Review- Sigma 18-50mm f2.8-4.5 DC OS HSM Lens
May 2011, Carl Garrard
Sigma 18-50mm f/2.8-4.5 SLD Aspherical DC Optical Stabilized (OS) Lens with Hyper Sonic Motor (HSM) for Sony Digital SLR Cameras
COMMENT HERE: MY COMMENT
I've been using this lens for over three months in many different conditions. I use it for backpacking, as a lens on the DSLR I have in my vehicle at all times, and as an indoor shooting lens because of it's decently bright aperture range starting at the wide angle (f/2.8 at 27mm APS-C equivalent, or, 18mm). Also I've shot a test chart here for those who like to see a more controlled set of images for comparison to go along with real life images.
So know that this review comes from quite a bit of practical and technical experience.
Size and Handling
The Sigma 18-50mm DC OS HSM (abbreviated for ease of reading) is larger than any standard 18-55mm kit lens you'll see included on most makers DSLR kits (see size compared to Sony's 18-55mm SAM). It also has a larger front element that takes 67mm filters. This size increase is due to the fact that the Sigma has a brighter max aperture range than all "standard" kit lenses. Note that in the image below the lens hood makes the Sigma appear larger overall than it actually is. It's definitely not as small as other kit lenses but it low overall weight and mid range size shouldn't be an issue either.
Sigma has marketed this lens as an economic replacement/alternative for the 'standard kit lens', offering more features for near the same retail price had you bought the kit lens separate from a DSLR. What Sigma doesn't market about this lens but certainly should, is the fact the the slightly larger size affords better handling with larger rings for focusing and zooming. It has well placed controls for the image stabilization and AF switch on the left side of the lens. Length itself never changes due to the fact that this is an internal zooming lens- a pretty rare feature for a lens of this price. This comes in very handy, and gives the lens the feel of a fixed prime lens build wise.
Ask anyone who knows anything about DSLR lenses if you can get HSM focusing, Optical Stabilization, Internal Zooming, and a non-rotating front element for under $350.00 and they might say you are crazy. Not to mention this lens has an included lens hood, metal rear lens mount, and a decent fast f/2.8-f/4.5 max aperture range, and, it has close focusing under 12" that equates to about 3 1/2" wide minimum capture area, or about a 1:4 magnification ratio.
Lens elements wise the Sigma has two super low dispersion elements and three aspherical lens elements that helps to combat chromatic abberations and optical distortions. The elements are also coated to help reduce flare and ghosting. Sound attractive?
There's no doubt in my mind that this Sigma has the best build quality for the dollar over any consumer zoom lens at this price. Granted the lens is mostly made of plastic, yet it is covered with Sigmas trademark rubberized crinkle finish and this includes the lens hood too. Focus and zoom rings are pleasing to the sight and touch, and the rubber surface and spacing on the surface texture is also pleasant. It gathers or traps little dust which always tends to bug me with the Sony lenses.
There's nothing on this lens that seems cheap or budget kit lens in feel or performance, and it grew on me very quickly in this regard, in fact almost immediately out of the box. This is the first Sigma lens to impress me so much, and it just so happens to be the most affordable one I've purchased yet. Seems pretty unbelievable right? The optical performance must be a bust, you say. Let's take a look at that now.
Fact, this lens is very sharp in the central area of the image in any focal length (about 70% of the image, centered), or any f/stop and increases up to f10. Where you'll see performance variations in sharpness are the corners. At wide angle the Sigma has its weakest extreme border and corner performance at f/2.8 but shapes up very quickly by f/4.
At 50mm it seems to be much less, softness decreases automatically because it's aperture at 50mm can go no larger than f/4.5. After quite a bit of use I've determined that the Sigma has the best center performance of the lenses at this price or class, but that it falls slightly short in the corners.
Considering that it shapes up quite well at f/5.6 and beyond to f/11, and that this lens is in a totally different league feature, build, and quality wise compared to those lenses, I find the Sigma easy to forgive in this regard. Also it's never terrible at all in the mentioned weak areas, decent at its very worst.
Vignetting (corner shading) shows similar traits as sharpness through the range, typical of APS-C coverage lenses. Shading isn't all that pronounced though, even the much more expensive and highly revered Tamron 17-50mm f/2.8 has worse vignetting than this lens does throughout the entire zoom and aperture range. Shading seems to fall about 1-1.5 stops at f/2.8 wide open, nothing to gripe about at all- especially considering that you won't be using this lens wide open very often at its widest settings in scenes where vignetting can be spotted on real life images. In other words, nothing to get in a tizzy about, or worry about.
Ghosting was near non existent, couldn't get this lens to show any, and Flare was well controlled even at wide angle with no lens hood on in bright indoor or outdoor light sources. It helps that the lens is internally zooming, at wide angle most elements are recessed quite a bit back from the front element- so the body itself acts as a sun shade. In all my use with this lens I never found a reason to attach the lens hood- pity because it's a very nice one.
Barrel distortion is just less than average and tames/flattens by 28mm wide, pincushion distortion is also less than average- neither being a major issue at at all. Some correction to the wide angle barrel distortion was easy to do in photoshop, requiring little correction because of a slight and consistent curvature (not moustache shaped).
Contrast and color are above average here for a lens at this price. Contrast is really only slightly low wide open at 18-22mm, and never bad at all. Color is neutral, the coatings do a good job of not showing a blue or yellow bias cast, and falls in the middle where it should be. Very nice colors from this lens- it'd be fun to try it out on a film camera if only it covered full frame (sigh, can't have it all I suppose).
