Can anyone explain me the aperture mechanism FA28-105 F3.2-4.5 IF-AL

Started 6 months ago | Questions thread
KentG Veteran Member • Posts: 4,690
Re: Can anyone explain me the aperture mechanism FA28-105 F3.2-4.5 IF-AL

In most DSLR/SLR lenses the aperture ring and aperture itself are never really connected mechanically, unlike a Cine lens where the aperture is usually pure medchanical. That is because the SLR/DSLR is thru-the-lens viewing and metering. This means the aperture never closes with the aperture ring because it has to meter wide open so the viewfinder does not get dim at small apertures. It only closes down when you either trip the shutter or use the stop-down button. At all other times the aperture ring and diaphragm are never connected one to one mechanically. They were in the M42 era up until they added open aperture metering in some bodies. The "click" as you call it are the standard aperture values that allows the metering to figure the rest of the solution like the shutter time, ISO, etc. If you disconnected any electronic coupling, then the aperture is likely never going to function properly.

That is the reason most of the AF mount lenses are known as "broken" k-mount lenses, because they removed the mechanical lever from the camera that allowed the camera to tell what the aperture setting was mechancally and went full electronic. Lenses with no aperture ring are A lenses all the time, which means only the camera can stop it down electronically. That is KAF2 and up. KAF still had the lever but the the lever acted on the aperture's fixed values, the click stops, the  lever stopped at the click setting (stop-down mode). Without the click stops the lever will just push the aperture ring to the bottom I think. Of course you have to have a camera body with the lever still in it which goes back a ways.

Don't take this as a perfect explanation as I am generalizing things. but if the aperture does not close down when you turn the ring you are basically screwed as its de-coupled now.

Kent Gittings

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