any other factor contribute to noisy picture beside high ISO?

[schumionbike]

I was wondering because sometimes I notice there is slight different in the amount of noise given the same ISO.

 

[Mav]

There's an almost infinite number of variables such as your specific subject, what light levels you're actually shooting at, the background, if there's shadowy areas or not, etc. I have ISO1600 shots of off of my D80 that look perfectly clean, and then some iso400 ones that actually look pretty gritty, all depending on what I happen to be shooting and how I'm shooting.

"Generally" if the light level is reasonable and you're just trying to maintain a faster shutter speed, high ISO will tend to look a bit cleaner. If you're down in the gutter with no light and a longer shutter speed, high ISO will "tend to" look worse here. That all depends on everything above though too. The subject, specific exposure, etc.

 

[Seefutlung]

Under exposing is a big time contributor. Often, in the shadows of a properly exposed photo you'll see noise in an otherwise noiseless image.

Sensor is important. Generally speaking, Canon CMOS sensors generated less noise than other sensor makers/types.

Recently, Nikon's D300 and D3 sensors are holding their own or better with Canon.

Processing produces noise. Every time you touch those sliders, your noise levels increase. Go to 100% crop and start fiddling with the sliders and see what happens.

Heat will produce noise. If you leave your camera/cards in the car on a hot day ... you got noise. Even self generated heat from a long exposure will create noise, especially in the corners.

Once again, the biggest and most consistent producer of noise is under exposure. A proper exposure at high ISO will produce less noise than an improper exposure at the same ISO. A properly exposed ISO 1600 image will have less noise than an underexposed ISO 800 image.

Gary

 

[Sideburns]

Above poster nailed it all...cept it doesn't matter what temp your card is...doesn't affect noise...could stop working though if it gets too hot (it won't get that hot naturally).

One other thing is long exposures. You'd think it wouldn't...and that's why you'd do it over higher ISO...but it does add noise. Not as much as a higher ISO, but it happens.

 

[Alex_B]

yes, has been well put already.

nothing much to add

As for the noise at longer exposures, it must be due to the increasing heat of the amplifier then?

 

[schumionbike]

thanks guys for the info, I was supspecting that long exposure might add some noise but wasn't sure. I did not know about the rest so thanks for all the info!!!

 

[Seefutlung]

yes, has been well put already.

nothing much to add

As for the noise at longer exposures, it must be due to the increasing heat of the amplifier then?

Yep ... at least that is my understanding but not my experience. The astro guys are the experts on this one. I think that is one of the reasons they take a bunch of shots and sandwich them together rather than just one long exposure (and tracking).

Gary

 

[jstuedle]

Exposure is everything, as has already been stated. One thing I find helps a little, is use EV compensation to slightly overexpose in low light situations. Only 1/3-1/2 stop. This is the opposite you hear to do with normal situations to prevent blown highlights. There you want to underexpose that same 1/3-1/2 stop. It helps me, give it a try.

 

[Sideburns]

yes, has been well put already.

nothing much to add

As for the noise at longer exposures, it must be due to the increasing heat of the amplifier then?

I would think so. I've done it plenty of times. It's plenty less apparent on higher end cameras, but my XT showed signs of noise at 30 seconds when I did some skyline shots during the summer at night...

Coulda been something else, but it was annoying.

 

[Alex_B]

i have never really seen this long exposure noise, but then my camera is pretty noise-free anyway and i rarely do ultra-long exposures.

it makes sense though.

 

[Sideburns]

This image was shot at ISO 100 for 30 seconds.

The colour banding is from the jpeg compression or something...but the noise you can see is not. It got fuzz all over it.

 

[Alex_B]

quite convincing.

might try some ultra-long exposures myself to check with the 5D.

 

[schumionbike]

Exposure is everything, as has already been stated. One thing I find helps a little, is use EV compensation to slightly overexpose in low light situations. Only 1/3-1/2 stop. This is the opposite you hear to do with normal situations to prevent blown highlights. There you want to underexpose that same 1/3-1/2 stop. It helps me, give it a try.

Thanks for the advise. I have been underexpose by 1/3 stop in ALL situation. Just learn something new.

 

[schumionbike]

i have never really seen this long exposure noise, but then my camera is pretty noise-free anyway and i rarely do ultra-long exposures.

it makes sense though.

Haha, your camera probably have less noise at 3200 ISO then mine at 400 ISO. I have Kodak Z710