How can you force autofocus with a Canon teleconverter, and what are the trade-offs?
Asked 9/27/2012
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On many Canon DSLRs, autofocus is disabled when the lens and teleconverter combination reports a maximum aperture smaller than f/5.6. A common example is an EF 100-400mm f/4.5-5.6L with a 1.4× teleconverter.
A commonly mentioned workaround is taping certain contacts on the teleconverter so the camera does not see the reduced maximum aperture. Which contacts are typically taped, and what side/orientation is this based on? What side effects should be expected, such as incorrect EXIF data or loss of distance information? Are there any practical alternatives, such as third-party teleconverters that still allow AF without taping?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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Basically tape the last(left) three pins of the converter. EXIF distance data will likely be lost for most lenses.
You will find your answer at this link: Fred Miranda Tips Page
As quoted from the site:
Just place a small transparent piece of tape on the last 3 pins of the converter. The tape should be placed on the left hand side of the converter when looking at it from the lens connection side.
They also have a picture example of doing so if you need that guidance.
As far as other consequences to taping the pins, I found a bit of information and some anecdotal data for you as well from here:
You should be aware that the EXIF data will not be correct with regards to focal length, however.
Another thing to be aware of is that these three pins obviously do a little more than that with some lenses. Whilst my 100-400 is fine with a taped 1.4x my 70-200/f4 didn't like it at all. It hunted like crazy and hardly ever achieved focus lock. Without the tape it was as quick to focus (as far as I could tell) as without the teleconverter. The solution was to put the tape on the corresponding contacts on the back of the 100-400, now both lenses work just fine with the teleconverter. -chris maddock
Originally by user4892. Source · Licensed CC BY-SA 4.0
user4892
13y ago
0
Generated from our catalog & community — verify before relying on it.
A common workaround is to cover the last three contacts on the teleconverter, on the left side when looking at the converter from the lens-mount side. This prevents the converter from reporting itself properly, so the camera may keep AF enabled.
Trade-offs: AF may work, but performance is often unreliable and slower, especially in weak light or with low-contrast subjects. EXIF data may be wrong, particularly focal length, and distance data may be lost on many lenses. Because the camera is no longer getting full information, communication can also become inconsistent; some users report occasional lens communication errors.
A more practical alternative is a third-party teleconverter such as some Kenko models, which may allow AF at effective apertures around f/8 without using the tape trick. Even then, focus accuracy is not guaranteed, and you may need to check or adjust autofocus microadjustment for the specific lens+TC combination.
So yes, the tape method can work, but it is a hack with real reliability and metadata downsides.
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