Still have red dots on long exposures after a cleaning

[luciferini]

Hello,
I have been reading many forums and posts about people with red dots showing up on long exposure shots. I even seem them on short exposure on black backgrounds. I am heading out to Utah in a week and want to get some night shots, but I don't want to ruin them with these hot pixels. I have a Canon Rebel XTi and I have recently cleaned my sensors. I have used multiple lenses and can demonstrate the issue is not in the lens as it follows the body.

I have had this camera for about 5 years, maybe it is just time to upgrade? Or could it just be the nature of older model XTi? I have tied taking the pictures in RAW and JPG format and get the same results.

I've attached what I consider a ruined picture because of these red dots. There are also blue dots. No, not the stars, but check the beach/lake shore in the foreground and you cant miss them.

Any thoughts? I prefer not to do any post processing.

 

[luciferini]

PS. I can duplicate the spots with a lens cap on, so these are not reflections on the dirt/sand/silt.

 

[ShaneF]

Im on my phone so its kind of hard to see but they look like - Hot pixels- its happens during long exposures when your sensor starts to heat up.

 

[table1349]

That's why there is post processing. Get rid of the hot pixels then.

If it is the noise you are talking about, then lower the ISO down from 1600.

 

[KmH]

Red dots and blue dots in very dark segments of a digital photo are usually image noise. Image noise - Wikipedia, the free encyclopedia

All digital images are post processed.

http://wwwimages.adobe.com/www.adob...ly/prophotographer/pdfs/pscs3_renderprint.pdf

Another technical problem prevents us from seeing all the way into the darkest regions of the scene.

The sensor is sensitive to a wide range of radiation, not just the visible kind. This other radiation is all around us and is also emitted by components of the sensor itself. In the illustration the extra radiation is represented by condensation and leaking pipes.
Each time we measure how full the bucket is, part of the sampled data is extra. It’s mostly random, and we don’t know how much of our measurement is this extra radiation.

To compensate, the chip has rows of sensors with opaque covers. It measures the signal in these “dark” buckets to determine the average and maximum amount of stray radiation during the capture. This “dark current” measurement defines a level beyond which we can’t be sure of our data. In the vocabulary of signal processing we call this the noise floor.

...Illustration here ....

Figure b: During a dark exposure (shutter closed)the sensor buckets will still begin to fill even though no light is arriving from the scene. In our analogy the pipes leak and the humidity causes condensation inside the buckets themselves. The amount of water in the fullest sensor bucket over the time period to be measured is the amount of measurement uncertainty. This amount is called the noise floor. The noise floor determines the lower limit of the sensor’s dynamic range. We can’t see any farther into the dark areas because we can’t tell the difference between real scene data and what came from the leaky pipes.

 

[Garbz]

Hot pixels happen. A lot of RAW processing software will perform automatic hot pixel removal by detecting portions of the sensor where one single pixel is significantly brighter than it's neighbour (which shouldn't be possible given the presence of an anti-aliasing filter).

Even if you shoot JPEG hot pixels happen in a deterministic way and the long-exposure noise reduction routines of the camera will remove them for you, the problem is this effectively doubles the length of your exposure and may suck if you have to wait for your camera for minutes at a time before you can shoot the next photo.

 

[xxWesxx]

To high of an ISO. You gotta turn it down. Or getting a noise remover. I use the Camera Raw plugin to get rid of unwanted noise.