MAXIM DL guide star selection

[multiweb (Marc)]

Well thanks for all the tips and links guys. Got some pics on Sunday night and it all worked really good. Still not 100% sure what I did different from the night before but all the bits worked together. Just need to do some more reading now about the fine tweakiong and calibration grous in MAXIM as well. Not too clear on how this works. But I got some 5min cool subs in Ha. Just before the clouds and the moon. Thanks again. Will post a pic of the rig (frankenstein noodle monster) and the test results here.

[multiweb (Marc)]

Here's the bag of noodles as promised. Highly portable.

[naskies (Dave)]

Good stuff, Marc. What is your "AO 5V" for (the Jaycar transformer)?

I've started controlling my rig remotely recently too, and bundled up all the various cables running to the scope/cameras into one big cable. The one big cable is then firmly attached to the mount at such a point that I can slew anywhere in the sky and know that it won't snag on anything.

A little bit of peace of mind for when I'm remote controlling the mount and can't see what it's doing. (Though I have plans to set up an IR webcam to solve that too.)

[multiweb (Marc)]

Originally Posted by naskies

Good stuff, Marc. What is your "AO 5V" for (the Jaycar transformer)?

My AO is one of the first one that came out. There wasn't enough power through a laptop USB port so I have this box that I feed 5V to into the serial cable. Actually now I go through the hitecastro I might not need it anymore. Maybe there's enough voltage as it's a powered hub.

Originally Posted by naskies

I've started controlling my rig remotely recently too, and bundled up all the various cables running to the scope/cameras into one big cable. The one big cable is then firmly attached to the mount at such a point that I can slew anywhere in the sky and know that it won't snag on anything.

A little bit of peace of mind for when I'm remote controlling the mount and can't see what it's doing. (Though I have plans to set up an IR webcam to solve that too.)

I used to tie things up but I use so many different configurations everytime I do something it wasn't practical anymore. Maybe one day if I have a permanent set up. Not for a long while though.

[naskies (Dave)]

Originally Posted by multiweb

My AO is one of the first one that came out. There wasn't enough power through a laptop USB port so I have this box that I feed 5V to into the serial cable. Actually now I go through the hitecastro I might not need it anymore. Maybe there's enough voltage as it's a powered hub.

Aah, gotcha.

I used to tie things up but I use so many different configurations everytime I do something it wasn't practical anymore. Maybe one day if I have a permanent set up. Not for a long while though.

Very good point! I've started to settle on a single configuration to streamline things because it was taking me too long to re-configure for each set up.

[naskies (Dave)]

In case anyone else is interested... here's a typical example of what my SX AO + Lodestar can do. The image is an 800% centre crop (i.e. 8 pixels here represents 1 pixel in the original image) from an unprocessed sub with only screen stretching applied.

The original image scale is 0.68''/pixel from a 30 minute Luminance sub, at 1625 mm focal length (GSO RC8) and 5.4 um pixels (SBIG STF-8300M), mounted on a black Skywatcher EQ6PRO. The big square blocks are warm pixels due to the dark current.

The uncorrected periodic error on that mount is about 40-45'', with a maximum error rate of 6.5'' in 1 second - i.e. the guide star dances around the screen between each exposure. I was getting eggy stars in *every* long exposure using standard guiding (anywhere from 0.2 - 3 sec guide exposures), hence the addition of the AO unit.

I usually run the AO unit with 0.1 sec exposures from the Lodestar at 2x2 binning, which results in an overall tracking and correction rate of about 6.5 Hz.

As you can see, the result gives me nice round stars even when heavily oversampling. It's also resistant to minor perturbations like small gusts of wind, vibration in the ground, etc.

It's very impressive tracking performance - akin to what you'd expect from a premium mount that costs 5x the price, for "only" 2x the price of the EQ6. The downside is that AO requires a bright guide star to be in the field of view, and it obviously doesn't help with pointing accuracy, backlash, reliable meridian flips, etc that you'd expect from a high end mount.