How do I fix this/what did I do wrong?

[FreeStar Houston]

I was having some fun with a long-exposure shot. I did a 20 second exposure at 400 ISO. It was an otherwise great shot (in my opinion), except that it is speckled to hell and back. The only thing I can think is that it was refraction from the window glass I was shooting through. I deally I would have preferred to do it in the open air, but I didn't have a choice.

Take a look:

Whole image:


This is full resolution inset of what ruined the shot:


What can I do to fix/avoid this problem? Could it just have been the window?

[d2creative]

In photoshop you can go to FILTER --> NOISE --> DUST & SCRATCHES.
It should take care if that fairly easily.

I know that 'bux.

[Teddington]

Yeah, what he said. 20 seconds is a long time and you are bound to get some noise. Even better than PS action, Noise Ninja does a great job of cleaning up a noisy shot.

[brad]

Nevermind that.. what is that ring hanging in the middle of the image?

[CobyPhoto]

Steet Sign at the intersection of Post Oak and Westhiemer in Houston, TX. It just looks like it is floating in this image. They are suspended by cables in this section of town.

CJ

[rwwright]

some cameras have a setting just to help keep this from happening on long exposures. I know d300, d70 and d2x have it. check the menu

[FreeStar Houston]

Thanks for the tips. I used the noise filter in CS2. It softened the image somewhat, but it took care of the noise pretty well at 2px.

[rockin-photos]

Originally Posted by brad

Nevermind that.. what is that ring hanging in the middle of the image?

Originally Posted by CobyPhoto

Steet Sign at the intersection of Post Oak and Westhiemer in Houston, TX. It just looks like it is floating in this image. They are suspended by cables in this section of town.

CJ

Yeah, it's part of the "Uptown Improvement District". The engineering company I work for is responsible for them. They (floating circles with street names, street light poles & traffic light poles) are all made of pretty well polished stainless steel. When we moved to our new offices downtown, they threw away a 10' piece of SS pipe.

[Imagebuffet]

The colored specks are image noise, generally produced by transistors that are trying to amplify your signal as much as they can, but bleeding current in the dark areas. You could try increasing your ISO to 800 and, if your camera has a setting for noise suppression, using it.

You don't say what camera you use, but if it is a point-and-shoot, you are not going to get much less noise from the image. Then, you have to rely on post-processing.

[Kevin C. Haggard]

Originally Posted by brad

Nevermind that.. what is that ring hanging in the middle of the image?

COME ON! Dont you know a UFO when you see one?

[UberPhLuBB]

When doing long exposures, it seems like common sense to up the ISO. You think "low light = high ISO." Well, you see what happens.

When you expose for longer than a few seconds, turn the ISO all the way down. The lower, the better. If you're exposing something for as long as 20 seconds, higher ISO isn't going to make any difference, and if you actually can detect that the exposure is lower than you intended, expose it another 5 or 10 seconds to compensate, it's already been going for 20 seconds. Unless your subject is some lumbering thing that's only going to be in frame for 20 seconds, it doesn't matter how long you expose for.

I've noticed that anything over about 5 seconds looks exactly the same, whether it's 6 seconds or 3 minutes at the same f-stop. The only difference is that moving light sources are longer, obviously. Lower that ISO next time!

[BigEasy]

I agree with the others… don’t think your problem is shooting through glass. That normally creates other problems like glare (see post). You didn’t say what camera you are using, or what fstop you were at… but I would suspect ISO 400 at 20 sec was just too much for your sensor. The colored specks are sensor noise. Other settings in the camera can exacerbate this.. (for instance Night or Vivid) if your camera has those.

Since you are already shooting from a tripod there is no need to crank up the ISO. Long exposures of dark areas can easily produce sensor noise as you cameras software “try’s” to capture tonal range in these relatively black areas.

Try shooting at ISO 100. I also find DOF at long exposures reacts differently than “normal” lighting conditions (I’m sure someone can say why).. so I tend to shoot at around f8 on night landscapes. Shoot manual or speed priority and adjust speed using your preview. There is a lot of data in a 10+ sec exposure, so I tend to underexpose then punch up the highlights in PP.

U owe me 2 cents…

Night stuff

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