If you refer to Canon 70-200mm 2.8L IS II USM + Extender 2x III, then you'd get f/5.6 all over the focal length range vs. the EF 100-400 f/4.5-5.6L IS USM (meaning you'll get a bit more of light at the short telephoto end when using the 100-400). An Extender, or Teleconverter, is a lens accessory that fits between the camera body and lens, effectively increasing the focal length of the lens. I'm much happier with 2-stops-down 2x III results than wide open results. BUT, ONLY If you had all three of the correct ingredients to make this work;- You had to have the most modern af system in the most up to date bodies. These same lenses have results from the version II extenders and provide a lens-by-lens basis for comparisons between the two extender versions. 6lll&USMandIV -EFOO~ 200 mmf /4 .. 5 LUSMandlll&IV -EFS 10 ~ 22 mmf / 3 . Often better (when available) is to use Live View AF, which is generally supported with f/11 max aperture lens combinations. But I notice no slow down in AF on the new 70-200 mk II . With the MKIII T-Cons and the most modern DSLR AF Systems these "brakes" were finally removed. Because the Canon EF 2x III Extender is multiplying the aberrations/flaws of the lens it is mounted behind by 2x and because there are now 9 Well, it really depends on what youre looking for. (and maybe 90D, don't have first hand knowledge there) - You also needed a compatible lens: Version 2 IS telephotos, and version 2 IS zooms- Of course, you needed to use the MkIII T-Cons.Substitute any part of the chain, and AF brakes would be applied. [ very little use so far , but specs say it does slow down AF . I own the 1.4x II and III, AF improvement alone makes the 1.4x III worth the cost. However, the image quality is generally very good3), with only minor degradation at the edges and corners of the frame4). Has anyone out there tried both and able to offer an insight into whether the paying extra for the newer version is worthwhile? Both have their pros and cons, but which one is the best? Note that Canon does not recommend stacking extenders. The answer is yes! An image with low contrast has lesser perceived sharpness. With an R5 in my future as well, why waste money on older design Mark II. by Dan Carr | Aug 29, 2011 | Gear Check, Lenses. I believe the OP has the older NON-L version of the 70-300 IS. So, which one should you buy? With good lenses mounted on a 1-Series body and high-contrast subjects selected for AF, I'm not finding the 2x III AF speed a problem. The lens is also at f5.6 so its only stopped down a tiny bit from its maximum of f4.o. -- DSLR cameras will continue to calculate auto exposures properly when used with Canon Extenders. A 2x extender will decrease your maximum aperture by 2 stops. I have the 70-200f2.8isII and the 1.4II, 2xII, 2xIII. The Canon 1.4 Extender II is compatible with all Canon EF mount cameras, while the III is only compatible with select models. Due to the nature of the work (and the fact that I was working) , it wasnt possible to do comparative photos tediously switching from one extender to the next. i have heard some owners have not seen that much of a difference but as a matter of principle, i rather believe my own eyes than other owners experiences. Considering that an extender can have nearly $20,000 worth of camera and lens attached to it, the extra strength insurance can be appreciated. If youre a Canon shooter, then you know that the companys line of 1.4x extenders can be a great way to increase the reach of your lenses. into a 140-400mm f/5.6 IS lens (yes, IS still functions normally on all compatible IS lenses). Capture One is a, Theres a lot of debate in the photography world about which lens is better for Nikon cameras, the 17-55 or the 16-80. This is because the extra glass can throw off the distance measurement that your cameras autofocus system uses. Said another way, you generally will get better results from a 400mm lens than with a 200mm lens plus the Canon EF 2x III Extender,