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Lens Tests

| EF 28mm f1.8 USM | EF 50mm f1.4 USM | EF 100mm f2.8 Macro USM |

| EF 180mm f3.5L Macro | EF 180mm f3.5L Macro + EF 1.4X II  | EF 180mm f3.5L Macro + EF 2X II |

| EF 200mm f2.8L II | EF 200mm f2.8L II + EF 1.4X II | EF 200mm f2.8L II + EF 2X II | EF 200mm f2.8L II + EF 1.4X II+ EF 2X II |

| EF 300mm f4L IS | EF 300mm f4L IS + EF 1.4X II | EF 300mm f4L IS + EF 2X II | EF 300mm f4L IS + EF 1.4X II + EF 2X II |

| EF-S 18-55mm f3.5-5.6 | EF-S 10-22mm f3.5-4.5 USM | EF 17-40 f4L USM | EF 24-105mm f4L IS USM |

| Tamron SP 150-600mm f/5-6.3 Di VC |

| Primes | 17mm Region | 24mm Region | 28mm Region | 35mm Region | 50mm Region | 100mm Region | 300mm Region | 400mm Region | 600mm Region |

| EF 180mm f3.5L Macro + TCs | EF 200mm f2.8L II + TCs | EF 300mm f4L IS USM + TCs | Tests With the Kenko TC | Macro Tests |

| Filter Effect on Sharpness and AF | Flare and Filters | Image Stabilizer Tests | TC Sharpness | Best of the Best | Method | Understanding the Results | Real World 100% Crops | Tripod Tests | L-Plate Test |


Lens Tests with the Kenko Pro 300 1.4X

EF 100mm f2.8 macro USM | EF 100mm macro No TC vs K1.4XEF 24-105mm f4L IS | EF 24-105mm f4L IS No TC vs K1.4XEF 200mm f2.8L II | EF 300mm f4L IS | EF 180mm f3.5L Macro + Kenko 1.4X | EF 180mm f3.5L Macro + Kenko 1.4X + EF 1.4X II | EF 180mm f3.5L Macro + TCs |


Lens Tests With the Kenko Pro 300 1.4X TC




Physical Construction

Test Plan



[Updated with the EF 180mm f3.5L Macro USM]


The Kenko Pro 300 1.4X DG is an independent Canon EOS AF fit teleconverter by Kenko.

This formal lens test report measures the converter with the EF 100mm f2.8 macro USM, EF 24-105mm f4L IS, EF 200mm f2.8L II and EF 300mm f4L IS and EF 180mm f3.5L Macro {new}. Where appropriate the Kenko is compared against the Canon EF 1.4X II and the double stacked configuration of the Kenko 1.4X plus the Canon 1.4X II is compared against the Canon 2X II.

The manufactures information states:

KENKO Teleplus Pro 300 converters are made with precision quality multicoated optical glass supplied by Hoya Corporation, the worlds largest manufacturer of optical glass. These glass elements were designed to match the optical quality of the prime lens (even at the edges) and telephoto zoom lenses. The optical design of the elements and light path is wide enough not to cause vignetting.

The PRO 300 family are designed specifically to be used with prime telephoto lenses of 100mm or above, such as the Tokina AT-X 300 AF PRO, 300 mm f/2.8 lens, and work best with telephoto lenses of 200mm to 500mm. The PRO 300 can be used with telephoto zoom lenses as well as prime lenses. However, Kenko does not recommend them for zoom lenses that have a range starting under 50 mm.

KENKO PRO 300 AF Teleplus converters have genuine Gate Array IC (Integrated Circuitry). It means that the converter’s own unique circuitry maintains signal integrity between the camera body and lens. These converters are designed to electronically operate the same way as an original manufacturer’s converter.

An advantage of the Kenko converter is the front element is non-protruding, unlike the two Canon converters,  permitting:

a) Use with lenses not compatible with the Canon converters

b) Double stacking with another 1.4X converter to permit AF operation to be retained on non-pro bodies with lenses of f4 maximum aperture. (NB the EF 2X II and EF 1.4X II can be double stacked together).

  Canon EF 1.4X II Canon EF 2X II Kenko Pro 300 1.4X DG
Weight (grams) 220 265 132
Length (mm) 27.2 57.9 19.4
Construction 5 elements in 4 groups 7 elements in 5 groups 5 elements in 4 groups



Physical Construction

The construction is not as good as the Canon TCs in that the outer shell is plastic rather than metal. The camera mount is nice and secure, there is a little movement on the lens side but not enough to be a concern. The release spring and lock torque is not as strong as with the Canon TCs but not as loose as in the Kenko extension tubes as to be a major concern about accidental release.

