Canon FD - Fuji FX Adapter

[Plain Nev]

I bought one of these lately and have used it with good results. But, I must admit I didn't really understand the purpose of the open and closed ring. Still not sure I do now. If the adapter is closed, or locked, you have full manual control of your apertures. However when opened it's at full aperture. I don't quite understand the purpose of this. And, as there are no instructions, I'm hoping somebody might explain it to me, as I can be a bit hard of thinking on occasions.

 

[Musicman]

On 'modern' SLRs, Through-The-Lens metering is done with the aperture wide open ['open-aperture metering']. That allows the most amount of light through so that the viewfinder is as bright as possible, to make it easier to focus. Otherwise, for example , composing and focusing with the lens stopped down to f/22 could be quite difficult with a dim viewfinder.

Then, just as the shutter is about to fire, the diaphragm is closed down to the the aperture that has been set for the exposure. This was known as 'automatic aperture', in contrast to 'stop down metering' that was was used on older SLRs. In Canon's case the FL lenses that were the predecessors of FD mount used stop down metering. There is a pin on FD mount bodies that engages on FD lenses to indicate that is used to stop down the aperture when the shutter is pressed, and that is what the lock button on your adapter is mimicking.

As an aside, FL lenses could be mounted on an FD body, but don't engage that pin, communicating to the body that the lens will only work in stop down mode.

If you set your adapter to open, you get similar benefits to what you do with an FD body - when 'open' there is more light available to compose with (meaning less noise and faster refresh in your EVF image) and, since the depth of field is at it s most shallow, focus is most accurate.

However, your Fuji body is then metering with the aperture wide open and. the Fuji shutter is not coupled to the pin to stop down the lens at the point it's about to fire, so you would have to switch the adapter to 'closed' or 'lock' to set the lens for metering at the taking aperture. Once you have done that, you get to see the depth of field you will get in the final shot, as the aperture is stopped down (like pressing the depth of field preview button on an SLR or DSLR) and you are ready to release the shutter.

Personally, that's too much of a faff for me and I buy FD adapters such as Metabones ones that have the pin permanently engaged so that the lens is always in stopped-down, there is no switch on the adapter.

 

[Plain Nev]

Thank you. That's a very comprehensive reply and explains it nicely.

 

[Musicman]

You're welcome

A couple of other points that may be worth mentioning while we are here

- if my memory serves me well, you won't be able to switch the lens between an f-number setting and A (automatic) while the switch is in Open position. Don't try to force it! A is for FD lenses to operate in Aperture Priority mode or Program mode. Your Fuji body won't be able to control the aperture on the lens anyway, so you probably won't ever need to set the lens to A.

- for the pin to engage properly on this design of adapter, you should mount and unmount the lens with the switch set at Open

There's a short video illustrating how it all hangs together here

View: https://www.youtube.com/watch?v=siMEngsGWf0


It's all a lot simpler with a fixed position adapter with the only downside being a worse EVF image while composing at smaller apertures (but I rarely shoot much beyond f/8 anyhow so it's rarely a problem).