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MartinB

NGC 891 with wonky active optics

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Friday was a strange night at kelling. The field was bathed in a fine dewy mist yet the sky was crystal clear with good transparency. Once again our blue field had the best of the conditions. The dew was amazing though. Everything was dripping. My Dew Not filter strap performed heroics.

I am awaiting a change of flange for my motorised focuser to reduce the profile in order to be able to use a 6.3 reducer with my 10"LX200R. Until then it's native focal length - 2500mm F10. The problem with this is that the AO uses an off axis guide star. It is very difficult finding a star bright enough to deliver the really short guide star exposures that allow AO to do it's stuff. Occasionally the AO needs to adjust the position of the mount and for some reason this wasn't working so I had to do it manually.

After hours of setting up I finally did got some time on NGC891. Not as much time as I should have spent since I wanted to have a look at M1. This is just 5x10mins lum and 4x150secs binned x2 RGB with a QSI 532ws cam.

Captured and stacked in Maxim and processed in PS. Turned out better than I thought really. Need to get the reducer sorted though.

8944_normal.jpeg

(click to enlarge)

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so what is the outcome of the Active optics.

how exactly does it work. is it based on the principal of adaptive optics used on multi cell mirrors.

Could you estimate the increase in resolution or FWHM of a star taken with the active optics and one without.

What are the drawbacks to active optics.

Thanks for the help, i am curious to see if it is worth getting

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And yet another 'goodun', what a weekend you had!! :)

Lovely detail showing in the 'dust band', and from only 50 mins.

Pretty good eh!!

Dave

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Crikey, that's colossal Martin. I bet you kept this under your hat in order to shock us. Well, it certainly jolted me, it's a real humdinger.

Ron.

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After watching you suffering with problem after problem on Thursday and Friday Martin, it's nice to see you got at least something out of it :) , and I'd be pretty happy with it too! Good work sir.

Tony..

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Great work Martin.

At F10 that's a very tight image. :)

Cheers

Rob

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That's gorgeous Martin, NGC891 is one of my favourite objects. It's made all the more impressive by the efforts we all saw you put in to get it!

James

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Like that Martin, thats a corker , like Rob said really tight, excellent work . Gordon Bennet my job is really cut out for this weekend Pow :)

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I was chatting with you that night and watched as you have to almost continually adjust that little star in the little box (see how technical I got there?).

Thats an amazing image.

Well done that man.

Ant

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Thanks everyone, I thought this was the least promising image of the week end because of the problems I was having but pleased with how it's turned out.

so what is the outcome of the Active optics.

how exactly does it work. is it based on the principal of adaptive optics used on multi cell mirrors.

Could you estimate the increase in resolution or FWHM of a star taken with the active optics and one without.

What are the drawbacks to active optics.

Thanks for the help, i am curious to see if it is worth getting

Paul, SXV sensibly call the unit active optics rather than adaptive optics. There are no adjustable mirror cells, the unit uses a piece of optical glass which can tilt in 2 axis. Behind this is an off axis guider and then the chip. The glass can move through it's full range in 5ms which means that with the right guide star you can get very rapid adjustments. With a mag 7 star and the lodestar guide cam at 2500mm f/l and F10 I can manage over 10 guide cycles per second. At this rate the guiding keeps pace with the seeing and allows effective use of much higher sampling rates than conventional. I can't really quantify this since the improvement depends on conditions and the s/n of the guide star, also I haven't managed to capture many images with it.

The guide star I was using for the above was mag 10 and I could only manage 0.4 sec exposures which is too long to really tighten things up. The other problem I had, which Ant refers to, is that for some reason the AO wasn't communicating with the mount. The AO has a limited range of adjustment. As it gets towards the limit of it's range the mount should make a correction to reset the guidestar. This doesn't cause trailing because of the rapid readjustment of the AO window.

I plan to use it with a 0.63 reducer but need to lower the profile of my focuser before I can do this. At 0.63 guide stars are much easier to find and have better s/n ratio.

The downside is the complexity and the normal restrictions of OAGs. It definitely adds another layer of complexity to the guiding process and many in on the forum will have heard me grumbling about. Getting the AO working consistently is now my lifelong mission!

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Beautiful image Martin. And may I add, once again as lucid and informative in your technical answerings as ever.

Anthony

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Thanks again everyone. Ant - I thought I was rambling on!

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