Menkaure Loc: Michigan

I'm also looking for any opinion if I should or should not get one. Also any comments/suggestions/etc.
Thanks.
Menkaure

CHG_CANON Loc: the Windy City

What lens do you plan to use with? Have you checked to confirm this lens can be physically connected to a "Canon Extender EF 2x", if that's what you're looking for.

What camera do you plan to use? Will your camera retain autofocus with the lens and extender combination?

Assuming an 2x extender, do you know the differences between the vI, II or III (current) models?

ken_stern Loc: Yorba Linda, Ca

Excellent & appropriate questions

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Only a handful of Canon lenses are good enough to work with a 2X extender - The 400mm F2.8, 300mm F2.8, 200mm F2, 70-200 F2.8. These are all fast, incredibly sharp lenses that have high resolution and can still autofocus with a 2X extender.

So this begs the question - what lens are you planning to use the extender with?

Jrhoffman75 Loc: Conway, New Hampshire

If you are speaking of a Canon brand 2X (the white one) then be you need to know it only works with longer L (red ring) lenses (135mm f/2 or longer, except the 70-300 f/5.6 zoom).

Also, except for some of the higher level cameras, auto focus will not work if the effective f/stop is grater than f/5.6. So, with a 2X converter, it will not autofocus if the lens has a smaller max f/stop than 2.8.

All converters will, to a greater or lesser degree, reduce image quality and slow autofocus.

Third party converters will generally fit all lenses, but they can also be more unreliable relative to their electronic connection with the lens.

I have a Kenko TELEPLUS HDpro 1.4X which works well electronically, and also doesn't disable AF if the f/stop is smaller than the recommended value, so it will AF (slowly) with my f/5.6 lens. The 2X version also claims electronic compatability.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

A 2X extender, on a lens, could put it beyond the limits for AUTO FOCUSING on your camera. Many DSLR's have a auto focusing ceiling of F8, if you go higher than that, you will have to use manual focus. ex. if you have a lens that goes beyond f4 at any point, you will loose auto focus if you put a 2x on it.
A 2x extender makes your viewing darker, takes the camera longer to get focus, and or, maintain focus.
A 2x extender will never provide that same sharpness as not using it.
Personally, I do not recommend any extender, but if you insist, I would not recommend anything over a 1.4 extender.

bleirer

You left the 100-400 and the 400 f5.6 off your list? Not in the same price category, I know, but reviews say they perform well with extenders, and a couple of cameras can auto focus with it. What are your thoughts?

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Not with the 2x.

Karl's Bird Photography Loc: Oregon

The Canon 400 DO works great with the 2.0 TC III

rehess Loc: South Bend, Indiana, USA

I got lots of negative push-back when I got a Kenko 2X for my Canon Rebel. I had no f/2.8 lenses - I was told that it would not AF ....... but it did.

dsmeltz Loc: Philadelphia

As already noted, more info is needed;
What lens(es)? Which version of the 2x are you considering? What camera body will you use? What will you be using it for (birds in flight, stationary wildlife, astro photography, landscape (thinking subject/background compression)....?

Mustanger Loc: Grants Pass, Oregon USA

Ask Regis

Blurryeyed Loc: NC Mountains.

Regis uses the 2X extender on a 300/2.8 II, arguably Canon's sharpest lens and also a fast lens, unless you are using a mirrorless camera you will lose autofocus on any lens slower than f/4.

I think that the OP needs to take some time and learn more about the extenders and their applications, I own both the 1.4 and the 2.0 and only ever use the 2.0 on my 300mm prime lens.

amfoto1 Loc: San Jose, Calif. USA

As some have stated, it *really* depends upon what camera and what lens you'll be using the 2X teleconverter with, as well as which 2X you're thinking about getting. Some combos work pretty well. A lot don't. Some combos are impossible or might even cause damage to gear.

There are 1.4X and 2X teleconverters widely available (1.5X, 1.7X, 3X are out there, but far less common).

The first concern is whether or not autofocus will work. When you add a 1.4X you "lose" one stop of light. When you add a 2X, you lose two stops. Autofocus needs sufficient light to work. (And modern DSLR viewfinders aren't very manual focus friendly... especially if dimmed down by light lost to a teleconverter).

What that means is that if a lens has an f/2.8 aperture, with a 1.4X it will "become" an f/4 lens... Or with a 2X it will become an f/5.6 lens.

Or, adding a 1.4X to an f/4 lens will make it an f/5.6.... Or, instead using a 2X will make for an f/8 lens.

Likewise, if a lens is f/5.6 already, adding a 1.4X will make it f.8 and adding a 2X would turn it into an f/11 lens.

Some Canon DSLRs can autofocus an f/8 combination: T7i, 77D, 80D, 7D Mark II, 90D, all the current/recent full frame models (incl. 5D Mark III w/firmware update). In most cases, these cameras are only able to autofocus with select points in their AF array... Some with only the single, center point. This also may vary depending upon the lens being used.

