Jupiter with the 9.25 - Page 2

matt · #21 16-04-2006, 01:06 PM

No Asi. Didn't think you were making a smart-A comment. Quite honestly meant that you are a clever lad. You've got that 9.25 moving at a 1000mph and I'm floundering in your dust!!!

matt · #22 16-04-2006, 01:09 PM

Interesting, Bird. I was also thinking the seeing was a bit dodgy. Thanks for that. Yeah, hopefully will do better tonight. Thanks mate. Although the jetstream's looking a bit rough?

asimov (John) · #23 16-04-2006, 01:18 PM

Oh ok, lol. Not really mate. I've had one night of good seeing & that's it!

The night I got those 2 AVI's, I got rained on twice. Then after stacking the first AV & realized what I had...I deleted all the other AV's I had (including my best Saturn) with the intention of racing out & getting heaps more!.....Only to find it clouded over! NOOOOOOOO!!!! So I waited & waited & waited. It stayed cloudy. I was livid!! No doubt woke the neighbours at 4AM with all my cursing & shouting!

Last night, well, I got one AVI....stacked/tweaked/deleted. The jetstream was/is here travelling at the speed of sound lol.

Robert_T · #24 17-04-2006, 08:01 AM

Matt, you've got the makings of something really great here, all the macro detail is very well defined and you've got the colours I want. Could be seeing or collimation that's not letting you get just that extra step in sharpness (and wavelet settings as Asi will point out), however, I'm beginning to think focus is perhaps an often under-rated factor. When I look back at my images, the biggest single improvement wasn't gained when I changed scopes or cameras, but when I got myself a meade motorfocusser.

Keep up the great work!

matt · #25 17-04-2006, 09:13 AM

Thanks Rob. Funny you should mention the issue of focus. I was thinking exactly the same. I was noticing the other night that these SCTs present a couple of probs in this dept. I was familiar with the obvious image shift as you rack the focus in and out, and also the not-so precise nature of using the focuser knob. However, I've also discovered another issue which makes focusing even harder using the standard knob. The simple act of applying inward or outward pressure by your hand on the focusing knob, pressuring the focus mechanism in a lateral direction - towards or away from the corrector - also impacts significantly. I've noticed some quite considerable loss of focus the moment I take my hand away from rotating the focus knob precisely when the image is crisp and sharp on the screen. Honestly, it's a nightmare!!!!! Does this problem have an astro/techo name i'm unaware of?

Robert_T · #26 17-04-2006, 09:28 AM

Quote:

Originally Posted by matt

Thanks Rob. Funny you should mention the issue of focus. I was thinking exactly the same. I was noticing the other night that these SCTs present a couple of probs in this dept. I was familiar with the obvious image shift as you rack the focus in and out, and also the not-so precise nature of using the focuser knob. However, I've also discovered another issue which makes focusing even harder using the standard knob. The simple act of applying inward or outward pressure by your hand on the focusing knob, pressuring the focus mechanism in a lateral direction - towards or away from the corrector - also impacts significantly. I've noticed some quite considerable loss of focus the moment I take my hand away from rotating the focus knob precisely when the image is crisp and sharp on the screen. Honestly, it's a nightmare!!!!! Does this problem have an astro/techo name i'm unaware of?

Matt, not sure if this has a name, but I'm not surprised by this action given the mechanics of mirror shift focussers. Perhaps Dennis can shed some light. He mentioned something about a mirror lock that he has for his C9.25? I tend to approach focus with an anti-clockwise turn and then do the fine focussing with the motor focus unit. Re focussing every now and then in the hope I'll jag perfect focus for some of the avis.

matt · #27 17-04-2006, 09:48 AM

Thanks Rob. Regarding the collimation issue. I'd be really keen to see a few NexImage shots taken through your scope of a star test. Mine look good at about 300x, but I've noticed a difference in the size of the central obstruction in the outside and inside focus images.

