Sigma telephoto zoom lens - 70 mm - 300 mm F/4.0-5.6

...more 'ordinary' status in the Sigma hierarchy, this AF 70-300mm f/4-f/5.6 DG APO Macro, has none of the more elaborate 'bells and whistles' evident on the more expensive EX range. What does this mean? Well, you don't get Sigma's superb HSM (Hypersonic Motor) AF (auto-focusing) for near silent and very fast AF, resulting in a somewhat more unsophisticated, noisy (although not overly so) and slightly 'harsh' action. It still works well however! Also, ...
...to use.

Sigma market this lens as an APOchromatic lens which I suspect, is slightly exaggerating the reality. In fact, they do use two SLD (Special Low Dispersion) elements in the design which comprises 14 elements in all, in 10 groups and, I have no doubt it is this, that 'lifts' the performance of the lens above that of it's less well endowed sibling - the non APO version. It also benefits from improved lens coatings, enhancing it's ... more

I have owned and used the APO Macro version of this lens in NIKON mount for around a year before selling both the lens and my Nikon outfit. I now use Canon DSLR's but please, don't hold this against me! I also have a friend who has the cheaper non APO version, so it is interesting for me to be able to compare the two directly.

This is not a 'EX' (Excellence) designated lens and as such, finish is not quite to the same high standard as those so marked, although still a similar black, slightly crinkly finish, which is, it has to be said, very nice. Generally, build quality is of a pleasing and substantial quality. Certainly better than Canon's budget lens range in my opinion and frankly, I would be surprised if most in the know, did not agree (Canon excluded of course!).

Finish and fit is to a good level and materials used are of good quality. I don't know if it is simply a variation between samples but my own APO version appeared to have somewhat 'smoother' zooming than my friend's non APO one. As usual for Sigma, a decent lens hood (barrel type) and a soft case are included in the package. The lens sports a 58mm filter thread, so filters are relatively inexpensive to purchase.

Being of more 'ordinary' status in the Sigma hierarchy, this AF 70-300mm f/4-f/5.6 DG APO Macro, has none of the more elaborate 'bells and whistles' evident on the more expensive EX range. What does this mean? Well, you don't get Sigma's superb HSM (Hypersonic Motor) AF (auto-focusing) for near silent and very fast AF, resulting in a somewhat more unsophisticated, noisy (although not overly so) and slightly 'harsh' action. It still works well however! Also, you get no FTM (full time manual) focusing, as you would with HSM in One Shot AF mode. If you 'do' want to focus manually, by Jove, you have to physically switch to MF (manual focus). Also, there is no internal focusing or zooming mechanism, so the lens tends to extend considerably towards the close end, adding significantly to the overall length of the lens. This can effect 'balance' in the hand, particularly when used with very small and light cameras. More disturbingly, the lens barrel also rotates during focusing, making polarising filters significantly more troublesome to use.

Sigma market this lens as an APOchromatic lens which I suspect, is slightly exaggerating the reality. In fact, they do use two SLD (Special Low Dispersion) elements in the design which comprises 14 elements in all, in 10 groups and, I have no doubt it is this, that 'lifts' the performance of the lens above that of it's less well endowed sibling - the non APO version. It also benefits from improved lens coatings, enhancing it's resistance to flare and ghosting which is more of a problem with digital cameras and their highly reflective sensors. Hence the DG (Digital) designation.

The lens is compatible with both FF (full-frame) digital, 35mm and cropped sensor APS-C digital SLR cameras. In the case of the latter, the lens effectively behaves like a 105-450mm f/4-f/5.6 lens (Nikon APS-C), 112-480mm f/4-f/5.6 lens (Canon APS-C) or a 119-510mm f/4-f/5.6 with Sigma DSLR cameras. Really quite a useful range of focal lengths, particularly appealing I would think for the sports or wildlife fans out there.

Rather unusually for a lens in this price bracket, it also features a nine blade diaphragm mechanism which provides greatly improved bokeh or OOF (Out Of Focus) highlights than might usually be expected. Closest 'normal' focusing distance is 1.5 metres which provides a maximum magnification ratio of 1:4.1 at 300mm. However, a manual 'macro' switch (limited to being used between 200 to 300mm focal lengths), provides a much improved reproduction ratio of 1:2 or half life-size. Very impressive and extremely useful but NOT true 'macro' which, is generally considered to be 1:1 or actual 'life-size'. This is still impressive however , as the lens does not boast the sophistication of floating elements to 'aid' close focusing.

