Oak Park Photo Loc: Los Angeles, Ca.

Besides loosing 2 stops with the 2X extender, more importantly, you lose sharpness. I would recommend the 1.4X, but not the 2X.

jeep_daddy Loc: Prescott AZ

I have that same lens and a Canon Mk II 1.4x teleconverter. It's NOT a good combination for birds. You loose autofocus and even if you tape the electrical contacts the autofocus is slow and inaccurate. If you want tack sharp images don't buy it. Oh, by putting the 1.4x on the 100-400 your fastest stop will be f/8 @ 400mm. You could sell your 100-400 and buy a 400 f/5.6 prime and then use the teleconverter on it but you'd still loose a stop and be shooting at f/8.

Swamp Gator Loc: Coastal South Carolina

I'm glad you enjoyed looking at my photo blog, and I appreciate the kind words.

CAM1017 Loc: Chiloquin, Oregon

My experience has been the same with the canon 1.4 and the canon 100-400. The degraded functionally and image quality was such that I sold it. Granted most of my shooting is hand held of birds in flight, but when I tried to do controlled tests on a tripod the quality fell far short of what I wanted. I think that Canon on their web site does not recommend this combination. Some people have report good results with these tele extenders on prime non-zoom lens and have presented very nice results.

Swamp Gator Loc: Coastal South Carolina

Thanks a million Jim, I greatly appreciate your very kind comments and support!

mainshipper Loc: Hernando, Florida

Again, on my 70-200 f2.8 I see little degrading of anything.

gessman Loc: Colorado

There are so many variables in this equation, not the least of which is operator control and error that it makes it nearly impossible to sort out what exactly is behind the good and bad experiences others have and "your mileage may vary." I use a 1.4x II on a 5D2 with a 70-200 2.8 II and a 400 5.6, usually on a gimbal head, and I see very little degradation of image quality when I keep my filthy lil' shaky hands off the equipment. If you get sharp images with the 100-400 and don't mind a little manual focus, you'll probably do so with the 1.4x also. "And the return policy of where you purchased it is..."

shutterbum

I have a Canon 70-200 f2.8 used with the 7D, a 2X and still have autofocus. Yeah, I loose a couple of f stops but I have NEVER found that to be an issue. To my eye the images are perfectly fine. I have absolutely no regrets with this combination.

gregoryd45 Loc: Fakahatchee Strand

mollymolly has let me use her 100-400 with my tamron 1.4X and I did not lose auto focus, and it handled very well

Bill Emmett Loc: Bow, New Hampshire

As my departure for my latest trip to Costa Rica, came, I purchased a (of all things) a Kinko 1.4 teleconverter, and a Tamron 2x teleconverter. I intended to use these on my Canon EF 70-200 f4L USM lens, and my Tamron 200-500mm lens. I tested both in my backyard. I found the Kenko did not loose auto focus, but did loose one f stop. The photos were taken during bright and sunny days, with plenty of contrast. The Tamron 2X did focus on bright days, although slow. As the sun began to set, the 2X failed to auto focus and did loose 2 full f stops. I took both extenders on the trip, and mainly used the 1.4 extender on the Canon 70-200 f4L lens. During a day at a ferry landing I got some good pictures of frigate bird fighting for scraps thrown from fishing boats, while cleaning their catch. These photos were shot against blue clear sky, with plenty of contrast. I'm not really satisfied with the images, they look a little soft. I plan on running the 1.4 extender attached to the camera, and Canon 70-200mm L lens through the micro adjustment using FoCal to see how much adjustment I will need to sharpen the lens and extender. I only wish I would have had the money for the 70-200 f4L with IS.

pigpen

I'm not sure about your 100-400mm, but I bought the 400mm L f/5.6. I had the Sigma 150-500mm, and got rid of it for the Canon. My Canon 400mm is so much sharper.

But let's talk about reach advantage. During my research of the Canon 400mm f/5.6, I found a review that compared it to the Sigma. He photographed a $100 bill @ 500 with the Sigma, and 400 with the Canon. Besides pointing out the quality difference, he wanted to point out that the Sigma @500 is not at all much more "reach" than the 400mm. I have read later that some attribute this to different brands, and others attribute that difference to being about a zoom and a prime. So, your lens being a zoom, I don't know if this will be an issue.

I looked at the 1.4x III for my 400mm, and found I would loose AF. Swamp gator has the 300mm + 1.4x, and he produces at least as good (usually better) than I do with the 400mm prime.

T20

Thanks a lot Oldtool2. I just did & it works :)

imagemeister Loc: mid east Florida

If you use Tamron extender you do not have to tape the pins. If you are on crop frame, the image degradation from 1.4 TC is negligible assuming you have a state of the art lens in front of it. And, you may not discern any difference even with 2X - again on crop frame. Keep in mind that shorter teles are inherently sharper than longer ones - so that even with a TC they are often equal. A 300mm is sharper than a 400 - and a 200 is sharper than a 300mm ! (- speaking of equal technologies here). Image below shot with Canon 80-200 2.8 L with Tamron SP 2X on crop frame.

fstop11 Loc: Huntington Beach Ca

I have Canon 5D2 and 7D and a Canon 100-400 .

I broke my 50-500 Sigma 4 - 5.6 non stabilized. I shot mainly BIF. Sharper lens than 100-400 sigma auto focus was slow so I used manual focus but was always a problem with BIF. I also used the sigma 2x & 1.4x extender with manual focus. Stationary subjects OK.

I damaged this lens so I now have a 100-400 Canon. I like the telescope zoom feature very seldom do you loose you subject in flight if you do a quick slid action and your back in the shot. I miss the sharpness of the Sigma.

On the 1.4 canon extender Ive taped the pins but AF does not always hold with a BIF.

Bruce with a Canon Loc: Islip

From what I have seen, the combo I will be using will be the 1.4 II on the 100-400 on a gimbal mount, sitting on Manfrotto 055xprob is plenty sturdy, that will eliminate the the issue you describe.

Thanks for your opinion