First long exposure DSLR

04Stefan07 (Stefan) · #1 20-12-2012, 10:15 PM

I just went outside to get some shots of the moon before it clouded over.

Was mucking around with settings and exposures.

Took a few good Moon shots with my lens but when I had the exposure on for a few seconds or roughly half a second there were random colour dots (blue, green, red) that appeared on my image.

I know the white streaks are stars because they move over the long exposure but what are the other dots I have circled? They appeared in all the other images as well.

04Stefan07 (Stefan) · #2 20-12-2012, 10:22 PM

Ummm I opened the images in Bridge had a look, and opened them up in Photoshop ready for editing and the coloured dots vanished??

Eggmoon (Geoff) · #3 20-12-2012, 10:24 PM

Given they are not moving I am guessing they are "hot pixels" on your camera.

Not that I have gotten that far yet, but this is apparently why you need to take 'darks', 'flats', and 'bias' frames for detailed photo processing.

Otherwise..... they could be an alien invasion fleet coming to get us in time for the end of the Mayan calendar.....

Screwdriverone (Chris) · #4 20-12-2012, 10:25 PM

Hi Stefan,

These will be hot pixels (or dead pixels), due to the temperature and the long exposure.

DSLRs are especially noisy when the temp is 15 deg C or more. The longer you keep the shutter open, the more noise like this will occur. You can normally remove it by turning on the In Camera Noise Reduction (ICNR) which takes an internal dark frame after each light frame.

Alternatively, you can leave this off in the camera and take your own dark frames and stack these together to subtract them from the stacked light frames. If you take say 5 x light frames (exposures), then take 5 dark frames straight after (lens cap on) so you have the same amount of noise on each dark.

Cheers

Chris

04Stefan07 (Stefan) · #5 20-12-2012, 10:32 PM

Ahhh did not think about hot pixels at all!

Does this damage the camera over the long run in anyway?

Oh yeh the alien invasion is starting early here, I better buy that massive $50,000 telescope off ebay

naskies (Dave) · #6 21-12-2012, 11:54 AM

Nope, hot pixels are a part of life with imaging chips.

By the way - some of those dots will occasionally be geostationary satellites. They may even flare up at times (which you can see if you capture lots of shots in a row).