Why AF confirmation doesn’t work with a manual lens on an unchipped adapter
Asked 1/25/2011
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On a Canon EOS 450D/XSi, focus-confirmation works with one of my manual lenses only when I use an adapter that has an "AF-confirm" chip. With a plain mechanical adapter that has no electronic contacts, the AF confirm light never activates, even though the camera’s phase-detect AF system should still be able to detect focus.
Why does the camera need electronic contacts just to provide focus confirmation? What information is the body expecting from the lens, and why is a chipped adapter enough even if it reports bogus EXIF data? Also, is there any practical DIY workaround to make the camera think a lens is attached so focus confirm will work with fully manual lenses?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
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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 :)
Originally by user3458. Source · Licensed CC BY-SA 4.0
user3458
15y ago
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Generated from our catalog & community — verify before relying on it.
On EOS bodies like the 450D, focus confirmation is only enabled when the camera believes an electronic EF lens is attached. A plain adapter has no contacts, so the body sees “no lens” and does not activate AF/focus-confirm behavior.
An "AF-confirm" adapter includes a small chip that imitates an EF lens. It doesn’t need to provide meaningful lens identity; it just has to report enough basic lens data—commonly things like a plausible focal length and maximum aperture—so the body enables its AF sensors and focus-confirm indicator. That’s why EXIF from these adapters is often fake or generic.
So the contacts are needed not because the AF system can’t detect focus optically, but because Canon’s firmware is designed to require electronic lens communication before it will use that feature.
As for DIY: the practical workaround is exactly what those chipped adapters already do—spoof lens presence electronically. A purely mechanical workaround won’t make the body enable focus confirm. Any custom hack would amount to building or installing an EF-compatible chip/emulator, which is what commercial AF-confirm adapters provide.
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