Build

The Pentax-M 50/1.7 is a compact and light lens, at 185 grams it is only 25 grams heavier than the smallest lens in this shootout. It is made from the same materials as most M-series lenses, with a metal barrel and rubber focus ring. The build quality for this lens is better than the SMC Pentax-M 1:2 50mm in Match 3 but not quite up to many lenses from the previous and future generations. Still, the focus throw is long and smooth, and the aperture clicks into place.

The Micro-Nikkor 55/3.5 is an all-metal lens, with a scalloped focus ring but simple notched aperture ring. It is still a very light lens, at 235g, but it is much larger physically than the Pentax. This has an overall effect of making the Nikkor feel almost hollow in your hand and on the camera. The focus throw on the Nikkor is smooth, but has more of a paper-sliding-on-paper feel. The aperture ring works fine, with definite clicks at each half-stop, but the ring (and the click) is softer than comparable Pentax lenses.

The Pentax-M 50/1.7 shares a 6-element, 5-group design with the other Pentax 50/1.7 lenses, and focuses down to about 0.45 meter for a maximum magnification of 0.15x. The Micro-Nikkor 55/3.5 is a 5-element, 4-group construction and on Nikon bodies it can focus to 0.25 meter. The focus distance is slightly altered when mounted on the Pentax because the lens-to-film distance is different between the models.

Physical Usage

The Micro-Nikkor 55/3.5 is obviously not intended for use on a Pentax K-mount camera, but as I've discovered the Nikon F mount fits flush within the Pentax K mount. For two of my other Nikon lenses, I've removed the F mount and replaced it with a K mount. This lens, however, is unmodified; because of its size, shape, and weight, it fits cleanly on my Pentax bodies. I primarily use the Nikkor 55/3.5 as a macro lens, so I have in fact converted a set of extension tubes to have a Nikon F mount on the lens side and a Pentax K mount on the camera side. For the purposes of this comparison I did not use the extension tubes.

One of the problems with this and other stop-down-only macro lenses is that in order to maximize depth of field, they often must be used at apertures too dark to effectively focus. This leads to sometimes missing accurate focus, especially with bugs and other fast-moving objects.

The Pentax-M 50/1.7, like the M 50/2 previously is again the worst-implemented manual focus lenses for modern Pentax cameras. In a nutshell, you need to shoot in full manual mode and press a button to stop the lens down and get a meter reading. It is not very nice to use, and especially not good for moving objects in changing light levels.

Side view of both the Nippon Kogaku Micro-Nikkor Auto 1:3.5 f=55mm, left, and the SMC Pentax-M 1:1.7 50mm, right.
Click here for to see the front elements.

This shot demonstrates both the positives and negatives of the Pentax-M 50/1.7. It is tack sharp, but the distracting aperture blades draw your attention away from the penguin.
Click here for a gallery of samples of these two lenses.

Sharpness

Macro lenses are generally lauded for their sharpness. At like-sized apertures and distances though, the little Pentax-M 50/1.7 performs every bit as good as the Micro-Nikkor 55/3.5. The Pentax-M 50/1.7 appears to have more contrast, giving an impression of being even sharper, like in the samples of the hydrangea or in the crops of the guitar. For my needs, both of these lenses are perfectly sharp, and I'll even give the edge to the Pentax.

Magnification

Here is where the Micro-Nikkor 55/3.5 competes in another league compared to the Pentax-M 50/1.7. Its close-focus capability transforms otherwise ordinary scenes. The close-focus comparisons demonstrate this - the same shot rendered by the Pentax-M 50/1.7 is here whereas the Micro-Nikkor 55/3.5 is here.

Bokeh

If both lenses performed admirably for sharpness, neither gets flawless marks for bokeh.

The Pentax-M 50/1.7 shows considerable axial color (green or purple rings inside out-of-focus objects) at f/2.8 and wider. It has unevenly-bright highlighs, with typical bright rings around specular highlights. It also suffers from its 6 straight aperture blades, which serve to distract heavily in shots like this one. Certain shots show an atypical (for Pentax lenses) bokeh, as in this shot, which looks like the out of focus area is wrapped in plastic wrap.

The Micro-Nikkor 55/3.5 also suffers from its 6 straight aperture blades, although it does not exhibit as much axial color as the Pentax-M 50/1.7 and has a more evenly lit blur disk.