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Imaging obstacles tonight. I have a Celestron 8SE>Starizona SCT Corrector IV>ZWO OAG-L>ASI2600MC Pro, backfocus is correct at 90.3mm. I also use a dew strap and shield. I'm trying to ID what these artifacts are. I thought it could be dew, but right now there is not enough humidity. Thought it could be stray light, so I put electric tape around the joint seam between the Starizona and the spacer that connects the rest of the train. I don't think they are clouds as they remain in the same position across subs. What could these be? Below are sequential subs, 300" 250 Gain. Sensor temp is about -2c. I've been seeing these anomalies for a while now and they don't always appear. Sometimes they go away over time. I just turned my dew heater to 100% to see if they go away.         |
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Have you tried rotating your image train by 90 degrees to see if the problem comes from the image train or from the outside (moon, crazy reflections from stray light) One thing in your frames puzzles me a lot, has likely nothing to do with your problem, but why does the framing change so much between subs in this sequence? And why is the vignetting on the right side depending on the framing? First picture has little vignetting on the right and there is a bright star on the right side that is close to the border of the picture, next frame the same star is >> 50 px to the left and much more vignetting, looks like the whole image train moved or the Dewshield moved a lot between frames. I see the same thing with the last 3 frames, the Star moves to the right and vignetting decreases. Michael |
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| If there are any shiny surfaces inside your imaging train, a bright star slightly outside the field of view can produce a reflection. I have had such reflections in the past with both a C8 and a C11 EdgeHD, but in both cases, they were thin and strongly curved. Your reflections are much wider, more diffuse, and irregularly shaped. I wonder if it is an external light source (e.g., neighbor's spotlight) reflecting off the inside of your dew shield? |
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| These look like stay light coming from the outside in. Are you using an off-axis guider that might be open, or is there any lights osurce as small as an LED that might get into the light train? |
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| @Michael Ring I haven't tried rotating yet, I'll try that tonight if I see them again. For the puzzling images, they're cropped from a screenshot of the original raws. |
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| @rhedden I checked for any light that could potentially spill into the dew shield, nothing. The tripod is extended so the OTA sits quite high, and I built a shield on my fence to blocky neighbor's lights. |
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| @Joostie I'll put more tape on any seams I can find. I tested this theory with a flash light and didn't see any light spilling in when I shined the light around the image train. But one morning I wanted to image the sun with this image train, and tons of sunlight was pouring into the train and made weird patterns, so it might just be the seams and joints need to be sealed. Edit:. Yes I used a white light filter😆 |
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In case anyone else has this issue and finds this thread, I'm going to think out loud (as usual) 😁 I'm going to take some dark frames tonight and see if they're still there. If so then light is definitely leaking into the image train, unless there's a hole on my OTA somewhere. |
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I have the same setup, except no OAG, with a C925. Can't say I have seen anything like it. First color is red, so the source is red. The red streaks from M1 could be some sort of reflection of M1, or something on the optics in the image train that is really dirty/wet or oily, scattering light in all directions. It is really suspicious that two rays seem to originate at M1 and they are red like M1 (the sky is typically a little green in a raw image, so the green from M1 won't be so obvious in a reflection). And the other red ray is parallel to one of the rays from M1. But awfully strong reflection/scattering to do that. Do the two reflections follow M1 if you move M1 in the FOV? Better yet, get a really bright star in the FOV and see if you get an even stronger reflection/scattering from that. If it is something on the optics, rotate you camera and see if it rotates with the camera (it is on the sensor) or not (it is in the telescope optics). It could be external light--if so that light source is red since you are seeing red streaks--could it be a red LED from a power bar, etc?. Do a dark with the lens cap on in a dark place and then do one with light around the telescope. If there is light leaking in it will show in the dark when there is light around compared to the dark with the telescope totally in the dark. If there is no difference then there is no light leak. If there is stray light in your dark with lights on, you do have a stray light issue. In that case, run some darks again in the dark, but take a flashlight and for each dark shine it on a different place on your telescope--this way you can see where the light is coming in and isolate the problem very quickly. If it is a leak my guess is the OAG, as hard to see how light would get in the train anywhere else typically--you don't mention if you have a filter wheel or drawer, another possible problem for light leaks. Good luck Rick |
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300sec 250 gain, with the cap on, pointing at zenith. |
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| @Rick Veregin I don't have a filter wheel. This is a new issue for me, and I think it started happening since I started using shim spacers. I already put tape on one seam/joint, I'll have to do the rest of the train. Instead of 5min exposures with the flashlight as you suggested, I could do a live 3 second loop with a bright LED flashlight. As I've stated there are no light sources nearby that could be causing this, I've made sure to put the rig in the darkest corner of my yard, where my garage and fence meet. The only light source near the train is the red power LED of the motor focuser, but that light is pointing down, is recessed, and not very bright at all. |
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Yes, sounds like that might be a good possibility. Any chance the shims themselves are into the light path that they might reflect light onto the sensor? Good luck, you should be able to find the issue. Rick |
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I think I nailed it. Covered the entire image train from visual back to the camera's vents with a towel. No more light leakage. I know this isn't a solution to the original issue but at least I can mitigate it.  |
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| The dark looks perfect--that's great news. |
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| Congrats on solving the issue. It was a perfect who-s-done it :-) |
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| Thanks to all for their inputs. I never thought it was light leakage. It also started happening around the time I was having issues with the dew heater ring. I was turning the power down and thought dew was forming on the corrector plate. Now I gotta get some black towels and make them part of my rig. |
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| Glad you solved this one. I had some reflection problems (for the first time) with my rig, and a blackening of the inside threads of my assortment of spacer shims did the trick. |
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| @Ian Dixon My spacers are a little shiny, and I could give them a matte black finish, but it is much easier to just get a black towel and cover the train. I'm wondering if/how this will affect temps inside the train. |
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gfunkernator: What is the ambient temps you normally shoot at? Perhaps the towel is the way to go... simplicity is wonderful too.  |
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Should not be an issue with temperature in the image train that should equilibrate fine with external temperature--just don't cover the camera itself especially the vents, particularly if it is warm out, you will just make the cooler work to hard and may have trouble keeping the temperature down where you want it on the camera. Rick |
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| @Rick Veregin Right good point. The camera itself still has leaks, seems like the area where the tilt plate meets the camera body. The towel isn't wrapped tightly around the camera though, just enough to block the seems. The vents are wide open. |