The Kenko is shown below together with the two Canon Extenders (TCs) for visual comparison.


Test Plan

Four lenses have been tested with this converter using my standard SFR/MTF methods; the 100mm f2.8 macro USM,  24-105mm f4L IS, 200mm f2.8L II and the 300mm f4L IS.

As always, use the menu structure shown as hyperlinks at the top of the page to navigate around the results. 100% crops of the test areas will be shown under the individual f-stop results where appropriate, look for the "View Crops" link on each f-stop web page.

As Canon only publish information on MTF data for their own converters there will be no 'comparison with Canon MTF data' web pages in this section.

However, comparison of either Canon converter vs Kenko Converter or Converter or no converter are provided as appropriate in plot form. For convenience 100% crops of centre and top left corner are shown side-by-side for wide open and f11. Note that all the crops can be found by navigating the menu system at the top of every page

It should be noted that on the 100mm macro and 24-105mm lenses the Kenko converter is effectively non-reporting, i.e. the 100mm appears to have a maximum aperture of f2.8 where it is now f4 because of the converter's 1 stop loss. Users need to remember not to stop these lens down so much when used with the converter to avoid diffraction, i.e. an indicated f8 is actually an f11. EXIF information will also report the f-stop and focal length as if no converter is fitted. However, electronic control of aperture and operation of IS both function as expected.

For the 24-105mm only 100mm (70mm setting) and 147mm (105mm setting) are tested because converters are not optimized for use under 100mm.

For the 200mm and 300mm which do accept Canon converters reporting operates as expected, showing the 1 stop loss of aperture and 1.4X increase in focal length both on the camera and in EXIF.

For these two lenses the performance with the Kenko converter is compared with the Canon EF 1.4X II. 

Additionally, the process of double stacking the Kenko converter with the EF 1.4X is tested and compared against the performance of the Canon EF 2X II. Things to note about this configuration:

i) Only one converter is reported, i.e. the camera thinks it only has a multiple of 1.4X and 1 stop loss of aperture instead of 1.4X1.4X~=2X and 2 stops loss.

ii) Because of (i) the camera AF speed seems to be the same as with a single 1.4X.

iii) Because of (i) the camera AF is operating beyond its design parameters, essentially the phase range-finding system is being told the baseline is 1.4 time larger than it is.

iv) Because of (ii) and (iii) there are two possible undesirable side effects, possibly dependent on range, light levels and target contrast:

a) AF accuracy may be reduced with a bias error and/or increased shot-to-shot random error.

b) The AF may tend to hunt. This might show as "chatter" in AI Servo mode if the AF button is held down on a stationary target.

No "chatter" was observed during testing, and AF operation seemed fast and positive both in formal testing and real world use. 

It should be noted that the standard sharpness tests effectively include an AF accuracy component; the standard test method being to take a series of three tests with different AF operations and use the sharpest.

To further investigate the issue of AF accuracy, in each case 10 shots are taken with different AF operations from alternately MFD or infinity to allow a 50% MTF statistical comparison with normal lens configurations.

For all results and discussions the f-stop and focal length appropriate to the lens and converter configuration in question are used, regardless of if this is reported correctly to the camera or not.




EF 100mm f2.8 Macro USM

EF 24-105mm f4L IS

EF 180mm f3.5L Macro

EF 200mm f2.8L II

EF 300mm f4L IS



EF 100mm f2.8 Macro USM

The converter knocked off an expected amount of sharpness off the centre of the lens, although stopping down a stop improved this. The edges and corners suffered more. Wide open the corners should give a sharp A4 print (10X8) but to get a reasonably sharp A3 print in the corners it would be necessary to stop down to f11 (indicated f8).

Chromatic aberrations more or less double from around 0.5 pixels to around 1 pixel.

The 100% crops indicate there is possibly some loss of contrast in the corners and some vignetting wide open.

NB This lens only produced a good focus in one of the three test cases. Normally these are fairly close. The Kenko instruction sheet talks about possible malfunction of the AF with this lens, perhaps this is the reason. If this is typical of real world performance it makes the use of the converter with this lens a bit hit and miss.

The reason for this issue may be that the converter is non-reporting on this f2.8 lens and so the camera is attempting to use the high precision f2.8 AF sensor causing more degradation than otherwise. If so one would expect this problem to occur with other lenses of f2 or less that are not designed to work with a Canon converter; however only this lens is mentioned.

Also note that this level of focus error is probably not easy to spot in the viewfinder as can be seen from the two down-sampled full frame images at the bottom of this section.

