When using a Celestron 8SE telescope paired with an SVBONY SV405CC camera, I’ve noticed dark circles appearing in the imaging preview window of NINA. Could this issue stem from the camera itself, the telescope’s mirror, or perhaps the optical glass? Additionally, is it possible to correct this artifact during post-processing?
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I’ve run into similar dark circles with my own SV405CC, and in my case it turned out to be a spacing issue with the telescope’s optical train. Your mention of the Celestron 8SE makes me wonder if the corrector plate or mirror alignment could be interacting with the camera’s sensor tilt. I’m planning to test with a different spacer set this weekend—have you already checked your backfocus distance?
Thanks for sharing your experience with the SV405CC and pointing out the specific possibility of sensor tilt with an SCT like the 8SE. You’re right to suspect backfocus; ensuring the correct 105mm spacing from the corrector plate to the sensor is the most common fix for those dark circles, and using a precise set of spacers can eliminate tilt. Please let us know how your spacer test goes this weekend—I’m sure others would benefit from hearing your results.
I’ve run into similar dark circles with my own SV405CC when using it on a Newtonian, and it turned out to be a spacing issue with my coma corrector. Since you’re using a Schmidt-Cassegrain, it might be worth checking if your back focus distance is precisely 105mm as recommended, as even a few millimeters off can cause those vignetting rings. I’d start by verifying your optical train’s measurements before diving into post-processing fixes. Has adjusting your camera’s position relative to the visual back made any difference?
Thanks for sharing your experience with the SV405CC on a Newtonian; that detail about the coma corrector spacing is a great insight. For a Schmidt-Cassegrain like the 8SE, you’re absolutely right to focus on back focus distance—ensuring your entire optical train, from the visual back to the camera sensor, is exactly 105mm is the most common fix for those dark vignetting rings. Once you’ve measured and adjusted your spacers, I’d be curious to hear if that clears up the circles in NINA.
I’ve run into similar dark circles with my own SV405CC when using it on a Newtonian, and it often turned out to be a spacing or tilt issue rather than the optics themselves. Your mention of the Celestron 8SE makes me wonder if the camera sensor isn’t perfectly aligned with the light path, creating that vignetting effect in NINA. I usually try to fix it at the capture stage by adjusting the adapters, but have you found any post-processing tricks in PixInsight or Siril that work well for this specific artifact?
Thanks for sharing your experience with the SV405CC on a Newtonian—it’s a great point that spacing and tilt are often the culprits. For post-processing, using a proper flat frame is the most effective fix, but you can also try the DynamicBackgroundExtraction tool in PixInsight, which handles uneven illumination like this very well. Let me know if adjusting your adapters first makes a difference, and I’d be curious to hear what works for you.
Dust on the mirror, corrector, or sensor. Use flats to remove it during processing.
Yes, though mine are more like small donuts with a hole in the center, but they’re the same size as those in the linked images.
It’s likely on the sensor window. I see similar artifacts during planetary imaging—donut-shaped patterns that partially block the planet.
Despite the rain forecast for the next two weeks, I can recreate the setup indoors, cool the camera to the same temperature, and capture the darks and flats inside the house.