Long exposure time artifacts: Hotspots; Whitespots, what are these?

[rammy]

Hi all, I did my first set of 240 second plus exposures at night and have been getting a couple ready for printing but have found that on the ones that I exposed for about 244 secs, there are many "white spots" all around the image.

Anything I have exposed for a lesser time, such as 20secs, it appears fine.

Would you be able to advise as to what these are and how I can get rid of them at time of taking pic? Is it a factor of the sensor or some other light in the scene that may be affecting this?

Here are two 100% crops taken on the same night. Relevant exif given for each image.

Help and advice is very much appreciated please.

Whitespots/hotspots? on a long exposure: 17-40 F4L - 24mm, 244 secs, F/22, ISO100.
151359

No whitespots/hotspots : 17-40 F4L - 19mm, 20 secs, F/16, ISO100.
151360

[Mike R]

The spots might be caused by hot pixels from a long exposure.

[rammy]

The spots might be caused by hot pixels from a long exposure.

Yeah thought so but I presumed that hot pixels where always red, which there are some in the pic. Didn't realise you could get so many white ones too.

I used Raw Shooter Essentials 2006 to convert this to JPEG which doesn't remove the hot pixles but the ACR in PS CS2 does when you convert through there. Doesn't get rid of all of them so I did a search on net and found this cool freeware app Hotpixels Eliminator that does get rid of all of them:

http://www.mediachance.com/digicam/hotpixels.htm

[DocFrankenstein]

I'd rather shoot at ISO 400 f/16 or f/11 and stay under a minute. You'll get rid of the artifacts that way.

[rammy]

Thanks, I'll remember this when I am next out doing "long exposures". But even though, you know star trails that need many minutes if not an hour or two, what then? Also, I wanted to have a go at some moonlight landscape pics, especially at lunar eclipse time when the light reflection will be red.

Do the better cameras like the 30D or 5D perform better in situations like this?

[DocFrankenstein]

I dunno about better cameras, I only have 300D

If you want an exposure for a few hours, then use film... or tolerate hot pixels... or cool your sensor.

[rammy]

I dunno about better cameras, I only have 300D

COOL! :-)

I did run the Hotpixel Eliminator on this shot and this is what it looks like now: