The astronomers curse

[Gneiss]

Prompted by my earlier post, I have just spent the best part of an afternoon collimating my SNT...

Ok, I noticed a few specks of dust had gathered on the main mirror and the corrector - so I completely stripped it down and cleaned it with air and a squirrel hair brush. Then I decided to do something about the focuser (it still has to go) and managed to reduce the slop - Then I collimated it.

And now…

It’s completely overcast!!!

[vet]

if overcast continues, here's a trick that might help & be fun---you probably don't have an 'artificial-star' set up in the basement, but if you have a 'line-of-site' shot at a mall, street, whatever---you may scan the chrome bumpers of autos, either in sunlight, or under strong street-lighting---the idea is to scan for one distant enough for its relection of the light-source to produce an 'airy-disk'---which you may examine at field's edge---

while a clear night is best, of course, there are ways to test your results on other terrestrial objects---most tall buildings will have some , usually red, 'clearance lights'---i'm 'downtown' and often use those atop a bank some blocks away for testing surplus, very high initial cost, optics for their use as oculars. with some ingenuity, you may think of others---

[Gneiss]

Yes I have used the ball bearing trick in the past and it works well, I have also sued the sun reflected off the insulaters on some very distant electricty pylons where I used to live.

Unfortunately or fortunately depending on how you look at it we are surrounded by trees and bushes where we are now and don't have a good horizon - great for filtering out stray light at night though!

So my only option here is to use a real star... either that or transport the scope, which probably voids accurate collimation.

[vet]

Originally posted by Gneiss@Mar 16 2005, 09:02 PM
Yes I have used the ball bearing trick in the past and it works well, I have also sued the sun reflected off the insulaters on some very distant electricty pylons where I used to live.

Unfortunately or fortunately depending on how you look at it we are surrounded by trees and bushes where we are now and don't have a good horizon - great for filtering out stray light at night though!

So my only option here is to use a real star... either that or transport the scope, which probably voids accurate collimation.
boy howdy, is the collimation on that critter That tenuous? another 'trick' i've used is removing a window-screen, placing it beyond the 'scopes minimum focus range and looking at the image---not a big ronchi-grating, but at least any gross deviations of field may be seen. as for 'collimation-instability'? sounds like either bad design, or maybe just a steep learning-curve---assuming the secondary remains 'stable' and the tube is short, the quickest way to get the primary 'in-line' seems using a star, and adjusting the rear so the 'spike' moves towards the star.

[Gneiss]

Last night was clear at last... In fact I had a fantastic days observing, starting with the Sun in the late afternoon using the PST.

Anyway, this is amazing...

Later I lined up a star in the SNT and I had the collimation absolutely perfect!! I don’t suppose I'll ever repeat that again but it did make me smile… :rolleyes:

Turning the scope to Saturn, it is at least performing like a 6" scope again. It still can't be pushed as far as my f/8 in terms of magnification but at least it is now performing as well as it can!

Interestingly, Meade has managed to produce defraction spikes in an SNT!! It is by no means the first time I have noticed this and it can be traced to the primary mirror support… I mention it as it comes down yet again to poor design!