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Sigma X1.4 Tele Converter AF
Latest Review Posted Sigma X1.4 Tele Converter AF
I came across this oddity recently in a LBA rage and could not resist purchasing it. An internet search later concluded this TC is either uncommon and/or poorly reported. In reality it is probably both scenarios as the performance was completely unexpected.

I tested the TC on the FA*80-200 and F*300. Wide open, the TC showed some CA in both lenses, but by comparison to other 'comparable' TCs it was either as good (Tamron-F 1.4X Pz-AF MC4) or better (Kenko 1.5X Teleplus DG). Stopped down, the CA is almost completely gone and IQ very good.

Contrast was slightly down by comparison with cropped images of the master lens sized to match. Not a major concern as post processing can easily account for that.

Sharpness was weaker than comparable cropped images, but not noticeably so. See below images of the F*300 - the first is cropped (no TC0 and the second is cropped (with TC).
F*300 (no TC) @ f8
F*300 (Sigma X1.4 AF) @f8

Focusing was fast and not fussy - although I only tested bright light conditions.

In summary, I found the the F*300 + TC combo exceptional. While cropping the F*300 (minus TC) is likely to produce a better image than use with the TC, it is possible that far field images would benefit from TC use. I speculate that the combo may even be equal to, or better than the max zoom range of...

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