• Cameras

  • ASI294MC Pro - strange artifacts on image

Does anyone know what might be causing these artifacts?
The attached image of Betelgeuse was taken on my ASI294MC Pro in dark skys, high in the sky, 30 sec exp., unity gain. I've had the camera for a couple of years and don't recall this happening on bright stars before. The camera sensor looks pristine (I've never opened the inside of the camera). When I rotate the camera on the telescope, the stars rotate around the field, but the artifacts stay in the same place, seeming to indicate the camera is the source of the artifacts. Any ideas would be appreciated.
Thanks,
Jim

    That looks like a ghost caused by Betelgeuse, try to take a frame of a dimmer image, does it disappear?

      jc010 It is caused by the reflection inside the imaging train, the halos will appear around the bright stars. Usually, adding an IR cut may reduce the reflection.

        @Tech@ZWO#60316 To be clear, I am referring to the 8 point "star" pattern, not the internal reflection from the lens elements.
        Thanks,
        Jim

        chaosnix68 It lessens with dimmer stars, but does not disappear.
        Thanks,
        Jim

          Hi, i have the same problem and the same pattern on extra bright stars (without filters)

            Marco_B What camera do you have this problem with? Is it there when you use a filter?

                @Tech@ZWO#60316 The 8 point pattern is always in the same rotational position, that is, squared with the sensor, even when I rotate the telescope. This points to the sensor as the source of the pattern. My question is, is there a problem with the camera, or is this normal for very bright objects?
                Thanks,
                Jim

                jc010 294MC Pro. Telescope is a reflector, hence the diffraction spikes.

                This is the only image I've got like this.

                    franco This is the only image I've got like this.

                    Now I've looked more closely and I can see the same pattern on other images with bright stars.

                        franco Thanks for the reply Franco. The pattern looks the same as what I am getting. Maybe this is inherent to this type of camera. That is the question I would like answered by a ZWO tech. BTW my scope is a refractor.
                        Jim

                          @Tech@ZWO#60316 The 8 point pattern is always in the same rotational position, that is, squared with the sensor, even when I rotate the telescope. This points to the sensor as the source of the pattern. My question is, is there a problem with the camera, or is this normal for very bright objects?
                          Thanks,
                          Jim

                          • w7ay replied to this.

                            jc010 The 8 point pattern is always in the same rotational position, that is, squared with the sensor, even when I rotate the telescope.

                            Jim,

                            This is from ZWO's ASI294MC Pro page:

                            See if your four screws that are holding the sensor window are also shiny stainless steel. If so, blacken them with Sharpie pen, or replace them by black screws.

                            The fact that you also have a problem at 45º points to other potential problems, too. See if you can get a thick black (matte, not shiny) paper and cut a rectanular hole that is smaller than the octogonal shaped aperture (but larger than the black part of the sensor shown in the above picture). See if that helps.

                            If you have a filter in between the camera and the OTA, and the filter's anti-reflection coating is only on one glass surface, make the anti-reflection surface face the sensor side. Good filters are not directionally sensitive, but there are a lot of cheap filters out there where direction matters - you pretty much get what you pay for in the filter world.

                            Franco, your secondary problem appears to have a four way symmetry, so check the screws to see if they are shiny. The thin bright spikes are of course the diffraction pattern of your spider.

                            The problem could well be internal to the IMX294 sensor itself. Sony never intended for that sensor to be use for such a large dynamic range. (FWIW, I don't see this phenomenon on my IMX571 based cameras.)

                            Chen

                                w7ay Chen,
                                I will try these solutions out. The shiny screws could well be the cause of the 90 degree artifacts.
                                Thanks so much for your assistance,
                                Jim

                                  What is your focal ratio John? I'm pretty sure I only see this on images taken at F12, can't see any at F5. Same exposure time - 5 minutes.

                                  jc010 my camera is 294MC and i get the problem without filter

                                    Write a Reply...