Do I need to get a different guidescope?

Using SharpCap's Polar Alignment feature
Nimitz
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Do I need to get a different guidescope?

Post by Nimitz » Fri Feb 08, 2019 4:03 am

I've been trying to get PA to work with my new guide camera (ASI 120 mini) & guide scope (ZWO 60mm guide scope) but SC will not plate solve the initial image. I've played around with settings and can get 100 stars visible & using 15 but it doesn't solve. At first i thought I was too far from from polaris but its clearly visible in my PS when i do my rough PA. The trouble shooting guide says that too small fov is another cause. using astronomy tools my fov looks to be .98 x.74 degs which I'm assuming is too small?

The SV F50 50mm guidescope has a FL of 210mm which works out to a fov of 1.31 x .98 degs. Do i need to switch to this guide scope?

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Re: Do I need to get a different guidescope?

Post by admin » Fri Feb 08, 2019 8:45 pm

Hi,

That field-of-view should work, so is most likely something in the settings either for the camera or the polar alignment star detection. First of all please check out the polar alignment troubleshooting page which you can find here - https://www.sharpcap.co.uk/sharpcap/fea ... leshooting . There are lots of hints and tips on that page that may be enough to get you going. If you have still got a problem once you've tried all the suggestions there then please capture both the screenshot of the application showing the problem and a single frame of your polar view by using the snapshot button in SharpCap and share both of those images with me.

Hope this helps, Robin

Nimitz
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Re: Do I need to get a different guidescope?

Post by Nimitz » Fri Feb 08, 2019 10:23 pm

copy, hopefully i can get out again tonight. One question which may actually be the answer. Once the camera is on & it says it sees 100 stars there are red & yellow squares which appear & disappear as each frame updates but I don't actually see any stars? I have a feeling that this is not correct? Do I 'simply' have the camera out of focus?

cuivenion
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Re: Do I need to get a different guidescope?

Post by cuivenion » Fri Feb 08, 2019 11:27 pm

You need to play with the settings. Increase the minimum pixel size, the noise reduction and possibly the black level until you're capturing 20 + stars and you're getting regular plate solves. Make sure your focus is good too.

Nimitz
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Re: Do I need to get a different guidescope?

Post by Nimitz » Sat Feb 09, 2019 6:35 pm

update: after getting up and running on M45 I turned SC back on and the PA tool to see if I could see the cluster. with the ASI120 nose piece off I could see some faint blobs but could not reach focus. put the nose piece on and the attached capture files were the best i could do .... at the end of the night I was going to try and capture the SN in NGC 3524 but my camera power died and i was so annoyed at not being able to do this i completely forgot about doing a GOTO back to polaris ti see if I could focus & platesolve ..... getting old sucks.

looks like clouds. forecast looks promising for tomorrow so I may reserve that session to do PEC training on my mount, try PHD2 for teh first time as well as PA again with SharpCap.

After looking at the attached files please let me know what you suggest I do next ... thx!
Capture_00001.png
Capture_00001.png (921.5 KiB) Viewed 425 times
Capture_00001.Histogram.csv
(2.48 KiB) Downloaded 11 times
Capture_00001.CameraSettings.txt
(673 Bytes) Downloaded 12 times

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oopfan
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Re: Do I need to get a different guidescope?

Post by oopfan » Sat Feb 09, 2019 7:00 pm

The supernova is in NGC 3254 not 3524.

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Re: Do I need to get a different guidescope?

Post by oopfan » Sat Feb 09, 2019 7:18 pm

You say you could not reach focus. I am guessing you have this one:

https://astronomy-imaging-camera.com/pr ... ider-scope

It has a focal length of 280mm.

I have this:

https://www.telescope.com/Orion/Orion-M ... word=guide

It has a focal length of 162mm.

I also have an ASI120 that I use for polar alignment. I have no problems.

Last year I was using a Celestron TravelScope 70 with a focal length of 400mm. I had to use a 0.5x focal reducer in order to satisfy SC's polar alignment. You "should be" ok with 280mm.

I am more concerned with the fact that you can't achieve focus. I think you need to solve that problem first. Just my opinion.

Brian

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Re: Do I need to get a different guidescope?

Post by BlackWikkett » Sat Feb 09, 2019 8:22 pm

@Nimitz

I've used the Stellavue 50mm guide scope with the ASI120MM for over a year and your focus looks to be very close. You may want to try to reduce gain. I never used this combo to polar align (have Polemaster) with SharpCap but used it successfully for PHD2 using gain of 75 and exposure of 1.5 to 2.0 seconds. If you're having trouble with the PA follow the troubleshoot link Robin posted earlier in this thread

-Wikkett

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Re: Do I need to get a different guidescope?

Post by nexusjeep » Sat Feb 09, 2019 10:02 pm

I polar align with my main scope it is a 130/780 and works fine at the native focal length I don't actually use the guide scope other than for guiding not sure if that is an option in your case. if I stick the ASI1600 at 300 gain I can plate solve for PA in 0.5 seconds and do full plate solves in 1 sec. The 0.5 sec for PA makes it very easy to dial in as the updates are almost instant for the error other than the delay of me walking close enough to the laptop to read the display getting older sucks in some ways.

Just an edit on my old Altair guide scope I used to have to use an extension on the focuser as I had similar issues with not enough back focus on the guide scope focuser travel. Perhaps try focusing on a distant object in the day to see how good a focus you can get on an object in daylight. On the new 60mm Altair guide scope I do not have the same issue but still use a small 60mm bahtinov mask to focus it if you have access to one or make one you could also use this to test if you are achieving focus as you will be able to tell from the position of the centre line.

Cheers
Nick

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Re: Do I need to get a different guidescope?

Post by admin » Sun Feb 10, 2019 8:48 pm

Hi,

So the image you post above (which seems to come from a declination of about 24 N.) has some stars that are so large that they are not picked up by the polar alignment star detection because of their size. This might be confusing the algorithms because they tend to work on the brighter stars in the image and the brighter stars would be not detected in your image because of their size. So I would suggest when you retry the polar alignment to make sure that the star detection boxes are appearing around all of the brighter stars in the image and if they're not then try turning down the brightness or gain until they do and see if that helps.

In any event if you still get trouble with the polar alignment not solving at the next attempt then please capture an image of the polar area and share that and that will give me a lot more to be able to work on.

Cheers, Robin

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