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Past Article Calendar

August 2009
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Sigma 18-250mm f/3.5-6.3 DC OS HSM

Practical use

I used the Sigma 18-250mm when preparing the article ‘Crop or Cram‘, partly to see how it held up in comparison to the 70-300mm SSM G and the Sigma 70-200mm f/2.8 HSM. Here’s one the shots from the Alpha 700, at 210mm and f/8, showing that good geometry is important even when straight lines are only incidental to the subject:

And here is one at full 250mm from the Alpha 380:

These have been processed with CA correction, the one aberration which the 18-250mm shows. It is not a strong CA colour fringe, and it is also very sharp, meaning that once you hit the right correction values using Adobe Camera Raw, Lightroom or any other CA-correcting process (including Photoshop>Distortion>Lens Correction filter) the effect disappears entirely leaving a sharp image. Clicking either shot will open a pBase option including a full size version and EXIF data. This is a direct URL for the full size 14.2 megapixel shot above:


I suggest you take a look at this regardless of bandwidth. It’s complimentary to the abilities of the new Alpha 380, and even more so to the sharpness of the Sigma. It’s an action shot and even at 1/1000th you can see the effects of motion blur, but if you know how to read image sharpness, it’s easy to tell from focus error or lens aberration. The Sigma 18-250mm has one quality which our Sony 18-250mm lacks, and that is dead-accurate focusing, no FF or BF on any of the bodies we have tested it on. This is just as well, as the view through the Alpha 380 finder is so small and becomes visibly dark as you zoom to 250mm. Manual focus would never be an option on this camera.

How about 18mm? Well, the good news is that the lens shows excellent geometry again, and of more note is the absence of mechanical vignetting to the corners. As owners of the Carl Zeiss 16-80mm, or the Sony 16-105mm, or the Sony 18-200mm and 18-250mm lenses will already know it’s not unusual for a dark corner to appear. Sometimes this is consistent, other times it seems to be a result of the SSS tracking the image to a darker place. I certainly know that I end up cropping the height of most shots on our 16-105mm taken at 16mm because the top right corner vignettes.

The huge 72mm front glass of the Sigma, and its overall generous optical design, seem intended to remove vignetting – probably a necessity with the OS mechanism. The lens must have extra coverage to allow the moving element/group to do its work without losing resolution or brightness. Consequently, this lens (like the even bigger Canon 18-200mm f/3.5-5.6 IS design) has been made to a different standard than non-stabilised superzooms.

Here you can see 18mm on the Alpha 350. Some CA correction improved the shot, but this was just -18 Red/Cyan, compared to a typical value of -30 Red/Cyan needed by nearly all other lenses at 18mm. You can see the geometry – just a hint of barrel distortion, but not enough to make those flagpoles look wrong. Depth of field at f/11 is just right for the 14.2 megapixel resolution, without diffraction sharpness loss setting in as it does at f/16 and f/22.

Finally, a shot which is taken under all the wrong conditions. Wide open, 18mm, by natural light at 1/8th, hand held, with the photographer crouching on the top of a desk opposite the bookcase – a very unstable shooting position, ducking down to get the shot in below a chandelier and avoiding treading on my Mac wireless keyboard after hearing it crunch under my heel once… it took a few shots to get the focus right, the light level at ISO 320 on the A700 was fairly low, and the natural movement of the shooting stance meant firing very quickly after securing focus. Otherwise, as with many shooting postures, the camera could move two or three inches fore and back with just the stabilising movement of remaining balanced.

You can see that at close range, the 18mm barrel distortion is more visible – this is always the case, and a good reason why test charts should never be used to test distortion with wide-angles. Of course, the weight on those shelves is responsible for some of the curvature otherwise the distortion would be of a type never seen before in lenses. American Red Oak is a good choice for bookcases but after 20 years the shevles could do with reversing!

There is hardly any vignetting (the window light is more responsible for the brighter centre of the image, along with the coincidence of some lighter coloured book spines). I have not corrected CA in this image at all, and you can view the full size version by clicking the image for the pBase page, or directly here:


Considering the conditions of shooting, the OS has worked well and the lens shows good sharness corner to corner. Every book title is legible right down to the old copy of ‘The Family of Man’ lying flat on top of the centre bottom shelf.

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8 comments to Sigma 18-250mm f/3.5-6.3 DC OS HSM

  • Photorer

    OK – time has come to decide between new lenses for the A77 that is on order –

    Sigma 18-250 OS HSM or Tamron 18-270 Pz motor?

  • scooter

    I managed to take some more shots today, did some experimenting with
    aperture and ISO settings. Double checked that OS was off and SSS on.
    I took a number of pictures in the f8 – 11 range. 18mm, 250mm and a few macro shots. For the macro shots, I tried both manual and Scene/Macro settings, didn’t make any difference that I noticed. I tried the f11-16 range.

