Help: lens okay on 30D/NOT okay on 40D????

Help is appreciated in understanding why a lens, an older Quantaray pictured here, and found working on a FILM Rebel, does not work on a 40D....well, it focused, but the aperture wouldn't...I got the "no communication between lens and body" error message to clean contacts...but of course that wasn't enough....

I was going to sell it with the film camera, thinking that it was the case of old film lenses not connecting with digital bodies...but out of curiousity I tried it on my 30D and IT WORKS...

Anyone with a clue about this...??????

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If it's an EF mount, it'll mount to an EF body.

Some 3rd party lenses need to be re-chipped to work on newer cameras (because of changes Canon makes). That's probably your issue.

I guess they simply reverse-engineer the body-lens comms, make some assumptions and it turns out they're wrong. A perfect example might be Canon leaving a bit spare to indicate additional metadata but don't bother using it initially, then one day decide to use it - old Canon lenses recognise yet ignore the data, third party lenses just assume it's always "off" and expect a smaller packet. Of course this is just a basic example of something MIGHT happen, but gives you some idea of the dangers of reverse-engineering.

^What he said^

Had a sigma push pull and it was the same case.

It should work wide open but that will be it.

Johnsoir wrote in post #10924173
^What he said^

Had a sigma push pull and it was the same case.

It should work wide open but that will be it.

And the winner is.....big John...
Here are full frame crops of wide open shots hand held @ 1/50 (F5@ 162mm) and 1/80 (F4 @ 70)
Not bad...

kitacanon wrote in post #10924294
And the winner is.....big John...

Pssh, I mentioned it first.

TheBurningCrown wrote in post #10924310
Pssh, I mentioned it first.

Yeah, but you didn't explain why it works on the 30D...
and for the record, it does work on the 40D @ wide open apertures....

kitacanon wrote in post #10924609
Yeah, but you didn't explain why it works on the 30D...

"Newer cameras." The 40D is a newer camera than the 30D, and obviously Canon changed the circuity to stop the lens from functioning.

Right, but it won't talk to the body. Like how you can use a pinhole lens on a DSLR.