Collimation

[highlander2287]

Well my laser collimator and cheshire finally arrived. I am not 100% sure that the laser is collimated itself so at this stage I am relying on the cheshire. I have attached a photo which hopefully is clear enough for people to see. It is better when zoomed in. Can someone confirm that it appears the primary mirror is out of alignment, and possibly the secondary. Any thoughts and advice is appreciated. I have added 3 from the laser so I would be curious if anyone could compare and comment if the laser is an accurate comparison to what the cheshire is possibly representing.

[glend]

It would appear your secondary is out of alignment. There dot should be hitting the centre of the primary centre spot. Do that first.
Suggest you download Astro baby's collimation guide.

PS details of your scope would help us help, like f ratio. Secondary offset varies slightly by f ratio in newts (Dobs). I suggest you check that all your struts are at maximum travel and locked in place, a schewed top section can offset the beam too.

[highlander2287]

Glen, Are you making that decision on the cheshire rather than the laser photos. Thanks. I have downloaded that guide. The scope is a 10" skywatcher collapsible dob goto setup. Some quick measuring appear to confirm the secondary mirror holder is central with all spider vanes at the same distance from the centre to the outside of the tube.

[rrussell1962]

If I am making out the crosshairs correctly in the Cheshire / sight tube in the first photo they do not seem to be hitting the centre spot. Also the photos with the laser show the outgoing beam not hitting the centre of the primary spot and the return beam not lining up with the outgoing beam which indicates the primary is not aligned correctly. If the secondary, with the Cheshire / sight tube appears circular and in the centre of the focuser tube just adjust the mirrors, secondary first. I actually find a Cheshire better for adjusting the primary but use a laser for the secondary.

[glend]

As Russell said. The third photo needs fixing first. That laser should be hitting the centre spot on the primary, do that first. Then worry about adjusting the primary to get the laser to centre on the grid in the tube. Watch the offset, as described in Astro Baby's photos, but yours is not to fast to need much offset, frankly I try not to touch offset.

[rrussell1962]

I've just had a quick look at Vic Menard's book on collimation. Your telescope is, I think, F4.8. If you are not using a coma corrector you have a fair bit of latitude on the secondary alignment, your tolerance for that is actually around 7.5mm, but if you are going to adjust it you should get it as close to the centre of the centre spot as you can. Not such good news on the primary collimation at F4.8 I'm afraid - you should be looking to get that to within 0.5 of a mm or so. Much easier with a Cheshire. If you are doing it when it is getting dark shining a torch in the hole on the side of the Cheshire can be helpful in making things stand out more. As Glen said don't worry about the offset at all - it may already be built in to the way your secondary has been attached anyway - it is on my 130mm F5 Skywatcher, if not then your primary adjustment will just tilt the primary a little bit, which you will not even notice.

[highlander2287]

Thanks for all the advice. Will give it a go.