Examples showing the Maximum center MTF 50% frequency for the 100mm macro (below)

And for comparison the 24-105mm f4L IS at 100mm.


Example down sampled full frame focus cases; first is good, second is bad.


EF 24-105mm f4L IS

Only the two longest focal lengths are tested with the converter.

In general the centre holds sharpness very well but the edge and corners less so. The fact that the TC has a relatively small impact shows the very high  sharpness of this lens.

The corner sharpness with the TC should provide a sharp A4 print wide open although the 100% crops look at bit mushy, and a sharp A3 print at f8. 

In the 147mm case it was noted that the average corner sharpness did not improve beyond f8; this effect seemed to be dominated by the lower left corner which actually lost sharpness going from f8 to f11.

Inspecting the crops suggests mammal vignetting and loss of corner contrast.

Corner chromatic aberrations were close to that of the lens alone, increasing slightly beyond f8 for the 100mm case.


EF 180mm f3.5L Macro

The performance of the Kenko compared to the Canon EF 1.4X II is very poor throughout the image, double stacking with the EF 1.4X II was much worse than even the lackluster result using the EF 2X II and manual focus. The Kenko is clearly poorly matched to this lens so its use is not recommended even in extremis.


EF 200mm f2.8L II

The Kenko 1.4X could produce better sharpness in the centre than the Canon 1.4X II but in the edges and corners the sharpness was worse and contrast generally lower. If this trend is continued for larger formats users of APS-H and Full Frame formats would be best served by using the Canon 1.4X with this lens, even on APS-C the Canon still produced better results overall.

The "Double Stacked" configuration of the Kenko 1.4X plus the Canon EF 1.4X II was compared with the Canon EF 2X II. The double stack setup is capable of slightly better sharpness in the centre, similar at the edge and somewhat worse in the corners. Once again APS-H and Full Frame formats may emphasis this trend.

However the double stack configuration suffered from twice as much variation in autofocus accuracy and only achieved equal centre sharpness in 3 out of 10 trials and in just 2 out of 10 trials had better sharpness.

The double stacked configuration showed no sign of AF hunting in AI Servo at light levels of less than EV 6 @ 100 ISO.

So overall the Canon 2X is a better solution than double stacking two 1.4X converters with this lens. However, one advantage of the double stack is it does keep autofocus faster which may be an acceptable trade-off for some applications.


EF 300mm f4L IS

The Kenko performed very well with this lens compared to the measured data for the Canon 1.4X across the f-stop range and the whole APS-C frame although the crops suggest the Kenko has slightly lower corner contrast than the Canon 1.4X II.

This double stack approach maintains autofocus operation by fooling the camera into thinking it has a f5.6 420mm configurations attached rather than a f8 600mm configuration. The autofocus sharpness variations over ten trials was better controlled than on the 200mm tests. 

The double stacked configuration showed no sign of AF hunting in AI Servo at light levels of less than EV 6 @ 100 ISO.

This it is possible to compare the sharpness of the double stack with AF focus with manual focus of the Canon 2X II. 

Sharpness is very comparable in the centre of the frame but the 2X is better in the edge and corners, specially once the lens starts stopping down. The EF 2X II has slightly better corner chromatic aberrations by about 0.25 pixels throughout the f-stop range.

In summery the EF 2X II provides better optical performance on APS-C and probably much better in the corners of APS-H and Full Frame.

However, is does provide that rather handy thing called autofocus which can not be obtained with a 2X on a non-pro body.  However if your body will AF at f8 or you will use manual focus anyway (e.g. for close-up work) you are probably best to use the Canon 2X.



The Kenko Pro 300 1.4X is a handy accessory that can be used with lenses not compatible with the Canon converters and can be double stacked with another 1.4X to permit faster autofocus and autofocus on bodies that will not provide AF operation with a 2X converter.

Performance on APS-C is generally good although the Canon converters seem to provide better edge and corner performance. This trend suggests APS-H and Full Frame users may be better served with the Canon converters.

Problems with autofocus accuracy were encountered with the EF 100mm f2.8 macro USM. Kenko warn about issues with this lens and the EF 50mm f2.5 Compact macro. From the context one would assume this is taking about focusing in close-up distances, but perhaps this is a more general issue.

Interested readers should note the Kenko instructions specify the lens is not compatible with the EF-S 18-55mm due to "... the shape of the lens.". Presumably this is a reference to this lenses short back-focus construction; if so there may be compatibility issues with other EF-S wide angle zooms.


Last Updated 26/07/2009

All Content © 2005-16 Lester Wareham All Rights Reserved     

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