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partial eclipse

I was taking shots of the 2017 eclipse using my D7200 camera with a 1000 ND filter. As I was going through the pictures after downloading them to a pc, I noticed that there's what appears to be a tiny light source present off to the side of the sun. I have circled it in the picture below. It is also present in the pictures during totality, which I took without the ND filter.

It doesn't seem like a camera or a lens artifact, since it showed up pretty consistently in different shot configurations, but I did not know that a 300 mm zoom with an 1000 ND filter could capture a light source besides the sun and the moon in full day light. If it is not an artifact, what could be the source of this light?

enter image description here

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    $\begingroup$ Given it's size and location (not symmetric to any light source) it could be a hot or stuck pixel. $\endgroup$ – StephenG Sep 6 '17 at 19:26
  • $\begingroup$ It's less than half a degree from the sun. If real, it'd have to be unspeakably bright. I saw a red sun-doggish spot about 5° from the sun shortly after the end of totality, with cirrus clouds messing the view, but 0.5° is awfully close for any genuine, discrete atmospheric optical phenomena. $\endgroup$ – Wayfaring Stranger Sep 9 '17 at 15:31
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I agree with the comment by StephenG. This is a stuck pixel. As the link suggests, they are a very common flaw in digital cameras, and not an astronomical feature.

I think this because it appears, on zooming in, to be a single pixel defect, most light sources even with the best focus, cover more than 1 pixel. The filter you are using is very powerful removing nearly all light. An object would have to be exceptionally bright to be seen through such a filter. If it was real then it would be so bright that when you removed the filter, that one spot would have totally overexposed your image. Since stuck pixels are pretty common, and you might not have noticed them in a picture taken at day, or of a star-field, it is a safe bet that that is the problem.

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  • $\begingroup$ Thanks, I'm going to try additional troubleshooting on this. If it is a stuck pixel, I should be able to shoot a completely black wall with manual settings and still see it, correct? $\endgroup$ – Cpu1 Sep 6 '17 at 20:13
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    $\begingroup$ @Cpu1 It depends on gain (ISO setting), exposure duration, and sensor temperature. When gain, exposure and temp are the same, the hot pixels (which is a slightly better term than "stuck" pixels) tend to be the same; when those vary, hot pixels also vary a little. It is common in astrophotography to take "dark frame" libraries at various gains, exposures and temperatures, and use those to subtract hot pixels from your images. Most astrophoto apps know what to do if you give them the correct dark frame library. DeepSkyStacker is one such app, but there are many others. goo.gl/1WVVFk $\endgroup$ – Florin Andrei Sep 6 '17 at 20:43
  • $\begingroup$ @Cpu1 BTW, to take dark fames, don't shoot a black wall. Just put the cap on the lens, and make sure you're not in a bright environment, to prevent light "leaking" into your camera. I usually do it indoors, and as a precaution I throw a blanket over the camera (usually not necessary, but just in case). Even a small amount of leakage will ruin your dark frames. The procedure is the same for regular cameras and for astrophotography cameras. $\endgroup$ – Florin Andrei Sep 6 '17 at 20:50
  • $\begingroup$ Note that many DSLRs have something typically called "long exposure noise reduction" which does dark frame correction automatically. You'd typically have to turn this option on and it's often buried deep in the camera's menu. $\endgroup$ – StephenG Sep 7 '17 at 6:36
  • $\begingroup$ I looked through other images, and it is indeed a defect pixel. It is not stuck all the time, I had to shoot a few normal shots during troubleshooting before this pixel would get "stuck" and show up in all following shots. I'll see if I can exchange the camera, since it is still pretty new, or have to send it to Nikon to remap this single pixel. Everyone, thanks for the help! $\endgroup$ – Cpu1 Sep 7 '17 at 15:56

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