Slow response

Using SharpCap's Polar Alignment feature
Ray Hansen
Posts: 39
Joined: Sun Jun 11, 2017 5:54 am
Location: Scottsdale Arizona

Slow response

#1

Post by Ray Hansen »

I was using SharpCap for the first time last night. It was a nice clear night here in the desert. I was running with
my SSAG on an 80mm guidescope that connected without any problem. I centered Polaris in the guidescope and
started polar alignment. Steps 1 and 2 took about 15 minutes apiece. Step 3 took about 20 minutes and left me
on a screen that said I should just move the mount right and down 1 and 2 degrees and then rerun from step 1.
I moved the alt/az knobs a bit and restarted. After another 12 minute wait, I stopped and just did a drift align so
I could get some pictures taken.

I'll try this all again tonight, but is there anything I can do here to get results faster? Would it be possible to put at
least an indication on the field image of the direction and amplitude of the required move? Anything would be better
than leaving me to guesswork. If so, SharpCap could be a huge help for me. I'm working with an 11" EdgeHD, and on
a normal night I'm spending about two hours total doing polar alignments. I can knock it out a couple degrees just
changing filters or slewing to a different target.
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admin
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Re: Slow response

#2

Post by admin »

Hi Ray,

I think the most likely cause is that not enough stars were being detected, making the plate solving hardly work at all. There is no point waiting more than 3 or 4 frames for the plate solving to work - if it still failing after a few frames then you need to try adjusting some parameters.
Capture.PNG
Capture.PNG (41.6 KiB) Viewed 3546 times
In the image above I've highlighted the info about the number of stars, the time spent trying to plate solve the most recent frame and the solvev status of the most recent frame. Keep an eye on these. If you are not getting 15+ stars then make adjustments to try to detect more like increasing exposure, gain or using the digital gain control in the polar alignment.

If you are still having problems after making these sort of adjustments then it may be worth just adjusting the mount a bit - you could have just been unlucky and ended up pointing at a patch of sky with few stars. Finally, the ST80 is near the limit for plate solving in terms of how small an FOV you can work with (assuming a ZWO120MM sized sensor here) - some people have had more success with these scopes by using a 0.5x reducer to give a wider FOV.

cheers,

Robin
Ray Hansen
Posts: 39
Joined: Sun Jun 11, 2017 5:54 am
Location: Scottsdale Arizona

Re: Slow response

#3

Post by Ray Hansen »

Another session tonight and got duplicate results from the previous night. I always see 80-100 detected stars, but it takes 15 minutes
or more to get a solve. When it does, it reports FOV at 0.52x0.61 and after step 2, I see no visual indication of the required movements.
I thought the 80mm scope would work, but if you're saying that's likely the problem I'll change it out.

How small does the calculated error have to be before we get the yellow arrow?
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Re: Slow response

#4

Post by admin »

Well, I've had more reports of it workign with that focal length than of it not working, but it is the longest focal length (smallest FOV) at which I have heard of success.

If you have a chance before you change scopes, could you use the very latest 3.0.3971 build and snapshot a few frames during the polar align process (using the snapshot button, not screen captures)? If you could send those to me I can see if I can work out why they are being so difficult to solve and maybe improve the solving for the next version.

The arrow should show all the time when you get to stage 3 as long as the incoming frames are being plate solved correctly - and I think the fact that only 1 frame in 50 or 100 is solving is the root of all your problems, so we need to sort that out.

cheers,

Robin
Ray Hansen
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Location: Scottsdale Arizona

Re: Slow response

#5

Post by Ray Hansen »

Robin, thank you for the help. I tried to attach a snapshot (479kb) but got a file too large message.
Resaved them as jpg files (190kb), but still got the too large message.
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Re: Slow response

#6

Post by admin »

Sent you a PM regarding sending the files.

Robin
Ray Hansen
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Location: Scottsdale Arizona

Re: Slow response

#7

Post by Ray Hansen »

After looking at the snapshots, it was clear I wasn't picking up enough real stars; that a large percentage of
them were actually hot pixels. I turned on binning, increased exposure to 4s-8s, and scanned along the RA
path for areas that had noticeably larger numbers of stars. Using those areas for steps 1 and 2, I was able
to get to, and complete, the final step and get polar alignment done a couple times. I did a drift alignment
in PHD as a check and got numbers that were very close and below 1 arc/sec. I'm waiting now for a reducer
to arrive and will post back with those results. Robin, thank you so much for all your help.
Ray Hansen
Posts: 39
Joined: Sun Jun 11, 2017 5:54 am
Location: Scottsdale Arizona

Re: Slow response

#8

Post by Ray Hansen »

Seriously, the reducer just arrived a couple days ago. I tried alignment again, and I'm getting
pretty much the same results; unable to solve with Polaris centered. It seems the only way
to get this working is using a different guidescope. Those are all on backorder as well.
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Re: Slow response

#9

Post by admin »

Please send me some image captures (snapshot button in SharpCap) of the polar field and I will see if I can work out what is going wrong. Without images to work with I can't tell you for sure why the plate solve is failing.

Don't buy any more hardware just yet until I've had a chance to examine the images!

cheers,

Robin
cuivenion
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Re: Slow response

#10

Post by cuivenion »

Just a suggestion but if you're getting a lot of hot pixels have you tried using darks, if you didn't know Sharpcap has the ability to apply dark frames to the overall captures and previews.
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