Pentax FA 31mm/1.8 AL Limited performance

Started Dec 26, 2013 | Discussions thread
Brett St Pierre
Brett St Pierre Veteran Member • Posts: 7,024
Re: Pentax FA 31mm/1.8 AL Limited performance

I tend to agree with others comments. I've had the FA 31mm F1.8 for about 8 years and used it on various Pentax models. It is an excellent lens in terms of edge to edge sharpness (very good at F1.8 and excellent from F2.8) and pleasing bokeh / rendering. I've only had my K-3 for a week but the combination with my FA 31 is looking as positive experience as I've had previously. I love it as a short portrait and general purpose/walk about prime.

But it's well known the Sigma 'Art' 35mm F1.4 HSM is a high quality lens with excellent centre sharpness (see Photozone test below which show the FA31 has better edge to edge sharpness) and generally good optical qualities so it's hard to see you switching from the Sigma unless it's the extra weight (almost twice the FA31 which is already the biggest & heaviest Pentax Limited).

Here is a snap at F1.8 of one of my boys yesterday


K-3 + FA 31mm 1/60 F1.8 ISO 200

Original cropped

It could have been better focused, I was focusing for the eyes but haven't fine tuned focus for this lens yet. DOF is narrow.

As mentioned, Klaus from Photozone tests comprehensively and his test of the FA 31 on a 16mp K-5 is here.

Although he points out you shouldn't compare lenses shot on different cameras, you can see his test of the Sigma 35mm F1.4 DG HSM on a Nikon 7000, which all but has the same Sony 16mp sensor as the K-5.

I think all you can get from this is that both lenses deserve applause. The Pentax FA 31 tests as having better/ even edge to edge sharpness (which has become really important to me over the years) but the Sigma has a sharper centre.

From what I see there and other reading, test and photos, I'd personally see no reason to switch from the Sigma to the Pentax (except for the edge to edge performance - important to me when shooting groups of people at weddings / events and architecture) but likewise there isn't anything about the Sigma that would lure me to double the weight of my general purpose prime.

PS Having said that, I've ordered the Sigma 15-35mm F1.8 HSM but that will have an entirely different use (event + corporate photography along with my DA*50-135mm F2.8) that what I use my primes for.


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