I am using this 2X extender with my 135L, and I must say that after a little micro adjustment of +5, this is incredible! I now have a 270mm f/4 lens, and the images are very, very nice. Wide open (f/4), there is a little softness or dreamy effect, but stopped down to f/5.6, images are extremely sharp and contrasty. Yes, this will enhance any flaw in your lens, but with higher quality lenses, should not be much of an issue. AF is fast, I have not had any problems with its speed or accuracy. Overall, I am extremely pleased with this extender.
Back in the 1960s, I was impressed to see Canon lenses on TV cameras in a TV studio I was doing an appearance in; a subsequent trip to Tokyo's Ginza led to some serious camera shopping- a Canon 35mm SLR and lenses (50mm+ 200mmtelephoto) which served beautifully for the balance of my 'round-the-work-journey following a year of travels through India.Years later, I upgraded the body to an A1 and ultimately transitioned into a 5D/ii, which evolved into an SL-1 with impressive zoom lenses. the comfort, ease of use,reliability and impressive images have always been present in all Canon photo products, and have consistently justified my continued investment in these quality products.
Sigma lenses have proven to be excellent choices for me since my first (of now 4) lense. Pleasing photograph results has netted my confidence and trust in the name. Certainly a bargain investment in my unprofessional opinion.
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