Fortkentdad
Senior Member

I decided to put my Tamron 70-300 to the test with the Kenko TC.
This is the Tamron Di 70-300 F/4-5.6 USD with VC (it was on).
The TC is Kenko's 300 PRO N-AF 1.4 model.
On the D7100 in it's yellow jacket.
I was not using a flash for these shots.
It works.
It has some drawbacks.
Of course you lose some light - it becomes an F 5.6 to F 8.
And it isn't as quick to focus - hunts too much - way too much.
For still subjects, this isn't an issue.

managed to focus in the shadows well enough, took longer than I'd like but got it.

Even a running dog can be managed - some of the time, keeper rate wasn't great with lots of blurry running dog shots.

Birds on a wire - sure

BUT BIF shots - well I was not able to get this hummingbird ... qualifies as an "almost" shot


But that bird was darting about and it may be my lack of Hummingbird shooting experience but I could not get a focus before it flew away.
It did give a reasonable shot of a dragonfly - at rest - the dragonfly in flight were too blurry to keep.

These shots were taken in the evening - low level sun. Not dark but not mid-day sun either.
Conclusion
I would not use it for birding unless I really really needed the reach, and it was bright daylight.
It would be OK for sightseeing where you wanted extra reach. Could easily be added when needed, but that is a bit of a bother.
Tomorrow I will try again - this time without the T.C. for comparison sake.