Darks - what happens if there is no dark frame for the sensor temp? #1297
Replies: 9 comments 10 replies
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I managed to get a range from 11 to 31 degrees and that should cover the interim for a while. The first three images were very black for some reason as well as being much smaller than the others but they then sorted themselves out. Probably some hiccup with the exposure perhaps? The new images are significantly improved. Great job with this feature. |
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@Stephen2615 Stephen, take a look at this Wiki page, especially near the end, for an answer to your question. It's concerning that 3 pictures were dark and smaller. Can you upload one of them plus a "good" dark? I'll see if I can tell what happened. Also, if you have the log file when the "bad" files were create, please upload it as well. |
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Sorry, I deleted the three files to get a good time lapse. The log showed ERROR: Failed getting image: ASI_ERROR_TIMEOUT #2 (with 0.8 exposure = YES) (11) around the time of the three images. This happens every once in a while. The darks at the relevant temp were used last night so they appear to be good. The three files were created after I started Allsky after making the darks. I could try that again tonight to see if there is any issue from a cold start.. |
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@Stephen2615 I would appreciate it if you could try to reproduce the problem. If it happened to you it will happen to others. Occasional ASI_ERROR_TIMEOUT's aren't anything to worry about. When they happen, no image is written to disk, so it's unlikely that was the cause of the 3 small frames. |
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I believe I found the fault. The dark for 11 degrees is a light frame. I have no idea how that happened. The 120MC-S isn't a very good camera for this project so I am thinking that a better camera might be on the cards. It has an awful lot of unwanted noise and hot pixels. It's a good camera for polar alignment with SharpCap. |
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@Stephen2615 I had that once when I forgot to cover the camera... Many people complain about the 120MC/MM and hot pixels. Someone else posted some pictures and the noise was terrible. |
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I see ZWO has an 178 MC on sale. It's tempting. The 120 is pretty dismal but you get what you pay for.
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@Stephen2615 I think the 120 is pretty old, too, which probably explains the issues. |
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I just installed the camera and it is great but my night images are too dark as they default to 50 gain as auto gain if not switched on. Can you please share your camera settings? |
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@Stephen2615 Most settings depend on the camera, lens, and sky brightness, so what works for one person often doesn't work for another. Take a look in the Wiki for an explanation of all the settings. Which ones you increase will vary depending if Auto-Exposure is enabled or not. |
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I spent ages getting the 120 working and now I have to do it all again with the 178. Max gain seems to be around 400 going from the ZWO website. I have to figure out some way of cooling the camera as it is cooking in the enclosure at 50C when it is only 11C outside. But that is another story. |
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@Stephen2615 Unfortunately you have to "do it all again" whenever you get a new camera with a different chip. The 120 is pretty old with old technology so any new camera's settings may be quite different. If you change the Debug Level to 4 and restart Allsky, then look in The next version of Allsky will display those values in the WebUI and not let you enter too small or too large of a value. Most people concerned about heat use a fan. I have a fan controlled by the CPU temperature. It's below the Pi, which is below the camera, and blows air up, into the dome, and then outside. This keeps dew from forming. |
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@Stephen2615 Let me know how you like the 178 compared to the 120, and if you feel you need to take darks with the 178. |
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Hi Stephen - Are you using the lens that came with the ZWO ASI178MC? If so, what is the diagonal field of view you get. I have the ASI224MC, w/the 2.1mm and get around 150 degree. At 41d lat, Polaris is just off frame. Looked for replacement lens, but it appears the 1.55 Starlight (LNS01) is no longer available. |
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I am using the Fish Eye lens that came with the camera and it probably is around the 150 degree of view but I can't be certain of that. It certainly shows a lot of the sky and does a good job. I am at 35 south and the south celestial pole is easily seen. |
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Thanks Stephen. Is this the lens that came w/your 178MC? ZWO lists it as a 170d diagonal (2.5mm 170 degree lens w/1/2" sensor). Using SkySafari (SF) and measuring star distances, my 2.1mm 150d diagonal give approx. 120x90 degrees fov (1/3" sensor). Just cutting of Polaris (~2d). If you don't mind, can you add an image w/date-n-time and provide approx. lat/long? I can try to estimate fov w/SF. Here is one of mine - processed in Affinity Photo. Would be nice if allsky could do some image stretching before conversion to jpg. Banding occurs when attempting the stretch w/8-bit jpg. Take care, Paul
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Unfortunately I don't have individual pics taken at night that show the whole sky. The dew here in winter is fierce and I have a camera dew heater around the acryllic dome which severely restricts the view. Any single pics without the dew heater would be automatically deleted after five days. I have created a small resistor based dew heater for inside the dome but I am waiting for some roof repairs before the camera goes on my roof and into production. It's all on pause for a couple of months. I currently have the camera sitting on a table which is surrounded by vegetation so it doesn't show the sky very well. This is the only time lapse without the lens warmer and the camera is not focused and the dome froze over. That fisheye is the same. https://southernskies.space/allsky/videos/allsky-20220719.mp4 |
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Appreciate the link Stephen. Looks like your celestial pole is just below the satellite dish - presume it will still be in FOV when rotated with N @top of frame. |
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Greetings,
I was wondering what would happen if there is no dark frame for the sensor temp? Eg, if I have a range of dark frames from 5 to 15 degrees and the sensor temp is 3 or 18, what happens? My ZWO 120 MC-S has a lot of hot pixels and I was wondering if having the 15 degree dark copied and renamed from 16 to 20 degrees would be a suitable "fool" until I can get real darks at that temp. I am trying to determine a good dew control and as my RPi 4B case makes it impossible to get to the GPIO pins, I temporarily have a small dew heater wrapped around the camera dome. The day temp is about 23 and the night can get down to 10 depending on the ambient temp. Having a fake dark is probably better than no dark at all with the large amount of hot pixels. Comments are most welcome.
Regards
Stephen
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