SXV adaptive optics - no images from me for a while

[MartinB]

A few weeks ago I decided to buy the SXV adaptive optics unit to work with my H9 camera. Adaptive optics have been a recent exciting development in professional observatories. Basically scope mirrors are designed to be deformable. A laser is shone high into the atmosphere to form an artificial star. The star image is analysed and its position is compared to where it should be if it weren't being distorted by the atmosphere and a correction is applied to the mirror.

An off shoot is now being applied to guiding for long exposure astrophotography minus the laser artificial star. Light passes through a tiltable glass window. Behind the glass is the imaging camera and an off axis guide camera. The guide camera picks up any movement of the star and the adaptive optics unit tilts the window. The light is moved by refraction to correct the star drift. It takes 5ms to move the window into it's new position. Thus there is the potential to make multiple corrections every second with a suitably bright guide star. There are none of the problems associated with adjusting heavy mounts - inaccuracies, sticktion, backlash and time delays. No need for a seperate guide scope and problems associated with these such as flexion and mirror flop (on SCTs - an especially important consideration for me - not aware of any but there must be a little). Rapid adjustments can go someway to correcting poor seeing.

Well that's the theory anyway. The reality is that this is a complicated little beast to get up and running. I am making slow progress. Here are the issues I have had and am still dealing with.

Marrying the camera AO unit and filter wheel - complicated series of adaptors positioned with set screws to make sure that the guide and main chip are properly aligned to avoid impingement on the main optical path. Inserting and extender for the guide camera so that the system will work with a filter wheel - SORTED

Getting the guide camera par focal with the main camera - no simple focusser here. The guide camera is attached to an adaptor tube with the prism at the end. Held in place with a couple of set screws. Focus main camera then loosen and slide the guide tube in or out a bit at a time until guide camera also focussed. Very tricky in the dark. Tried during the day and thought my guide camera had packed in. Returned it to Ian King who said it was fine so have now discoved the camara just refused to register an image if sufficiently over exposed. Tried a daytime focus and got pretty close but not close enough it suspect - WORK ONGOING

The AO mirrior will correct up to 25 pixels, beyond that the mount needs to apply a large correction to bring things back into place. This can happen with periodic error or small errors in polar alignment - 25 pixels is less than 20 arc seconds at 2000mm focal length. So the mount has to be calibrated by Maxim so that it knows which way to move it. Problem was the mount wasn't responding to the commands. Long, frustrating time getting this sorted but finally a change in ASCOM drivers and some settings in the nextar handset has done the trick - SORTED

Getting a guidestar is an absolute B. The chip is small and because it is off axis it is tricky working out where it is in relation to the main image - trick is to work out where the guider is in relationship to the main image so that a star on the main image can be moved onto the guider without totally messing up the framing. Have spent hours trying to find guide stars and have only been successful once! You can move the guider up and down to change the view but still been difficult to find anything. Think nailing the focus of the guide camera will help. Another phone call to Ian King for some tips I think - WORK ONGOING

Once you have focussed your the cameras, framed the image and found a guide star it's time to bring up the AO software. 1st the AO has to lock onto the guide star. Run an exposure - as short as possible so bin 4x4 unless you have something like arcturus! Then run the mount calibration routine keeping fingers crossed that you don't get one of the multitude of error messages - gude star faded, guide star moved out of field, camera error #04 etc. Then run the AO calibration routine. Then set tracking exposure, the aggressiveness and ignore fancy settings that I don't understand yet. Start tracking. Then set up the main image exposure in Maxim and off you go. Now the one time I got a guide star I was able to get the calibration and tracking sorted very easily so the Maxim software rocks. Ran a 5 minute exposure in the general vicinity of Vega and got slightly fluffy but round stars (the seeing was awful so not good at F10) so tracking was perfect. WORK ONGOING BUT VERY PROMISING

Ian King tells me SXV are bringing out a new guide camera in the near future with a larger chip. Can't come soon enough for me.

Anyway, I wont be copping out and reaching for my trusty guidescope just yet. I will master this thing and then it's straight onto M57 if there's a moon and M63 if not.

Sorry about the ramble, just collecting my thoughts really but hopefully this gives some insight into the pain and toil that goes into photographing little chunks of the night sky

[Kaptain Klevtsov]

Sounds facinating Martin. Keep us informed on developments.

Would it be worth using the guide 'scope as a finder for guide star candidates I wonder?

Captain Chaos

[geppetto]

Oooooooo!

That sounds interesting Martin 8)

Good luck getting it going

[themos]

This sounds like the steady-shot technology in camcorders. Can anyone confirm?

[daz]

I think I have issues getting a guide star on my web cam!!!

I'm sure you'll get it cracked Martin, and soon we'll see your name being dropped into "awesome images" conversations!!!

[Greg]

Looking forward to seeing the results...

I'm just getting a grip on stacked images

:D

[MartinB]

I'll keep you posted. Was out in the garden yesterday evening in daylight and think I've managed to get things par focal. Spoke again with Ian King who shares my pain! He suggests are start somewhere with lots of stars and confirms par focal is critical (M13 here I come). Have also now worked out where the guider is in relation to the main camera so I can look for suitable guide stars using the main camera and then move them onto the guider - might have some oddly framed images though (KK a guidescope might help but it will be easier to use the main camera I think.

I do have very high hopes, when the set up is up and running, of getting some long focal length images with very tight guiding. Targets I have in mind at the mo are the obvious ones - M57, close up M13, M63, M27 and a close up narrow band M16 (this is one I really want to get)

[FLO]

Fascinating report Martin 8)

Will watch with interest.