I don't get it!?

[asimov]

No jetstream.....no wind.....Yet the seeing conditions here right now (2:20am) I'm giving 4/10!!! :sad: :sad: :sad: :confuse2: :mad2:

Mars in the scope looks like I'm looking thru the bottom of a empty stubbie!

No nice mars photo's from me! Hope you guys in Adelaide are having better luck than me!

I hate astronomy sometimes!:sad:

[DSO]

Frustrating, isn't it? I can get set up for an observing session sometimes, or drive to our local observatory only for the dreaded water vapour to build up. Astronomy is a frustrating hobby, but the good times far outweigh the bad.

[Starkler]

Scope well cooled?

[Itchy]

Astronomy is a lot like Golf. My worst night doing astronomy is better than my best day at work. :lol:

Cheers :cheers:

[seeker372011]

:) :) :)

[asimov]

6 hrs worth of cool-down time. I usually setup just after sundown, chuck a cover over the scope then go back inside till I'm ready.

I've found the jetstream maps to be not quite accurate....this confirms that theory in my mind at least.

The proof is in the seeing.

[33South]

I'll drink to that :drink:

[ving]

well its not my fault! :P

[atalas]

You were the first suspect David :lol:

[asimov]

I gave up work cos' it was cuttin' in to me viewing time!.......

[ballaratdragons]

Yep! Frustrating indeed!!!! But it makes it worthwhile when the sky is good.

[rumples riot]

Asimov, we setup with my scope for a impromptu drinking session and some imaging with EXFSO, Gadget, another mate and myself. Seeing was initially around 1/10. Really bad and the image looked like a mix master going on 1000. No detail was visible at all and trying to focus was impossible.

Thinking that maybe the collimation was off, EXFSO and myself set about checking it at 2am. Yes collimation was ever so slightly out but we quickly made the adjustments; mind you this would not have accounted for the bad images. See the collimation shot below. Dont worry about the pinch, it is tube current related.

By about 3am EXFSO and myself were the only ones still attending and by this stage very under the weather. Peter went home and I decided to wait out the dreaded tree for the vain hope of some good seeing. Around 4am Mars was once again visible and it was the first time I had seen it since 2am and before that 1am. Damn tree on my neighbours block is treading on dangerous ground. Very frustrating.

At 530am after taking a couple of AVI's of Mars that were at best ordinary and looking at Saturn with a 12mm (which gave a beautiful view) I decided to pack it in. Seeing over the course of the night would have only gotten to a very shaky 3/10 and transparency would have been very low also; no doubt contributing to the haze. Very disappointed and goes to show that all the preparation in the world cannot account for the weather.

Paul

[asimov]

:lol: I must admit I nearly fell for the: "It MUST be the scope!!" :sad: .....trick!

I started thinking "hmmm...perhaps theres a smudge on the eyepiece/collimation out/dew!???"

Then I had a closer look: Sirius was twinkling like crazy. A dead give away for totally crummy seeing. I stuck it out though & waited, just in case it came good, which happens a lot around here.

At least you had a nice night under the stars with your mates. :) You had nothing better to do did you Paul?? ;)

Please don't mention trees! I love trees...but not when they get in my way astronomically speaking.

Drill 1/4" hole on 45 deg angle (with hand-drill) pour in roundup, block hole up with sawdust from drill.

[davidpretorius]

Guys, for collimatioin, what eyepiece, what star and how much out of focus so you go to get that image.

i can get the cd's coming up and they are pretty good.

but a "star test" still has me beat thru lack of knowledge???

[asimov]

I'm guessing when you see these 'CDs' you must mean you de-focus a lot.

I do a star test in increments: bung in 15mm get shadow of secondary in centre of CD. bung in 7.5mm do the same thing. bung in 5mm do the same thing....then get closer to focus with the 5mm. As you get closer to focus, the CD decreases with size obviously....& hence so does the more accurate your tweaking of your primary has to be to..........I'm finding this real hard to explain!! :sad:

Put it this way: You must use fairly high magnification. If you see a gigantic CD with a black shadow in the centre, it's too hard to guess if that shadow is in the centre of the bright disk. You need to get the image smaller by getting closer to focus. As you get closer to focus the image will change.

You must use a medium bright star. it must be close to zenith. it must be 7/10 plus seeing. Your scope must be ambient.

Sorry Dave. Not very good at explaining myself here.:help: I'll see what articles I can find (I have heaps on the puter) & email you with an article/s...

Unless someone here can explain it better! I KNOW how to do it....but can't describe it! (go fiqure)

[asimov]

Heres a good example Dave. If you were to try to get a perfect focus with this kind of collimation, the result would be a star with a comet tail (as you described in a previous thread)

[asimov]

Another thing I should mention: I find it easiest to pick a star. centralize the star in the FOV. de-focus star slightly until you think you see a star with rings around it. Get the star off-axis to allow the star to 'drift in' to the dead centre of the FOV THEN decide which way you must tilt the primary. Thats the hardest part, working out which way to take it!! You have approximately 2-3 secs at that mag to make a decision with no tracking. :scared: :)

[davidpretorius]

i am following you,

If i look at the stars say in the "trap" with my 12mm, i have the stars going to points, but if i move the focusser slightly out of focus, i get the outside focus, ie the star grows hair for want of a better term!

Given image is upside down and back the front and the focusser is on the left hand side, which primary screw should i start adjusting and by what increments ie 1/4 turns???

thanks mate

[davidpretorius]

i am actually yet to see rings! I think!!!

