Tamron-F AF Tele-Converter 1.4x C-AF1 MC4

Aperture Loss of 1f stop (decreases light by 2x) Closest Focus n.a.
Dimensions 0.7 x 2.6 in./ 18.8 x 66.5 mm Magnification Ratio 1.4x  focal length of the attached lens
Weight 6 oz./170g Filter Size Compatible with long EF Lenses

The Extender has been tested on 1 lenses, the Canon Lens EF 135mm 1:2 L USM 135mm f/2, because quality of this lens itself is nearly flawless.

Analysis of the Extender with the 135 mm Canon lens at various f stops is given below.
lens quality test
The system (making a 189 mm lens) is not particularly sharp in wide open apertures, and it's best at f/5.6. At f/8 the sharpnes is most uniform thoughout the entire frame. Dependence of the image quality in various parts of the full 24x36mm frame is shown below, with the average resolution in hundreds of line widths per picture height (LW/PH) given below each chart.

lens quality test

At the full aperture (which is only f/2.8 insead of 2.0) there is a very poor sharpness especially in the mid-ranges from the center. The contrast is also low. At the optimum aperture, f/5.6, the Teleconverter becomes useful and the entire picture is sharp, with a somewhat lower contrast in the mid-ranges between the center and the sides. There is no significant reduction of the circle diameter at the sides of the frame compared to the circle size at the center, but vignetting is relatively high. Chromatic aberration is visible, but not very high low. Using it at f/16 is questionable due to lack of sharpness.

This Tele-converter quality is somewhat worse than the 1.4x Canon Extender, described here. The image quality is significantly compromised at the wide open lens, but it is reasonable at f/5.6 and 8. It maintains autofocus of the f/4.5 and faster lenses.


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