Hi there,
I thought I'd start a new thread rather than tack things into the focus question.
But I got myself a laser collimator and checked out the video below (thanks Dujon). Well my collimation, according to said video, was Major Ugleage. Yep, the laser came straight out the front of the scope
well I made significant improvements to my collimation. I think I still have some ways to go to perfect the technique though. One thing I couldn't do was Step one. align the seconday mirror. That part seemed to still require a collimating cap. Well, I thought I would be able to do all the collimating with the laser collimator, but it seems that I still need a cap.
Is that right?
Yes you do need something. El cheapo method is to drill a hole in the centre of the bottom of a 35mm film canister. It fits nicely into a 1.25" drawtube. The better way is to buy a cheshire (or collimating) eyepiece and do the whole thing visually. ($69 from here https://www.bintelshop.com.au/welcome.htm ). This works better than the basic laser routine shown in the movie, which can be grossly wrong, even if everything is done by the book. (see http://www.smartavtweaks.com/RVBL.html or http://www.obsessiontelescopes.com/l...ml#Collimation).
The technique I use is to use the cheshire eyepiece to centre the secondary and then the laser to adjust the tilt of the secondary (both of these as shown in the movie), but then use the so called barlowed laser technique to adjust the primary (see the link above or google "barlowed laser"). It's pretty similar to the basic technique in terms of time and difficulty. You only need a small, easily made piece of extra equipment plus a barlow lens.
I use a chesire-crosshair to align the secondary with the focuser..then the secondary with the primary to as close as I can in seeing the reflection of the primary in the secondary..
On location and after the scope has cooled down...I then use a laser to fine tune until the laser can be seen returning to it's source precisely!....
Also...it is a good idea to check that your focuser is in alignment..ie if you remove the secondary mirror and insert the laser..the spot marked by the laser on the inside of the tube should be directly to the opposite side of the focuser...most focusers can be adjusted for this purpose.
A word on laser collimators...check to see that it too is collimated before using it!!
Cheers!
Is there a film processing shop anywhere near to you? There are lots of people who still use film for photography and I'd lay you odds you'd collect a bag full of old canisters if you ask nicely.
On the collimation tool subject: I too purchased a laser collimator but found it too sloppy to be of practical use. I'm sure that not all laser collimators are the same - it was probably just the unfortunate coincidence of tolerances. I then purchased what is known as a 'Cheshire' collimator (I don't trust my DIY skills) and have found it to be good - although, to be honest, I've not had much chance to put it to a real test. You know, cloud, smoke, no time when the sky is clear . . .
I picked up a laser collimator today and plugged it into my Starhopper. While a cheshire shows pretty good alignment, the laser showed the red return beam nearly an inch off. It was very easy to adjust it, but I wonder how accurate the laser is. It has to be a precise fit in the eyepiece, I imagine. I'll see how the scope performs tonight.
When I brought my laser it came with it's own collimation block..( you can also use the middle of an large open book ) the laser's body has 2 adjustment allen screws...set the laser to mark a target (a piece of masking tape on the wall will do nicely) about 4 metres away and mark the spot with a pencil..rotate the laser 180 degrees and mark the spot..make an adjustment then rotate back 180 degrees to the first spot..keep doing this until the spot is in the same position after rotating.
The focuser uses 2 thumbscrews to hold the eyepieces..I use the right-hand one first so I would do the same when using the collimators as I would do with the eyepieces.
Cheers!
. . . but I wonder how accurate the laser is. It has to be a precise fit in the eyepiece, I imagine. . . .
Precisely, Mr A. Mine turned out to be so sloppy in the focuser that a light touch (or even changing the 'scope's altitude) would cause the 'dot' to wander anywhere from the centre spot to close to the mirror's edge. I didn't even bother collimating the collimator as it was obviously totally useless. Hence the Cheshire which is fits nice and snugly.
If anyone wants a laser collimator and is prepared to pay the postage then mine is yours. You'll have to buy new batteries as I've (well my son did) used it as a pointer.
Hi and G'day to youse all,
My first post only joined ISS yesterday and the telescope owning fraternity a few months ago. I'm a complete amateur and worried about taking a screwdriver and allenkey to the 6'' and 10'' GSO dobs. I found Andyshotglass's collimation video really helpful but the first images on the video didn't match what I could see through the Cheshire eyepiece. I bought a laser collimator - still no corellation, though it proved I was facing a situation of major uglage only with the 10''. The visual correlation key came from http://skytonight.com/howto/diy. The article on collimation was brilliant and the cardboard did the trick. Now I see what Andy saw through the peephole. Where's the screwdriver!
See attached view of a simple wooden V-block setup, which is held by a clamp or vise. Place the laser in something like this and aim it at a vertical surface 5m or so away. Hold it reasonably firmly down in the V and turn it slowly. You will probably see the laser dot wander round in a circle. Using an allen key adjust the laser alignment with the recessed grubscews you should find around the laser housing, until you cannot see the laser dot wander.
The V-block device does not need to be especially accurately made, but it should be rigid, have surfaces hard enough not to deform easily, and be firmly clamped during the test. The procedure is more sensitive over a longer baseline, and i have found it to be repeatable to within 1mm or so over 5m. I use the inside of the garage door.
I found also I had to re-collimate the laser collimator after replacing the batteries, which were 3 button LR-44 (it is a Bintel type)
. . . wrap a bit of contact round it to take up the slack John . . .
Thanks, Geoff, but I tried that. In my case I used a bit of masking tape - which is hardly 'thick' - to give me some idea as to whether or not it'd work. It did, but I found that the tape was a tad too thick for the purpose as a full wrap wouldn't fit (well it did but left a mess of scrunched and sticky 'stuff' which took ages to remove). Anything less than a full circuit of material, logic told me, was likely to tilt the collimation light off axis. Putting that idea into practice confirmed it.
Good old Aussie ingenuity. Just a thought but Sticky tape would be a bit thinner than masking tape if need be. 'Tis only a thought from my fishing rod building days.
Cheers,
Duncan
Good old Aussie ingenuity. Just a thought but Sticky tape would be a bit thinner than masking tape if need be. 'Tis only a thought from my fishing rod building days.
Cheers,
Duncan
I have used some 12mm sticky tape wrapped around several times. This was obviously too thick, so just unwrapped and trimmed it a little at a time until I got a very snug fit.
I've been following this thread with growing interest (tending towards alarm!). I rigged up one of those little collimator holders, and sure enough the beam traces a nice little circle when I spin it around in the holder. A frustrating 30 minutes with allen keys finally got it more or less lined up. I'll try the barlow laser method out and see how that goes.
heres a quick tip when collimating a laser. spin the laser and mark the spot in the center of the tracked path. adjust only one half (1/2) of the error. works every time!
