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01-30-2010, 07:08 AM   #1
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Question regarding street lights at night (Includes sample picture with a K-x)

Hey guys.

I went out yesterday night to take some pictures and I couldn't get round an "issue". I am new to DSLR (I had SLRs before - a Praktica, and several P&Ss) so I hope I'm not asking something too stupid.

The street lights on my long exposures (over 20 seconds) always look like stars. What can I do to make the star effect go off? Please consider the fact that I am a noob to the DSLR world.

Settings are below. Here is the photo (please view full size):

Pentax K-x | 18-55 kit lens





Last edited by G-Diesel; 01-30-2010 at 07:23 AM.
01-30-2010, 07:13 AM   #2
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Try to use the widest aperture and see whether you still get the "star".
01-30-2010, 07:19 AM   #3
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The stars in your image are caused by the aperture blades. This effect is more pronounced the more you close your aperture and at f/13 (which your EXIF data show) the aperture is already closed very much. Open it more and use a shorter shutter speed instead and the stars will get smaller and eventually be gone.

I think it would be a good practice to make a series of images with different aperture settings, to get a feeling for the effect.

Ben
01-30-2010, 07:30 AM   #4
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Thank you very much for your input. I usually use pretty long exposures because the pictures usually turn out better than using a shorter shutter speed. I will try it at several combinations then, thanks a lot for your help again. I am glad to see there is a place where I can get some help improving my photography.

01-30-2010, 08:45 AM   #5
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Btw. normally people like those stars.

And to further expand your knowledge:
If you have an even number of aperture blades, the number of diffraction spikes is the same as the number of blades.
If you have an odd number of aperture blades, the stars will have twice as many rays as there are blades and their intensity is lower.
01-30-2010, 09:21 AM   #6
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As an old film guy, I've been having trouble convincing myself to trust the high-ISO capabilities of these new cameras. '3200 ISO? That's gotta look like &^$%!'

But I've been working to free myself from the tripod and embrace the new way. Here's a night shot of Whistler, hand-held K-x with the kit 18-55 lens. f/3.5 at 1/13 second. (Pentax SR seems to work for me...)
01-30-2010, 10:49 AM   #7
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High Iso is definitely usable on my K-x but there is no way I can get a perfectly clear shot like the one I posted using a much higher iso...Your photo looks fine nonetheless. I usually only use higher isos for portraits and "I have to do it now" shots.
01-30-2010, 11:38 AM   #8
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High quality lenses with many aperture blades are able to produce round aperture shape at most f stops. Usually those are lenses with 9 or more blades. Some older manual lenses have such aperture. I have Jupiter 37A and Industar 26m that both have approx 20 blades, and the aperture is always round.

Still, when stopped down very much you'd get a flare. Btw, with some lenses you can use a custom shaped aperture:
DIY - Create your own Bokeh | DIYPhotography.net
and try to make it completely round - only smaller.

Very nice picture you have made. Actually, in most of the cases people like those stars. Sometimes i just wish that their angle could be adjusted, or some strong flare crosses some important subject.

01-30-2010, 12:08 PM   #9
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Thanks a lot. I am actually amazed by the quality my K-x is delivering on night shots.

That like you posted is awesome, thank you. Really, really interesting.

I would prefer a round light other than a star, I guess it's a matter of personal taste.
01-30-2010, 01:36 PM   #10
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Diffractions spikes are different from bokeh, in that the spikes are stronger the more in-focus something is, and bokeh is more noticeable the more out-of-focus something is. They're both related to the shape of the aperture, but they are distinct phenomena.

As for the effects of an odd number of blades, here's a picture of the effect as produced by the DA* 16-50mm. It has 9 blades, and so creates 18 diffraction spikes around point sources.

01-30-2010, 01:39 PM   #11
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This has nothing to do with the camera so I'm moving it to Beginners Corner. This discussion should be useful information there.
02-01-2010, 01:29 PM   #12
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My apologies, I should have picked the right forum. Thank you all for the extremely useful input guys.
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