I understand that my Canon 450D's (XSi/Kiss X2) passive autofocus system knows a spot in the view is in-focus when its nearby contrast is adequate. Then the camera blinks AF confirm lights to inform me which parts are in-focus (or if the chosen spot is in-focus).
I have few older all-manual lenses, which I use with an adapter. Why the AF confirm lights won't blink when the spot is in-focus while using an all-manual lens with an adapter without any connectors?
I do have an adapter which was marketed as "AF-confirm" and that it has a "chip". With it the camera does blink the AF confirm lights. What I fail to understand is why the connectors are needed? What data the camera needs from the lens? Camera does record some EXIF information when using the "chipped" adapter, but for example the "Lens" field is "1-65536" so it really couldn't be much of an use.
Added some specifics after Staale S's answer: Can I DIY-hack this around firmware/hardware/MacGyver wise so that the camera thinks a lens (any) is attached when triggering the AF?
Answer
The AF gizmos won't do their thing unless they are told that there is a lens on the camera. (Remember that the EOS/EF lineup was designed from scratch to be the latest and greatest all-electronic autofocus camera system back in the late eighties. The legacy Canon lenses would not fit physically so there was no need to accommodate them at all.)
When using the non-chipped adapter, the camera has no idea that there is a lens there, and the AF is not activated. The chip in the chipped adapter just tells the camera that there is something there, and - I think - that it has a certain focal length; this is enough to get the camera to play nice and activate the AF sensors. This may seem a bit pedantic of the camera, I agree, but let's be charitable and remember that they didn't have this scenario in mind when they designed the system :)
No comments:
Post a Comment