Sunday, October 13, 2013

Collimation and imaging train tilt

After the CalStar desaster, I decided to try to improve focus, collimation and imaging tilt.

First, I wanted to improve collimation. In order to remove as many sources of errors as possible, I started just with eyepieces.

1. Visual
First using the 40mm eyepiece and then the 4mm, I collimated to scope as good as possible out of focus. Seeing wasn't great - when I tried to use in-focus collimation, I could hardly see any Airy disk.

2. Camera directly on scope
I removed the focal reducer, spacers, filter wheel, OAG. I couldn't get the scope to focus anymore, but that was OK. I used CCDInspector's out-of-focus collimation. I used ΞΆ Cygni - it was very high up and has no other bright stars around it. Used 30 sec exposures to minimize atmospheric and other distortions. And always waited at least 3 images with similar errors.
I started with a 16" collimation error! I turned the camera around to make sure that the error that I'm seeing is purely the scope and not the camera. Moved it slowly down to 4". Then it changed direction. And then it got funny: for the other 2 collimation screws, the star moved away from the screw when I tightened it. But for the third, it moved towards the screw when I tightened it. That certainly explains the difficulties that I had to improve collimation earlier. After I figured this out, I could bring collimation below 1" (then it changed direction from picture to picture).
Also, at this point the image had no tilt at all!

Now I could have slowly added equipment to it.

... but instead, I'd rather focus on Hyperstar imaging. I know now that the camera is completely orthogonal, so I can use it for collimation of the Hyperstar lens. So, reconfigure the entire scope (cables, secondary mirror, hyperstar lens).

Collimating the Hyperstar lens turns out to be a major pain in the ...
I have to use multi-star collimation - because of the wide field of the Hyperstar lens, I couldn't find a brigh enough start that didn't have other stars in its vicinity. Furthermore, to defocus a start enough for out-of focus collimation with CCDInspector is outside of the range of my focuser!
Because of stray light and the moon light, I have to use a shield on the scope to get correct collimation. But that means that I have to take the damn shield off whenever I need to adjust the Hyperstar lens, then put it back on.
This is the initial state:
Tilt and quite a large collimation error.

This is the final result:

Almost no collimation: good!
Almost no image tile: good!
But look at that curvature!!! I have absolutely no idea what to do about that...

Sunday, October 6, 2013

CalStar - 3rd night

After last night, I had high hopes to make good progress on imaging. First to finish imaging the Fireworks Galaxy. And then start imaging the Trifid of the North.

Setup went well. Starting taking the remaining images of the Fireworks Galaxy. Then I woke up in time to check if SGPro started imaging the Trifid. Looked good. Went to bed.

Next morning, I checked the images. Fireworks looked good. Luminance of Trifid looked good:

But the RGB all looked like this:

I guess, the battery that powered the imaging equipment and the laptop wasn't fully charged and the camera or the USB hub dropped pixels.

After something major went bad every night, I decided to call it quits and not stay for a fourth night. Also, I was really yearning for a warm bed!

Saturday, October 5, 2013

CalStar - 2nd night

I spent the day trying to figure out what is wrong with my scope:

  • I checked the flatness of the image - minimum tilt
  • Cleaned the OAG prism
  • Cleaned the corrector plate (very careful - there was a lot of sand and dust on it)
  • Took exact latitude and longitude from the GPS system
  • Checked all mechanical connections on the mount
Then at the beginning of the night, I continued to focus on improving the guiding (if I can't figure it out, I could go home).

I used AlignMaster for polar alignment again. I did 3 iterations and in the last iteration, the correction was minimal. Verified collumation - good (below 1").

Mark Scrivener and John Wainwright gave me a couple of good tips:
  1. Use the ASCOM driver for guiding - not through the RJ45 cable
  2. Disable guiding commands in PHD and just see where the guidestar moves
  3. Guide (or test) with the main camera - not the Lodestar. This rules out any issues with the OAG or such.
I calibrated PHD near the equator and ran it without guiding. It showed an almost perfect polar alignment - even after 10 minutes, the trendline looked completely horizontal. And the RA trendline went up very straight and smooth. So, the scope is fine, polar alignment is great. Repeated the same with the lodestar - same result. So, the OAG is fine too.

When I was almost ready to declare defeat, one of my neighbours came over to me and asked what was wrong. I walked him through everything. He then wanted to look at my PHD parameters. And he pointed out that my "Max Duration" was too low (I had it at 200). He recommended to set it to 800...
... and voila! Suddenly guiding errors dropped below 0.2 arsec!!! AAAAAHHHHHHH!

I then started guiding again. Watched it for a little - looked really good.

I woke up at 1am to check if SGPro started imaging the 2nd target - worked!!!

And then in the morning, I found out that at 2am guiding completely stopped!!!!!! NOOOOOOOOOO!!!

But the images from the first target were now MUCH better:
This is much better. Although for a 1x1 binned luminance subframe it's still a little blurry.

Friday, October 4, 2013

CalStar - 1st Night

I arrived at 4pm, setup my tent and my scope - all without a hitch. Yes - all ready to get going once it turned dark.

When I connected the Mach1 scope, I couldn't remember which location number was CalStar - it would be awesome if I could assign names... Next surprise: the Mach1 mount can't run off the same battery as the rest of my equipment! The motors sounded horrible and slews stopped half way there. So, I needed to use one battery for the mount. And the other battery for the rest of the equipment. Had to improvise to connect the second splitter to the second battery. And I hope I can recharge both batteries enough tomorrow.

Next, I did a rough polar alignment with the RAPAS, star sync and then wanted to do a more accurate polar alignment with PEMPro. But it complained that my camera was rotated in a bad way and that it couldn't do it. No idea where that came from.

So, I used AlignMaster instead. Not sure how exact this was as I needed exact longitude and latitude of the place.

Next, I wanted to work on collimation with CCDInspector. I could improve it, but at some point the results didn't make sense again. I think I got it somewhere below 1" - good!

And finally PHD...
... complete desaster! I have no idea what was going on with that. I could barely get the accuracy below 0.6" and very erratic. In San Jose in my backyard, I could get it below 0.4". At some point - it was almost midnight by now- I got too tired and too irritated to continue trying things out. I setup the scope to start imaging anyway. Maybe guiding would improve later that night.

I got up in the middle of the night when SGPro had to slew to the next object. And PHD could not resume - didn't find a guide start. I checked everything. Finally I took new darks for the autoguider (this time from a REALLY dark side) - and that fixed it! Guiding by now was a little better - but not by a lot.

Next morning, I checked the images - they were all very bad.
This is a 1x1 binned luminance subframe :-(

Clearly the guiding is not suitable. Need to figure out what to do about PHD. I compared my guiding graphs from last night to guiding graphs at home - they don't look that much worse. But much more erratic.

Now I had to use my solar panels for the first time. Needed to cut some cables and make some connectors and got one battery to recharge. I hope that the other (the one that powered the mount) doesn't need recharging.

Oh, and: IT WAS REALLY COLD! I do remember that I was camping once in England when it froze and snowed. But last night felt worse. I guess after 20+ years I need a new sleeping bag :-S