With the favourable exchange rate some months ago, I started to long for an improved laser collimator compared with my existing GSO deluxe laser collimator and its “sausage” shaped laser spot. After reviewing options and admitting to the financial restrictions that prevented me from going to the top end collimators, I purchased the HoTech SCA Laser Collimator (
http://www.hotechusa.com/collimator.html ) which came as a combined 1.25” and 2” unit, with the collimator having a 1.25” barrel and packaged with an additional 1.25” to 2” adapter. Price was US$114 plus some US$20 shipping. The collimator arrived without incident, packed in a well insulated hard case.
However, with all we have seen of laser collimators, the first question is – what about the laser’s alignment?
In due course, I obtained a suitable jig to test this laser collimator’s alignment. See more information on the jig here:-
http://www.iceinspace.com.au/forum/s...ad.php?t=39108
I set up the laser collimator as I would be using it, in its 1.25” to 2” adapter. I set the jig 5m from a wall to which I stuck a piece of paper. I clamped the jig to a solid table. Pleasingly, the laser spot is a 5mm diameter circle at this distance. I then rotated the jig 45 deg at a time and marked the outline of the main laser spot. The spot rotates in an 8mm circle at this 5m distance.
Please see attached images.
HoTech supplied me with the specification for the laser:- “Laser pointing error within 0.05 deg full angle which yields an 8.7mm maximum diameter circle at 5m.” So I concluded that the laser was within specification.
A question that does arise is - What is a reasonable specification? Someone has suggested to me that 20 thou at the primary mirror of a normal 12” scope is required. This corresponds to 0.51 mm at the primary of a 12” f5 at about 1.5m distance, or 1.6mm at 5m distance (extrapolating a linearly diverging beam – umm - is there another?). Clearly this is considerably less that the 8.7mm above. Given the size of the laser spot (5mm) and its fuzzy edges, 1.6mm at 5m seems much less than would be reasonable?
Yes, I didn’t do a few things, eg. place the 1.25” laser in the other end of my tool to eliminate errors, if any, in the adapter (cause at that stage, the hole was a little small and needed opening up a little), or reinstall the laser several times and repeat. But I’m comfortable with the result I obtained.
Experience in the field is that once I have adjusted secondary and primary mirror tilts with the HoTech laser collimator (having separately checked the position of the secondary mirror under the focusser), two different Cheshire tools show the scope to be collimated and a star test is very close to “collimated”.
I have located the grub-screws most likely to be the alignment screws on the laser collimator, and once I know exactly which are which, I will try to improve the laser alignment a little further.
Thanks for reading.
Eric
but for now im loving the learning experience that collminating other peoples scopes is giving me. ( i found out what sloppy springs does and how hard to collminate a scope with them is! ARGH!!!!!!!, okay is this moving the circle to the dot the right way, yes ---> tell me when its enough ----> its going the wrong way now ----> ummm??? i havn't moved to a different collmination screw and im turning this one the same way when the answer was yes....????, fix ---> tighten up the lock screws onto the adjustment screws and then collminate from there!)
