Question Re AO

[PRejto]

As I consider whether to venture into long FL astrophotography with an f10 12" I think I might need to consider AO as well as OAG or ONAG guiding. I understand what this does and how it works, but from a practical point of view am confused. I get that you need a fairly bright star to the guide camera which is running at a high rate, and this provides info back to the AO to make corrections to the light path. But then, how does the mount receive correction? Does the same AO unit provide output to the mount, or do you need a second guide camera driving normal guiding software to provide periodic mount corrections? I did read on the SBIG site a statement that AO can replace mount guiding entirely....is that what is normally happening or how those of you with AO are using it?

Also, is it possible to run an SBIG AO8 with the ST-i camera?

Thanks!

[RickS]

The AO does most of the work but every so often the guide star will wander too far for the AO to correct (the optical element will only tilt so far) and then the guide software should detect this and do a mount "bump". This means a short slew to get the guide star back in the right place with the AO element brought back to its central position. If you have extremely good polar alignment and a mount that tracks accurately then you might never need a bump.

[PRejto]

Thanks, Rick. So how does the AO communicate to the mount, in my case, the PMX running with TSX? When AO is running I assume guiding in TSX would not be running. Is that correct? How do mount movement commands get to the MX?

[rat156]

The AO unit in the Sbig case communicates directly to the camera, which, in turn, communicates with the software. You need to calibrate the AO unit, then the software tells the AO how far to tip/tilt, if it's too much, then the mount will need to be "bumped", TSX will take care of all of this, read the manual on AO, it's not rocket science. I've never used anyone else's AO unit, but I hear good reviews about the Orion unit, again, I think TSX can control these.

With your PMX, you should be using Directguide to make guiding corrections.

OAG is great if you have the backfocus available. I don't know about the ONAG unit, not many about.

I have had to give up on AO, as the scope doesn't have sufficient backfocus available. It's great when it's working and you can use OAG to guide in front of the filters.

Cheers
Stuart

[cfranks]

I use the SX-AO which, unfortunately, is not supported by the TSX Camera Add-on. I have to use Maxim to do the job and it works well driving my PMX. The only snag, for me, is that CCDCommander also doesn't support it so I can't fully automate my imaging process. I insert a 'Wait for 30 seconds' step in the action list, start the AO guiding then continue the automation actions. I have to do this for every image and therefore have to be up all night but I'm getting used to it and the virtually perfect tracking is very worth the effort.

[Terry B]

I use an AO8 infront of the filterwheel and my ST10XME. The ST camera has a connector attached to the DB9 output port with a socket for th eguide cable. This allows me to directly connect the ST10 to the mount with a standard guide cable.
You calibrate the AO in 2 ways separately. One is the standard way that moves the mount via guiding corrections. The second is to calibrate it using the "tip/tilt" of the AO unit.
As stated above when you guide with the AO it will preferentially just move the tip/tilt until a predetermined set point is reached. This defaults to 50% movement of the tip/tilt using CCDSoft.
When 50% is reached then the guider will "bump" the mount with the mounts motors to bring the guide star back within the 50% of the AO and then it will continue to guide with the AO.
You don't have to use a high speed with the AO.
I will often just use it like a normal guider with exposures of 1 -2 sec.
The advantage is that it is faster and probably more accurate to move a few grams of a tip/tilt mirror to guide compared to moving 20kg of scopes and camera. It also doesn't suffer from any backlash in dec like almost all mounts.
When you do have a bright guide star then use short exposures like 0.1sec but if not then it is still very useable.
Cheers

Terry

[bert]

Maybe you should try ccd autopilot. It can drive the sx ao through maxim DL. I am using Sbig ao though.

Ccdap runs unattended all night for me.

[cfranks]

I have a current copy and used to use it before I got (the simpler) CCDC, so I will give it a try again. Thanks.

Charles

[PRejto]

Thanks for all the feedback. It has helped to clarify most of my questions about AO.

I don't think it is possible, but just in case, does anybody know if I could use the ST-i together with the AO-8? Reading the literature at SBIG, I do not think so, but I have had some private messages from someone who seems to think I could. Have written to SBIG but no answer yet.

Many thanks,
Peter

[Terry B]

I think it depends if your ST8 has the ext guide port. This is a little port on the body of the camera not near the other ports.