From: Milton Aupperle <maupperl@shaw.ca>
Date: November 3, 2012 1:26:18 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Re: ONAG Review
Hi Tim;
On 3-Nov-12, at 10:16 AM, doobisary wrote:
Hi Milton:
That may be where I saw the instructions. I'll look that up, thanks!
Not a problem. Jim e-mailed me and told me he'd already built one. The missing thing on his design is the X/Y adjuster. Orion used to offer something like that (about $150 or so for guide scopes) - but here is another option.
http://www.us-astro.com/XYF.html
That would allow one to shift the guide camera around.
I posted a question on the SBIG group the other day, where I've been pondering using the AO-7 as an active secondary in one of my Newt construction projects. I would mount the AO-7 and the SBIG camera on a sled focuser, so they're fixed with respect to each other. I was thinking about using a 12.5" f/3.5 mirror I have laying around, but it had a huge secondary, so the AO-7 probably isn't big enough not to vignette. I would think this should work, so long as the cable to the camera is long enough (or I could add an extension), but I hadn't gotten any replies last time I checked.
On the C8, I had to add a bunch of extender tubes to get enough Back focus with a focal Reducer and my Celestron OAG unit.
I corresponded with Terry Platt about their AO device when it was new. I think he said it wasn't fast enough for planetary, but he might have stopped at the fact that it was for use with their OAG, so couldn't guide on the target planet. But if it can correct as fast as you suggest, and one had an ONAG device,... Hm... But it is expensive. The AO-8 is currently about $800. I missed out last year when they had them on sale for $500 over the Holidays. Keeping my fingers crossed that they might do that again this year!
With planetary, at least the brightness it should be fairly consistent as they all reflect the sun's light.
It would be interesting to use an IR Pass filter (750 nm or higher) with a monochrome camera and see what sort of exposure times one gets with it on various targets. If the frame rate was high enough directly imaging targets, then one could expect to get a similar correction rate when guiding.
But these AO units only work with these company's cameras, right?
Yes and No. All of them should work with any camera - but one has to be able to talk to the AO unit to control the tilt. So it becomes whom supports what operating systems and is "open" to third party developers.
I know that the "Xpress SXV AOL" uses a simple serial protocol (and include the commands in their manual too) to control the device. So if I had unlimited funds (I'd need to win a lottery before that happens though), I could probably write something to control it in Astro IIDC using any camera.
SBIG does have a Mac framework and driver and it may be possible to access their A07/A08 unit products via that. So that might work if one wrote for it. Darryl Robertson already has this working in Equinox Image.
I know Orion's hasn't released any information on their product on how to control it. You have to use Windows to control the AO unit.
Orion has one as well, so they must be workable with other cameras, I suppose.
Orion has discontinued their AO units. They have them on sale to clear out stock. I read mixed reviews on the Orion units - some said they work good - other people had issues.
The AO-2 is completely self-contained. It must use either a beam splitter or track the planet via reflection off a window or something. It's a nice and tidy device, though. Wish it were more sensitive. It might be fun to try it out on a bright double star, though.
I suspect they used the same guide camera CCD as they did the old ST4 - a Texas Instruments CCD. The other issue will be how fast it reads out at.
With the tiny pick off prism on the Celestron OAG (about 1 cm wide / high) on the 8" Astro Tech RC Scope, and my old Grasshopper EXHAD camera, I run can do 4 corrections per second via the ST 4 port for the HEQ5 mount with a Mag 7 guide star AND dark skies. With a bigger scope and an Xpress SXV AOL unit and the ONAG I could likely do a lot faster and wouldn't' need to wait for the mount to settle down between movements. My centroid code is all written in SSE3 / Altivec, so processing 16 bit 1384x1028 frames isn't a CPU bottleneck. The biggest limit would be the serial port - and with a bit of work, I could have Astro IIDC use the GPIO pins on the PGR cameras as a serial port, so there would be no USB limitations there either. Sending over firewire would take 0.015 ms, but the 9600 baud protocol would take 5 ms to read/write a command.
Of course, I have no idea if any of the AO units work under my normal winter conditions (-20 to -50°C) or if they even test them under those conditions.
TTYL..
Milton J. Aupperle