Wednesday, September 24, 2014

PHD Version 2 review and the Little Dumbbell (Messier 76)

It's another time out for the Bright Nebula list this week. There was some discussion about polar alignment methods in our club's forum, which reminded me about the new PA wizard in PHD 2. Which reminded me that I hadn't upgraded from version 1 yet.

A few clicks later the upgrade was finished. The first time you start PHD 2 it will ask you to set up your default autoguiding configuration. You can create a number of configurations to invoke upon later runs, which can save some time. You'll need to know the name of the autoguiding camera you'll be using, the focal length of your guide telescope, and the way you'll be communicating with your mount. That last one is a little tricky. I tried ASCOM, assuming that because I connect the guider to my CGEM through the aux port. It turns out the correct option is "On Camera." My camera is an Orion StarShoot Autoguider, and the mini autguider telescope has a focal length of 162mm--A thank you to Orion for listing this in the product specs.

In point of fact, saving your time is what version 2 seems to be all about. When you start it, it will assume you're using your default configuration. You can do the camera and mount connection with one click or do them separately. (I experience some problems with the all at once connection, but I think this was a problem with the actual physical connection, not PHD.)

What follows is base on one experience using PHD 2. I'll be using it this weekend (fingers crossed for clear skies) and will update this with corrections if any emerge.

Start it scanning, stop it, select a candidate star, and you see the first surprise. The familiar green square is much smaller. I don't know if that's because of my short FL min guider, or is the case for all hardware.

As you did with PHD 1, you next click the little PHD icon and it begins calibration. Now the really nice surprise hits you... PHD 2 is fast! I didn't time it, but it takes probably 1/3 to 1/4 of the time the older version did. You'll be rolling in almost no time, so don't wander off for a sip of coffee or hot chocolate.

The gain control is more important now. If you switch exposure time the display may wash out in a way that might remind you of what version 1 did when it lost hardware connection. If this happens, adjusting the gain setting may restore the display.

And now the Polar Alignment Wizard. It's basically a camera-assisted drift alignment, which means the quality it provides depends to some extent on your patience. Here's how you use it:

  1. Find a star at south azimuth that's near the celestial equator
  2. Calibrate PHD using it. Center the star in your field of view and resume tracking it.
  3. Start the wizard and allow it to watch the star drift (basically it will begin tracking with declination corrections disabled, and then watch the star drift in declination). It will try to estimate the rate and direction of dec drift. This estimate will bounce around for a while, but eventually it will steady itself--the greater your patience, the better your handle will be on the drift rate. 
  4. Shift to Adjust mode, in which you change the azimuth of your mount. PHD gives you an estimate of how far you should move the mount, which is nice. I would suggest not moving it the full distance PHD suggests (indicated by a magenta circle).
  5. Jump back to Drift mode (PHD will automatically reacquire your guide star!) and see if your correction was adequate. Chances are you'll have to iterate in order to get the right adjustment.

At this point you repeat the entire process for a star near the eastern horizon (adjusting the mount's altitude in this case). The instructions don't suggest recalibrating for the new orientation.

Chances are that at this point your alignment is good enough for long exposure photography. If you want it even better, repeat the azimuth process. If you have absolutely nothing else to do, iterate the night away until your PA alignment is almost perfect.

If there's a trick to this, it's the same one that causes confusion for the drift mode: The direction to adjust the azimuth and altitude for a northward or southward dec drift. PHD lets you enter notes to remind yourself of how this is done for your mount. If you've done drift before, a northward dec drift reported by PHD, indicated by an upward sloped red trend line, is handled the same way as a northward visual drift.

What PHD 2 PA offers is freedom from needing a reticle eyepiece; freedom from trying to establish the direction of dec drift, and a sort of entertainment factor as the program display shows the trend line being updated and the magenta adjustment circle resize.

One other feature that I think is a wonderful improvement is the ability to have PHD put the calibration start back where it was in your field of view before you started calibration. PHD 1 could often leave an offset. Usually this is so small that it's unimportant, but for long focal length imaging--like solar system imaging it can be a bother). I haven't tried this out yet, but when we get some planets back I will.

The image from two nights ago was M 76. Here is an improved version of what I posted on AstroBin:

Messier 76
This is a Ha/OIII bicolor image using almost six hours of data. The center is burned out, but because this is narrowband it's not actually saturated in the light frames. I'll try doing a reprocess to generate a less stretched version to act as a second input to Photoshop's High Dynamic Range merge tool.

Coming up on Friday, it's the fall Mini Messier Marathon. The current forecast is for clear skies! I hope to get some imaging done while others are hunting down Ms.

No comments:

Post a Comment