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what are these strange artifacts on this photo?

how to avoid them?

photo is shot with canon 1200d 50mm f1.8 4seconds shutter

artefacts

thank you

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This is flare. These occur because you're shooting into a light source, and the rays are reflecting off internal glass surfaces--most probably a UV filter if you have one on the lens. Note how the bright images "echo" the bright light sources in the image. Removing the filter can help.

I also note the image is overexposed. This is because auto-exposure systems use metering a specific way. They measure all the light in the scene, "average" it, and then set that average to be the middle point in the camera's dynamic range (middle gray). When you're night-shooting and the scene is mostly black, then that average value is actually darker than the "middle gray" value, and when the camera shifts the settings, you get overexposure. If you want black skies in your night shots, you'll want to learn how to override the AE system with EC (exposure compensation) in the Av/Tv/P modes or explicitly setting the aperture, shutter speed, and iso in M mode.

See also: What causes these green dots in my image?

  • no filter here. what lenses are good then for this kind of shot? – alexpoly Dec 25 '14 at 0:06
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    @alex there is nothing wrong with your lens. Unless you want to spend a significant amount of money for a minor improvement to lens flare there no point in spending money on a new lens. – dpollitt Dec 25 '14 at 10:26
  • Just tell people you were trying a J.J.Abrams style. – JDługosz Dec 25 '14 at 14:59
  • For more about how to deal with this problem, please see this answer: photo.stackexchange.com/a/35054/15871 – Michael C Dec 25 '14 at 18:15
  • Although I've never tried it, you could make a mask for the front of your lens that blocks half the field of view. Then combine two exposures, one with the mask on the left, the other with the mask on the right (or you might do the same thing with a strong graduated Neutral Density filter). The reflections would still show on the "dark side", but you would mask them out when combining the two images. – Michael C Dec 25 '14 at 18:38

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