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Review – Sigma AF 105mm f2.8 EX DG Macro for Pentax

Pentax Mount Sigma AF 205mm f/2.8 EX DG Macro Lens

Words and Photos by John Luther Garcia of Silver Frame Studios

Sigma… mention that to non-photography folks and all you’ll get is a blank stare. But most of you who are currently reading this article knows better.

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The Sigma AF 105mm f2.8 EX DG Macro, is based on an old design but now optimized for the digital format (hence the DG acronym) and is usable for both crop & full frame bodies.

The Sigma 105mm macro also comes in a variety of mounts (Canon, Nikon, Sony, Sigma) but we’ll be reviewing this one mounted on a Pentax K100D Super & K10D. As it’s name suggests, this is primarily for macro applications but is not just limited to that as it excels in other uses such as portrait and as a medium telephoto alternative.

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Specifications (from Sigma)

11 Elements in 10 Groups Angle of View 23.3 degrees

Number of Diaphragm Blades 8 Blades

Minimum Aperture

F45: CANON, SIGMA,SONY F32: NIKON, PENTAX F22: FOUR THIRDS

Minimum Focusing Distance 31.3cm/12.3 in.

Maximum Magnification 1:1

Filter Size Diameter 58mm

Dimensions Diameter 74mm X Length 97.5mm 2.9 in. X 3.8 in.

Weight 457g/16.1 oz.

Corresponding AF Mounts:  SIGMA, CANON, NIKON (D), SONY/MINOLTA, PENTAX,  FOUR THIRDS)

Build Quality

The Sigma AF 105mm f2.8 EX DG Macro is made of high quality plastic and is topped off by the EX (Excellence) matte black finish. The feel is felt paper like and is quite different from the usual shiny plastic and cold metal lens that I have, the downside is that it’s more prone to be smeared by dirt, water spots can form around the focusing barrel and scratches can be easily seen.

On the other hand, the construction feel is very solid from the wide and well-damped focusing ring to the inner barrel that extends out when focusing closer. A screw-in circular hood is also included but unlike my other lens, it cannot be attached when the lens cap is in place.

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That’s a small compromise as like the Sigma AF 105mm f2.8 EX DG Macro it is solidly built more so when it is already attached and the non-rotating front element is recessed by around two inches from the tip of the barrel.

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A lens hood or 58mm UV filter in this case does little to protect the front element from accidental smudges or breakage but I still use the latter to maximize contrast and the former to keep unwanted insects when out in the field (yes, this is true – a very small bug went found its way to the recessed front element and took some time before we were able to dislodge it).

Operation

The focusing ring also doubles as a pull down/up quick switch for AF/MF. But for Pentax this is doesn’t work and is more of a design after thought as you should just leave it in MF and you switch between AF/MF in-body. This is one of the only downsides of having a third party manufacturer produce a lens for several different mounts.

An aperture ring is still included and is a big advantage when using macro extension tubes or bellows. However, the aperture is quite narrow and hard to turn especially that you need to press a small button while doing it.

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There is also a limit/full switch right, a really good feature as switching to “limit” will lock the focus from 0.4M to infinity (for normal shots) or 0.313M to 0.4M (for macro applications), depending on where the focus point is at when you switch it. This helps the auto focus mechanism from hunting too much in low light or high contrast situations.

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Speaking of auto focus, I believe that its speed and accuracy slightly depends on the body too more so that this is a third party lens.

With the Pentax K100D Super, there were occasions that the focus will hunt from macro to infinity but has been minimized with the Pentax K10D.

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Even with that, its speed is just normal for a screw driven motor mechanism and is very noisy compared to USM equipped lens. As the Sigma AF 105mm f2.8 EX DG Macro can already be considered a moderate telephoto alternative for crop sensor bodies at 105mm, keep in mind the shutter speed value that you will be using.

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With Pentax’s in-body Shake Reduction system (and also Sony & Olympus), shooting in 1/30 sec for portraits can already give you sharp images. Up to 1/15s is even possible with slow moving or static subjects.

Though for Canon & Nikon users without an in-body VR or IS system, it would be best to shoot at 1/100s or faster. If you need a slower shutter speed than that, use the burst mode of your camera to get the best possible chance of a blur free image.

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Bokeh

With 8 aperture blades, the bokeh produced by the Sigma AF 105mm f2.8 EX DG Macro is smooth and creamy but turns into a hard edged octagon when a relatively high aperture value is used.

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Image Quality, Color and Contrast

Center sharpness of the Sigma AF 105mm f2.8 EX DG Macro is excellent even at wide open apertures although the border takes a slight performance hit but this can be easily remedied.

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Stopping down to around f/4 will give a boost to overall quality, especially the borders, and its peak performance comes at f/8 where the edge to edge sharpness will be outstanding.

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The Sigma AF 105mm f2.8 EX DG Macro renders details, color & contrast very well regardless of aperture value and it only takes a few tweaks in Adobe Photoshop Lightroom 3 to bring out great quality photos.

Distortion and vignetting is negligible on the Sigma AF 105mm f2.8 EX DG Macro while chromatic aberrations is minimized as well. It is also very resistant to flares due to its recessed front element and more so with the lens hood attached. Adding an extension tube magnifies subjects even better.

Conclusion

After being able to use the Sigma 105mm macro lens for Pentax for quite sometime, I can heartily recommend this to anyone who wants a dedicated macro lens for a reasonable price.

Sure, Sigma may have already introduced newer macro lenses like the 150mm with HSM but it’ll also cost you more, so the Sigma AF 105mm f2.8 EX DG Macro is a great buy for both portraits and macro usage.

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