CHG_CANON Loc: the Windy City

They won't for a 70-300. The design of the extenders limits the EF lenses they can be physically attached. None of Canon's 70-300 models allow the two pieces of equipment to be joined (and support full functionality). Without listing each specific lens, the extenders are limited to EF primes at 135 or longer. For zooms, the options are only the various 70-200L models and both versions of the 100-400L.

If you desire longer focal length, your best option is the 100-400L II. This is a big expensive lens, but worth the investment.

CHG_CANON Loc: the Windy City

Can and should are clearly not different sides of the same coin ...

Bob55 Loc: Valhalla NY

Thanks again for all that great input and advice guys. It's much appreciated. Bob

juanbalv Loc: Los Angeles / Hawthorne

I'll revisit this with info as to effects using the Kenko extenders with the 70-300. It is true that the 70-300 does not appear on the Canon chart as being compatible with extenders. By the way, and I may be repeating the obvious, the 135mm limitation is applied to primes, TP's and zooms can use the extenders at below 100mm.

To me, as long as you are not hurting your equipment, all is fair in the pursuit of that masterpiece.

CHG_CANON Loc: the Windy City

Kenko, Canon and Masterpiece are three words rarely found in the same sentence ...

amfoto1 Loc: San Jose, Calif. USA

Something is wrong... the EF-S 18-135mm IS Nano USM is every bit as sharp and capable as either of the 24-105s you mention... maybe even better than them at some apertures and focal lengths.

Do you have a "protection" filter on the 18-135mm? If so, remove it and try without.

Also DO use a lens hood (buy one if you don't already have it.... that lens doesn't come with a hood).

If that doesn't help, Micro Focus Adjust the lens on your camera. It may be that both are in "factory tolerances", but just don't quite "sync" 100% correctly with each other. That's why 80D and many other modern DSLRs have means of user fine tuning auto focus accuracy. (See user manual for more info on MFA.)

Still not happy? Some "standard" zooms that might improve upon the 18-135mm:

Canon EF-S 15-85mm f/3.5-5.6 IS USM
Canon EF-S 17-55mm f/2.8 IS USM
Canon EF 24-70mm f/2.8L USM II
Canon EF 24-70mm f/4L IS USM

But, really, the 18-135mm IS USM is pretty darned capable...

See review at https://www.the-digital-picture.com/Reviews/Canon-EF-S-18-135mm-f-3.5-5.6-IS-USM-Lens.aspx

Also, there you can compare highly magnified test shots, other image quality factors and specs of that lens side-by-side with any of the other lenses mentioned.

For example, here's how the 18-135mm USM fares against the 24-105L "II", with both lenses wide open and zoomed to 85mm:

https://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=1045&Camera=963&Sample=0&FLI=4&API=1&LensComp=1072&CameraComp=963&SampleComp=0&FLIComp=4&APIComp=0

To my eye, the 18-135mm looks sharper than the L at those particular settings! Of course, the 24-105L is f/4... while at 85mm setting the 18-135mm is a stop slower f/5.6.

OTOH, the 18-135mm offers both significantly wider and a bit longer than the 24-105.

FWIW... The main "issue" I see with 18-135mm USM is that it has fairly strong chromatic aberration. But that's not uncommon in zooms, especially those that cover a wide-to-normal-to-telephoto range of focal lengths and those in the low to moderate price range... and is pretty easily fixed in post-processing.

juanbalv Loc: Los Angeles / Hawthorne

Which only proves that all is possible.

imagemeister Loc: mid east Florida

Well,the 24-105 is not wide enough on crop frame for my taste. Tony Northup prefers the Sigma -

https://www.youtube.com/watch?v=UlOL4-9b_TY

I would prefer the Sigma 17-70 2.8-4 on crop frame -cheaper too !

..

lwhitehall Loc: St. Louis

My walk around lens is a Tamron 18-270, which I am extremely happy with. I have taken this lens on my 7D to Xian and shot inside the museum where the Earthenware Solders are (kept dark to protect the old paint and no flashes allowed) and my shots came out fantastic. I have take the lens to Niagara Falls in the middle of summer and bright daylight and got really good shots there.

danatek

Sorry to say I experienced the same disappointment with several Canon lenses...EF 28-105, EF100-300L and 18-135. For sheer sharpness, color rendition, and contrast, even my old Tamron Adaptall lenses (28-105 and 80-200) were outperforming them.
Eventually I just went Nikon. Their bodies may have their 'eccentricities', but their glass is superlative at every price level.

TriX Loc: Raleigh, NC

If I had difficulties with 3 lenses (including an “L”), I’d be looking at the body (which may have been defective or required adjustment), not the lenses. While the Nikon lenses AND body combination may have yielded results more to your liking, independent lens tests do NOT confirm your assertion that Nikon lenses, as a whole, are superior to Canon. Your latest comment is right up there with your previous one suggesting a Nikon lens for use on the OP’s Canon body - ‘nuff said.

Both Nikon AND Canon make some of the most highly rated lenses available, hence the reason that you’ll see a plethora of white Canon L series lenses at every major sporting event. Apparently the pros know something you don’t. Again, Nikon makes world-class lenses and bodies - no denigration intended, but Canon lenses are equally well regarded.

Photocraig

I have an EOS 77D. It is a close 24MP cousin to the 80D. I use a Sigma 17-70 f2.8-4 Contemporary stabilized Zoom. I'm on my second copy and it works really well. I chose to re-purchase it after a theft. My choice was between your lens which has longer reach, but is heavier. I can't comment on the sharpness comparison between the lenses, but I am very happy with the sharpness, speed of focus and the larger maximum aperture of the Sigma at about $400.

Other Canon folks strongly favor the Canon EF-S 15-85 lens. It is reputed to be among Canon's sharpest lenses. It is heavier, has a smaller max. aperture and it is more expensive than the Sigma but I think physically comparable to the EF-S 18-135. I suggest you research the reviews on all of the lenses you're considering. Good luck.
C

DJphoto Loc: SF Bay Area

I bought my 80D with the same lens and it is very sharp; it is on my camera most of the time. I suspect you got one on the wrong end of the tolerance spectrum. I would contact Canon about a replacement. For my uses I wouldn't want anything above 18mm at the lower end and often use the long end. I also have the EF-S 10-18 and it is a great lens.

Jakebrake Loc: Broomfield, Colorado

Agreed. I too received the 18-135 with my 80D and certainly not the IQ of my 24-105 L II, or my Tamron 24-70 Di VC G2, it's still no slouch in image quality as my walk around glass. (plus it's a lot lighter) Contact Canon because you may have simply got a bad copy.