collimators anonymous - I may need help...

[kniclander]

help, I can't stop collimating :shock:

It started when I got my 250px which I haven't been able to use yet cos of clouds raind and snow ( :shock: ). My wife and kids are away so there's nothing to stop me collimating all day (and night) long. I've got a laser, a cheshire and a collicap and I use one method then check it against another and then, cos it's never quite the same, recollimate, check it again etc etc etc...

Some interesting (well, to me at least) conclusions -

1. I need psychiatric help

2. the laser and non-laser methods now marry up quite well . Interestingly, the extent to which they "match" actually depends on which screw I tighten first on the focusr when I put the laser in - because there's a tiny bit of slop, gravity pulls the laser down at an angle so if I tighten the lower screw first, that gets it straighter (I suppose I should remember that when I put an eyepiece in)

3. the hardest part is getting the secondary so that you can just see all of the mirror clips (using the collicap - this doesn't work at all with the Cheshire sight tube cos the FOV is too narrow to see the edge of the primary). The hardest hardest part is when you get it just right and then try to tighten the adjuster screws, it moves again . Just how tight do the adjuster screws need to be? I imagine quite tight to stop it moving again?

4. the hardest part of adjusting the primary is trying to see when the centre of the primary is centred cos the x-hairs of the cheshire seem to get in the way and it's very hard to see when the primary's centre ring is right on the dot. Also, when I finish my cheshire x-hairs are a little offset - now I know the secondary may look offset in the primary in a fast scope but the x-hairs?? Having said that, looking at the cheshire, I'm not certain that they are exactly centred anyway.

5. dear Flo, please don't send me any more collimation equipment (even if I beg)

6. the true test is yet to come.....

I'm not necessarily looking for answers (though obviously very welcome) - just needing to "unload" somewehere until I can find my local CA.

cheers

Dan

[661-pete]

I'm no expert here but one or two thoughts:

1. have you checked that the laser itself is properly collimated? (rotate the laser in the focusser, the spot should not move around in a circle on the primary). I know that lasers have their own little adjustment screws but they're rather fiddly!

2. What about collimation of the focusser? That can be the tricky one especially if it isn't the sort with its own adjustment screws. In fact I'd welcome some tips on this, myself.

3. If gravity is causing slop on your focusser (I've had that too) try setting the OTA exactly horizontal with the focusser pointing straight upwards?

[Doc]

3. the hardest part is getting the secondary so that you can just see all of the mirror clips (using the collicap - this doesn't work at all with the Cheshire sight tube cos the FOV is too narrow to see the edge of the primary). The hardest hardest part is when you get it just right and then try to tighten the adjuster screws, it moves again . Just how tight do the adjuster screws need to be? I imagine quite tight to stop it moving again?

Mine does this as well.

you get it so the laser goes through that little hole and then you tighten the locking nuts and hey presto the red laser appears out of the hole.

I've tightened mine so the locking screw touches the mirror but does not move it. I've then tested it by mmoving the scope from conservatory to ppatio quite a few times. then rechecked with laser and it seems ok.

[TheThing]

Repeat after me: -

'If it aint broke, don't try to fix it!'

Far too many people get hung up on collimation, when it is rarely necessary. With careful handling, you shouldn't need to touch collimation of your scope for many moons.

I said as much to a chap who collimates every 5 mins during an observing session. You should have sen the viens on his forehead stick out like they were going to explode!

I've had a Skywatcher 130, a Tal 2M and the Soligor and none of them have need touching. The Skywatcher kept perfect collimation for the 18+ months I had it.

[661-pete]

'If it aint broke, don't try to fix it!'

Good point. Also, collimation is more critical for imaging than visual working. If you're doing only visual at low power on a Dob it may never need it.

I decided to take the plunge when it was fairly obvious that in my images the coma was lopsided; mostly concentrated to one side. I also knew (from the noise) that I had primary flop - it turned out to be one of the mirror clamps not being properly felted.

I also wanted to flick off some of the dust on the primary: this isn't always necessary but in my case it was beginning to get noticeable and obtrusive.

I'm not sure if I improved things, but judging from the images I probably got back to where I was before...

[Astro_Baby]

1. I need psychiatric help

Me too - I suuefr a mild compulsive streak at the best of times.

2. the laser and non-laser methods now marry up quite well . Interestingly, the extent to which they "match" actually depends on which screw I tighten first on the focusr when I put the laser in - because there's a tiny bit of slop, gravity pulls the laser down at an angle so if I tighten the lower screw first, that gets it straighter (I suppose I should remember that when I put an eyepiece in)

I had the same with a laser but mine never did marry up well at all - its easier with the compression fit focuser I am told. I find the whole thing is easier with a compression fit focuser with the Chesire for sure

3. the hardest part is getting the secondary so that you can just see all of the mirror clips (using the collicap - this doesn't work at all with the Cheshire sight tube cos the FOV is too narrow to see the edge of the primary). The hardest hardest part is when you get it just right and then try to tighten the adjuster screws, it moves again . Just how tight do the adjuster screws need to be? I imagine quite tight to stop it moving again?

I have the same problem with my Cheshire - I do the same and use a cap for the 2ndary alignment.

[Foo Fita]

4. the hardest part of adjusting the primary is trying to see when the centre of the primary is centred cos the x-hairs of the cheshire seem to get in the way and it's very hard to see when the primary's centre ring is right on the dot. Also, when I finish my cheshire x-hairs are a little offset - now I know the secondary may look offset in the primary in a fast scope but the x-hairs?? Having said that, looking at the cheshire, I'm not certain that they are exactly centred anyway.

I have the same scope and have noticed this also. However, on the 2 occasions I've managed to use the scope all has seemed fine.

FF

[kniclander]

Repeat after me: -

'If it aint broke, don't try to fix it!'

well, it aint broke no more (and I aint fixin' it no more...)

clear skies at last and brilliant views. I don't know if the collimation was spot on or not but it can't have been too far off - craters of the moon stunning and sharp at x150 - I could have fallen into Copernicus - and detail fantastic - eg Rima Gay-Lussac (just north of copernicus) - Virtual Moon Atlas says you need a 300mm reflector to see it - well that's cr*p cos I saw it through my 250 and I didn't even know it was there! ; star colours fantastic and I think I even saw diffraction rings!

So thanks all for being patient and helpful particularly Astrobaby for those very clear instructions - definitely the best I found (and believe me I looked at a few ) :shock:

Dan

[acey]

Also, when I finish my cheshire x-hairs are a little offset

I get this too, and I wonder if it might be to do with:

1. Focusser not exactly square to tube,

2. Secondary not exactly square on, but rotated a little.

I also agree with the point about lasers not fitting neatly in the tube, and moving when the screw is tightened. The "barlowed laser" method is meant to get round this, but I've never tried it.

Andrew