long exposures

mentos_007

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hi. I'm just wondering if long exposures can harm your sensor?
I'm really waiting for my 350d to arrive and would like to try some star trails... but also I'm electronics student and I've learned a bit about sensors... so it gets warmer and warmer (and buffor as well) while taking the picture... so.. is it safe to try long exposures.. let's say.. 20 minutes?
 

doenoe

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im am by no means a techie, but i dont think it can cause any harm. I never read anything about long exposures and things going wrong with your sensor in the manual. Only thing i can think of is when there is a bright light or something in the frame while making a long exposure. But im not sure, so just wait till someone with knowledge will handle thins :)
 

DepthAfield

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I’ve never heard of long exposures causing any damage. You are correct about the heat generated though, and sensor heat can translate into noise.

From what I’ve read on the subject, it takes a fairly long exposure (15 minutes or more with a newer DSLR) for the device to start generating noise. I’ve never attempted anything longer than about 20 seconds, so I have no personal experience.
 

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This is a 60.2 sec example at F4.5. I cropped it but did not resize it. This was taken with a D50 18-55mm kit lens. I have not had any problems so far.


(Click for Full Size)
 
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mentos_007

mentos_007

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wee I can't see any noise there.. .cool!
 

Digital Matt

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I agree with Philip. You'll get really great exposures using ISO 100, and staying under 1 minute. You can easily go over 1 minute though, and yes you will get noise, but that can be dealt with. I've taken 5, 10, and even 40 minute exposures, and the noise was manageable.

Gotta love Canon ;)
 

Xmetal

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This thread has got me thinking...

Since us Aussies are deep in winter at the moment would we be able to pull off longer exposures than you guys in America who are living it up in Summer?

The only thing that's preventing me from trying this theory out is crap weather at the moment but i'm willing to give it a crack if someone America is going to do the same. :)
 

Soocom1

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I am by no means an expert in sensor technology.
Keep this in mind however: Sensors unlike film are designed not necessarily to react to light per sei, but rather to record the intensity of light. If you take a picture of the sun, damage WILL defiantly result unless you use a Sun Filter which they made many a moon ago. This damage is caused by the intensity of the light, as well as the magnification effect from the lens. (Think magnifying glass and ants.) So I am assuming you would know this.
Thus the longer the exposure in lower levels of light, the ‘cooler’ the sensor actually will be. (Heat also dissipates.)
Unlike film that will ‘burn up’ with light exposure over a longer period of time, the sensor works off of the electronic signal coming from the ‘pixels’ themselves. All that will happen is the longer the exposure, the more light is recorded in one spot. Thus, the image becomes lighter and lighter until, pure white is achieved. The image recorded is in the form of ones and zeros. Thus, long exposures wont damage the sensor in that fashion.
HOWEVER!!! The sensor is an electronic device, and that by default results in electrical current, thus heat is the result. If such heat has no means of dissipation, then the material of the sensor could theoretically become damaged. I do not know what the material is in most of the sensors, but logic dictates, (and I am treading on dangerous ground here) that the engineers knew this and thus developed the sensor to deal with such heat build up.
The simplest example I can give is the KM 7D that will shut down if the sensor moves around too much in its anti-shake feature. That action generates a great deal of heat. (I have felt the camera when this happens, and it can get quite warm). KM engineered the camera to shut down in case of such a situation. It does work.
 
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mentos_007

mentos_007

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thanks soocom for your great answer! But to be honest I'm not going to use bulb mode in a direct sunlight.. I was rather thinking about star trails and night city life :)
 

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just remember though that you'll need a remote if you're gonna shoot bulb for 30 minutes. If not you'll have to stand there with your finger on the shutter button for half an hour...not fun (I only mention this because I'm waiting till I get a remote to try the same thing).

The other thing I've read is that DSLR sensors have a certain "life," and so presumably if you shot a lot of long exposures you would be killing off a lot more of the sensors life then if you are shooting 1/125th of a second. Or maybe I just made that up...
 

Xmetal

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Miss Mentos. ;)

Just priced the remote I bought for my 350D, cost me $50AUD which translates to around 30 Euros, even though you're probably broke now you should be able to scrape together 30 Euros in no time i'm guessing. :)
 

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Does the 350D have an overheat shut-off feature? I know when I took my km dimage z6 to cancun and shot for 3 hours in 90+ degree heat, it eventually got mad at me - it gave me a "Camera is overheated. Shutting down" message. I'd imagine that yours would do the same, as it's a much nicer camera :) Plus, I agree with soocom - if the engineers put in a feature that will allow you to take a 20min exposure, it stands to reason that it should actually be able to do it.
 

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