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Hello, does anybody wonder about dead pixels? This test is 8 sec, gain 400 bin3x3. It can be calibrated away, but are that many normal? Thanks & Cheers Robert  |
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Hi, Robert! The colored tiny pixels aren't likely dead, their resting energy rate is just higher than their neighbors. They otherwise still function. The number looks about right to me. While a brand new camera usually shows fewer, more develop as the unit ages. The location of such active pixels will change slowly over time. Up-to-date dark calibration frames almost exactly null these out, lowering their amplitide to match neighboring pixels in an image. Using a camera that has a cooler will reduce the strength of these pixels significantly, as well as lower the sensor's overall noise. The lighter "lifesaver" circles are almost surely dust particles on the protective front glass of your camera...easily cleaned off with a lens brush or lens-cleaning kit (I can endorse the Pentax dust pen). https://www.bhphotovideo.com/c/product/618600-REG/Pentax_39357_O_ICK1_Image_Sensor_Cleaning.html?sts=pi When I use the same dark frames for a few weeks, a dozen, or so, new hot pixels eventually appear and aren't nulled out in an image. Easily fixed—Shoot new dark frames and restack. Or, if it's just a few, rubber stamp them out in photoshop and make a note to update the darks next time 'round. Here's my current dark frame. ZWO ASI2600, BIN1 at full gain and cooled to -15C. Despite being quieter, it shows similar activity. But, remember, I had to amplify the levels of this frame a thousand times to even be able to see the hot pixels. So the difference between them and their neighbors is actually pretty small...though they can become visible when image levels are really pushed. Dark frames applied to an actual image pretty much makes them invisible, however.  |
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Hello Dave! Thank you so much for the detailed explanation and sorry for my ignorance, I'm brand new to DSO imaging with CMOS cameras. Thanks to you I am much wiser now. Highly appreciated! The rings on the image appeared because I saved the frame before focusing. The sensor cleaning kit may be great for my DSLR. Sure I can source it in a photo shop here in Japan. CMOS cameras are usually protected with an AR filter though they too are better cleaned carefully. We have high humidity in Okinawa thru the year in that even the sensor under the AR can get contaminated. Since almost all the time clouds are quickly ending my sessions, I usually omit dark frames, but I realize they are worth the time. All the very best and CheerS, Robert |
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| Haha! Of course! I wasn’t properly evaluating the lifesavers. You just wen’t focused on stars, yet. I stand corrected. I don’t see any other evidence of dust, then! |
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Welcome to astrophotography! It’s a terrific hobby because there’s always something new to master (or overcome)! I’m only three years into it myself. Oh, BTW, did you make this image manually or with the camera on automatic? |
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| Manually, in Sharpcap but I couldn't finish as clouds stole the show. All on auto would probably end up in a phototechnical disaster🥴 |
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| What was the ISO setting? Hot pixels shouldn't normally be that visible. I'm wondering if the ISO was too high...after all, your exposure is only 8 seconds. What if you exposed for 30 seconds and reduced the ISO accordingly? |
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| The snapshot is not from my DSLR but from Player One's Uranus-C CMOS camera 8 sec at gain 400, 3x3 binned. |