    I hate to say it, but I am not impressed.
    The image quality at low ISO (800 and below) is about the same as my P&S up to about ISO 200; but going to higher f numbers forced me as high as 1600 ISO …in bright daylight. So stopping down the aperture starts to cut into the advantage of the better ISO noise.

    Macro IQ is definitely better on the P&S.

    I do see some stunning images on the web from this setup, but right now I’m thinking there may be a lot of PP involved. I certainly never came close to “stunning”.

    This being a lens review article, I feel a bit guilty bringing the camera body into it, but I can’t really separate out whether it is a limitation of the lens or the body. I concede it may be me, but I sure don’t see what I’m doing wrong.

    I really was hoping for better low light performance (got it), more features (got those), and better IQ both in good light(nope) and macro (nope).

    I’m pretty disappointed. I did a lot of research and this combination came out as about the best all-round setup I could find. I really wanted it to knock my socks off … but I think it goes back in the box and back to the dealer.

    I don’t know whether to bother trying one of the other manufacturers, or whether to give up on the superzoom idea and go to lens swapping.
    Or maybe just forget DSLR’s altogether.

    Anyway, thanks for your help David. I’m glad the lens/camera works for you, I guess maybe I just had unrealistic expectations.

  • scooter

    Thanks for the quick reply and the tips David!
    It’s raining here in southern NH/USA so I can’t get out and do test shots right now, but as soon as I can I will and will get back to you.

    Your tips about aperture may be the issue; the quick shots I did last night were as wide open as the lens settings would allow; so maybe that’s the problem.

    I was using SSS, with the lens OS off. I doubt I can be patient enough for that long wait for the OS to activate !

    I hope I can get this IQ straightened out, other than that (which is key of course) I really like the setup.

  • scooter

    I guess I’m looking for a sanity check. Never had aDSLR before, just bought a Sony a55 and Sigma 18-250 and am surprised at the relatively poor IQ compared to my Canon Sx120 P&S. I expected IQ to be better in all lighting, but so far (only a few test shots, can’t do many if I want to return it – which I think I do), disappointed.

    At high ISO, the a55/Sigma is clearly superior.

    At low ISO, outdoor shots in good light, both macro and wide, the Canon P&S IQ is better. Much unexpected!

    Is this common, that a P&S IQ be better at low ISO?
    Or maybe there is technique I’m missing … maybe just because I’m not at the ‘sweet spot’ aperture for the sigma?

    Been shooting at the lowest f-stop possible. Maybe that’s bad?

    Reviews for both the a55 and the Sigma are all good … so if this is as good as it gets I guess there’s no point in trying other DSLR / lens combinations 🙁

    • Clearly something is very wrong as the A55 image quality at low ISO is superb – and the Sigma is the best lens of its type. First of all, the Sigma is generally at its best around f/8 to f/11 on the A55. It will not be capable of good macro shots at 250mm and f/6.3 (wide open is never sensible with any long range zoom) and the depth of field will not be sufficient for many subjects, so for macro work I would always try to use f/11 or even f/16 and move to a higher ISO. It is noise free up to ISO 1600 if processed correctly from raw, and this is very useful for macro. If you try to stop down to say f/16 or f/22 for routine work you’ll just get soft images (diffraction) and probably subject movement at low ISOs.

      One thing to be absolutely sure about is the SSS setting and OS on the lens. We use the lens OS, it really helps with viewing at longer lengths. This means the SSS in the camera MUST be set to OFF in the menu. If you leave Steady Shot set to ON, you will get very unsharp images when the Sigma lens is also set to OS, the two systems will overcompensate or even work against each other and blur the image badly.


  • Daved

    Thanks a lot for the review, very detailed and very interesting indeed. Did you try it on an Alpha 55 which you reviewed as well?

    Thanks again for what you do David for the Alpha users.

    • admin

      We’ve used the 18-250mm on the A55 and our sample works well enough except for one small issue, from time to time the lens can lose contact with the camera. It needs a factory fix to be perfect because it is an early example of the lens. Service is restored by simply pressing the lens release button and briefly shoogling the lens, it seems to be a mount-fit issue nothing else.

  • Photorer

    A very interesting review….. I have the Tamron 18-200 and really loved it when I first bought the lens, but now it is starting to feel a little long in the tooth, or my photographic skills have improved! The implementation of HSM is an obvious drawcard for this lens, and thanks to your review, I might have to start saving up for it……..

    Your reviews always show the users’ perspective, not just the technical jargon that you get elsewhere. The important part of how a lens performs is how if feels on the camera, and the resulting images that it takes along with how much extra work you need to put in afterwards to get the image right! To me, the less that has to be done, the better!

    Thanks again!