Getting plate solve to work with ASTAP and iPolar

[bokemon]

Hello,
I am trying to get an iOptron iPolar camera to plate solve. The default ipolar software can plate solve just fine near the pole with only .25 s exposure. But when I use sharpcap I can only get 0.5 s max exposure (same with iPolar software). This is not near the pole, but then astap only "finds" 8 stars and fails. astronomy.net can plate solve this ok. I used a dark file, so that should help. Aside from trying other plate solvers, what can I do here to give ASTAP the best chance to solve, e.g. command line parameters. Can sharpcap stack and then send the image to the platesolver, to get around the 0.5s exposure limitation?
I submitted a png file of a "capture" under sharp cap. It looks really dark, but if you stretch it you can see more than 8 stars. (Lemme know if the dark file applied correctly, since there still seems to be some patterned noise)
Also, here is a link for when i uploaded this file to astronomy.net
https://nova.astrometry.net/user_images ... #annotated

[admin]

Hi,

it's a long time since I used an iPolar - I do recall the limitation to 0.5s exposure, but what I can't remember is if you have a gain control to adjust. If you do, try turning that up to increase the brightness of the image further, which will possibly help Astap find more stars.

From the SharpCap side, you could try using live stacking to stack multiple frames from the iPolar, then choose 'Deep Sky Image Annotation' and use the plate solve button in the annotation window. It's important to use that button because it will ensure that SharpCap tries to plate solve the stacked image rather than the individual frames.

From the Astap side, there are some options to do with the plate solving - run Astap manually, press 'Stack', go to the Alignment tab and look at the 'Solver' section. You can also play about inside Astap trying to solve your captured image with different settings without needing to get back out under clear skies.

On the whole though, the limitation of 0.5s on the iPolar might be a real blocker here - I would normally recommend using 2-4s exposures and a fairly high gain for polar alignment and/or plate solving.

cheers,

Robin

[bokemon]

Hello again,
I think just raising the gain did the trick and now I have many more stars. However, ASTAP still doesn't solve, and I guess the problem is maybe sharpcap isn't sending it the right parameters?
Does it send the mount coordinates? (assuming the mount is mostly aligned)
When I start the plate solve, I see in the mini yellow astap window that it's choosing a FOV of about 1 deg, instead of some number near 10 deg. I have only the V17 (wider field) database installed.
I hope sharpcap invokes ASTAP with it's own parameters because I have tweaked a few ASTAP parameters around trying to get it to manually plate solve. (which failed also)
Am I missing any Sharpcap settings for iPolar? All I did was set focal length to 25mm, but there didn't seem to be any setting telling the sensor size, which is needed to know the FOV.

Anyway, here is the image capture. Can you please see if Sharpcap + astap can solve this?
https://nova.astrometry.net/user_images ... #annotated

[admin]

Hi,

I'm afraid that I can't get that image to solve correctly with Astap at all (loading it into the main Astap program and playing around with all the plate solving settings still seems to get me nowhere).

SharpCap will pass the current known co-ordinates as a search start point when using plate solving and an ASCOM mount is connected. It will also pass along the field-of-view if that is known, otherwise it will tell the plate solving engine to try all different fields of view. In your case, because the iPolar is a webcam, the field of view will be unknown (SharpCap does not know the pixel size, so cannot work out the FOV even if the focal length is known).

I suspect that there are two issues at work here that are causing problems

1) The stars are still poorly defined (except for the single bright one) - the fainter stars are there, but there is lots of noise that is not much dimmer, meaning that detection of the fainter stars is hard.

2) There may be distortion of the view due to the short focal length (wide angle) lens used by the iPolar.

You can try for better stars by using SharpCap live stacking - stack maybe 100 to 200 frames and save (as 16 bit FITS) from the live stacking save button. Then you can try loading that into Astap to see if it will solve that - hopefully with some stacking the stars will be easier to detect. If that still fails, but with good looking stars in the stacked image, it might be worth posting on the Astap forum to see if the author can work out if distortion is the issue.

cheers,

Robin

PS. Do make sure you have the very latest Astap installed - it gets updates and bug fixes quite frequently.

[bokemon]

Thanks for continuing to work with me on this. I will try out the live stacking next.
I know what the sensor size of the iPolar is from the instruction manual. Is there a way to either "tell" sharpcap, or "tell" ASTAP the FOV?

As a backup, I got All Sky Plate Solver to work, so that's good. Would you have a suggestion which of the astronomy.net-based plate solvers is the fastest?

Edit:
got to try live stacking.
https://nova.astrometry.net/user_images ... #annotated
I used the deep sky annotation sub-program.
Realized that I should probably take flat frames?
astap still fails. does it need stars to be saturated?
somehow asps doesn't seem to get invoked?
If I plate solve in the deep sky annotation sub-program, how do I sync mount?

[admin]

Hi,

looking at the latest image, there is just so much noise in the background that I am not surprised that it is difficult to plate solve. In fact I *am* surprised that anything manages it! I don't really understand the cause of the noise - very odd... It's also odd that the downloaded FITS file will not load into FITSLiberator, but GIMP manages to load it.

Anyway, back to the plate solving applications - all of the astrometry.net plate solving engines are basically the same code behind the scenes (AstroTortilla, ASPS, Ansvr). What distinguishes between them is the installers that they provide (some are more reliable than others) and the user interface (but SharpCap bypasses this anyway and uses the engine directly). If you have one working, no point in changing to another.

Syncing the mount only occurs when you use the 'GPS' button in the mount controls to do the plate solving. If you use deep sky annotation then the plate solve information is used for information only (if the mount co-ordinates are out compared the the plate solve ones then SharpCap remembers the offset and uses it to make sure the anotations go in the right place).

I suspect that if you can get a clean, non-noisy image from the iPolar then we would have more luck, but I don't know what the right approach for that is. You shouldn't need to worry about flats - plate solving programs will not worry too much about the dark corners.

Finally there is no current way to tell SharpCap the pixel size manually - that information currently only comes from the camera driver itself.

cheers,

Robin

[bokemon]

It looks like the astronomy website modified the fits file because that came directly from sharpcap. And also their displayed image is stretched way too much. The image doesn't look all that bad. One corner is dark due to telescope blocking the view. The streaks and speckle noise is probably due to individual pixel sensitivity (?) which presumably flats will fix.
Do you know why some stars have a dark ring around them?
Does astap require the stars to be saturated as in a long exposure? (Because the live stack does not saturate them)

Screenshot 2023-01-18 111201.jpg (251.28 KiB) Viewed 7488 times

[admin]

Hi,

to me, the stars with dark rings around them look to be single bright pixels, so probably they are hot pixels from the camera rather than actual stars. I suspect the dark ring is a result of image compression happening somewhere along the way (either in the transmission from the camera to the computer or in saving as a JPG file).

I think getting rid of the background 'glow' might help with plate solving at least a bit. You could try dark frames or SharpCap's background subtraction feature.

cheers,

Robin