CHG_CANON Loc: the Windy City

No, beginning with the newer EOS releases, from the Rebel T7i through the 80D through the 5DIV, they all retain the wide array of AF points at f/8, another positive consideration of the 1.4x / 100-400L combo.

imagemeister Loc: mid east Florida

It is my experience that AF @f8 with Canon cameras and the exact number of focus points depends on using a CANON extender on a specific CANON lens - and then depends on WHICH version extender and which version lens !

So that means even tho a Canon extender might physically fit the Tamron 100-400 - it will not allow the camera to AF @ f8 period - because it is NOT a CANON lens - unless someone with direct experience can say otherwise ! ?? And, Who knows what the focus points will be - IF it works - which will probably only be ONE.
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alggomas Loc: Wales, United Kingdom.

I thought that 2x extender (canon) only works with fast lenses.
Also unless the Tamron extender is canon fit, it will not work.

Cookie223 Loc: New Jersey

Bill, I have the 7D MKII-II and the Canon 1.4 III. I don’t have the skills to really get the most from my kit, but I don’t really notice any difference in my shots as long as I keep the lens below the max of 200. However, I have no doubt that others with more experience may.

I also have the Tamron 150-600 G2, and my extender doesn’t fit it.
Good luck.

amfoto1 Loc: San Jose, Calif. USA

Original poster is using the lens on a Canon 7D Mark II. That camera's 65-point AF system only has a single "f/8 capable" focus point, at the center.

So it's a moot point with that particular camera. It will only be able to AF at the center point, when using an "f/8 combo" of lens + teleconverter.

Canon 80D, 6DII, 90D, 77D, T7i/800D (and possibly T8i/850D?) have a different, 45-point AF system that has as many as 27 f/8 capable points... with particular lens/teleconverter combos.

The only lens/TC combos I know of that allow these cameras to utilize all 27 of their f/8 points are...

1. Canon EF 100-400L "II" with Canon EF 1.4X "III".
2. Canon EF 200-400mm f/4L 1.4X Extender lens with Canon EF 2X "III" teleconverter (lens' built-in 1.4X TC not used).

Canon 1DX Mark II and 5D Mark IV 61-point AF systems are able to perform f/8 autofocus at all 61-points with certain lens/TC combos, but are reduced to 13 points or 9 points with some other combos.

More info about Canon DSLRs with Canon Extender teleconverters can be found here: https://shuttermuse.com/canon-cameras-autofocus-extenders-f8-aperture/

Whether or not this applies to the Tamron 1.4X on a Tamron lens... who knows!

FYI, the Canon R-series full frame mirrorless take it a step further with ability to AF up to f/11 combos.

Loss of image quality from an added teleconverter varies a lot depending upon the specific lens/TC combo. There are so many possible combinations, it's difficult to predict. I've used Canon EF 2X II and 1.4X II with select lenses for many years. I've found the 1.4X II to work very well with Canon EF 135mm f/2L, EF 300mm f/4L IS, EF 300mm f/2.8L IS, EF 500mm f/4L IS and EF 100-400L "II" zoom. It's not quite as good, but okay with EF 70-200mm f/4L IS and EF 70-200mm f/2.8L IS. The Canon 2X II teleconverter works well with 300mm f/2.8L IS and 500mm f/4L IS, but I find the loss of image quality excessive with other lenses. Some have reported acceptable image quality using EF 70-200/2.8L IS II and III lenses with EF 2X III TC... I haven't tried those combos combo personally.

In the original poster's case, wanting to use the TC on a Tamron 100-400mm... If the Canon 1.4X will physically fit onto the lens (protruding front element needs to fit inside the lens barrel and not interfere with any moving rear lens elements), I suspect that might offer the best image quality. The Canon EF 1.4X III bought new is fairly expensive. Optically there is very little difference between that and the EF 1.4X "II", which might be bought used for a lot less. (Note: The most current Tamron 1.4X TC appears to also have a slightly protruding front element that will need to fit inside the rear barrel of any lens it's used upon. It doesn't appear to protrude as far as the Canon TCs do, though.)

Reviews of the latest Tamron 1.4X seem pretty good... at least when it's used with the lenses Tamron recommends (which includes their 100-400mm).

I might be tempted to order one of each from somewhere that allows no-questions-asked returns, give them each a try and make my choice based on first-hand testing. The Tamron 1.4X costs $419.... it's too new to find used copies for less. The Canon 1.4X III sells new for around $430 and can be bought used for around $350, while the Canon 1.4X II can be found used for around $200. (P.S. With virtually no moving parts, I would have little concern buying a used teleconverter. The Canon TCs have been around long enough that they're pretty commonly available used.)

FYI, the images below are tests I did using the Canon EF 100-400mm "II" lens with and without EF 1.4X "II" teleconverter. I see very little loss of image quality using that combo... In fact I was very surprised how well they work together. Previously I'd used the 1.4X a lot with prime lenses, but rarely with any zooms. These waxwings were extremely fast and challenging to photograph, but in good light the Canon zoom, teleconverter and camera were up to the task. The fourth and last image isn't the sharpest of the bunch, but is my favorite pose and composition:

Canon EF 100-400mm II (lens only, no TC) at 400mm & f/9 on 7D Mark II

(Download)

EF 100-400mm "II" with EF 1.4X II Extender at 450mm & f11 on 7D II

(Download)

EF 100-400mm "II" with EF 1.4X II Extender at 560mm & f/8 on 7D II

(Download)

EF 100-400mm "II" with EF 1.4X II Extender at 309mm & f/7.1 on 7D II

(Download)

joer Loc: Colorado/Illinois

Some photographers use extender but be aware they are intended for long, fast primes and very few zooms, unless image sharpness is not critical for your application.

Mubashm Loc: Gaithersburg, Maryland

That is why I always use Canon 1.4 extender on Canon 400mm 5.6. This set up gives me very sharp images whether it is close up of a flower, humming bird or BIF.


Mohammed

imagemeister Loc: mid east Florida

yahart53

Not sure about the Tamron 100-400, but my canon 100-400 I works well with Tamron 1.4x converter on my 7D2. Of course you get expected degradation in quality but all mechanics work pretty much the same (auto focus, etc).

dave.m

Perhaps someone needs to tell that to Canon

The EF100-400 II + x1.4 III is excellent and better than a few long primes that I have compared with. Also The 2020 road map for RF lenses announces a 100-500 zoom, x1.4 and x2 extenders. The only native RF lenses they will work with are the 100-500 or 70-200 as the longest prime is still 85mm - although even with RF focusing I think a 1000mm f11 ish lens will need a serious tripod and manual focus!

Bill Golden Loc: Briarcliff NY

Thank you

imagemeister Loc: mid east Florida

Interesting ......WHICH Tamron 1.4X - there are 3 versions ??
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gouldopfl

I have Tamron lenses and I've been told by professionals to use the extender from the lens manufacturer. I have no problems with the 1.4x but I tried the 2x and was not happy with the results. I sent the first one back and had it replaced, same results so I returned it.

rehess Loc: South Bend, Indiana, USA

Be careful of anyone who tells you {without trying} that the combination won't work. A few years ago when I was still a Canon user, I received all kinds of advice that a 2X TC wouldn't AF on my Rebel ..... but the combination did.

Bill Golden Loc: Briarcliff NY

Thank you for the information