[asimov]

I would suggest your not seeing rings because the 'criteria' is not being met. good seeing, close to zenith blah blah

[asimov]

Grows hairs.....your not defocusing enough, keep going......no good doing this at low mag mate, I must stipulate this, you'll get confusing results

[davidpretorius]

cool, ok i will try later tonight, scope has been out there for 4 hrs, i will point to zenith and defocus with a few ep's

by the way, the iss is about to poop on your head! in 10 minutes frm now!

[rumples riot]

Always go for the minimum amount of rings and aim for a magnitude 2 star.

[asimov]

ok. If you were to get the image as seen in this pic, & you were to stick your finger over the end of the OTA you would see something similar to that black bar in the pic. Then you kinda run your finger around the circumfrence of the tube until it looks something like in the pic. You then run your eye along the OTA to find the closest primary screw corresponding with your finger. Now it's just a matter of finding out which way to turn that screw (trial & error) incriments of 1/16th

[asimov]

Am I explaining this right rumples? I'm no expert!

[davidpretorius]

making sense, thanks guys, i really appreciate it!

so start with 12mm (100 x), then go to 6mm (200x)

[asimov]

No sign of ISS BTW 80% cloud cove, 4/10 seeing..(hehehe)

[rumples riot]

Yep sounds good to me.

[asimov]

That's what I would do if thats the magnification ranges you have, yes.

[davidpretorius]

saw a -8 iridium heading north, right into the moon.

the iis past into eart shadow shortly after clearing the horizon.

and how nice venus and antares area looks.

my 5 yr old asked to turn her bed around to look out the window, right at venus and the red of antares.

how could an astro mad father say no????

[RAJAH235]

Paul H, IIM ask a simple Q? It seems strange to me that you have to 'tweak' your collimation before each session. You have one of the best SCT's designed. Why is it nec. to re-collimate? They don't 'go out of coll', AFAIK. Something loose? I know you're doing high scale stuff, but it just seems a little............:shrug:
NOM. :D L.

[davidpretorius]

ok will do,

and mikes 2x and 2.4x barlows

[asimov]

Could be hard though....what R seeing conditions like there?

[asimov]

Forget about the barlow....just use the 6mm...(IMHO)as ur highest mag

[davidpretorius]

ok, will do!

guess who has just stuck his nose over the eastern mountain, hello mars!

[davidpretorius]

very clear conditions, no real sparkle, looks settled!

haven't looked thru the scope to see if the moon is boiling, but will check when i have a rip at mar and saturn for imaging and star test as well.

[asimov]

While your at it, pop the toucam in a take varying out of focus pics for us! (that should keep him outa our hair for the next 6 hrs ay fella's!?):lol:

joke joyce!

[davidpretorius]

jet stream non existant, should be a great night again.

i don't go out unless 9/10 seeing, which means i only go out 3/4 nights, It is not fair!

God must be punishing me for something!!!

Exagerating???

Only hassle is that at 5mm fl, the adjustment of the focus is soooooo sensitive and the image goes every where!, I have had my stepper motor controller fixed for weeks and still have not hooked it up for electronic focussing!

bad bad dave!

[asimov]

Stars at zenith twinkling here....minus 58 seeing conditions!!:)

[asimov]

That's nothin' mate! wait till U move your primary & go to find that same star again!

[asimov]

If I only went out on 9/10 conditions I'd sell all my scopes!! That happens 2 times a year if I'm lucky!!

[rumples riot]

Rajah,

I collimate each imaging session to ensure that I get the very best out of my scope. Most of the top imagers suggest at least checking the collimation each session. Yes, while it is a very good scope it does have its flaws. SCT's do hold collimation very well but little knocks can cause small deviations, as does weather conditions. So I like to fine tune the colllimation. Usually no more than 1/16 of a turn. I have seen SCT's that have never been colimated, they look good at 200X but when you whack a barlow in the image degrades so much due to the collimation.

Anyway, thanks for asking sometimes I wonder too.

[asimov]

Thats not quite true: I had a dream the other night: I was observing on the moon: seeing conditions 11/10 trans 12/10.....:lol:

BTW I check collimation every time I go to a new object! (I'm possessed by the collimation devil):wink2:

[asimov]

Dave, unfortunate but true: you will have to re-align your finder just about each time you move your primary......That's one of the many reasons why it's best to get it as perfect as you can using the cheshire before hand. If youv'e already done this, hopefully you won't be far away from perfect collimation.

[asimov]

Even tracking doesn't help here. At the mag a 5mm EP gives you, & you move the primary screw 1/16th turn, thats usually enough to throw the star out of the FOV....then you have to find the star again, centre it, re-align the finder! It really is an exercise in frustration......the patience & precise movement of a surgeon is needed lol.

30 years ago if my collimation was out by just a little bit it would take on average 1-6 hrs to get it right.....If it was freezing out, I'd end up sweating like a pig from my temper on the border-line of throwing a tantrum the size of everest!

I suggest you stick with the 12mm & get it the best you can perhaps. You can check with the 5mm......but it's up to you weather U wanna attempt tweaking using the 5mm..I don't suggest U try it @ 5mm until your more familiar with doing it..

[RAJAH235]

Thanks Paul. Just wondered. :2thumbs:
Will have to relay message to our guys next Ob. session, as they have, AFAIK,never collimated their SCT's.. :D L.
ps. Maybe that's why I prefer the views thru my DOB. :P :P :P

[acropolite]

I can verify what Paul said, my SCT was collimated perfectly on delivery but as winter approached the collimation had changed significantly. Like Paul, I check the collimation every time, easy when you have Bob's knobs or similar.