Another daft collimation question

[Gasmac]

I'm the proud owner of a SW 250 px flextube which i'm enjoying very much. I'm enjoying the views (been splitting doubles and had some good views of the planets). However i have messed around a bit with the secondary after a 2 hour journey in the car. I'm happy with primary collimation using a barlowed laser but not convinced with my secondary allignment.

I use a premium a premium cheshire (using a HG parallizer) and a home-made collimation cap but they contradict each other. What looks perfect in the sight tube looks a little off center in the cap view. The question is which to trust (my money is on the pro made tool)? When i defocus on star test (not convincing as i seem to always to have a bit of atmospheric disturbance) the central dark area looks off centre.

I know the sweet spot is very small in a fast scope and i want to get collimation perfect (i plan to get the HG laser & tublug but saving up first ). I have read at least half a dozen different how to article/blogs on t'interweb but have ended up getting more confused than ever. Any help would be much appreciated ( i wonder if the paralelizer is pushing the cap off centre as is it not affected by the paralizer centering voodoo.

Thanks in advance. I attach the view i get down the sight tube

[Northern Soul man]

Hi Gasmac and a very warm welcome to the SGL mate - the image looks bang on to me, but its the star test which I would rely on mate - you say its off a little, it needs a tweak under the stars if that's the case, you can't really tell from the image if the secondary is central in the focuser, but when I had my newt I always extended the focuser all the way out, but the star test is the one that I would make sure that I corrected at the scope under the stars obviously - wait for more of the collimation experts to post, as I have an SCT now and not had to collimate for ages - but I think its the star test that's the most precise from my experience.

Regards  Paul.

[jetstream]

When using your cheshire does it turn out like this?

[Moonshane]

I cannot tell if the secondary edge is filling the view or not? can you pull the Cheshire out a bit and take another pic?

once done this is stage one of the process. you then need to adjust secondary tilt and then the primary

my guide is less complex than some and may help (although I only use a Cheshire for the whole thing)

http://stargazerslounge.com/topic/197640-collimation-and-star-hopping/

[Gasmac]

Thanks for the replies. In that picture the thin black line alway around is the edge of the secondary. I move the cheshire so i have the smallest distance from the edge of the secondary and sight tube as i thought that would help me centre it as close as possible. I will post again later with a few more pics but I have just returned from the Lakes and in the "scottish restaurant" with the kids.

[NGC 1502]

For me, the out of focus star test is the final and ultimate check, but it's important to have the image central in the field of view, and with a fast system like the SW 250, not to defocus too far, because the secondary offset can make things look wrong, when all is ok.

Regards, Ed.

[Gasmac]

I think i may have developed a case of collimation hypochondrical neurosis. I think NGC has described what i have been doing so i'm a lot happier with what i have done.

[Moonshane]

in that case stage one is sorted. you will also need to adjust the tilt of the secondary so the donut intersects the cross hairs on the Cheshire. then your primary.

[Gasmac]

I can get it close with the cheshire but never perfect. I'm ordering some new thumb screws and hopefully the hg laser to get it pin point. The focuser has very little slop so i'm confident it will work well with a laser. Thanks for all your and help and putting my mind to rest.