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DPChallenge Forums >> Tips, Tricks, and Q&A >> Ugly artifacts when doing IR with Canon G5
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 05/27/2004 05:02:48 PM · #1
Take a look at this 100% crop from an image I took recently with an IR filter on my Canon G5:

The picture was taken with a 15s exposure at f/5.6. I have taken a lot of nightshots with long exposure times, but have not seen such artifacts. Are those typical for the G5, or is something wrong with my filter? I will try setting the camera to "sharpen less", haven't tried out if that makes this better yet.

05/28/2004 01:05:53 AM · #2
bump ...
 05/28/2004 01:16:52 AM · #3
What IR filter do you have again?
 05/28/2004 01:21:33 AM · #4
Originally posted by faidoi:
What IR filter do you have again?


It's a Hoya R72. But I can't imagine that that's the problem, because the artefacts are much too sharp to come from the filter (IMHO, anyway).
 05/28/2004 09:07:50 AM · #5
is it possibly dust on the lens or filter?
 05/28/2004 09:35:39 AM · #6
You should check the ISO setting. Normally 200 and 400 are very noisy. You should use the 50 setting for the ISO. Then another very important thing that I noticed is the temperature. The nightshots I've been taking during the wintertime in the open are less noisy then the summer ones... Actually I've tried a funny thing in order to avoid the noise: I've let my cam in the fridge (4 Celsius) for about half an hour before taking a 15s picture and I could see some difference: it was a 30% less noisy....
Another trick is to blind the camera during the "dark frame": after the 15s it needs another 15 for the dark frame. The thing works sometimes for me...
 05/28/2004 09:56:00 AM · #7
The picture was taken at ISO 50, so it's not that. But AlexHugel's point about the temperature is a good one. I only got the camera in November, so most night pictures so far were taken when it was really, really cold ;). I just checked a few night pictures I took two weeks ago, and they also show some similar artifacts, though to a lesser degree (which makes sense, because the exposure times were shorter, and it was cooler in the night).

I don't think it's dust, that wouldn't produce such sharp effects. Also, the distribution is unequal, there are more in the dark areas than in the light ones (that's not very clear from the small image I posted, I guess).

Looks like I will have to try that fridge technique next time I take a night/IR picture when it's warm ... thanks for that suggestion!

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