Alley in Pisa, Italy

by Lars Kotthoff

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I have a Canon 550D and bought a Sigma 17-70mm lens to upgrade from the 18-55mm lens kit. I decided to go out and try the new lens with some night shots. To be honest, the results were bad. I used a tripod but found that images were blurry in almost all cases. I experimented my ISO range from 100-1600 and aperture from 4-20 with not one great image!

Any light source was completely over saturated. Even when reducing it in photoshop. I also notice that when I do my metering I have to set the exposure to nearly 2 stops down to shoot a photo at the correct exposure than what the light meter is telling me. Should I be expecting more from my lens?

Here are links to 2 images which were "in" focus. There is heavy saturation on the blue lights.

heavy saturation

and this picture, the focus was set on the clock face!

Focus was set on big ben clock

Do I send this back? Its my first lens I've bought besides a 50mm 1.8

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5 Answers 5

In the first picture, unless you were using spot metering, the meter was telling you what to set the camera to in order to get a midtone sky. The lights (and the Eye) constitute only a relatively small portion of the image; to achieve an overall average exposure, the camera is telling you to significantly overexpose. The picture is probably still somewhat overexposed as shot unless it was a particularly overcast and smoggy night. If the Eye is bluer than you think it should be, you can put that down to the difference between the way your eye sees different lighting and the way the camera sees it. Note that in the building to the left, the light is too yellow, and the colour balance of the light in the smaller building at centre bottom is just about perfect. Different lights were used for each, and your eye doesn't see the difference in colour temperature nearly as acutely as the camera does (film or digital doesn't matter; neither does the lens). Since you won't have the budget to control all of the lighting, and you don't have a single main source of light to even everything out (like the sun), you'll probably find that the riotous circus of different lighting types used in the city is going to be a constant problem Remember that you can always fix that in post by developing the RAW image several different ways, with setting that best suit different parts of the image, then blend those various versions (sort of a colour-based version of HDR).

In the second picture, the exposure was better, at least for the Palace (the famous logo of the world's greatest brown sauce), but there is significant flare. It looks like you were using a pretty small aperture there (the "star" patterns around the brighter lights and the shape and size of the flare blooms are a giveaway). That is what's leading to the details in the clock, etc., being washed out. Diffraction around the lens's iris blades is causing the bright lights to spread out. In the reduced-size JPEG it's hard to tell for sure, but it looks to me like the focus is actually much closer to the camera than the clock* (somewhere closer than the bike lane marking, going by the apparent detail on the pavements and in the street proper just left of the centre of the picture).

So perhaps the pictures aren't what you were hoping for, but it's not the lens at fault. It's more likely that you have little experience shooting outdoors at night. The rules are not quite the same as they are during daytime. That is, circumstances are different enough that you really need to understand what your camera is metering, and how to "place" tones in the picture. The only way to do that is to take a lot of pictures, get a lot wrong along the way, and get increasingly more right with experience. It helps to keep a record not only of your camera settings, but of your assumptions and reasons for setting the camera that way, and the results you obtained -- even for images you don't keep.


* Big Ben is the bell upon which the hours are struck.

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Wow, thanks for the awesome feedback guys. I have been using evaluative metering but will have a look at changing to spot metering for more accurate exposure settings and yes, it was overcast that evening :-) Your answer was amazingly comprehensive and has restored faith in my lens and a little less faith in my own skills.. haha. –  Grooverinthesouth Oct 2 '12 at 14:07
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Lenses have very minor effects on colors. One can usually measure them but not see them so easily. The saturation part of your question has to do with exposure. In particular, the blue channel appears to be clipped which you can see by looking at the blue histogram in a photo application like Lightroom on Windows/Mac and Geeqie on Linux.

Softness on the other hand can be a result of the lens. In order to determine if your lens has a problem, you have to make some controlled test and set your expectations too. Not all lenses are equally sharp, particularly if you compare across types of lenses. A moderate zoom like the Sigma 17-70mm is somewhat softer than a prime lens at the same aperture.

