Pentax K30 + Sigma 17-50mm F2.8 EX DC HSM

A few days ago I took possession of a new Sigma zoom lens.

It is essentially a replacement for the Pentax DA 18-55mm AL lens that people often buy bundled with a Pentax DSLR.

So here are a few comments on the Sigma with a simple comparison to the old Pentax.


The very first thing to note about the Sigma lens is that it is big and heavy. It is big because it has an f2.8 aperture over the full zoom range. It is heavy because it is big.

Amazon list its weight as 567g. But using our kitchen scales, the lens + lens hood + lens cap weigh in at 20.75oz, which I calculate to be 588g in new money. Buy the time I've added a 77mm diameter UV filter there won't be much change out of 600g.

Its a short zoom that looks like a long zoom

So when attached to my 702g Pentax K30, the all up weight will hit 1.3kg. I wonder how this compares with my very first SLR from the mid-1970s, a Russian Zenith (a.k.a. Zenit) which had a brilliant Helios 58mm f2.0 lens.

Little niggles

Most Pentax K mount lenses seem to have a large, reassuring red/orange blob of paint which I carefully line up with the large red/orange blob on the camera body when attaching a lens.

Sigma apparently don't have any red/orange paint in their workshop. So you have to use the small white blob that indicates the selected focal length. (hand me that red marker pen!)

The lens has a manual/auto focus button. This (of course) is in addition to the cameras own manual/auto focus button. (I guess they had their reasons!)

Photo comparison

I'm not really very good at comparing photographic equipment. In the past I've tried to assess focus using text or line drawings. This time around, I simply sat in my favourite chair in the conservatory, and took 2 photos; one with K30 + Pentax 18-55mm and the second with K30 + Sigma 17-50mm.

The difference was quite striking;

using Pentax 18-55mm lens

...oooh I love spot-the-difference pictures!

using Sigma 17-50mm lens

...so I opened both images in The Gimp and took a look at the histograms;

Histogram for Pentax lens

Histogram for Sigma lens

Without worrying too much about the technical reason for these differences, I have decided to conclude that I like the new Sigma very much. I also like the fit between lens and lens hood; it is nice and snug and does not feel like it could drop off.

Now I just need to get out there and take a few prize winning photographs!