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12-27-2011, 12:55 PM   #1
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Sigma 30 F/1.4 on K10D

This is the first time I've used this lens for outdoor night time shots downtown. When home I noticed all the distortion on the Christmas lights.

What's going on here? Is this just what I should expect for this lens and lights at night?
I have to add that I was shooting hand held with ISO400 F/1.4 1/50 sec Shake reduction ON

I like the compact size of this lens and the ability to shoot without flash indoors. But this really surprised me!

How would the Pentax 31 F/1.8 do in this situation?


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Thanks,
George

12-27-2011, 01:24 PM   #2
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Oppositz, were you using a filter?
12-27-2011, 01:38 PM   #3
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No filter.
12-27-2011, 01:58 PM   #4
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Well, I think the scene has many disadvantages, along with your choice of camera settings that would make the photo turn out like this. It is low light, and the camera I am guessing was set to full scene metering. At f1.4 the depth of field is going to be relatively thin - when you're shooting a larger scene like this and don't necessarily need/want subject isolation something towards at least F4 would be more beneficial. This could have been achieved with a slower shutter speed - you probably could have gotten away with 1/15th handheld with shake reduction (if you have steady hands perhaps even 1/10th). Since the metering is averaging for the whole scene, the lights on the tree will also become over exposed and harshly lit. Overall the image appears soft due to shooting wide open at f1.4 (could also be a small amount of shake). It is just a difficult scene, especially for the k10d which does not perform well in dimly lit situations. A tripod and some trial error or bracketed photos would have netted a better result.

12-27-2011, 03:08 PM   #5
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Distortion

What concerned me was the distortion of the lights. I've been playing around with the camera and lens at home and find the same thing. Guess once the rain/snow stops I should get out with tripod, and experiment. Maybe this is just the price we pay at F/1.4? Maybe it is my poor focusing?

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12-27-2011, 03:25 PM - 1 Like   #6
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It's a documented issue by a few lens reviews, for instance, this one: Sigma 30 mm f/1.4 EX DC HSM review - Coma and astigmatism - Lenstip.com

In general, aspherical elements are designed to reduce spherical aberrations like coma and astigmatism. The lens design of the Sigma 30 1.4 has one aspherical element. In your photo, what you are noticing on the tree lights is coma. If you stop down around a stop or two, you will see the coma reducing significantly.

EDIT: The Pentax 31 Ltd also has some comatic aberration, review from the same site: http://www.lenstip.com/321.7-Lens_review-Pentax_smc_FA_31_mm_f_1.8_AL_Coma__...and_bokeh.html Anyways, the moral of the story is that as you go wider aperture, coma tends to start becoming an issue.
12-27-2011, 03:25 PM   #7
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My guess is motion blur. Admittedly with a 30mm lens at 1/50 sec with SR on, I wouldn't expect this. Probably wouldn't be nearly as noticeable if the shot had been exposed for the highlights. Easy enough to test; go shoot something similar but use a tripod, and see if you get the same little triangles.

Edit: icywindow's answer much better!

Last edited by baro-nite; 12-27-2011 at 03:26 PM. Reason: correction
12-27-2011, 03:31 PM   #8
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Thank you so much.

Great link too!

12-27-2011, 03:55 PM   #9
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You're welcome; before I forget, I really like that shot, cone lights and all.
12-27-2011, 06:32 PM   #10
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Most photographers who shoot this kind of shot use a tripod, which will allow a smaller aperture, which, in turn, will give you better focus and less lens blur. No lens gives its best output wide open. For most very fast lenses like this you'll get maximum sharpness somewhere around F4-5.6. As a matter of fact, portrait photographers take advantage of lens softness wide open to create more flattering faces shots with less background clutter. With hand held, available light photos shot at wide aperture you can focus just on a face, which is generally fine.

Also, even with shake reduction on, you'll get some motion blur shooting hand held. If you don't want to carry a full tripod, the Gorillapod is a great option. You can usually find somewhere to use it and get the advantages of a steadier camera.

Besides, the 31mm 1.8, while an excellent lens, is very expensive.
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