17

The Sigma 17-50mm f/2.8 EX DC OS HSM Lens features a nice range of focal lengths, a wide f/2.8 aperture, HSM autofocus & OS (optical stabilization) in a well-built andreasonably-priced lens.

Bạn đang xem: 17

Most of us need at least one general purpose lens - & the focal length range is usually my primary qualification for such a lens.The 17-50milimet focal length range falls squarely in the recommended general purpose lensfocal length range for the APS-C sensor format DSLRs it is compatible with.

This focal length range delivers that same angle of view that a 27.2-80milimet lens on a full frame DSLR would deliver,but again, this APS-C-only lens is not compatible with the larger format SLRs.Here is an example of what this focal length range looks lượt thích.

*


17milimet | 18milimet | 20milimet | 25milimet | 30milimet | 35milimet | 40milimet | 45milimet | 50mm

My field work for the Sigma 17-50mm f/2.8 EX DC OS HSM Lens đánh giá was done in early spring.After a long, cold winter, the bright new growth on the trees was looking gorgeous lớn me.The 17-50mm focal length range is nice.It works great for around-the-house shots (inside và out), for landscapes, for full toàn thân and head-and-shoulders portraits, for cthất bại sports & for a huge range of other uses.

For many, their first general purpose lens is the one available in-the-box with their first DSLR.While the kit lens is very economical, it is also the source of many emails I receive sầu - especially when being used indoors without a flash.If there is any subject movement, the max aperture available on these lenses is not wide enough lớn allow the action khổng lồ be stopped - resulting in motion-blurred images.

The Sigma 17-50 OS" fixed f/2.8 max aperture across the entire focal length range provides 4x as much lightto the sensor (2 stops) as most kit lenses offer at their longest focal length (f/5.6).This aperture difference can translate inkhổng lồ a big difference in your image quality.

There are many lenses with longer focal length ranges available.The longer focal length lenses frequently sacrifice image chất lượng to obtain their range & most bởi not offer the fixed f/2.8 max aperture across the entire range.There are, however, many 17 khổng lồ 50mm (or 55mm) f/2.8 lenses available from other manufacturers - I"ll reference some of these later in this nhận xét.

As I indicated already, a wide aperture is a great advantage for a lens to lớn have sầu.Use the wide aperture to lớn stop action (or camera motion) in low light by allowing a faster/shorter shutting speed and/or khổng lồ blur the background.(a wider aperture results in a shallower depth of field - all other factors remaining equal).At 17milimet, you are going to need a close subject lớn generate any significant background blur at 17milimet f/2.8,but, at 50mm, blurring the background becomes an easier accomplishment.

If your subject is not moving, the Sigma 17-50"s 4-stop-rated OS (optical stabilization) will be a great help in achieving sharp handheld shots in low light,in the wind, on unstable footing, on a boat ... & in other situations where holding a camera steady is difficult và a tripod is not being used.

At 17mm, I am getting a good rate of sharp images from the Sigma 17-50mm f/2.8 EX DC OS HSM Lens at 1/4 sec exposures for a net 3-stops of assistance from OS.I have some sharp shots taken at .6 và .8 seconds, but the keeper rate is very, very low at these exposure durations.At 50mm, 1/10 or 1/8 seems to be my shutter tốc độ limit for sharp images.This is, again, a net 3-stops of assistance from OS.I have a couple of sharp images made at 50mm and 01/05 sec, but the keeper rate is very low.

*

The Sigma 17-50milimet f/2.8 EX DC OS HSM Lens is shown mounted on a Canon EOS 60D above.

With a wide open f/2.8 aperture, the Sigma 17-50milimet f/2.8 EX DC OS HSM Lens is impressively sharp in the center throughout the focal length rangewith 50milimet showing very slightly reduced sharpness.The corners are soft at f/2.8 with the 50mm corners looking the best.Stopping down does not significantly affect the center of the frame image quality - nor does it need to.

By f/5.6, corners show a little improvement overall & improvements are again realized at f/8.Stopping down at 50mm, the center shows slightly more improvement & the corners show somewhat less improvement than the rest of the range -due lớn the slightly worse/better 50milimet f/2.8 center/corner sharpness.At f/11, diffraction begins to lớn show - reducing image sharpness over most of the frame (though corners continue to improve).

The Sigma 17-50 OS controls vignetting quite well.With a wide open aperture, expect to see about 1.5 stops of peripheral shading in the corners at the two focal length extremes with noticeably lessin the mid focal lengths.Stopping down lớn f/4 reduces the corner shading lớn about 1 stop at 17mm & about .8 stops remain at 17milimet even at f/11.chú ý that a normal thickness circular polarizer filterwill add a small amount of mechanical vignetting at 17mm - even at f/11.

Xem thêm: ▷ Bình Bông Mai Có Tác Dụng Gì ? Những Điều Cần Biết Về Bình Bông Mai

Some chromatic aberration is noticeable in the corners in the wider half of the focal length range.As a generalization, CA is worst at 17milimet and slowly improves through the balance of the focal length range.The amount of CA exhibited is not unusual for a lens in this class.