But many current and recent Canon DSLRs are "limited" to an f/5.6 combo: T7, SL2, SL3, 4000D, T6i, T6s, 7D, 70D, 6D, 5D Mark II, etc. Those cameras cannot autofocus an f/8 lens/teleconverter combo.

The Canon R-series mirrorless cameras are able to autofocus f/11 combos at least (maybe even smaller aperture, depending upon the lens/teleconverter).

There have been some third party teleconverters that "fooled" the camera into trying to autofocus with what would normally be considered a "too small" aperture. Older Kenko 1.4X and 2X were among these (someone mentions this in an earlier response).

It's also possible to apply some tape over a couple of the electronic contacts on the teleconverter to "fool" the camera into trying to autofocus. This trick makes the camera unaware that the teleconverter is installed. If interested in giving this a try, do a search online for illustrated examples how this is done.

It may not be very practical though, because there's a reason for the limitations. "Fooled" camera/teleconverter/lens combos are more likely to autofocus slowly, "hunt" for focus, have focus errors or fail to focus at all.

And... besides autofocus limitations, there also can be physical limitations. Canon's own teleconverters... and I noticed recently the current Tamron TCs (there may be others)... have a protruding front element that must fit inside the rear barrel of the lens it's used upon. Not all lenses are large enough diameter. For example, none of the Canon 70-300mm or 75-300mm lenses can accommodate a Canon (or Tamron) teleconverter. OTOH, all the Canon 70-200mm and 100-400mm lenses can be fitted with those TCs.

In addition, some lenses may use a rear focusing or zooming design where the rear element of the lens might interfere with the protruding front element of these particular teleconverters. This might damage the lens or the teleconverter. To be safe, look closely at the functions of any lens that's not listed as compatible, before fitting it with a TC.

Other teleconverter (such as Kenko), do not use a protruding front element design and might be physically able to be fitted and safe to fit to more lenses.

Finally, a teleconverter will "magnify" any existing lens short comings. The stronger the teleconverter, the more it will do so. Generally speaking, TCs work best with lenses that have extra high image quality... lenses that are so good they can best tolerate some of the inevitable "loss of image quality" inherent any time you add more optics. It's really hard to predict, though, because there are so many different possible lens/teleconverter combinations. In another camera system I used years ago I had a 300mm f/4.5 lens that was excellent... I tried at least a half dozen different 1.4X and 1.5X teleconverters on it before I found a particular model that worked very well with that lens. Another 500mm lens I never found a TC to work with... IMO, there was just too much loss of image quality, even with relatively weak 1.4X TCs.

Teleconverters also typically work best with prime lenses, rather the zooms.

I use Canon 1.4X II and 2X II on select lenses. I don't care for either of them on my particular Canon 70-200 lenses (I have both f/2.8 IS and f/4 IS)... Too much loss of IQ, particularly with the 2X. But I understand that many people find the EF 70-200mm f/2.8 II and III IS USM lenses to work well with the Canon 1.4X III teleconverter. Some even report using the Canon 2X III TC successfully on those newer lenses.

I use my 1.4X II on more lenses. It works great on EF 135mm f/2, EF 300mm f/4, EF 300mm f/2.8, EF 500mm f/4. I've also been pleasantly surprised how well it works on EF 100-400mm "II" (never owned or tried it on the earlier push/pull zoom version of that lens). In a pinch, I'd use it on my 70-200s... But there is some loss of IQ so I prefer not to and have a 300mm with me most of the time anyway, so really don't have much need to use that combo. I *only* use my 2X II on 300mm f/2.8 and 500mm f/4 lenses. It works pretty darned well on them.

As you can see... the only way to answer your question is "it depends". Without more info from you about the particular lens and camera involved and what particular 2X TC you're considering using with them, there's no way we can predict whether it will work well or not (image quality)... or if it's practical (autofocus)... or if it's even possible (physical fit).

amfoto1 Loc: San Jose, Calif. USA

Yes, I imagine the 400mm f5.6L would work well with a quality 1.4X. It's a sharp lens to start with and it would still be able to autofocus on some Canon DSLRs. My concern with it would be that lens' lack of image stabilization making it tough to get a steady shot without using a high ISO and a fast shutter speed or requiring a tripod, especially if using the combo on a crop sensor camera.

I don't know about the original 100-400mm "push/pull" zoom, but the 100-400mm f/4.5-5.6 II IS USM works pretty well with Canon 1.4X II teleconverter. That makes for a 140-560mm f/6.3-8 combo, which some Canon cameras are able to autofocus. I haven't tried it with 2X (f/9-11 combo, so no autofocus on any Canon DSLR). Below is a test shot done with Canon EF 1.4X II on the EF 100-400 II (on 7D Mark II)...

(Download)