Re: RAPAS on Mach2
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Just want to throw this trick into the mix. I've posted this before in more detail, but I'll keep it very simple. If you don't want to use a polar scope:
After basic polar alignment (any basic method that gets you close) I send the scope to a star at or very near the zenith and take an image. It won't be in the center, but hopefully somewhere in the frame. I put the exposure on "continuous" and center the star, followed by a recal. This is my overhead reference star for the next step.
Step 2, I slew to a star in the south near the meridian line and on the same side of the meridian. I then use the Azimuth adjuster to bring that star to the centerline in the RA direction. Dec may have an error, but ignore that. That's it, you're done with the Azimuth axis. Takes about 2 minutes.
Now all you have left is the Altitude axis. That adjustment can be done by doing a meridian delay and slewing to that same star in the south on the opposite side. Now bring the star 1/2 way to the centerline using the altitude axis. RA may have an error but ignore that. That's it, you are polar aligned. Takes maybe another 2 - 3 minutes.
I might then watch the overhead star drift and maybe tweak the alignment, usually requires very tiny amount of adjustment if any. Usually good enough for 5 minute exposures with an 800mm focal length.
From: W Hilmo <y.groups@...>
To: main <email@example.com>
Sent: Thu, Apr 16, 2020 4:25 pm
Subject: Re: [ap-gto] RAPAS on Mach2
“Hi Wade, peace.. just trying to understand.”
No problem. Likewise, I’m just trying to offer some suggestions.
I tend to be overly verbose when I write, which probably overcomplicates things. It probably wasn’t clear, but I’ve ever even used an eyepiece with my two main imaging scopes. Everything that I’ve suggested is intended to be “imaging rig friendly” and fairly simple to do.
Regarding your previous attempts to image unguided, what kind of scope are you using? I do most of my imaging with an EdgeHD 8, and I simply cannot do unguided imaging with it with any kind of regularity. The issue is that the primary mirror just has too much movement, even with the focus clutches locked. There is obvious star trailing after 3 minutes, and 5 minute subs are completely unusable to me. I have to use an OAG. An APPM model doesn’t really help a lot with this because the mirror movement seems to be non-repeatable.
When you do an APPM run, how much of the time is spent waiting for the image to download? I was using a CMOS camera with USB 3 downloads for a while, and it would download a 1x1 frame in just a couple of seconds. My current camera is a CCD with USB 2, and it takes a *long* time to download a 1x1 frame. To mitigate this, I do 5 second exposures with 2x2 binning whenever I plate solve (either inside of SGP or with APPM). That speeds things up considerably. I spend less than an hour to get 100-150 points. I suspect that your DSLR can probably download a lower resolution as well. The last time that I binned a DSLR was many years ago with a Canon 20D, and it lost the Bayer matrix information when binned 2x2, but that was no big deal for plate solving.
My personal opinion that is unguided imaging is not something that interests me much. It takes me about an hour to really dial in a new guider (what with focusing through my OAG and such), but once I’ve done that, it’s all automatic. Since I always set up with the camera, OAG and guider at the same orientation, I don’t even need to recalibrate the guide software after setting up.
From: firstname.lastname@example.org <email@example.com> On Behalf Of Terri Zittritsch
Sent: Thursday, April 16, 2020 1:57 PM
Subject: Re: [ap-gto] RAPAS on Mach2
Hi Wade, peace.. just trying to understand. Like I said in my original post, it may be that I'm just seeking something that isn't really practical or possible. I have a full guiding setup, but when I get these posts using encoder mounts or my mount, showing incredibly flat controlled tracking, I'm trying to see if I can achieve this as well.
I see the same things in forums, on claims of incredibly precise polar alignment, and as I said in the previous post, I don't know how they can make such claims. I spent an hour one night polar drift alignment and had better alignment than usual, but it took an hour, and it still wasn't good enough for very long subs. Long subs for me, with a CMOS camera, are still under 10 minutes or less. I've done 20 minutes, but it's unusual. Most of my subs are 1 minute (luminosity). Although, having purchased some chroma 3nm filters, those seem to take some really long exposures to get a good amount of signal!
I measure drift in PHD2, using their drift alignment tool.. which takes forever to settle.. so it's a long process (for me). Usually when I'm doing polar alignment, I'm set up with camera, filter wheel, etc.. and want to do something that doesn't require me to take it apart and put in an eyepiece. And PHD2 also gives me an estimate of my polar alignment error, which is based on drift, not instantaneous bouncing around the mean which I understand is all atmosphere.
I've only done one model, a 35 point small model, and I think it took around 25 minutes (it's been a while since clear skies). And most of the plate solves were pretty fast. I noticed the meridian points, solved twice, and most others once, so it does more than 35 solves for 35 points. I use SGPro, which seems a bit slow to download files from my camera, which may make it slower than others. The results of the 35 point model did not allow 1 minute subs, and I had unacceptably elongated stars. But that's one data point, and there is a lot to learn.