LED-aided focusing with manual lens?

[pierrot]

When not in AF mode (set to off on the lens) it is possible on a 20d to check the accuracy of the manual focus setting in the viewfinder, thanks to the "focus OK" LED in the bottom-right corner.

But this seems to work only with Canon EF lenses... I'm trying to get the same service using a 3rd party manual lens: I change my EF 50mm f/1.4 for the old 3rd party manual lens, and the LED never turns on. :rolleyes:

Is it normal? Or is it me? :shock:

[PacAce]

If the lens is Canon EOS compatible and is an AF lens, then putting it in manual should still allow you to verify focus with the LED light in the viewfinder. The only time this is not true is if the lens has a TC attached which, in AF mode, would make it lose it's AF capability. But, having said all that, my only experience with 3rd party lenses are a few Sigma and Tamron lenses so what I said above may not be applicable for all 3rd party lenses. I only know that it's a fact with Canon lenses and maybe a few Sigma and Tamron lenses.

[pierrot]

Yes, I mean an old, manual lens, not a modern "compatible" one like the Sigmas, Tamrons etc.
On this old lens I have the only compatibility is in the M42-to-EF mounting ring... ;)

[PacAce]

Yes, I mean an old, manual lens, not a modern "compatible" one like the Sigmas, Tamrons etc.
On this old lens I have the only compatibility is in the M42-to-EF mounting ring... ;)
Then, yes, those lenses will not allow you to get focusing feedback via the focus led. For the focus LED to work, there has to be compatible electronics in the lens as well.

[pierrot]

I suppose I have to live with that... :(
But in fact I do not understand why this limitation, since focus detection is made by the camera (which pilots the lens in order to achieve a perfect focusing)...
Why should it not detect when manual focusing is perfect, then turn the LED on to signal it?