tried it at the weekend and was able to get the return spot to drop right down inside where it came from! (It is a Bintel deluxe with the target). I then dropped in the Cheshire only to find that it was out. After pondering what could have gone wrong I measured my new adaptor. It appears the central hole is not concentric with the centre of the adaptor by about 0.04mm...quite enough to show up in the collimation. I should point out my lathe was originally used in the ammunitions factory in 1945! In hindsight I should have rotated the whole adaptor rather than just the laser, this would have immediately shown the problem.
I have since measured the other 2 adaptors I have and found the one that came with the scope to be out by almost 0.06mm and the other, which came with the GSO focuser, to be out by a tad over 0.01...actually if I jiggle the vernier, I can make it close to zero all round. The remaining issue still remains with the slop, which is very hard to get rid of.
This weekend I will try again using the GSO adaptor and orient the tube so the laser points directly down rather than to the side where gravity will cause it to "drop".
The moral of the story? Try to get as snug a fit as possible for the laser and try to check concentricity if you are using an adaptor. Previously I used the GSO adaptor to align the mirror and then checked it with the Cheshire to find it was spot on, and took about 10 minutes to do (first time).
I would be interested to hear if others agree with my theory or have other points to add. Lasers are great, but as I found, they can cause you to get the optics "perfectly out!"
|
