6
$\begingroup$

There was a lot of smoke blowing high over the west coast of the United States last summer due to forest fires. It was thick enough that near the horizon, the Sun was all but invisible. It could probably just barely be discerned if one tried hard enough, but I thought it might be best to avoid staring directly at it, visible or not. Especially as my camera could still see it:

enter image description here

A closeup (in which you can even see what I think is a sunspot!):

enter image description here

Is this infrared light my camera is detecting? Why is it allowed through the smoke relatively unscattered, compared to visible light?

Additionally, could the invisible light be harmful if stared at? (Perhaps there are longer wavelengths than my camera is picking up which are even brighter?)

$\endgroup$
8
  • 1
    $\begingroup$ IR could be a slight factor: Si CCDs have considerable sensitivity out to about 1000nm in the near infrared. Moreover, that lilac color is interesting - light of this wavelength typically shows up on an Si CCD as this color, although of course in this case the smoky atmosphere might explain the color too. $\endgroup$ Dec 2, 2017 at 10:03
  • $\begingroup$ A lot of camera sensors are fairly sensitive to IR: there is usually a filter in front of the sensor (often as part of it) to deal with this. I have no idea of this is the sensor 'seeing' IR. $\endgroup$
    – user107153
    Dec 2, 2017 at 10:04
  • 1
    $\begingroup$ Why not to search for the specst of the detector aboard your camera? $\endgroup$
    – Alchimista
    Dec 2, 2017 at 10:33
  • $\begingroup$ All cameras have an IR filter in front of the sensor, except for the cameras specifically made or modified for astro or IR photography. $\endgroup$
    – safesphere
    Dec 2, 2017 at 14:30
  • $\begingroup$ @Alchimista I've tried, but I've yet to find information which mentions sensitive wavelengths or anything like that. $\endgroup$
    – gandalf3
    Dec 2, 2017 at 20:56

3 Answers 3

5
$\begingroup$

Well, as it turns out, CCD cameras are actually sensitive the infra red light. (See of instance here.) Infra-red light is better at penetrating clouds. So your camera seems to have picked up the the infra-red part of the spectrum that was able to penetrate the clouds.

$\endgroup$
2
$\begingroup$

So who is correct here? Are CCD cameras (and probably others) actually sensitive the infra red light? Or not?

Point a TV remote at your camera so you can see it's image, and then push one of the buttons. You should see the infra red LED flash the signal that button sends to the TV. (It's also how you can see that the batteries in the remote are good.)

$\endgroup$
-2
$\begingroup$

Well, unless your camera is an infrared one, the answer is no. In normal cameras there are three bands red,green and blue all of whose bandwidth lies in visible light region. The reason that your camera could see the sun and you can't is probably that the exposure time of your camera is more. If you increase the exposure time enough in a camera and point it towards night sky, you can see very faint stars of magnitude of around 5. And for the sunspot, it is probably a speck of dust on the aperture but I can't be sure :)

$\endgroup$
3
  • $\begingroup$ The exposure time of that image is 1/160 of a second, at F5.6, ISO 200. Not exactly a long exposure.. and the surrounding clouds look pretty much how they appeared to the eye. Perhaps a sunspot is a bit farfetched, but I think a spec of dust anywere inside/on the lens would be blurred to oblivion at the focal length the second image was taken at (600mm) $\endgroup$
    – gandalf3
    Dec 2, 2017 at 9:55
  • $\begingroup$ @gandalf3 Dust on the sensor is in focus, but as you say dust elsewhere is not. You could know if it was a sunspot by comparing it to astronomical images taken at the same time I suppose. $\endgroup$
    – user107153
    Dec 2, 2017 at 10:01
  • $\begingroup$ @tfb Good idea! The image was taken on September 9th, and a quick search finds this. It seems to me like it could plausibly match, though the unknown orientation of those images leaves some room for error. $\endgroup$
    – gandalf3
    Dec 2, 2017 at 10:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.