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07/08/2003 12:09:21 PM · #1 |
| My cam (and lots of others, I suspect) has a limit of 8 seconds on the shutter speed. It goes down to 1/1000, which is pretty good, but I wonder why it doesn't have the option of just opening it up and leaving it open as long as I want. What if I wanted to do astrophotography with it? Too bad - often you need 15 minutes of shutter time for that. Fuggedaboudit! |
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07/08/2003 12:19:11 PM · #2 |
because you'd end up with more noise spots than you would stars ?
The cameras with better sensors have more tolerance for 'dark current' so they produce less noise when left on for a long time, even in the dark.
Cheaper sensors produce more errors the longer they are on for, which becomes visible as hot pixels across the frame.
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07/08/2003 12:28:03 PM · #3 |
Not to mention that the longer the sensor is on the hotter it gets and that is what noise actually is if I am not mistaken.
John (TurboTech) |
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07/08/2003 01:51:02 PM · #4 |
Originally posted by Turbotech:
Not to mention that the longer the sensor is on the hotter it gets and that is what noise actually is if I am not mistaken.
John (TurboTech) |
I always thought noise was caused by electromagnetism, but come to think of it, heat sounds like a better explanation to me. I've just bought a Dimage 7i, which produces a lot of noise even at 100 ISO, and it gets pretty hot for a camera.
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07/08/2003 02:15:53 PM · #5 |
i have heard of people taking their webcams apart and makeing a cooling, usually peltier, device for the CCD or CMOS so that they can increase their exposure time to minutes... here is an example..
//www.pk3.host.sk/Astro/index.htm?astrophoto_vesta_sc2_mod.htm
then they take this webcam, and record for X ammount of minutes then take all the images, stack them, and resample them...go to that guys photo section, very impressive shots of the moon with a web type cam.
Message edited by author 2003-07-08 14:18:47. |
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07/08/2003 02:21:58 PM · #6 |
Originally posted by Turbotech:
Not to mention that the longer the sensor is on the hotter it gets and that is what noise actually is if I am not mistaken.
John (TurboTech) |
The noise isn't heat, though it is worse at higher temperatures. Basically it is just random motion of electrons in the sensors. They become more mobile at higher temperatures, so the thermal noise component can become worse.
This paper provides a high level overview of some of the sources of sensor noise |
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07/08/2003 02:47:27 PM · #7 |
Wow, the next time someone tells me I have too much time on hands I'm going to send them to that web site. Why would any one even THINK about modifying a webcam for Astro photography?
Message edited by author 2003-07-08 14:52:09.
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