Canon 300 2.8 stops focusing

[smrooker]

I have a used Canon 300 2.8 non is that I bought used. Tack sharp, great lens. But if you change from horizontal to vertical, it shuts off. in the repair shop now, they can't figure it out. any thoughts?

[ebiggs1]

Yes, send it to CPS.

[trulandphoto]

Sounds like it might be a fault with the AF/MF switch or the wiring so that it is switching without you moving the tab. Canon service would be your best bet.

[TCampbell]

Ouch... I happen to own one of these and can vouch for the fact that it is _not_ supposed to shut off AF when you rotate it.

If the shop can't figure it out... I'm wondering who you sent it to.  Is this at a Canon repair facility??