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DPChallenge Forums >> Photography Discussion >> Wierd LOng Exposure Sensor Things? Help!
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Showing posts 1 - 5 of 5, (reverse)
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 10/05/2006 09:40:18 AM · #1
ok, i've been trying to do the lovely star shots i've seen people post here, and just can't seem to get it.

when i do very long, very low light exposures, i get this odd plaid-like texture on my images. i assume it's the sensor. what should i be doing? or do i need something new?

pictures to follow in a few moments...

30 sec, f32, iso 100

30 sec., f9, iso 100

30 sec., f9, iso 100

Message edited by author 2006-10-05 09:46:40.
 10/05/2006 09:58:10 AM · #2
I don't know the answer, but I have noticed it too on the 5D. I'm pretty sure I didn't used to get it on the 10D though.

Someone here will have an answer - I'd be interested too.
 10/05/2006 10:03:02 AM · #3
Yes, what you're seeing is effects from the sensor. It's partly because you're "pushing" the image (raising the exposure in post-processing or RAW conversion). Here are some tips for better results:
- Increase ISO to 400
- Shoot at wider aperture. My night landscapes are usually shot at f/2.8 (sometimes faster), or at very least f/4. Your lens limits you to f/4, so try that, or f/5.6 if you must stop down for sharpness.
- Expose long enough so that you don't have to increase exposure in RAW conversion or post processing
- Use your in-camera "long exposure noise reduction." This will nearly eliminate the fixed-pattern portion of the noise
10/05/2006 11:40:35 AM · #4
Shoot with the aperture wide open unless there is a foreground object that must also be in focus. Even at ISO 100 you can still get acceptable results but 400 or greater is better. All celestial objects are at infinity for photo purposes, so use manual focus set to infinity; careful here, the lens 'infinity' setting may not perfectly match your camera, so check it visually in daylight on a distant object. A 30 second exposure should yield thousands of stars and a few deep space objects like nebulae and galaxies. Some noise will still be present but is usually not as bright as the stars, so use the 'curves' or 'levels' adjustments to reset the black level above the noise threshold. With a 30 second exposure there will be a slight amount of trailing in the image which can be eliminated only by using a "tracking" equatorial platform. With a 50mm lens, the trailing will not be obvious using a 15 second exposure.
 10/05/2006 03:26:39 PM · #5
thanks very much both of you. now i'm stoked to go and try this!
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