Ok, i've just returned from the OR...
> Anyway, i have a damaged Canon 1.4x TC lying around. I'm going to
dismantle it
> and see what's inside, apart from the glass obviously.
> That probably won't tell me much though, as its bound to be a single
unmarked
> chip.
I had to remove about 13 screws before the Canon TC opened up. This thing is
built like a tank. But to my surprise, there's no electronics in it at all -
only wires.
Most contacts are just passed through. The three extra contacts on the lens
side are simply wired together. One of the other contacts is passed through
the switch in the lens mount. If no lens is mounted, the circuit is
interrupted. If a lens is mounted, the signal is passed straight through.
Funny thing about that switch, though. The canon 1.4x TC has one, the
soligor 2x TC has one, my eos 50e camera has one, but my eos 30 camera
doesn't! I wonder what's it for... If your looking for the switch, it's at
the 10 o'clock position when your looking at the lens mount... (or not).
> Even if the innards of the Canon TC don't yield any usable information, I
might
> be able to transplant the electronics to my Soligor 2x TC.
Next I opened up the Soligor 2x TC, only 4 screws.
Disappointment: I knew the housing is plastic, but i hadn't guessed its this
cheap. If you squeeze it, the housing flexes - a lot. I think it gets most
of its rigidity from the metal lens mounts.
Second disappointment: There's a small but crowded smd printed circuit board
in it. It has a big 28-pin chip on it, a small 8-pin chip, and loads of
other small stuff. The pcb is connected to the contacts using lots of tiny
springs which jump out and get lost. Not very diy friendly. A search for the
number on the 28-pin chip at www.altavista.com finds only a page about model
train cars with a coca-cola add on them, i think, because the page is in
German... The number on the small chip is too small to be readable, even
with a 4x loup.
However, the pcb has two jumper islands on it marked "1.4x". I think soligor
(or whoever their oem is) uses the exact same pcb for both the 1.4x TC's and
the 2x TC's. The only difference is that for the 1.4x TC these jumper
islands are shorted.
I break out the soldering iron, and after pasting two blobs of solder on the
islands to short them, i put the TC back together.
I put it on the camera, add the 300mm/F4 lens, and BINGO! The camera reports
a F5.6 lens, tries to autofocus, and the af is slowed down just like with
the real 1.4x TC. I now have a 2x TC which pretends it's a 1.4x TC! Great!
The AF still has some problems locking on indoors (dark), but outside
(bright) it works perfect. It certainly works more reliably then when I just
taped over the extra contacts.
Anyway, to sum things up:
- If you want AF with a Canon 1.4x TC/lens/camera combo that normally
doesn't support it, don't bother with any modifications. Just tape over the
3 extra contacts on the lens side of the TC. The TC wont be detected, the
camera will AF, but it might hunt somewhat.
There seems to be no way to slow down AF to make it work better without
letting the camera know there's a TC.
- If you want a 2x TC to pretend its a 1.4x TC, you need to modify the TC.
If it's a third party 2x TC, see if the pcb matches the description in the
text above. I wouldn't be surprised if many brands selling TC's use the same
circuit board (perhaps even the same optics).
If it's a canon 2x TC, or a third party TC that doesn't match the
description, remove the electronics and just wire all the contacts straight
through, just like the Canon 1.4x TC in the text above. I don't have a Canon
2x TC, so this is just guesswork, but I think it'll work.
The modification will allow you to use a F4 lens with a 2x TC and still have
AF (if your camera is an eos 3 or 1v, you can probably use a F5.6 lens with
a 2x TC and still have AF).
This works better then just taping over the contacts, because the AF motor
is slowed down so the AF works better.
Of course, the best modification would be to just have the camera AF at F8,
without any tricks. The eos 30 is certainly capable of it. Maybe canon is
afraid the eos 30 would cut into the sales of the eos 3 if it would AF at
F8, i don't know. Does anyone know how to diy patch the firmware in the eos
30?
(I think I read in a review somewhere that the AF sensor in the eos 30 is a
copy of the one in the eos 3? Looks like they were right...)
A few reminders:
- The Canon TC's only fit on professional Canon L telelenses because of
their protruding front element. If you have a 'consumer' lens (canon or
brand-x), you'll need a brand-x TC.
- For 'consumer' lenses, you might not need the modification or the tape
anyway. You lens probably has only 8 contacts, so it doesn't use the extra
contacts on the TC (which has 11 contacts) anyway. I think only Canon L
telelenses have the extra contacts.
Disclaimer: Don't come crying to me if you damage your expensive gear during
any of the dismantling, rebuilding, soldering or taping i've described. Most
if not all i've described above might damage or destroy your lens, camera or
TC. Even if it works, it'll certainly invalidate any warranties. You've been
warned...
Good luck,
Martijn Stol
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