Needing a 400-600mm telephoto reach for a location recce, I purchased the Kenko 2x Teleplus Pro 300 Teleconverter (more popularly known as extenders, doublers, or T-cons).

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Kenko has two lines of teleconverters available: the Teleplus Pro 300 (1.4x, 2x and 3x) and the Teleplus (MC4 and MC7, 1.4x and 2x respectively). Being of the former, which is the higher quality of the two, the build quality of the Kenko 2x Teleplus Pro 300 teleconverter is pretty good. The mounts are made of stainless steel. The Teleplus Pro 300 features circuitry designed to electronically operate the same way as Canon’s own teleconverters. TheTeleplus Pro 300 is available in black or white.

Why I chose Kenko over Canon

The reason why I chose the Kenko over the Canon Extender EF 2x II is because there is no protruding front glass element on the former, meaning you can just about couple any EF lens with it; with the Canon Extender EF 2x II, the front glass element is designed to extend into the mount of certain EF telephoto lenses, thereby limiting the number of lenses you can use with the latter; specifically, only the EF 70-200 f/2.8L, the 70-200 f/2.8L IS, the 70-200 f/4.0L, the 100-400 f/4.5-5.6L IS zoom lenses and prime lenses of 135mm and higher. Do note that Kenko teleconverters are currently incompatible with EF-S lenses; if you require EF-S coupling, go for the Canon Extender EF 1.4x II or 2x II (it has to be the Mark II version).; Canon’s own Extenders are not compatible either. 

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As there is a loss of two stops with any 2x teleconverter (one stop with a 1.4x teleconverter), Kenko recommends using a lens with a minimum aperture of f/4 (opening of f/4 and bigger, not smaller) to ensure AF will work. Kenko also recommends the use of its 2x Extender only with focal lengths 50mm and upwards.

An initial test with an EF 75-300mm f/4-5.6 IS USM proved the limitations to be true. Using this lens on the recce, autofocus failed most of the time and, as a result of the already mediocre image quality of the lens, images turned out very soft and flat. Also, the fact that the Micro USM in this lens has abysmal performance to begin with. I cannot emphasize enough that you will need very good, sharp telephoto lenses if you intend to use a 2x teleconverter.

Next, I tested my regular walkaround lens, an EF 24-85mm f/3.5-4.5 USM. While AF works pretty fine in daylight, AF performance was average in low-light conditions or at night; AF lock is effective down to f/7 before it starts hunting.

In summary, I am very pleased with the performance of this teleconverter. It is a huge plus to now have the extra reach on the 24-85 without too big a dip in AF performance. Optical quality is barely compromised. Do note, though, that your mileage may vary.

The teleconverter tape trick

A teleconverter designed for the EOS system has 11 electronic pins on the end where a lens is coupled. Three of these pins on the teleconverter are responsible for reporting its presence to the lens which, in turn, factors in the teleconverter’s stop loss before reporting its aperture to the camera body. The result of this exchange is such that a f/2.8 lens will report its aperture as f/5.6. Based on this information, the processor in the camera body decides if it has enough light in which to engage AF effectively.

Autofocus functionality in EOS camera bodies are assured at either a minimum of f/8 (1D, 1Ds, 1DMkII, 1DMkIIN, 1Ds MkII, EOS 1 and EOS 3) or a minimum of f/5.6 (D30, D60, 10D, 300D, 350D, 20D, 30D, and 5D); any aperture smaller than either of the two above and AF is not guaranteed to work.

It has been discovered that, by applying a small piece of tape over the three pins, the presence of the teleconverter will not be reported to the camera body. As a result, it will not shut down AF even if the aperture becomes lower than the required minimum The tape trick is most useful for slower lenses, which, in the case of a 2x teleconverter, is anything below f/2.8.

If you look at the electronics contacts on your lens and see only 8 (7 square ones and 1 doubled), don’t bother applying the tape trick, since it means your lens is not teleconverter-aware in the first place. Only some Canon telephoto lenses have the three extra electronic contacts that make them teleconverter-aware. Also, some older teleconverters, either by Kenko or other aftermarket manufacturers, have only 8 electronic pins; if you have such a make, you won’t need the tape trick either.

Follow the steps below to apply the tape trick:

  1. Place the teleconverter in front of you such that the end where the lens is coupled to is facing you.
  2. Make sure that the row of electronic pins are at the 12 o’clock position (refer to photograph below).
  3. The three pins are the first three from the left of the row.
  4. Tape them over with a small piece of tape. I suggest that you apply the tape in such a way that it creates an upward slope over the first pin. This way, when you mount a lens, there is less chance of the tape dislodging.

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