Sunday, 7 June 2009

manual aperture control for G1 on legacy lenses

Cast your mind back to pre automated lenses (if you can) and you may recall that many old lenses had a ring on the front to allow full open focus then a quick rotate to "closed" to stop down for taking aperture.

While focusing on the G1 is not quite as dim as the older SLR's the viewfinder does indeed struggle with lower light. Combined with telephoto depth of field precise focus is sometimes a little cumbersome. Sure I use the zoom tool to confirm focus but it can get jittery (indoors available light) especially with anything longer on the camera (like even a 50mm [equating to a 100mm]).

I found myself focusing wide open, then winding the aperture ring around to where I wanted and taking. Sometimes I disturbed the focus when I was doing this. I have some Olympus lenses which happen to have the DoF preview on the side of the lens, so I thought Hmm, why not stop down with that button?

Essentially the idea is to mimic the operation of these lenses on their camera.

The lens aperture ring is set to desired aperture (say f8) although lens remains fully open to allow easier focus, then just prior to pressing the shutter you push a lever on the adaptor to stop the lens down. I have tested that the camera copes with this change using Olympus lenses.

To test this I took out the screw which moves the stop down lever on the back of the camera and tried it with an Olympus lens (which has DoF preview operation built into the lens not the camera). Works a treat!

I've got a number of FD lenses too ... and thinking about this more, how would I do it on the FD?

Well the adapter has a small "coupling pin" to activate the stop down lever on the lens. A quick movement of this moves the aperture iris from fully open to the set location

If you look at the image below this is the back of an FD lens with an adapter beside it. The coupling pin is in the adapter and rotates the lever (on the right hand side of the lens) during mounting to permanently engage the aperture at the chosen setting. In fact if you don't rotate the mount as to engage the pin as your mounting the lens you will be simply stuck wide open all the time.

This is the pair sitting together. In the case of the FD lens mount (unlike say Pentax K mount or simple screw mounts) there FD lens is a little complex (to allow the camera to get aperture information and also to open and close the aperture to give 'wide open' focusing not stop down focusing).

However looking at the adapter it would be a simple matter to make a change to place the coupling pin onto something which moves. This would then allow the photographer to focus wide open, stop down just prior to taking (by pushing the lever) then take. That adapter is by an eBay seller called ciecio7 (check him out on Toolhaus, personally I rate him very highly and I've been on eBay for nine years).

Another adaptor by RayQual (a nice Japanese maker) has this mounting method more clearly labeledon their adapter (see arrows on the adapter below)

rayqual FD adaptor

notice the direction of the the arrow showing how to rotate the lens before mounting to engage the coupling pin? You can see the pin at the back of the adapter.

To do the same for OM lenses is simple ... have a pin which can be lowered or raised.

I'm sure its doable for all legacy lenses and will greatly enhance operation of legacy lenses mounted to micro 4/3 cameras using these adapters.

To any maker who wishes to implement this I only ask that you perhaps send me an adapter done like this for FD lenses as a thank you. I will not ask for any royalty for this.


JB 明仔 said...

If I read your post correctly, what you're looking for is the FD-m4/3s adapter by Jinfinance. It has a moving ring that allows you to control the aperture pin, so you can open the aperture, focus, and then stop down.

obakesan said...


interesting ... must be new, I've not seen it on his list before ... glad to hear it :-)