Expectations - Page 2

Starkler (Geoff) · #21 11-07-2005, 11:18 AM

Where do you live BC ? Maybe if you can hook with somebody more experienced they can quickly tell what is going on there.

asimov (John) · #22 11-07-2005, 01:09 PM

BC. The cross-hair's are used to centre the diagonal, that's why some dude's centre spot the secondary, instead of guessing where the centre of the mirror is. If you can't focus on the cross-hairs, grab a dolphin torch & muck about moving the torch around at different angle's blah blah...(shine the torch in the hole in the side of the cheshire) There will come a time when the cross-hair's become fully illuminated brightly & you'll see em' easy...even though they will STILL look out of focus.

asimov (John) · #23 11-07-2005, 01:33 PM

After thinking about what I just wrote above.....Could I be wrong about why those cross-hair's are actually there??

Hmmmmmm..

slice of heaven · #24 11-07-2005, 03:12 PM

Is this a cheshire with the hole in the side? If so shine a red LED in the side to illuminate the crosshairs.

If the stars arent pinpoints then they aren't, no guess work needed.
Have you checked the mirrors to see if their held too tight in their cells?

If the scopes from Bintel they wouldve collimated it prior to shipping so it cant be majorly out of collimation. Only the angles of the mirrors should need adjusting.

Collimation is something you have to learn ,if someone can show you the way it'd be lot easier to understand.

BC · #25 11-07-2005, 04:08 PM

Yes it's the cheshire with the hole in the side, I'll experiment with a torch. I'm down near Canberra, I may need to chase up some helpful soul down here. I picked the scope up myself from Bintel so I know it wasn't bashed about too much on transit.

asimov (John) · #26 11-07-2005, 04:33 PM

If it hasn't got a hole in the side, it's not called a cheshire........not in my experience anyhow...lol

slice of heaven · #27 11-07-2005, 05:24 PM

Quote:

Originally Posted by asimov

If it hasn't got a hole in the side, it's not called a cheshire........not in my experience anyhow...lol

If youve seen one then your far more experienced than me, Because I havent

asimov (John) · #28 11-07-2005, 06:30 PM

eh? I think weve got crossed wire's or something, lol. a cheshire has got a peep hole at the top & a hole in the side with a polished 45 deg plate with a hole in it. If it's got cross-hairs, it's called a combo cheshire & sight-tube.

A sight tube is a longer tube with the peep hole, sometimes with or without the cross-hairs...with no hole in the side or the 45 deg polished plate. OR have I got it all wrong lol......

ps If this is wrong I'm going to blame the internet!

slice of heaven · #29 11-07-2005, 06:44 PM

Its not the side hole I havent seen, its the whole cheshire.

asimov (John) · #30 11-07-2005, 06:53 PM

OH! So you dont use a cheshire either.....like ME!!

slice of heaven · #31 11-07-2005, 07:21 PM

Exactly John!

I've a film cannister and extremely concise manual on how to collimate using a sight tube and startesting.
Definitely not recommended for beginners, I did the hard yards earlier on and now its a simple thing to do. Like you stated in one of the above posts the 'soft' image is a dead give away something is not right.

asimov (John) · #32 12-07-2005, 03:01 AM

Your one up on me then...I dont even have a sight tube! hehehe!

iceman (Mike) · #33 12-07-2005, 06:31 AM

BC, stringscope lives in canberra. I strongly suggest you PM him, or take your scope along to the next CAS meetup. They'll help you collimate it (and show you how to do it with or without tools), and they'll also be able to confirm if what you're seeing is normal (ie: yoru expectations are too high), or if there was something wrong with eyepieces or collimation or astigmatism which is affecting your views.

You'll also get the chance to look through some other types and sizes of telescopes to judge for yourself if your views are better or worse.

stringscope (Ian) · #34 12-07-2005, 10:34 PM

Hi BC,

I have just read this thread. Happy to help any time. I will be at work tomorrow if you want to telephone, or send me a PM. Next CAS meeting is 21 July at Mt Stromlo. Intro Group starts at 7 PM. Topic is Cold Weather Observing. We would have time to look at your scope durig the evening.

Cheers,

stringscope (Ian) · #35 12-07-2005, 10:48 PM

BC,

I have sent you a PM with ph no's.

Cheers,

iceman (Mike) · #36 29-07-2005, 07:49 AM

Hi guys.

I read in another thread that BC came around to Ian's house with his Dob.

Just wondering how it went - was there anything particularly wrong with BC's dob (collimation/astigmatism), or was it just a case of expectations?

BC · #37 29-07-2005, 09:03 AM

Hi there,

I went to Ian's house last night to check things over, which was very helpful in clearing up some things for me. After all my tweakings of the adjustments, it turns out that my collimation was pretty much OK, good enough that it didn't need any adjustment last night. So it comes down to expectations I think (and EPs to a lesser extent), not helped by some quite poor seeing conditions just about the time I was getting discouraged, as well as convincing myself that I'd mucked up the colimation. I might make a comment about collimation tools though. Ian's combo cheshire/sight tube (Orion I think) made all the difference to my confidence because it is long enough to actually see the crosshairs clearly, along with the centre spot on the primary. With that tool I would be able to confidently aim the secondary, whereas the tool I was using, worked well as a cheshire, but did not work for me as a sight tube. I was surprised how well the secondary was aimed at the primary centre spot considering that I had adjusted it by visually centring the primary reflection in the secondary. I will be purchasing the longer collimation tool.

Certainly Ian's better EPs made a difference, which gives me a good idea of what I might expect for a price, but it also shows that my GSO ones are quite acceptable for the time being. Ian had his modified 8" f/6 set up as well as his stringscope (which is a very clever piece of equipment) so that gave me an idea of what is "normal". We looked at plenty of DSOs from his place in the suburbs with good success (even a monthly challenge object). All in all a very informative evening and very good to have my expectations "normalised" and stop worrying that my scope is not OK. My little exercise in doubt demonstrates clearly why it is good to look through other's scopes before you buy, something that is constantly advised, but just didn't work out for me at the time. (gotta have a scope !!)

So a big thanks to Ian as well as the folks here who contributed thoughts along the way. Now with a fresh attitude, bring on the night....

iceman (Mike) · #38 29-07-2005, 09:09 AM

Well done BC and well done Ian, great to have that experience under your belt. A fresh look on things will rejuvinate you!

slice of heaven · #39 29-07-2005, 09:54 AM

Whew. For a while there BC I thought you might walk the plank.
Great to hear your on track now

Good point you've raised on collimation tools. As with most things, you get what you pay for. Though the cheshire from Andrews is recommended a lot here(because of the price), its not the be all and end all of collimation tools. Theres a vast array of tools available, from the cheap and better than nothing.....up to the expensive and well worthwhile. Each tool has a drawback and more often than not 2 tools are required, one to remove the errors of the other. Do some research on the tools available and grab a well designed and highly recommended unit.