First, I suggest you remove focus out of the equation and try to focus manually. Compare this to where the camera focuses. If there is a difference, you may have a front or back focus problem. Since your lens is a third-party lens, I am not sure who would do the calibration. When everything is the same brand, you send your camera and ALL your lenses and they get calibrated together. High-end DSLRs have AF Adjustments to do this yourself. You can use Live-View Contrast-Detect Autofocus to avoid front/back focus issues.

Next, you need to make tests at the lens' optimal aperture. It has to be stopped down from wide-open but without passing the diffraction limit. Note that on same cameras when using low-quality lenses, this may never happen, particularly at the long end of the zoom. For yours, it should be a F/5.6 near wide-angle and F/8 near the telephoto end.

Test your lens with a subject indoors where you are in control of conditions. Avoid having a light source directly in the frame which reduces contrast by introducing flare and can easily result in a soft-looking image. Use a tripod and mirror lockup with a self-timer or remote trigger to make sure the camera is completely still. Take a few shots. If these images still come out with a general softness, then consider returning or exchanging the lens.

BTW, Sigma is notorious about poor quality control and samples of the same lenses often show huge variations from being very sharp to being unusable soft. I have had some at each end of the spectrum.

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I thought the Big Ben picture was ok if you want to prevent parts of it from being blown out you could use a little black piece of cardboard and wave it at the top part of the lens to 'blacken' it out. Do it properly and you will under expose that portion so in the final picture it won't be as blown out.

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That's an interesting technique. Do you mean to wave it around during the exposure? –  mattdm Oct 11 '12 at 2:09
    
Yes, just wave/cover (depending on how crazy you want to look to other people in the street) for a short period. Let a little light in and repeat to your satisfaction. I should clarify you don't really need a big piece, just a small one that's enough to cover the part of the lens. –  Peng Tuck Kwok Oct 11 '12 at 2:11
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I would suggest that the camera is trying to expose for the whole scene, as it sees it. As you are shooting at night, the camera goes for that 17% mid-grey and brightens up the scene. It doesn't know that you are shooting at night, and is doing its best to make what it thinks is the best exposure. The opposite happens when shooting bright subjects (such as snow) - whereby the camera thinks everything is too bright and darkens it down a little resulting in grey snow. This is common to pretty much all cameras - this is completely normal!

In your first image of the Eye (from Waterloo bridge?) the sky appears brown like that because of the reflection of the predominantly orange street lighting from below, off the clouds above. This is enhanced by the camera trying to 'brighten' the scene to give you a correct exposure. To account for this your best bet is to use exposure compensation to manually 'under-expose' the shot. Try for -1 EV to start. Check the photo on your camera's screen and adjust +/- as necessary. It would also be good to ensure you are shooting in RAW so that you can then adjust for the colour temperatures and bright/dark areas better in post.

In the second image of Big Ben, again the camera is exposing for the whole scene, and if you look at the brightness of the rest of the palace, it's not too bad. But the clockface is totally blown out as it's such a relatively small area of the image. Again, use the same trick of applying some negative exposure compensation and you will see that the clock face retains the detail. I don't think that its out of focus as such - but you have the same effect here as many people experience when taking a photo of the moon, and it's just a white blob.

The alternative in both these situations of course, and to retain more control is to shoot in (M)anual mode. Shoot at ISO 100 since you're on a tripod. This will minimize noise.

You may also wish to make use of the Auto Exposure Bracketing (AEB) feature of your 550D to take three photos in succession, all at different exposures, then blend and tone-map them together in a third party app like Photomatix Pro (a free 30 day trial is available). See your camera manual for how to enable and use AEB. You don't have to have your HDR look all crazy - you can make it look very natural and "how your eyes see it" if you wish....

So just to confirm, I don't think there is anything wrong with your lens! I just think you need a bit more knowledge and experience about night shooting and how your camera works. This comes with time and asking questions like you have done on here! I hope my answer helps.

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I noticed something similar in pictures I took at night and found that when using a tripod one has a tendency to take ones eye away from the viewfinder. This changes the exposure value and metering on Canons. I suggest you try it again, at night, take an image without covering the viewfinder then take an image covering the viewfinder. I think you will find that the results are different. Take it from there. Its not the lens, LOL.

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