Yet another collimation question

[BC]

I feel I shouldn't be asking such newbie questions after almost a year since getting my scope, but hey. I've played with collimation many times and have been fairly confident that I have been doing OK. I've seen the cassini division and GRS and Jupiter's moon shadows on the planet, but basic stars have never been the way people describe them. Any brightness to the star transforms into a bright flair, until 2 nights ago. I hadn't collimated because it really doesn't seem to change that much and suddenly, bright stars looked like very small bits of light with 4 very slender, pure streaks of light, which of course come from the spider veins. This looked like the people always describe stars, so I'm wondering, does this mean that I have never really had "good" collimation? And that this time when the scope's collimation went "out", in fact it moved into a very good position? Do you get the 4 streaks even when seeing is bad?

Thanks very much for your thoughts,
Bruce

[matt]

Sounds more like you just had a night of very good seeing.

Stars suffer pretty badly when you use high magnification during less than good seeing.

I'm assuming you use the same high magnification eyepieces for planets as you do on stars during your observing nights?

[cjmarsh81]

Yes could be just good seeing. I had one of those nights about a month or so ago. I didn't collimate my scope and the view was the best I have ever seen.

Or you could be just collimating it wrong

[ballaratdragons (Ken)]

Don't be too dismayed. F5 or 6 Dobs aren't exactly 'crisp star' friendly without exceptional seeing, or low magnification.

The more you bump up the mag, the more crap you magnify as well.

Diffraction spikes are good!

It is weird though, F5 can get Joop, Saturn, Nebs, Globs etc looking fantastic, then aim at a bright star and it just won't focus quite right. Even the best collimation can't see pinpoints thru gunk.

[Starkler (Geoff)]

Originally Posted by BC

. Any brightness to the star transforms into a bright flair, until 2 nights ago.

A scope with pinched optics can make stars flare as you put it. It might be worth checking that mirror clamps and secondary holder arent putting any undue tension on the mirrors.

Do out of focus stars give nice concentric rings?

[BC]

I think I was using my QX 4000 20mm with a 2x Barlow at the time. The out of focus stars are round circles, if not a bit shimmery from those amoeba things. It sounds like I should just enjoy the view.

Thanks

[Gargoyle_Steve (Steve)]

I'll post this in as I've had my scope exactly a month today so my newby experiences may be relevant to you, and I seem to have spent 5 or 6 days collimating (mostly in the first 10 days) so I've had some practice at getting it right and wrong.

I have exactly the same kind of views that you do ..... 4 nice spikes on stars under good seeing, but only with 40-100 x magnification, my f5 10" dob can't seem to do stars at higher mag without seeing that small fizzing "blob" instead of a crisp pin point light source.

I had used the "traditional" 35mm film cannister type home made collimation tube, about 3 different versions actually, and in the end I figured I was still a part of the problem by not getting it collimated correctly. I shelled out $69 for the combination sighting tube / Cheshire tube at Bintel .... my opinion is GET ONE! If you have any doubts at all about your collimation these things are GREAT, and as I proved to myself this weekend. If you've transported the scope and still do have the collimation right you can confirm it's accuracy in bare seconds and feel confident that it's ok, if it needs adjusting you can see that clearly and immediately too.

We actually used my sighting tool on the scope of another member of these forums who is far more experienced than I am, and it showed straight away we had one small, but clearly visible, adjustment to make. We had his scope and mine collimated sweet in no time!

[leon]

If you want a good view of the stars leave the magnification alone, stay between 25 and 40, you can't see anymore with high power, you just increase the bad seeing.

[matt]

Yes. If you are just "viewing" stars don't worry about high magnification. Go low mag and wide field.

If you are planning on star testing your collimation, however. you'll need to push the magnification as high as the seeing will allow

You'll also need some degree of magnification if you're planning on splitting some fairly challenging doubles... again, if the seeing allows.