I am a hobbyists outdoor photographer and I use this teleconverter on the Canon 300mm f/4. The results were great. The focus was just as accurate with the teleconverter as without. I would recommend this one over 2X to keep the sharp focus.

My 1.4x EF Extender III (Teleconverter) works well with my Canon 400mm f/5.6 prime focus lens. At 560mm critters 100 yards away, images are slightly soft, but that was expected. What's good is that they are not nearly as soft as my 200m zoom plus doubler by a different brand. The downside is that the 400mm is autofocus, the ability of which is lost with the extender. Also noted and expected. Worth the money? For my purposes, yes ... long range wild life and birds.

I am currently using the 1.4 EF Extender III with an EF 500 f/4 IS for bird and wildlife photography and I have to say that this is a much needed accessory for this type of work. No visible loss of detail noticeable with the human eye. Photos are much sharper than trying to crop an image taken without it. The additional focal length does make hand holding your rig a bit more challenging, but that's how I do it. No tripod. Highly recommended to anyone looking for additional reach, without having to spend thousands. It's compact and light, which is nice for hiking and traveling. Some make comments about price verses size, but I look at it this way...If it increases my ability to capture a shot that I would otherwise miss, what value do you put on that? Clean/simple/robust design means you will not have problems with this piece of equipment. Very happy with this one!!

I am currently using the 1.4 EF Extender III with an EF 500 f/4 IS for bird and wildlife photography and I have to say that this is a much needed accessory for this type of work. No visible loss of detail noticeable with the human eye. Photos are much sharper than trying to crop an image taken without it. The additional focal length does make hand holding your rig a bit more challenging, but that's how I do it. No tripod. Highly recommended to anyone looking for additional reach, without having to spend thousands. It's compact and light, which is nice for hiking and traveling. Some make comments about price verses size, but I look at it this way...If it increases my ability to capture a shot that I would otherwise miss, what value do you put on that? Clean/simple/robust design means you will not have problems with this piece of equipment. Very happy with this one!!

I was really surprised at how well this teleconverter works with my EF 70-200mm IS II lens. Viewfinder clarity and picture quality is excellent. I used teleconverters in my film days and found the results compromising. I do not feel like I am compromising when using this on my 70-200mm lens.

A great addition to the camera bag. The model III does seem to be working more smoothly than my model II 2x extender.

This extender works great for me!...I attach it to my 135mm f/2.0L & my 300mm f/4.0L. In both cases, I get the 1.4 multiplier and I lose 1 stop and there are no noticeable loss of quality in my images with either lens. The extender is quiet and does a good job of quickly finding a focal point. I have no idea of the performance of the Mark II version, but I am completely satisfied with this extender. I was also going to purchase the 2.0 Mark III extender, but there were too many comments over image quality being compromised however, I'd still like to find out for myself. As for this one, I can say it's a great way to go and I'm glad that I can benefit from my being able to use it on 2 of my L lenses.

Comparing extender is actually comparing a combination of lens/extender. I did try before 1.4 extender version II with my 400/5.6 lens (on 5d MKII), and was not able to see any improvement in resolution/details (using ISO-12233 crops) compared to the bare lens (center to mid-frame, both at f/8.0). Neither did my wife, I've created several crops and let her choose the best ones (she did not know the origin of shots). In case of 1.4 II the result was about even (so I shipped it back), while with 1.4 III 100% crops were in favor of the extender. Since using extender is always a trade-off, I'm not listing any pros or cons.

Gives that sometimes needed extra reach. I use this with a 70 200 IS 2.8 L lens

Travel, wild life, sports and portrait. Excellent quality