plate solving

ernie
Posts: 16
Joined: Sat May 05, 2018 6:14 am

plate solving

#1

Post by ernie »

My camera image is 140 by 250 arc minutes. Which two settings should I choose for plate solving using ansvr?

Thanks,

Ernie
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Re: plate solving

#2

Post by admin »

Hi Ernie,

unfortunately, you cannot work out the right values from just the field of view.

The 'sigma' setting has to be set by a bit of trial and error. Try plate solving and watch for the number of stars that it says are detected. If bigger than 200, increase sigma. If less than about 50, decrease it. Ideally in the 100-200 range, but 50-100 is OK if the plate solving works fine.

The focal length setting should either be set to 'do not use' or set to the focal length of your telescope (including adjustments for barlow lenses/reducers/etc).

cheers,

Robin
ernie
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Joined: Sat May 05, 2018 6:14 am

Re: plate solving

#3

Post by ernie »

Screen says solving field 1 did not solve (index index - 4214.fits, field objects 21-30. Do I increase or decrease the sigma?
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Re: plate solving

#4

Post by admin »

Hi,

sorry, really can't tell from that - that is a progress message and all I can tell is that you found at least 30 stars.

Please let the plate solving run until it finishes (red notification, rather than orange) and then share the entire SharpCap log, which will contain a lot more info that is useful to working out what is going wrong.

cheers,

Robin
ernie
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Joined: Sat May 05, 2018 6:14 am

Re: plate solving

#5

Post by ernie »

Please see the log file attached

Thanks,

Ernie
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Log_2022-01-27T22_59_33-12576.log
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ernie
Posts: 16
Joined: Sat May 05, 2018 6:14 am

Re: plate solving

#6

Post by ernie »

Here is a more complete log file. Tried many options.

Thanks,

Ernie
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Log_2022-01-27T23_46_16-9416.log
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Re: plate solving

#7

Post by admin »

Hi,

setting your sigma to about 80 gives a reasonable number of stars in those logs (but anywhere from 50 to 100 isn't bad). If you had fainter stars you would need a lower sigma though, so do be aware of that.

I can see that your focal length is set to 120mm from the log - from that SharpCap calculates a field of view to help the plate solve engine run more rapidly, but if that is an incorrect focal length then it will prevent a correct result from being found. 120mm is unusually short unless you are using a small 'mini guide scope' or a camera lens.

If you are still getting no success after setting sigma to 50-80 and checking the focal length, please post a single captured frame here (just press snapshot and share the image) so I can investigate further.

cheers,

Robin
ernie
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Joined: Sat May 05, 2018 6:14 am

Re: plate solving

#8

Post by ernie »

Yes I am using a ZWO 30F4 miniscope with a reducer to get as wide a field as possible to use as a finder. Picture attached, was too large so sent as a GIF file. The location is near Alioth in Ursa Major.

Thanks,

Ernie
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Re: plate solving

#9

Post by admin »

Hi,

I ran that file through ASTAP with no field of view restriction and the results are interesting...

Code: Select all

Field solved to RA=12:19:46,Dec=+50:26:03, field Size {Width=4.100937, Height=2.30819}
Now, based on your 290C camera with pixel size of 2.9 microns and 1920x1080 resolution, along with a 120mm focal length, you *should* be getting an FOV of ~2.7 by 1.5 degrees. SharpCap calculates 2.66x1.50, and I put the same info into https://astronomy.tools/calculators/field_of_view/ and got 2.68x1.52...

The only thing that makes any sense at all is if the focal length of your mini guidescope is about 90mm not 120mm (or if you have a focal reducer in there). I also uploaded the file to nova.astrmetry.net to get a plate solve there, but it is still queued for processing : http://nova.astrometry.net/user_images/5574032#original

So, try setting a shorter focal length and see if that helps. For me, it solves very quickly in Astrotortilla with the focal length set to 90mm to 100mm.

cheers,

Robin
ernie
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Joined: Sat May 05, 2018 6:14 am

Re: plate solving

#10

Post by ernie »

Sorry I guess I forgot to mention I am using a 50% focal reducer. Should I cut the focal length in half?

Ernie
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