Lomo 35KP 140mm F1.8 projector lens adapted to Pentax 67

In the everlasting quest for large apertures on 67 format, the path to glory leads towards projector lenses. Among these, the Soviet Lomo 35KP 140mm F1.8 movie projector lens stands out for its affordability and quality. There are two versions of Lomo 140mm F1.8, a slender model with Petzval optics and a fat model with double-Gauss design. Only the fat one has a flange distance compatible with Pentax 67.

This lens has a long tube, so the rear end has to be cut off. The rear retaining ring needs to be redesigned to be thinner in order to reduce length further. Then, approximately 5mm of the lens shall be inserted into the mount. With such push-limit alteration, infinity focus can be reached. The lens tube diameter is 62.5mm, while the minimum inner diameter of the M65 helicoid is 61mm. Therefore, thinning of the tube is necessary, with the thinner section measuring about 2cm in width. This lens is heavy, weighing approximately 1.5kg. When mounted on the Pentax 67, the total weight reaches 3kg, making it substantial to carry around. The minimum focusing distance is 90cm.

Apart from being affordable, the biggest advantage of this lens is soft bokeh, along with a subtle swirl that I am particularly fond of.

In terms of resolution, the sharpness at the very center is good, comparable to P67 165mm F2.8. However, it drops off rapidly when shifted slightly towards the sides and becomes very poor at the corners. But this isn’t a major issue for portraiture. Spherical aberration is controlled relatively well, unlike many projector lenses which produce blurry images.

Contrast and flare resistance are inherent weaknesses of vintage projector lenses, and the golden coating of this lens struggles under backlit conditions indeed. Contrast is acceptable in frontlit circumstances, but adding a lens hood is advisable. One needs to be cautious in choosing the hood. Although the front retaining ring has some kind of 82mm thread, an 82mm hood will cause vignetting. A larger-diameter hood mounted externally is required.

Finally, regarding the concern whether this lens’ image circle covers the 67 format, I am actually quite satisfied with the result. A tight full body shot is fully covered. Environmental portraits may exhibit slight vignetting, but a minor crop would resolve the issue. I often crop in post-processing so that is no problem to me. At infinity, the vignetting is actually not that bad, as shown in the uncropped picture below. Note that beside no 82mm hood mentioned earlier, any 82mm filter shall be avoided as well, as this will also ever so slightly increase vignetting.

In Conclusion

Good:
1. Price/Performance. Lens with modification cost is under CNY1500 (~US$200). A F1.8 6×7 portrait lens for pennies.
2. Smooth bokeh with slight swirl
3. Good center sharpness

Bad:
1. Wider edge sharpness
2. Poor flare resistance
3. No full 6×7 coverage, but IMHO already quite satisfactory

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