Using 1970s Pentax Auto 110 lenses with a micro four-thirds mirrorless camera, 18 February 2024

Using 1970s Pentax Auto 110 lenses with a micro four-thirds mirrorless camera, 18 February 2024

I don't really have any proper lenses for my mirrorless cameras. Well, apart from the 18mm lens cap lens, which is made by Olympus so I guess that could be classed as 'proper', but it's fixed aperture and has a plastic lens so that's on the borderline. What I have used until now are some odd lenses like the Lomography Experimental Lens Kit and the Thingyfy Pinhole Pro pinhole lens.

So there I am, with a collection of weird and wonderful lenses but no 'real' glass. However, over the past few months I've been gathering some lenses that I've been after for a quite a while. The Pentax Auto 110 was an interchangeable lens SLR camera for 110 film. It's diminutive form came with a range of lenses, from wide angle to a telephoto zoom, that are well known as the smallest and cutest lenses ever made. The other useful feature of these lenses is that the image size of 110 film (17mm×13mm) is almost exactly the same size as the micro four-thirds sensor (17.3mm×13mm), so with an adapter close enough to the image sensor there's almost complete compatibility with the mirrorless cameras.

The Pentax Auto lenses have no aperture adjustment and are fixed wide open at f2,8. Originally the Pentax Auto body contained an adjustable aperture, but with the Olympus set to aperture priority or manual mode it's easy to get a good exposure. I have read that in bright sunlight you may need to use a neutral density filter to cut down the light reaching the sensor. In this instance I might have to invest in some step up rings. For reference, the filter size of each lens is 30.5mm (18mm wide-angle lens), 25.5mm (24mm f/2.8 standard lens), 37.5mm (50mm telephoto lens), 49mm (20–40mm zoom lens).

It was a nice sunny day today, and as we had planned to go to Costa Nova for lunch I thought it would be nice to take along the Olympus Pen E-PL1 and the Pentax Auto lenses. One thing I will mention before we start is that I discovered I'm not really good at distance focussing with these lenses and a lot of the images were a little bit out of focus. That said, it was fabulous fun using these old lenses on a digital mirrorless camera and the cheap Pentax Auto to micro four-thirds adapter worked like a charm.

You can see from the first few images that I had a real problem with focussing, wide open at f2,8 the lenses are really sensitive about getting the distance correct. Even with subjects that are, to all intents and purposes, at infinity sometimes the images were a little soft.

Most of the time I used the 18mm wide-angle angle lens, which is not as small as the 24mm standard lens but has a lovely wide field of view. In the harbour at Costa Nova, though I did a comparison with the wide-angle, standard and short telephoto lens. This time I did not bring the zoom lens along.

With these lenses a neutral density filter is certainly a must. Even though the camera exposed most of the images really nicely, the shutter speed was at the limit that the camera cam handle. I'm certainly going to be looking around for suitable ND filters and/or step up rings.

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