From: Milton Aupperle <maupperl@shaw.ca>
Date: November 2, 2012 11:42:29 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Re: ONAG Review
Hi Tim;
The instructions for the ONAG may have been from an article that Jim Chung wrote in the RASC publication.
I'd love to see if your A02 makes any difference on Jupiter. Your best bet is to use a moon as a turbulence / guide target so that it can use a discrete object for centroid monitoring.
Darryl Robertson (Equinox and Equinox Image developer) was telling me he could get the SBIG AO7 (used a mirror) running as high as 40 fps if the guide star was bright enough. With the SBIG A08 (tilts a piece of glass) - he was saying the mechanical limits were about 15 fps now.
While watching a hockey game (WHL) a month or so back, I was looking at the "Starlight Xpress SXV AOL" (tilts a piece of glass) which states it can do a tilt increment as fast as 5 ms (i.e. 200 fps). It's RS232 based (9600 baud) so you can probably expect a 10 ms response time (likely 100 fps) theoretical maximum movement. A few people that posted frame rates for their own guiding were saying 10 to 20 fps - but they were doing DSO imaging and most of these do not have bright guide stars.
Not that I can afford a $1800 AOL - but it's interesting to look at.
One of the benefits of the ONAG would be no field rotation at all, which is crucial for exoplanets. You want the same cluster of pixels to be gathering starlight over the 2 to 6 hours your doing your run. No matter how perfectly my Polar alignment is, I still get a 1 to 2 pixels (0.83 to 1.7 arc second) drift motion per hour with guiding. I think it's due to field rotation because the OAG guide star is 20 to 25 arc minutes off axis. It would also be good for cometary / asteroids too if you want to guide off the object.
TTYL..
Milton Aupperle
On 2-Nov-12, at 8:27 PM, doobisary wrote:
Hi Milton. I haven't read the article yet, but I remember seeing an announcement of the ONAG some months back, probably also in S&T. I'll poke around, but I think I saw instructions on how to make an inexpensive version of the ONAG, obviously not as sophisticated, on Cloudynights recently.
I don't think any of the AO units available today are fast enough to account for turbulent motion of a planet. The only device like that for amateur use that I know of is the AO-2, which came out 10 or more years ago, from Stellar Products (Don Bruns). Antonio Cidadao used one for planeatary imaging several years ago. After John Sanford passed away this past spring, his son brought a truckload of his astro gear to RTMC. John had an AO-2. I bought it from his son for $100 (they were well over $1K when new). I fiddled with it some, and quickly found it wasn't sensitive enough to hold Saturn steady in an 8" telescope. I didn't try anything larger (10-12.5" scopes I have) or brighter (Jupiter, Mars) with it, and I probably should. I contacted Don Bruns via email, since I didn't have a manual with the AO-2, which is essentially mint condition. He said he no longer had any copies of the manual and that it was obsoleted by fast frame rate cameras. So, Antonio graciously pr
ovided me a scanned copy of his manual.
Now that Jupiter's getting higher in the evening sky, I should pull out the AO-2 and see how it does on the 12.5" Cave.
-Tim.
--- In Astro_IIDC@yahoogroups.com, "milton_aupperle" <maupperl@...> wrote:
Hi Folks;
If you don't have a subscription - pick up the December 2012 issue of Sky And Telescope at your local news stand.
There is a really neat review on "Innovations Foresight's " ONAG (On Axis Auto Guider" product on page 60. Not cheap at ~ $1000, but interesting.
I'd never heard of it before, but it's basically a "cold mirror" that reflects 350 to 750 nm light and passes all light above 750 nm to the guide camera. So you can guide on the same or very close to the same object your imaging with a single scope.
My Grasshopper EXHAD camera with Sony ICX285AL CCS would have about 50% sensitivity at 750nm and drops to about 5% at 1000 nm.
I also wonder if one could use that with an Adaptive Optics units, for DSO / Photometry but also for imaging planetary targets to remove turbulence.
TTYL..
Milton Aupperle