I can't post any examples at this time, but I have a number of really badwrong seamingly several pixels in size Blue, Green and Red spots all across long exposures.
This is with my Canon Rebel 300D.
Is this sensor dust or something really wrong with the sensor that is causing this? (They almost look like bad pixels and they are ALL Over some shots I took.
Just as a supplement to Rikki's comment, neither the 300D nor the 30D, nor any other Canon DSLR uses a CCD type sensor... They use CMOS...
Hot or stuck pixels are a fact of life, and they occur on every type of sensor, at every level of camera, but what you are referring to is more likely to be noise based on your description...
The 300D has a fair bit of noise with the older hardware on the sensor...
An ounce of prevention is indeed worth a pound of cure...
Preventative steps:
1. shoot at ISO 100 or whatever is the highest... It's a long exposure, so it won't make a difference for camera shake, and I assume that under these circumstances that the camera is locked in to some sturdy tripod or something...
2. Shooting RAW can help... I've heard that there is Noise Reduction in some RAW converters, particularly in Adobe (which I am pining for right now with a big honkin' batch job of nearly 700 pics) software... Doing this in RAW can be better than doing it in normal JPG.
However, on shots that you have already taken, try out Neat Image or Noise Ninja... You will lose detail, but a fair bit of that noise can be dealt with... Do this to original images and restart your editing process.
On the other hand, if this is a stuck pixel or hot pixel issue, you have a bit more difficult issue to deal with... This can always be cloned out, or healing brushed, but in basic editing rules, you will be facing a bit of an issue...
How to deal with it? You will need to get the camera serviced..
Probably best to stick with advanced editing as this is not currently a cheap thing...
I've considered checking into getting a group started to hold a petition and post it to the forums to get Canon to be more responsible towards this major issue, but I don't really have the time...
As to the 30D, yes, it does have less noise than the 300D. It's two generations newer (although only the first generation yielded a really significant improvement in the noise handling characteristics - probably improved in-camera noise reduction)...
The 350XT also has pretty good noise, so might be worth checking out...
If you do a lot of astro-photography or other late-night, long-exposure type photography, it would definitely be worth it to look around for a used 20D... They are selling at excellent prices right now and are accepted in most astro-photog circles as being pretty much the best bang for the buck for low noise imaging.
As to the Hot pixel issue, something new that came out with the 5D and the 30D is an apparently undocumented feature that runs an in-camera sensor map for hot pixels after running a sensor clean cycle...
Pretty cool if you ask me :).
Incidentally, the physical nature of a CMOS sensor allows it to actually run cooler than a CCD, temperature-wise, and this directly translates to better noise performance. Some reviews that you may read confuse this issue because they refuse to treat sensor noise and in-camera noise reduction as separate issues.
As to the Hot pixel issue, something new that came out with the 5D and the 30D is an apparently undocumented feature that runs an in-camera sensor map for hot pixels after running a sensor clean cycle...
For long Exposures (1s+) the 30D also has Dark Frame noise reduction, just like the 1-series has it. The 300D also has some sort of noise reduction, but I'm not sure how it works as it isn't Dark Frame based.
Dark Frame noise reduction means that the camera captures another frame with the curtain closed after the original exposure. I then filters out the noise on this second exposure from the first.
Well, my next camera body is going to be a 30D. I was just a little concerned with the number of hot pixels that I had with a few nearing 30 second exposures that I had done.
one more thing to mention with all the other advice is that when you do a long exposure, it is a good idea to cover your view finder. stray light can go throught the finder onto your image during a long exposure.
one more thing to mention with all the other advice is that when you do a long exposure, it is a good idea to cover your view finder. stray light can go throught the finder onto your image during a long exposure.
It was covered.
I have been shooting with the camera for quite some time, I just never performed any long exposure shots until last night and I was shooting in a purposefully low light.
one more thing to mention with all the other advice is that when you do a long exposure, it is a good idea to cover your view finder. stray light can go throught the finder onto your image during a long exposure.
How do you do that?
(I had the exact same problem last night doing a long exposure)
The dark frame noise reduction makes a world of difference. My camera's sensor doesn't have terrible hot pixels, but it does have a few on longer exposures.. the noise reduction does a great job of taking them out. I usually shoot at ISO 400 at night to pick up the stars better, and it doesn't seem to be much noisier on a 1hr exposure than on a few second one.
P&S cameras either have EVF's which run right off the sensor, and are electronically (rather than optically connected via a mirror in DSLR's) fed... OR they are like smaller cameras which use an optical viewfinder which is not in line with the lens... Again, not an issue for long exposures.
Didn't I hear of some software somewhere that did dark frame subtraction for you?
You still have to take the dark frame yourself. This is best done at the time (sensor temperature, and a few other things can make a bit of a difference, although it's probably quite minor)... Take the same duration, just as the camera would...
Alternatively, I think there's a way to do it in PS....
Maybe take the dark frame, convert to negative, and use it as a layer or some sort?
Wouldn't be even close to legal in either basic or advanced though due to the second frame... which is why it would be nice to see if it might be acceptable to use a program specifically designed to implement dark frame subtraction... Might squeak through the rules... :)