Robert_T · #28 17-04-2006, 10:16 AM

Quote:

Originally Posted by matt

Thanks Rob. Regarding the collimation issue. I'd be really keen to see a few NexImage shots taken through your scope of a star test. Mine look good at about 300x, but I've noticed a difference in the size of the central obstruction in the outside and inside focus images.

that's normal Matt, your inner and outer focus images won't be exactly the same (unless you've got a refractor maybe). The key thing is that the rings are concentric either side of focus. You really need to be running >500x magnification for critical star collimation and the nights where seeing is good enough to use that aren't all that common...

anyway, I'll try and capture collimation some time soon and post. Be more interested to see Dennis's though - he get's diamon razor sharp images!

cheers,

Dennis · #29 17-04-2006, 11:04 AM

Quote:

Originally Posted by Robert_T

that's normal Matt, your inner and outer focus images won't be exactly the same (unless you've got a refractor maybe). The key thing is that the rings are concentric either side of focus. You really need to be running >500x magnification for critical star collimation and the nights where seeing is good enough to use that aren't all that common...

anyway, I'll try and capture collimation some time soon and post. Be more interested to see Dennis's though - he get's diamon razor sharp images!

cheers,

Hi Robert

Have a look at:

http://www.iceinspace.com.au/forum/s...ht=diffraction

Msg#2 contains inside and outside of focus star images with the x2.5 in the optical train.

Cheers

Dennis

matt · #30 17-04-2006, 11:13 AM

Cheers Dennis. You're the man.

I'd forgotten about this very handy post.

Collimation looks pretty much the same as mine. The only challenge will be waiting for a night of great seeing where I can push the mag to >500x.

I can only assume seeing has again fallen short of what was hoped???

This is Canberra, after all

And I'm also now in the market for a precision electric motor focuser. Wish you hadn't snapped up that JMI Dennis!!!

asimov (John) · #31 17-04-2006, 11:51 AM

when the scope is pointing up 45 deg +...gravity is coming into play with the weight of the primary mirror. Wind the focuser knob clockwise, the mirror is moving down towards the EP end of the scope & the knob is very easy to turn. Wind it the other direction, its fairly firm to move. This is because your fighting against gravity. When focussing, I get it to focus as viewed on the laptop, then I wind clockwise slightly, taking it out of focus, I then tweak it very slowly back the other way until I gain critical focus. This takes all backlash out of the system & will not shift on you while your imaging.

Lester · #32 17-04-2006, 11:59 AM

asi, your'e a wealth of information.

matt · #33 17-04-2006, 01:35 PM

Thank Asi. Actually, I'm aware of that issue with the mirror shift and backlash, but that other issue with the shifting is something altogether different.

I'm gettin' me a microfocuser

asimov (John) · #34 17-04-2006, 05:32 PM

I'm getting me one too....just a matter of making it.

matt · #35 17-04-2006, 05:40 PM

Good for you, matey!!!

I'll be paying for mine .... thru the nose ... big-time!!!

Lester · #36 17-04-2006, 06:57 PM

Okay chaps this is what I did many years ago with my mid 1970's Celestron 8". After removing the primary and corrector with secondary, I drilled 3 holes into the base of optical tube and threaded them to fit 1/4" thread. I then placed a small dob of silicone on the end of each bolt. Once focus is achieved the bolts are screwed lightly and evenly up against the rear of the primary to hold it in place.

DANGER.....DANGER.....DANGER! You do this at your own risk. But I am always looking for the easy way out.

Sorry I don't have any test results to say how successful this was, because at the same time I stopped using my C8 as a guide scope on the 16" Newtonian and went to a off-axis guider.

asimov (John) · #37 17-04-2006, 07:14 PM

Yes, I've seen that done on a C14. Works a treat!

[1ponders] (Paul) · #38 17-04-2006, 09:00 PM

You won't regret getting the microfocuser Matt. I know I'd be lost without mine, I don't have the patience to try with just the SCT focuser. I had a meade microfocuser with my LX200 originally, but with the new OTA I went for the JMI. Glad I did.

And btw one of the biggest reasons I bought a meade 8" rather than a celestron was because of the mirror lock (if the 9.25 was cheaper I might have overlooked it). Lock that sucker down and you are set for the night with just minor shifts in the microfocuser. If there is a kit around for the 9.25 think about that too.