Somewhere along the way, I’ve ended up with no less than FOUR 50mm lenses that mount on my Pentax K-3.
Three were older Chinon lenses: two copies of the f/1.9 (both the same model, but one more modern than the other) and one a f/1.7. I’d acquired these with old cameras, but they come up frequently on eBay, generally for less than £20. These are all fully manual lenses (that is, manual aperture and manual focus). I also own a Pentax SMC FA 50mm f/1.4. This is far from Pentax’s most modern lens, but does at least have autofocus and the ability to set the aperture from the camera body.
Four 50mm lenses is, for me at least, at least two too many. I decided to carry out a quick test to compare them, and pick two of the manual lenses to sell. For interest, I also took the same shots with my two standard zoom lenses set at 50mm. These are a Sigma 17-70mm f/2.8-4.0, and a Pentax SMC DA 18-55mm f/3.5-5.6 AL WR. This latter came as a kit lens with my camera and I find handy to hold on to because of its excellent weather sealing.
I shot the same five scenes, twice, with each lens. All handheld and in Av mode (as this is how I shoot general scenes). For the first time I set the aperture as close as the lens would let me get to f/2 and at ISO 400. For the f/1.9 lenses, this meant an aperture of f/1.9. For the Sigma and Pentax zooms at 50mm, this meant f/4.0 and f/5.6 respectively. For the second sets of shots, I stopped down to f/8 and set auto ISO. For the manual lenses, I relied on the K-3’s focus confirmation – but otherwise I used autofocus where it was available.
Exposure and Distortion
The first thing I noticed was that the Chinon scenes came out rather dark. The three modern lenses (the Pentax 50mm f/1.4 and the two zooms) exposed as expected, but the old Chinons all came out about two-thirds of a stop darker. To my eye, I couldn’t pick up distortion from any of the 50mm lenses, and only a little from the zooms. In this respect, the Sigma was probably a little worse than the kit lens. I didn’t note any vignetting with any of the lenses.
Despite the focus confirmation from the K-3, I did miss focus in a couple of cases – as is to be expected with a manual focus lens. Of course, under ideal circumstances this could be avoided – tripod-mounting the camera and focusing in live-view, fully zoomed in. However I wanted my test to reflect the way I usually shoot – and that generally means handheld.
We expect prime lenses to be sharper than all but the very best zooms, so it was no surprise that all four of the 50mm lenses gave sharper results than the zoom lenses here. Of the zooms, the Sigma was appreciably sharper than the Pentax kit lens.
While I’d heard that the Pentax 50mm f/1.4 was perhaps less sharp than its cheaper and newer 50mm f/1.8 SMC DA stablemate, I was a little surprised that it was the softest of the 50mm lenses I tested here. The Chinon 50mm f/1.7 was also slightly softer than the f/1.9 lenses. However, the differences are only really obvious at wider apertures and when viewing the images at a large size. By f/8 the differences had disappeared and all the lenses were extremely sharp.
The bokeh (the quality of out-of-focus areas of the image) was generally pleasing in all the lenses, but the Pentax 50mm f/1.4 had slightly octagonal bokeh balls, while the Chinon 50mm f/1.7 had quite mishapen balls of light. Shooting wide open, the two f/1.9 lenses showed the best characteristics (as the other 50mm lenses might have done had we shot been shooting wide open rather than at f/2. However, I only very rarely shoot wider than f/2 even on lenses that can do it, because of depth-of-field issues).
Three of the lenses – the Pentax f/1.4, ONE of the Chinon f/1.9 lenses, and the Pentax kit zoom exhibited colour fringing at high contrast areas. In the 50mm lenses, this behaviour was quickly eliminated by stopping down. However, in the kit lens it persisted at all apertures.
Lens Test Conclusion
While in some respects the Pentax 50mm f/1.4 appears the weakest of the 50mm lenses it’s still a keeper. The additional low-light performance of the wider aperture, and more importantly the added convenience of autofocus and camera-set aperture, outweigh the differences in sharpness for most situations. In addition, I’m holding on to the newer of the two 50mm f/1.9 lenses. It’s sharper than the other two Chinon lenses, and displayed no colour fringing.
The other two Chinon 50mm lenses, while extremely sharp and giving overall good image quality. are redundant and now heading for eBay.