…If the celestial pole is visible.
I’m late to the game on this, but I also think this tool has flown under the radar a bit. PHD2 added a Polar Drift Alignment tool in version 2.6.5, and it works great. SharpCap users might find the PHD2 tool similar to it’s polar alignment tool. I would even recommend Sharpcap users give this one a try. It is free after all.
Since using the Polar Drift Alignment tool in PHD2, the overall time for my alignment procedure has increased, but the accuracy has also increased so dramatically that my elderly mount is performing like a teenager. In the course of an evening, I save time, and I’m able to sleep. The reason for the increased time during the alignment procedure is actually a hands-off part where I’m just waiting for the alignment line to calm down. I usually walk away for a few minutes and come back. After the initial polar drift, I check and further adjust using the standard drift alignment tool. Overall, I’m all set within 10-15 minutes of plopping down the mount, and less than five minutes if I’ve left the mount in the yard from the night before.
I know the methodology is taken from Sharpcap, but I’m excited that it’s now built into a tool I already use (and it’s free). Note that it does take time, 10-15 minutes, but the increased accuracy will give you better results and save time in the end. Here are some quick and dirty instructions (Screenshots will be added when I get out):
- Roughly polar align. The closer you are, the more time you’ll save
- Turn on your mount and keep the guide scope pointing at the celestial pole (set the mount to the zero position).
- Fire up PHD2, connect your camera and mount and start looping images
- Click Tools-> Polar Drift Alignment
- Pick a star near the middle of your field of view and click the Start button. Let it go for a few minutes. The line will bounce all over for a while then seem to settle down. You really need to wait until it stops moving, and not jump ahead because it almost stopped.
- If you can see the circle at the end of the line, use the manual Alt and AZ adjustments on your mount to move your selected star onto that circle.
- If you can’t see the circle and the line goes all the way off the screen, move the star along the line to the edge of the screen. Select a new star close to the middle and repeat until you can move the star inside the circle.
- Click Start again to verify your alignment, and Close when you’re done. You’re done when the red circle comes to rest inside the green box.
This is where I go to the old drift alignment tool and try to get my total RMS under .5″. Anything under 1 will work for my field of view, but I like to have the wiggle room if needed. After some more time with the tool, I’m regularly under .3″ total RMS.
The increased alignment accuracy allows me to set an imaging plan and catch some sleep while imaging. For instance – in mid July, I followed this schedule.
- 9:45PM-11:00PM – Image M16 until it runs into trees.
- 11:00PM-1:00AM – Move over to M51 and set an imaging plan for it’s time between trees and doze off.
- 1:00AM-3:30AM – Move to the Wizard Nebula, start imaging, go back to sleep. Select the option in BYE to park the scope after imaging in case I miss the alarm.
- 3:30AM-5:30AM – Put the cap on the scope, set imaging plan for darks and go back to sleep.
- 5:30AM – Wake up at my usual time, take flats, break down equipment.
Because I have confidence in the mount’s performance I can get about 4-5 hours of sleep during a session where I would have previously either slept for 2 hours at the most, or just packed it in early so I could get some sleep. It’s also helpful to understand the sky to plan this out. I’m still getting familiar with the Summer positions for everything.
Combining the Polar Drift Alignment and the regular Drift Alignment procedure gets me more accurately aligned than I’ve ever been. And that’s crucial when using a 14 year old mount that was never intended for long exposure astrophotography. Last night, out of 78 exposures, I lost two. One to an airplane and one to a meteor. ZERO to tracking errors. Most of those exposures were 240 or 300 seconds. That’s unheard of for an LXD75 mount, but this has been typical since using both alignment methods. I moved over to Ha later in the month and start 420″ and 480″ exposures with a success rate over 90%.
If you’re having a hard time getting you drift alignment routine just right, or you’re using an old mount, or you just want to see it work, I strongly recommend using PHD2’s Polar Drift Alignment tool to get yourself as closely aligned as possible.
Clear Skies, Bleary Eyes – KA