Lens Tests: Teleconvertor Comparisons

The Holding Tank

Hardware

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 |

Teleconvertor Comparisons

| EF 200mm f2.8L @ f8 | EF 300mm f4L IS @ f11 |

The full results for the EF 200mm f2.8L and EF 300mm f4L IS with the EF 1.4X II and EF 2X II are on the following pages:

EF 200mm f2.8L II + TCs

EF 300mm f4L IS USM + TCs

This section looks at a specific stop for each lens and TC combination and compares the TC result with simple up scaling of a lower magnification image by a factor of 1.4X or 2X.

So the basic lens with no TC is up scaled by 1.4X and 2X to compare with the EF 1.4X and EF 2X aided performance and the EF 1.4X image is up scaled by 1.4X to compare with the EF 2X aided image.

In all cases the pre capture sharpened images were upscaled using the Photoshop Image Size control with the Bicubic Smoother resampling method.

The EF 200mm f2.8L II in general gained less advantage from both TC than the EF 300mm f4L IS despite having sharper native performance, this may be due to the match between the TC design and the lens.

In general it was better to use both TCs for both lenses, however the difference between the upscaled 200mm + 1.4X TC and the 200mm + 2X TC was limited, this was not the case with the 300mm.

Looking at the 50% MTF performance relative to the native lens value shows how much less relative loss there is with the 300mm although the 200mm absolute sharpness is better:

Double stacking the TC does not look too bad from the centre MTF value but the edge and corners were much worse and in the case of the 200mm overall contrast was poor.

*MTF 50% Relative to no TC (Centre Avg of H&V)*	EF 200mm f2.8L II @ f8	EF 300mm f4L IS @f11
EF 1.4X II	0.955	1.008
EF 2X II	0.674	0.866
EF 1.4X II + EF 2X II	0.33 @ f8; 0.55 @ f11	0.50 @ f11; 0.53 @ f16

*MTF 50% lp/mm* *(Centre Avg of H&V)*	EF 200mm f2.8L II @ f8	EF 300mm f4L IS @ f11
Lens Only	67	54
EF 1.4X II	64	55
EF 2X II	43	47
EF 1.4X II + EF 2X II	22 @ f8; 37 @ f11	27 @ f11; 29 @ f16

*Relative Sharpness* *MTF 50% / Lens X Mag* *(Centre Avg of H&V)*	EF 200mm f2.8L II @ f8	EF 300mm f4L IS @ f11
Lens Only	1.00	1.00
EF 1.4X II	1.34	1.43
EF 2X II	1.28	1.74
EF 1.4X II + EF 2X II @ f8/f11	0.92	1.40
EF 1.4X II + EF 2X II @ f11/f16	1.55	1.50

To conclude, it seems that TCs are worthwhile in sharpness terms but the degree of advantage may depend on the match between the TC and the lens as well as the native lens sharpness and how this rolls off at spatial frequencies normally above the point where the combined sensor anti-alias filter and sharpening processing is rolling off.

It must be said that sharpness is not the only IQ criteria, however this is beyond the scope of this section.

Last Updated 05/06/2008

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