does good collimation = better focus

[jobe]

Hi guys.

i have a laser coll tool which is a little out. also my secondary was also out.

the red dot on the primary was showing about 3/4" out.

i adjusted the secondary(seemed quite a faff) to get the red dot on the edge of the centre 'hole'.( the donut shaped centre hole punch thingy) when spinning the laser around in the focuser it constantly wound it's way around the centre so this must be 'ringing' the centre. i.e. allowing for the discrepency.

still following?

thinking about it, when i collimate the laser must still be showing out, as it's not perfect set from the start.

sooooo. how much would this affect the views i get?

the laser is the one from FLO. are they adjustable?

thanks for looking

jobe

[brantuk]

Sounds like you may need to collimate the laser - although you should check if the "ringing" effect is due to slacknes in the focuser tube first

[lukebl]

I've found that, no matter how well collimated the laser is, there will always be some wobble in the focuser so it's never spot on. Try barlow collimation, which works for me. It's accurate and less affected on the accuracy of the laser or focuser slop.

[ollypenrice]

I'd have thought your 'ringing' test would mean you are pretty close. At that point I would get a helper outside and do a star test.

Barlowed laser is also a good option, I agree, but I just go from laser to star test or just settle for laser only, depending on the projects in mind. Low power deep sky is not greatly affected by slight imperfection in collimation. Double star and planetary is another matter.

Olly

[Moonshane]

to answer you question I would say that collimation affects everything from contrast to sharpness and also to some extent brightness.

I would not personally use a laser to set the secondary. use a 'collimation cap'. most people use a film canister with a small (approx 2mm) hole in. this allows you to see the secondary shape (i.e. it should be round), position (once round it should be centrally positioned in the view) and angle (the primary mirror clips should all be visible and evenly spaced around the secondary.

then use the last (as suggested using it in a barlow will help get this more accurate) on the primary. what you will see when you barlow laser is a sghdow of the donut on the angled face of the laser. this might be big so turn your primary adjusters until you see it. centre the shadow around the hold in the angled face and you are done. you can star test to tweak if the seeing is good enough but often it's not in the UK. this is good enough for visual observing but you need to be a bit more accurate for imaging (I think).

hope this all makes sense.

I previously used a laser but now use a collimation cap and a cheap and nasty but easy plastic cheshire which came with a pevious scope and does not even have cross hairs. I do also have a 'proper' cheshire for times when the secondary has removed and replaced as the cross hairs help in setting the distance down the tube that the secondary should be.

[jobe]

Sounds like you may need to collimate the laser - although you should check if the "ringing" effect is due to slacknes in the focuser tube first

there is only a very tiny amound of slack in the focuser tube.

when you say collimate the laser, do you mean adjust it or check it?

Try barlow collimation, which works for me. It's accurate and less affected on the accuracy of the laser or focuser slop.

i'll have to read up on this thanks. tho it prob won't help the fact i don't have a barlow!!!!

I'd have thought your 'ringing' test would mean you are pretty close. At that point I would get a helper outside and do a star test. Olly

guess i'll have to read up on this too.

I would not personally use a laser to set the secondary. use a 'collimation cap'. most people use a film canister with a small (approx 2mm) hole in. this allows you to see the secondary shape (i.e. it should be round), position (once round it should be centrally positioned in the view) and angle (the primary mirror clips should all be visible and evenly spaced around the secondary.

.

i have a collimation cap already. looking down the tube the secondary seems ok, although tracing the lines i can see of the spider vanes of the secondary wouldn't quite meet the ring in the centre. not far off but not exactly.

thanks for the replies chaps. i may get back to you:D