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Title: I must have gotten a bad copy
Review: I had heard this converter would produce acceptable results when used on a nice fast prime lens and wanted to give it a try for sunny conditions. I used this converter on a 7D body and Canon 300 mm f2.8 IS lens. I was surprised that the results were very poor quality, both in sharpness and missing focus. The 300 f2.8 with the converter installed missed focus almost as often as my Canon 100mm - 400mm f4.6-5.6 IS lens and the quality was on par with the 100-400 so I returned the converter for a full refund.It seems some bodies don't play nice with focus and quality using 1.4x II converters. I expected some loss of sharpness but had heard that the 300 f2.8 was a lens that would produce acceptable quality with a 1.4x II converter. For some reason the converter I purchased new from a well-respected vendor did not produce acceptable results.
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