PLate solving with narrow band filters
PLate solving with narrow band filters
I very often find that plate solving fails using Ha, S2 or O3, approx 7nM narrowband filters. An information band comes up near the top LHS, then an announcement that plate solving has failed due to too many or too few stars. This is with an 8" Skywatcher Newtonian attached to an ZWO 2600MM camera. Take the filter off and plate solving works again. I do adjust exp time and gain for the reduced O/P from the camera. This is with a Sharpcap version a few months old.
Re: PLate solving with narrow band filters
NB imaging became easier for me after I purchased an electronic filter wheel (ZWO EFW 5-filter, but if I were to do it again I'd choose the 8-filter model.)
I stopped trying to plate solve with NB filters. So now I choose a Wideband filter (LRGB). Once centered, I switch to the NB filter and then focus.
Brian
I stopped trying to plate solve with NB filters. So now I choose a Wideband filter (LRGB). Once centered, I switch to the NB filter and then focus.
Brian
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Re: PLate solving with narrow band filters
Hi,
the first thing to check is that you can clearly see stars in the images that are being sent to the plate solving program - make sure that any display stretch is turned off too when performing this check. If you cannot see a good 20-50 stars then it is probably that they are just too faint due to the filter. You can also end up at the point where stars are so faint that the plate solving program (looking for something to work on) ends up picking up noise as stars, which gives a high star count when really there are hardly any.
If stars are clearly visible at the camera settings you are using for plate solving then feel free to post an image or two (FITS captures ideally) so that we can take a look to see if anything can be done.
Of course the idea of a filter wheel and switching over for plate solving is going to help lots!
cheers,
Robin
the first thing to check is that you can clearly see stars in the images that are being sent to the plate solving program - make sure that any display stretch is turned off too when performing this check. If you cannot see a good 20-50 stars then it is probably that they are just too faint due to the filter. You can also end up at the point where stars are so faint that the plate solving program (looking for something to work on) ends up picking up noise as stars, which gives a high star count when really there are hardly any.
If stars are clearly visible at the camera settings you are using for plate solving then feel free to post an image or two (FITS captures ideally) so that we can take a look to see if anything can be done.
Of course the idea of a filter wheel and switching over for plate solving is going to help lots!
cheers,
Robin
Re: PLate solving with narrow band filters
Robin,
I was out again tonight without a filter and my ZWO 2600MC colour camera this time and the same thing happened. Sometimes it would work sometimes not. Sometimes it says there are too many stars so I reduce the number but it's flaky and wastes a lot of time. One question. I have a 1000mm Newt and a coma corrector that extends this to about 1060mm. How precise does the f.l. have to be and how do I determine what it is to the necessary accuracy?
I do not have a filter wheel to reduce complexity and uncertainties and avoid dust bunnies. With the filter in place I can produce plenty of real stars. Which is the best plate solving charts to use? I am using Astap with 8 bit images. The plate solve test always works OK. Polar alignment was within 2 arc secs.
I was out again tonight without a filter and my ZWO 2600MC colour camera this time and the same thing happened. Sometimes it would work sometimes not. Sometimes it says there are too many stars so I reduce the number but it's flaky and wastes a lot of time. One question. I have a 1000mm Newt and a coma corrector that extends this to about 1060mm. How precise does the f.l. have to be and how do I determine what it is to the necessary accuracy?
I do not have a filter wheel to reduce complexity and uncertainties and avoid dust bunnies. With the filter in place I can produce plenty of real stars. Which is the best plate solving charts to use? I am using Astap with 8 bit images. The plate solve test always works OK. Polar alignment was within 2 arc secs.
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Re: PLate solving with narrow band filters
Hi,
the trick with the focal length if you are unsure is to tell SharpCap not to use it - then Astap will try a range of scales, which will take a bit longer, but avoids that uncertaintly. Once you get one successful solve you can work back to the focal length from the field of view (which will be in the plate solve results) and the sensor size. Try various focal lengths on https://astronomy.tools/calculators/field_of_view/ with your camera set as the camera until you get one that matches the measured field of view.
The plate solve test is not something to trust as far as the question 'is my camera set up OK?' goes. It feeds a known image from PNG file to the plate solving engine... It is there to answer the question 'is the plate solving engine installed properly with good index files'.
You might find that turning off the 8 bit option helps deal with some of the issues, but best to send a coupld of captured frames if you can so I can advise properly.
cheers,
Robin
the trick with the focal length if you are unsure is to tell SharpCap not to use it - then Astap will try a range of scales, which will take a bit longer, but avoids that uncertaintly. Once you get one successful solve you can work back to the focal length from the field of view (which will be in the plate solve results) and the sensor size. Try various focal lengths on https://astronomy.tools/calculators/field_of_view/ with your camera set as the camera until you get one that matches the measured field of view.
The plate solve test is not something to trust as far as the question 'is my camera set up OK?' goes. It feeds a known image from PNG file to the plate solving engine... It is there to answer the question 'is the plate solving engine installed properly with good index files'.
You might find that turning off the 8 bit option helps deal with some of the issues, but best to send a coupld of captured frames if you can so I can advise properly.
cheers,
Robin