Now to the lens's performance. Firstly, distortion is held down to low levels throughout the zoom range. Initially (at 70mm), there is slight barrel distortion, but certainly not enough to cause concern. This evens out to become pretty well neutral at around 135mm then changes to pincushion distortion between 200 to 300mm. Again, this is not serious and in fact, such a performance is to be commended.

With an image circle large enough to accommodate 35mm and FF (full-frame) digital, smaller APS-C sensor cameras can take advantage of using only the central 'sweet' spot of the circle, hence really quite low vignetting at maximum aperture. This remains so throughout the zoom range and the small amount of vignetting present is eliminated upon stopping down just 1 f/stop. Vignetting 'is' however, quite visible on full-frame digital and 35mm SLR cameras but does remain correctable in software. Alternatively, stopping down the lens gradually minimises the effect. Quite a respectable performance, particularly on APS-C cameras..

Resolution or 'sharpness' is a mixed bag. On one hand, with the smaller APS-C digital SLR's sharpness is really quite impressive, while on FF (full-frame) cameras, it is nowhere so good.

On APS-C, resolution right from maximum aperture f/4 at 70mm is VERY GOOD in the centre of the field and GOOD+ at the edges and corners. Stopping down to f/5.6 improves things considerably where central performance rises to VERY GOOD+ and edges and corners to VERY GOOD. At f/8, performance evens out to VERY GOOD+ across the entire field.

This is maintained throughout the zoom range to around 200mm focal length but, at 300mm, performance at maximum aperture f/5.6 is reduced to only GOOD++ in the centre and 'just' GOOD at the edges. Corners, it has to be said are 'just about' verging on SOFT. Stopping down to f/8 improves things considerably when central resolution becomes VERY GOOD with edges reaching VERY GOOD- Corners attain an acceptable GOOD+ rating. Stopping down to f/11 brings a further slight improvement to VERY GOOD both in the centre of the field and at the edges. Only the extreme corners show a slight falling off to become just GOOD.

The lens surprisingly performs just as well when used in the 'macro' 1:2 'half life-size' mode. Indeed, I have produced 8" x 10" prints from the central part of the field which represent 'sections' from what would be 20" x 30" prints. That 'is' really quite impressive for the price point of this lens and certainly a considerable improvement over the non APO version of the same lens.

The disappointment comes when used on full-frame digital cameras where performance is really quite poor. Even at 70mm, at f/4, the resolution can best be described as 'only' GOOD, with edges and the corners in particular, being SOFT. Stopping down to f/5.6 does improve things slightly, when GOOD+ is achieved in the centre. However, edges and corners hardly seem to improve at all. f/8 turns in the best performance (on full-frame) that this lens can achieve, where at the centre of the frame, it just about squeezes a VERY GOOD- rating. Even the edges improve very slightly to just about GOOD+ which I suppose, is not too bad.

Unfortunately, performance gradually worsens as you zoom in until at 300mm, it really isn't seriously useable on such cameras. Full-frame digital I'm afraid, is extremely demanding of lenses and generally, it is accepted that budget or cheaper lenses cannot hold their own at this level. This does seem to be born out by my own findings.

CA's (Chromatic Aberrations) or 'colour fringing' is quite well controlled with the APO version of this lens, when used on APS-C cameras and at focal lengths between 70 to 200mm where it is virtually non-existent (at 70mm), to slight (at around 200mm). Unfortunately, at 300mm focal length, the problem becomes far more noticeable and requires correcting in software. My friend's non-APO version of this lens is considerably worse, it has to be said.

Fringing is more of a problem on full-frame DSLR's, particularly at the edges and corners of the frame. This is exacerbated by the inherent softness of the lens, particularly in these same areas, making the fringing extremely difficult, if not impossible, to correct through software.

In my opinion, this is a pretty good lens for use on APS-C sensor digital SLR cameras but I could not possibly recommend it for use on full-frame digital. Results (on APS-C), can be very good indeed, particularly at this price point. Although the lens is not perhaps the easiest on the planet to use - long extension when focusing close, rotating front element, noisy AF, no full-time manual focusing and manual switching for the 1:2 macro mode - it is however, still a good choice for anyone who might use these longer focal lengths only occasionally and is therefore less willing to invest large sums of hard-earned cash on a more sophisticated model. For these potential purchasers and APS-C digital photographers in particular, definitely recommended.

David Chamberlain 

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