Until early 2005 a fast normal prime lens for an APS-C class DSLR meant either a 35mm f/2 or going into hock for a 35mm f/1.4. Having been impressed with the general consensus with regards to the Sigma 30mm f/1.4′s performance I decided to purchase this lens in August 2006 as my primary walk-around lens for my new Canon EOS 30D. After using it for two months I felt ready to talk about my experiences with it.
Resolution
The sharpest lens that I have ever used was my Carl Zeiss 45mm f/2 Planar--until now. Plainly put, the centre performance of the Sigma 30mm f/1.4 is spectacular. MTF Tests at Photozone place its centre performance on a par with Canon’s 35mm f/1.4; with Canon’s 35mm f/2 catching-up with both the Sigma and Canon 1.4′s by middle aperture. Border performance on the other hand sees Canon 35mm f/1.4 equalling it’s f/2 cousin’s centre performance at f/2 with better border performance at f/1.4 than the other lenses obtain at the borders throughout their entire aperture range. So, how much of a difference are we talking about for all practical purposes?
I ask this, because much has been made of the Sigma 30′s mediocre border performance below f/8. However, I’m inclined to believe that Sigma’s MTF50 border performance at wide apertures is more to do with field curvature issues than poor edge resolution. Specifically, I find that subject matter that is composed and focussed at the borders of the frame even wide-open contains ample detail. So, unless I was going to be photographing flat-field subjects at close range then I couldn’t see any practical optical advantage to purchasing the Canon 35mm f/1.4 L over Sigma’s 30mm f/1.4 unless perhaps I was going to do a lot of low-light flat-field work in museums and alike.
Bokeh
The bokeh of the Sigma AF 30mm f/1.4 at wider apertures and close range is nothing short of sublime. More importantly, it’s very forgiving of distracting specular highlights which is not surprising when you consider that it has 8 aperture blades.
Construction, size and handling
Some reviews have waxed lyrical about Sigma’s EX crinkly finish. I wish I could subscribe to that point of view. The EX finish is reminiscent of a soft, fine spray on finish that wears off if you even look at it--just kidding. However, it abrades very easily as I discovered on my Sigma 50-500mm and I would put the external finish of these lenses as not quite as good as some of the better Canon Consumer lenses (i.e. 85mm f/1.8) and certainly a long way from the professional ‘L’ series construction of the 35mm f/1.4. However, at a third of the price of its ‘L’ counterpart who cares 
Size wise, the Sigma is twice that of the Canon 35mm f/2 and around 35% lighter and smaller than the Canon 35mm f/1.4. It balances quite well on my 30D but you may want to look at the Canon 35mm f/2 for your Digital Rebel if you’re looking to keep the size and balance in check and can dispense with the extra stop. The focussing ring is reasonably well dampened for manual focus but not as smooth as the Canon 85 f/1.8 but certainly better than the loose and scratchy focus ring of the Canon 24mm f/2.8. Needless to say that dedicated manual focus lenses are streets ahead in this regard.
Depth of Field scales are absent as seems to be de rigueur nowadays alongside both Canon and Nikon. I really miss these not so much for the scale focussing ability but just so I could get an easy idea about what my DOF would be at a particular aperture. For instance, if I know I can only shoot at f/1.4 it would be handy to calculate my lens to subject distance for my required depth of field straight off the lens itself rather than having to try and remember distance scales or carry around a piece of paper.
Auto-focus on my Canon 30D is fast, silent and very accurate. However, I do find that it’s best to confirm focus by repeated half-depressing of the shutter button until the AF motor is silent--then I know the focus is nailed. That being said however, the majority of my use of this lens in under manual focus.
The lens hood is a mild petal type and can be reverse mounted on the lens. However, it’s strictly AF mode at this point as the hood completely covers the focussing ring--not a shortcoming and to be expected really.
Summary
All said, the Sigma AF 30mm f/1.4 is a very accomplished piece of glass and a testament to Sigma’s commitment to practical rather than theoretical performance issues when designing their lenses. By this I mean that Sigma could have spent a significant amount of R&D; building a close range flat field corrected lens to boast better MTF chart performance and gain bragging rights but instead focussed on delivering a sharp, practical and value for money lens that would be appreciated by the average camera punter like me.
Thank you Sigma, from the bottom of my wallet!
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