Small manual lenses for Micro Four Thirds
Using manual focus lenses on the Panasonic and Olympus Micro Four Thirds (MFT) digital cameras has become hugely popular. Many users have simple adapters and a wide range of lenses from manual focus 35mm SLR cameras, often with excellent results. However, these lenses can be quite large – reducing the benefit of such a small camera – and the required adapters add substantially to their length (if not their weight).

What's needed are lenses which will cover the MFT sensor, yet are smaller and lighter than adapted 35mm SLR lenses, and there are several possibilities. To keep the added length of the required adapter as small as possible, lenses with a short register are preferred, but if the back focus (distance from the lens flange to the sensor) is too small, the lenses won't focus to infinity. Two types of lens that definitely fit into this category are C Mount cine or video lenses, and Pentax 110 optics. Both require very slim adapters which hardly add anything to the length of the lens, but each type of lens has its problems for Micro Four Thirds users.
    C Mount lenses are designed for formats smaller than MFT, so many of them won't cover the full frame – vignetting (darkening or cut off at the corners) is common, especially with shorter focal lengths. Also, not all such lenses will screw fully into C Mount to Micro Four Thirds adapters, as the thread needs to be recessed to achieve infinity focus, and many optics are simply too fat to fit. Of the lenses that are usable, many can provide excellent optical quality, and 50mm or longer types can make great portrait lenses. The lenses are usually small, but older types have all metal barrels and can be surprisingly heavy. Modern 25mm f/1.4 and 35mm f/1.7 optics are available at very reasonable prices, and while the former has some vignetting (reduced in 16:9 format), the latter covers the full frame.
    Lenses for the Pentax 110 pocket SLR camera all fit the available adapters and cover the full format (110 film was about the same size as MFT), they're very good optically, and focus to infinity without any issues. Only a limited range was made in 18mm, 24mm, 50mm, 70mm and 20-40mm zoom focal lengths with a maximum aperture of f/2.8. Unfortunately, that's the only aperture you're likely to be using, as the lenses have no diaphragms – this was originally inside the camera body and combined with the shutter. The 110 lenses are compact and very lightweight (especially the shorter ones), and they can work very well despite this limitation.

Leica and rangefinder lenses
Another type of lens with a fairly short register that's popular with MFT users is the rangefinder optic – usually in Leica screw (M39) or Leica M bayonet fittings. Many adapters are available, from generic types to expensive Voigtlander and Panasonic models. As they're designed for 35mm film cameras, the lenses have plenty of coverage for the MFT sensor. The slightly longer register usually means that there are no clearance problems, though some wide angles extend beyond the rear mount, which can prevent them mounting, or interfere with the shutter. Another potential problem with some wide lenses is the acute angle of the light rays as they hit the sensor, which can cause issues such as smearing in the corners. Wide SLR lenses use a retrofocus design which causes the rays to strike at a more perpendicular angle. Moderately wide, standard and short telephotos can work extremely well, and while Leica lenses aren't cheap they can provide excellent results on MFT cameras. Older designs in Leica screw (M39) fitting can be less expensive, as can independent types such as the recent Voigtlander range, and older Soviet lenses from the Fed and Zorki rangefinder cameras. The Voigtlander Nokton 40mm f/1.4 makes an excellent fast portrait lens, with an effective focal length of 80mm.
    Carl Zeiss lenses from the Contax G auto focus rangefinder system present more of a challenge as the mount is a complex one, and the lenses are normally focused using a mechanical drive system from the body, instead of a conventional focusing ring. Adapters are now available, but they must incorporate their own focusing system – usually a wheel at the side, or a ring around the adapter – to operate the lens's focusing system manually. The wider lenses have clearance issues as they protrude considerably beyond the rear mount, but the 35mm f/2 Distagon, 45mm f/2 Planar and 90mm f/2.8 Sonnar all work very well indeed.

Comparative sizes of a Jupiter 8 50mm f/2 lens in Leica Screw fit on the left, and a Canon FD 50mm f/1.8 on the right, both fitted with suitable Micro Four Thirds adapters

A miniature SLR system comes good
Olympus has always specialized in smaller-than-average cameras, and long before it moved into digital the company had revolutionized the 35mm SLR camera market with the OM system in the 1970s. Even earlier than this, though, Olympus had very successfully sold a range of Pen compact cameras during the 1960s using the half frame format, accepting standard 35mm film but producing twice as many images of half the normal size at 18x24mm. The technical pinnacle of this range were the Pen F, FT and FV half frame SLR cameras, which were much smaller than the full frame SLRs of the day. They were solidly built, reliable and easy to use, and had an excellent range of Zuiko lenses. These lenses can now enjoy a new lease of life on Micro Four Thirds digital cameras.
    Because of the smaller format the Pen F lenses had shorter focal lengths (the standard lens was a 38mm f/1.8), were more compact and had a shorter register than full frame SLR lenses. Simple adapters for MFT are available and there are no clearance issues, so Pen F lenses can be an excellent choice for the Micro Four Thirds user craving a manual focus experience. There aren't any really wide angles in the system but most other types are covered, including a zoom. They've been quite reasonably priced for many years as the half frame format fell from favour, but prices are climbing now that they're useful again...

Added 25 July 2010
Updated 24th February 2011
Updated 24th June 2012

Updated 10th April 2017