Chromatic Aberrations (color fringing) of all types were well controlled at all apertures, but do show more of course at the largest apertures. Never found them to be an eyebrow raiser at all, what little shows is easily correctable if you really think you'll need too. I didn't.
No complaints optically, but I'm not raving about it either. Neither should I be complaining either considering it's price.
Focusing Speed, Accuracy, Battery Life, Image Stabilization
Focusing speed on the Sigma is quick, but not blazing fast. There are limitations to this lens after all! However it's better than the average kit lens here, which tend to be pretty nice lenses from the major manufacturers nowadays.
There tends to be a slight hesitation at times to find focus, but it's very slight and not consistent enough to present "an issue". The HSM motor is quiet but not silent. Accuracy on two different camera bodies has
been spot on (Alpha A580 and Maxxum 7D), even at wide angle/wide open.
I find that the HSM focusing lenses do tend to draw more battery life and this was evident much more on the 7D than the A580 which apparently isn't prepared to handle the extra draw of power. The optical image stabilization also contributed to a lower than average battery life on the 7D, but the Alpha A580 didn't really seem to be affected much (probably because I can get 1800 shots off a single charge of the A580, and about 500 off the 7D).
So just be prepared to see a bit more draw of power than you might be accustomed too when using both HSM and OS. Considering the trade offs of near silent focusing and its' OS system, I doubt anyone is going to complain about that.
Sigma's OS (optical stabilization) on this lens performs surprisingly well. I'd say you'll get about a stop extra performance than in-body stabilization seen on Sony Alpha, and Pentax DSLRs. The woozy effect of looking through the viewfinder while OS is engaged is the only minor disadvantage of this type of system. It doesn't bother me at all, and in a way it helps to actually see the system working and when you should make your exposure.
Since the OS system doesn't seem to affect its price, Pentax and Sony users really benefit from having two types of stabilization to choose from. The big two can't offer that to it's users! Smart of Sigma to offer this for these mounts while other makers such as Tamron exclude their version of OS. They could have easily made the decision to cut costs and not include it, but they did not.
Final Summarized Conclusion
Sigma 18-50mm f/2.8-4.5 SLD Aspherical DC Optical Stabilized (OS) Lens with Hyper Sonic Motor (HSM) for Sony Digital SLR Cameras
Well, how much does the Sigma 18-50mm f/2.8-4.5 DC OS HSM lens cost???
Since you've likely already skipped the written conclusion (and probably the other parts of the review) to view the image samples first, I don't need to convince you of much. In fact that isn't my job at all. My findings though of the Sigma are that this indeed is a lens that performs, feels, and operates at a cost much higher than it's shockingly good $199.00 USD Retail price tag. Sigma have never disappointed me on their lens prices, but don't get started on their DSLR prices (SD1 anyone?). You know I had to throw that in there.
Image quality may not be as high as the very best performing kit lenses from Canon and Pentax (Sony are good but samples vary too much) in terms of sharpness in the extreme borders or corners of the frame, but overall this lens is definitely an upgrade over the kit lenses. In all other areas of image quality (such as contrast, color, vignetting, ghosting, flare, etc.) this lens seems to perform better than the kit lenses. You'll probably notice those traits more than just sheer sharpness.
Bokeh is an often overlooked and huge consideration when buying a "kit" lens. That's too bad, many beginner photographers could really benefit from just a little research on this subject. The larger aperture of this lens in the range with it's excellent close focusing characteristics for its price mean prettier images for you, with more creative options. Score another point for the Sigma.
The image stabilization alone is worthy of an upgrade if your kit lens didn't come with it, and after you factor in the faster aperture, silent focusing, better build, smoother operating focus and zoom rings- it's simply a no brainer.
I've used and tested nearly all the better kit lenses from most manufactures (Nikon are the only exclusion to date of the big ones) and this one clearly is my favorite overall. In terms of optical quality it might get third place or so behind Canon, Pentax, or Olympus (in 4/3 not m4/3), but all three of those standard kit lenses are stellar performers sharpness wise, and the Sigma really is no slouch. Most buyers won't notice slightly softer corners than these lenses when zooming in on an image at 100%, and most won't print large enough for it ever to be noticed in the first place.
Yet none of them have all the features of the Sigma, the resale value of the Sigma, or the sheer pleasure of use the Sigma gives over the others. Sure they may be more compact, but really... so what. All of them are very close when apertures are stopped down to f/8 (less the Oly that starts to diffract), and the Sigma seems to offer less barrel or pincushion distortion that its rivals as well. The slightly added weight and volume doesn't even really enter your mind.
King of the budget zoom lenses? Absolutely, positively, without a doubt. No standard zoom lens I've used at or under $200.00 yet offers the value of the Sigma, and it ticks off wins in nearly every category against them to boot. Definitely worth the money. My advice to anyone looking for a new lens for their DSLR over the standard kit:
If you don't want to invest a lot of money in a DSLR kit but aren't satisfied with what you have currently, sell your kit lens. Make your photography experience better by using a much better handling, better optically performing (where it counts most), bigger aperture, internally focusing and zooming budget lens from Sigma.
Heck, personally I'd even pay $100.00 more for this lens. Remember, the overall hands on experience with your equipment does count and often is more important than being the overall winner of test chart numbers. If you can live with it's larger size than a kit lens (I can't see why not), go for it and don't look back.
And likely it doesn't matter what mount you are using since Sigma makes this lens in all the popular DSLR mounts- Canon, Nikon, Pentax, and Sony.
As usual, be safe and happy shooting.
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Hand held Image Samples, and Test Chart Samples ( To follow Next Week)