The Sigma 17-50 OS shows varying amounts of flare over the focal length và aperture ranges, but overall, it is a decent performer in this regard.Bokeh (background blur quality) generated by the 7-blade aperture appears to be mid-grade.The odd number aperture blade count will create 2x the number of light rays as aperture blades (14) from points of light when a narrow aperture is used(even blade counts deliver 1x light rays).

At 17mm, the Sigma 17-50 exhibits a noticeable bulge-in-the-middle barrel distortion.This distortion smoothly transitions khổng lồ mild pincushion distortion at 50milimet with approximately 25mm being the near-distortion-không tính phí transition focal length.

Overall, I"m pleased with the Sigma 17-50mm f/2.8 EX DC OS HSM Lens" image chất lượng, though the corner sharpness is the most lacking piece of the overall image unique puzzle.

The Sigma 17-50 OS incorporates Sigma"s (Hypersonic Motor) for moderately fast autofocusing.Though reasonably quietly, the 17-50 generates some gear noise during AF.Focus accuracy has been the biggest issue I"ve encountered with this lens.I"ve had many shots misautofocused for no apparent reason - especially in AI Servo mode.

Focusing is internal - the front element does not extkết thúc or rotate.Expect a relatively small amount of focus breathing from this lens - the subject/framing changes size a small amount when focusing.

FTM (Full Time Manual) focusing is not featured in this HSM AF implementation - the focus ring turns during AF.A printed-on-the-MF-ring focus distance scale is provided - and reveals the laông chồng of FTM.

The focus ring is nicely sized & in the position I prefer - as the front-most ring.The Sigma 17-50 focuses smoothly, but with a relatively short 42° rotation và low rotation resistance, precise focusing is touchy.

The table below review a large number of general purpose lenses" minimum focus distances & maximum magnifications.

ModelMFDMM
Canon EF-S 15-85mm f/3.5-5.6 IS USM Lens13.8"(350mm)0.21x
Canon EF-S 17-55milimet f/2.8 IS USM Lens13.8"(350mm)0.16x
Canon EF-S 17-85milimet f/4-5.6 IS USM Lens11.8"(300mm)0.20x
Canon EF-S 18-55milimet f/3.5-5.6 IS II Lens9.8"(250mm)0.34x
Canon EF-S 18-135milimet f/3.5-5.6 IS Lens19.3"(490mm)0.21x
Canon EF-S 18-200mm f/3.5-5.6 IS Lens17.7"(450mm)0.24x
Sigma 17-50milimet f/2.8 EX DC OS HSM Lens11.0"(280mm)0.20x
Sigma 17-70mm f/2.8-4 DC Macro OS Lens8.7"(220mm)0.37x
Sigma 18-125mm f/3.8-5.6 DC OS HSM Lens13.8"(350mm)0.26x
Sigma 18-200milimet f/3.5-6.3 DC OS Lens17.7"(450mm)0.26x
Sigma 18-250milimet f/3.5-6.3 DC OS HSM Lens17.7"(450mm)0.29x
Tamron 17-50mm f/2.8 XR Di II Lens10.6"(270mm)0.22x
Tamron 17-50milimet f/2.8 XR Di II VC Lens11.4"(290mm)0.21x
Tamron 18-200mm f/3.5-6.3 XR Di II Lens17.7"(450mm)0.27x
Tamron 18-270milimet f/3.5-6.3 Di II VC Lens19.3"(490mm)0.29x

With an 11" (280mm) MFD & a .2x MM spec, the Sigma 17-50milimet f/2.8 EX DC OS HSM Lens is not a strong contender in the close-up competition.But, these specs are in line with the other 17-fiftysomething f/2.8 lenses.And, these figures are good enough for many cđại bại subject needs.

However, that is not the end of the close-up story.The tested MFD for this lens is 9.17” (233mm) which should equate to about .24x MM.MFD testing uses manual focusing - and this lens indeed manually focuses closer than it will autofocus.

As I mentioned in the beginning of this Reviews, the Sigma 17-50milimet f/2.8 EX DC OS HSM Lens has very good build unique.I have not been a big tín đồ of Sigma"s matte finish - especially because it readily shows fingerprints và dust.The good news is that only the edges of the zoom và focus rings retain the conventional Sigma finish.The hood và mount areas, the main lens areas not covered by rubber zoom or focus ring, are a much nicer (my opinion of course) smooth finish.

Xem thêm: Hướng Dẫn Thực Hiện Chuẩn Kiến Thức Kĩ Năng Lớp 4 Đầy Đủ Các Môn Học

The focus & zoom rings are very smooth with no play.The zoom ring has an igiảm giá amount of resistance while, as I indicated earlier in the Đánh Giá, the focus ring is slightly too easy to lớn rotate.


Chuyên mục: Tổng Hợp