Canon 50mm 1.8 STM on 7DII with Tamron 2x converter...

I got a 50mm 1.8 recently, to use on the 7DII (mostly for portraits as it gives an effective 80mm f1.8) and, seeing as I have a Tamron 2x converter for use on my 100-400, I thought i'd give it a go and see if it'll work between the 50mm and 7DII body.

Now, it does fit, make connection and will a/f but...it mostly just hunts for focus, with the odd occurrence of bang on focus.

Am I going to have to use this in MF only, or is there a trick?

Does your Tamron 2X extender report its presence to the camera body? I have a Kenko 2X that doesn't, and you will get this effect, even when the combo should have enough aperture to work. I have demonstrated it to myself using lenses with max apertures of f/2 and f/2.8.

I suspect the cause, if the extender is nonreporting, is the 7D2 uses its f/2.8 AF points (since it thinks the max aperture is f/1.8) and then hunting because the max aperture is really f/3.5 and these AF points aren't working as well as they should. If the camera body knew it had an f/3.5 max aperture it would use the f/5.6 AF points.

[Followup] Just tried this with a EF 85mm f/1.8 to match your prime's max aperture. System worked fine, even in poor light, locking focus at center and intermediate AF points. Then I substituted my old Nifty-Fifty giving 100mm f/3.5 and the 7D2 could NOT focus with an of the AF points. Of course, the old 50mm f/1.8 is known for 'hunting' issues. Clearly has something to do with Canon's 50mm f/1.8 lens design.

Cheers for that...

Oh well, was just a thought, it's still useful on the end of the 100-400 for moon shots...

STIC wrote in post #18155125
Cheers for that...

Oh well, was just a thought, it's still useful on the end of the 100-400 for moon shots...

I think you're missing something here, and that is that if you set to single AF point using the center point, you may be able to get it to AF.

That's how I actually have mine set...I only use the centre af point...