Off Axis guider focusing

[JeffBevan]

Can I get some hints or tricks for setting up my off Axis guider ie. focusing the guide camera vs. the imaging camera? I'm using the Orion thin off axis guider unit and their Autoguider Pro camera.

[yobbo89]

Phd star profile fwhm, run auto focus or use bahitnov mask for the main camera., does your aog have a helix focuser?

[UlteriorModem]

Start with the basic mechanics. You will need to know the backfocus of your imaging and guide camera.

I start by making a sketch of things.

20171213_202910 by Tom Whit, on Flickr

Arranged things so that the length of the path to the imaging sensor of the guide camera and the imaging camera are about the same. Some spacers may be required.

Once that is determined focus with the imaging camera as best you can. Once that point is found then start moving the guide camera by whatever method in or out without changing the main focuser position until the guide camera is also in focus.

It can be a bit fiddly as every time you move the guide camera you will loose 'lock' on the star, or it may even move out of the frame entirely requiring you to move the mount a little to get a star in the frame of the guide camera.

Once it's set lock it down and you should not have to fuss with it anymore.

One more annoying thing that can happen is that some guide cameras will only show a wall of noise until it is close to focus and suddenly the star with a dark background will pop into view. This is why you strive to get the mechanical distances the same at the start.

Work slowly and carefully it's not as hard as it might seem.

[Star Dad]

I can tell you that I thought I had focus on my guide camera. But it wasn't until I ended up accidentally in a group of APers that it became very obvious that I was. The Orion TOAG comes with a variety of spacers. I have ASI cameras and I know that I used two different spacers. I hadn't realized that the guide camera needed a separate/different spacer. Suddenly my guiding stars went from 8 or 9 strength to 60+. We'll need more details on the cameras to be any more accurate, but I suspect you should have the spacers already.

[UlteriorModem]

His sig states he has a Star Shoot Autoguider pro. It looks like a decent guide camera. Better than the Star shoot at least.

But I went and looked at Orions spec page for that camera and I could not find where it mentions the cameras back focus!

So I had to dredge up the manual which lists it at 10.4 mm

[sdbodin]

What all have said is good. But sometimes there is no star in the tiny FOV of the autoguider. So, when fiddling with my setup, I center of a big star cluster, chances are you will have a star in the autoguider window. M44 and M35 both come to mind this time of year.

Good luck,
Steve

[Star Dad]

So far, my experience has shown that there is always at least one star. Sometimes, though I have to use PHD2's auto select guide star in order to find one. And then sometimes I have to take longer exposures. I try to maintain 1.5-2 seconds, but because of LP or whatever I've been forced to 3 seconds, though that is stretching updates pretty thin. Worst case, of course, is just let the mount do it's thing unguided and be prepared to throw out some portion of images (in my case roughly 5-10%).

[DEnc]

I try to maintain 1.5-2 seconds, but because of LP or whatever I've been forced to 3 seconds, though that is stretching updates pretty thin.

Exposures of three seconds aren't necessarily bad. Adjustments will be less frequent, but you may be chasing the "seeing" with shorter exposures. From the PHD2 manual describing exposure time and star selection:--

As the exposure time is increased up through 2-4 seconds, the effects of seeing are smoothed out. The camera is essentially averaging out the larger, high-frequency seeing movements, so the guide algorithms have less difficulty distinguishing "seeing jitter" from actual guide star displacements that need to be corrected. This is particularly noticeable if you are guiding with a long focal length setup. Of course, the convenience of using longer exposures must be traded off against the need for the mount to get frequent corrections.

[UlteriorModem]

3 seconds is not long at all.

One thing that may help you if your camera supports it is to tryin binning. That will increase the 'sensitivity'.

Also there is a slider bar in phd to change the brightness of the display. It has no impact on the program and or guiding whatsoever other than making the display easier to see.