Konica 38mm f2.8 from C35 converted for m4/3

SXR_Mark · Joined: 12 Jun 2010 Posts: 506 Location: England

I picked up a broken Konica C35 rangefinder cam cheaply so thought I would try and re-mount the lens for my Oly EPL1. I used a c-mount to m4/3 adapter and two rings made from 3 mm thick aluminium plate. The original mounting plate from the C35 was re-used after machining down.

The main issue is the lens has no aperture fitted. I assume the aperture is built into the Copal shutter that sits behind the lens. Thus, I used an aperture from a broken Tamron 28mm AD2 lens (bought cheaply ages ago just for the adaptall mount). This is a 5-bladed unit and is sandwiched between the two aluminium plates. At the moment, there is just a strip of plastic poking out from between the plates to control it. There are no click stops or indication of aperture. If the lens gave better performance, I would improve this, but probably won't bother.

Pictures of lens:

A few test shots. The first of each pair is shot wide open (f2.8 ), whilst the second is shot with the aperture closed down to halve the shutter speed and so should correspond to f4.

Wide open, the lens is a bit soft with a mild glow. At f4 the glow goes and the sharpness improves, but performance is not stellar. The lens also looks to get noticeably softer at the edges which is surprising given the fact this is on 4/3 and the camera is 35mm. Colour is good, whilst saturation is excellent at f4 but benefits from a small levels tweak wide open.

Wide open

Wide open crop, focus was on face of stauette:

At "f4"

Crop at f4

Wide open

At "f4"

Wide open

At "f4"

Wide open

At "f4"

ManualFocus-G · Expire: 2014-11-24

That is incredibly impressive work Shocked

Although performance is, um, not brilliant, the fact that you have managed to convert it AND insert an aperture mechanism is incredible!

F16SUNSHINE · Expire: 2011-11-18

Great Hack! Impressed by your ingenuity.

iangreenhalgh1 · Expire: 2014-01-07

Great work, shame the IQ is not so great.

I happened to test the Hexanon 2.8/35 today, the EE version, it's outstanding imho.

SXR_Mark · Joined: 12 Jun 2010 Posts: 506 Location: England

Thanks guys!

It's a shame this lens did not justify the effort, but as a frustrated engineer (who became an experimental physicist) I enjoy doing this sort of thing. I even bought myself a micro-lathe before Christmas so I could do this sort of thing more neatly.

When fitting the aperture, I had half a mind on making a Pentax 110 adapter with built in aperture. This should be possible as the 110 registration distance is 27 mm, giving me ~7.5mm of space over the m4/3 register, which the same as the spacer thickness I needed for the Konica lens. However, I would need to accommodate a bayonet flange for the Pentax lens, and without having the bits in my hand it is not clear whether I could make things fit. Unfortunately, the Pentax 110 stuff sells for too much on ebay for me to take the chance (and I would need a camera to get the female bayonet off as well). I guess I could buy the 18mm lens, this being the one of most interest, and do a full mount transplant. I assume that, without the need for aperture coupling, the 110 mount would be easy to remove.

Mark