Any consequences for Long exposure?

[domt]

Hello,

I got a D3000 for Christmas as my first dslr camera and I love it. I usually try to focus on night photography along with black and white. Ive been reading up on long exposures and was wondering if there's any problem leaving your camera shutter on, say...for 30 minutes? An hour? 2 hr max? Will this damage the image sensor or have any negative effect on the camera body or lenses?

Min

[Dave Humphries]

Hi Min,

This isn't something I do much of, but the answer rather depends what you have it pointing at, if you have a very bright, sharply focused point light source, I suppose there is a risk of burning the sensor, but I think it's more a theoretical risk than real.

Obviously the first thing to consider is whether the battery has enough juice in to keep the shutter open that long. In practice, for straight night photography, I don't think you will need that long.

Was there a reason for suggesting that length (e.g. star trails)?

There are quite a few other threads around here discussing such things, I, or someone else may provide links later, but for now, have you read this:
Intro & Common Obstacles in Night Photography techniques page here at CiC?
It was written by the site owner Sean McHugh, who took these shots around Cambridge

I will round off by saying welcome to the CiC forums and hope to chat later,

[Sahil]

Congrats on your new purchase. Even I bought the same camera a week back. I tried long exposures, but not as long as you are saying. (20-30 seconds.)

I guess the battery won't last for 30 minutes or so. I am not sure. I am sure someone will answer your query pretty soon.

[Sahil]

Oh! I was typing the reply, while Dave was posting it.

[Dave Humphries]

Hi Min,

Have a look at Sahil's night shots with a D3000

Cheers,

[Sahil]

Yea Dave,
Even I thought of giving the link to my pics to Min, but when I read he was talking of loooooooong exposure shots, I decided against it.
Here is the link to my night shots.

My New D-SLR!

[Colin Southern]

Long exposures (minutes to hours) won't damage the sensor - but you will get a LOT of noise. If possible it's better off to take a series of shorter exposures and then just combine them - you get much less noise that way.

Hope this helps

[domt]

Thank you for all your advices and opinions!

[AaronC]

Hi Colin,

Any idea why combining shorter exposures would result in less noise? I assume we're talking about, say, combining four 1/4 sec verses one 1 sec exposures (in other words, getting the sum of the exposures). It doesn't make much intuitive sense to me, so I'm curious.

Thanks

[Dave Humphries]

~ Any idea why combining shorter exposures would result in less noise? I assume we're talking about, say, combining four 1/4 sec verses one 1 sec exposures (in other words, getting the sum of the exposures). It doesn't make much intuitive sense to me, so I'm curious. ~

Hi Aaron,

Yes, that is what we mean.

At an individual pixel: think of noise as an extra small amount of voltage superimposed on that which is there due to the light hitting the sensor. The noise voltage can add or subtract from the 'light' voltage in a random way - so on one exposure it can be positive and on another negative. If you merge two, or usually more, exposures, the net effect is the noise cancels itself out, reducing what you see in the image. I probably haven't explained that very well.

For the full answer, with example pics, have a read of Sean's Technique page;
Noise reduction by image averaging

Cheers,

[GiantTristan]

The "long exposure noise" can be compensated for by turning the "long exposure noise reduction" in your camera to "on". This causes the camera to take a second exposure with the shutter closed. It then subtracts out the random noise. If your camera does not have this feature, you can take a second exposure with the lens cap on under the same condition and then subtract the "noise picture" in PP. It is best to work in raw to prevent any artifacts.

[Terry Tedor]

The "long exposure noise" can be compensated for by turning the "long exposure noise reduction" in your camera to "on". This causes the camera to take a second exposure with the shutter closed. It then subtracts out the random noise. If your camera does not have this feature, you can take a second exposure with the lens cap on under the same condition and then subtract the "noise picture" in PP. It is best to work in raw to prevent any artifacts.

One thing you need to keep in mind if you use your camera's "long exposure noise reduction" is the second exposure the camera takes for the noise reduction is as a long as the first exposure was for image capture. In other words, expose for 30 seconds for image capture, expose for 30 seconds for dark noise capture, for a total exposure of 1 minute. At least that's how my Canon does it. With the 30 minute or longer exposure times that domt is thinking of, we're now talking about 1 or 2 hour exposure times. The "stacked" image concept that Colin describes is probably a better way to go.

[belong]

no one answered what happens to the mirror being flipped for a certain amount of time, is it eventually bad for the mirror mechanism for flipped for a long time?

[Colin Southern]

no one answered what happens to the mirror being flipped for a certain amount of time, is it eventually bad for the mirror mechanism for flipped for a long time?

No - it can be retracted for as long as necessary.