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My mate Richard has a New Takahashi E180 ED and is having a few issues intermittently when imaging. I was wondering if any other users of the telescope have experienced any similar problems and know the cause or fix. Looking at it I tend to think it could be the result of internal reflections from nearby light pollution/ sources as the scope is quite fast. Anyone have any other ideas? Camera, ZWO asi 6200mc pro. Regards Greg    |
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That seems like a calibration issue with the flats, though the attached flat looks fine. I’d need to know more about the preprocessing parameters. It appears the vignetting isn’t being corrected properly. I aim for 40–50% of my camera’s maximum ADU for flats, which is about 28,000–33,000. For reference I have the Takahashi-180ed paired with a QHY 367c.
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Thanks David, I will pass it on to Richard and get home to redo the flats. regards Greg |
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I have had a similar problem. The cause was in the calibration of the flat. The actual gain and offset values taken were different from the flat gain and offset values. I don't know if this is the same cause this time, but please check it out. |
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Thanks , will do
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Hi, Yes, it really looks like a flat issue. Cheers JF |
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Hi Greg, I used a TAK Epsilon-180ED since 3 years with a QHY268 mono Camera in APS-C . In the beginning I have the same problem which you described. On calibrated lights and after removing the stars with starnet++ there remains some bigger spots ond the picture where night sky must be.... So I take my canon 6da and get at the end also after calibration process lights which shows these spots... After a longer testing and thinking about this problem I found the solution for that problem. There are a few points to which you pay attention when used this fast f:2.8 telescope... My location has a bortle 3 nightsky... 1. The spiders of the secondary mirror holder are very thick. So little light pollution from the surrounding (perhaps streetlamps, etc) can reach the sides of this spiders...to avoid this I came to the solution with an dew shild with two light baffle rings in it...the length of the dew shield is around 40 cm....and this works fine against light pollution from the side.... 2. I used for my exposure sequences the NINA Software...(gain 56, offset 25)...here I made at first flats with the built in flatgenerator and a led panel...because the Epsilon was so fast the flats were not good (to bright with and an ADU > 37000)...so I switched to Skyflats and this flats worked perfect. The Skyflats must be made with the attached dew shield.... The Skyflats are perfect between an ADU from 28000 to 36000 (16 bit resolution of my QHY268m). In 2x2 binning mode for my RGBs I used an ADU from 13000 to 19000.. That works fine, but a litte small problem remains.... 3. An additional problem can be the openening of the camera connection to the Espilon...the Epsilon and his corrector has an open wide threading of M56... On my QHY268m first I used a connection of M48...this gives a little amount of vignetting...so I switched on the M54 threading of the QHY268m and this problem was solved You used a fullformat color camera. So I would recommended darkflats to get ab better color corection. I hope that these points can help you to solve the problem. Best regards Peter My astronomy homepage |
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Thank you so much for this information Peter. I will get Richard to pay attention to the flats exposures and dew shield baffles and check the connection thread size. will try the dark flats as well. Regards Greg |
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Hello Greg. I had similar issues with my Ascar 150 HNT and the primary causes was that the flat pannel I used had different intensities on the R an G channel compared to the B channel. (there was almost no signal on the blue channel). I switched to sky flats to solve. regards |
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Outside what was mentioned above—flats taken at a reasonable exposure and properly calibrated—also look for light leaks. Any light leak in the accessories is a potential source of this problem. And you can also end up with light leak issues at the focuser if exposed to significant light contamination at a problematic angle (which can include light spill-over from a flats panel). |
