70D + Tamron 18-280

[drdroad]

I recently replaced my 60D with a 70D. I like it a lot, However, my Tamron 18 – 280 will not autofocus at longer zoom range, really anything above about 75mm.

Any ideas?

thanks.

[Skirball]

Is it not focusing at all, or just poorly?  Does the center point work?

I'd guess that the variable aperture lens is passing the max aperture f/5.6 as you're zooming in, and giving the outer focus points (rated at 5.6) some difficulty.  Why it's worse than the 60D, I'm not sure.

[ebiggs1]

"Any ideas?"

Yes, it is a Tamron.  It is not uncommon to hear of or have focus problems with 3rd party lenses!  

[cale_kat]

sage

[cale_kat]

To OP, the Tamron 18-270 mm f/3.5-6.3 ranges from f/3.5 on the short end (18mm) to f/6.3 on the long end (270mm). The D70 has a unique autofocus system which utilizes the sensor pixels for accuracy. Canon has identified certain Canon lenses which have limited compatibility with system.

My guess is that your lens does not offer full compatibility in part because of the too small maximum aperature of f/6.3 on the long end. This is pretty much the extent of the knowledge I was able to gleen from the web in a short while. Good luck with your work or play.

[Skirball]

Are you kidding?  Lenses like the 100mm Macro, the 16-35L, the 24 1.4, and a bunch of the long primes?  Those are some quality lenses to obsolete on your new AF system Canon.  Not to mention third party lens troubles.  I'm really surprised, I didn't realize the dual phase system was going to cause issues with current lenses.

[cale_kat]

Full compatibility is not the same as any compatibility. There are certain peripheral auto focus points which might not function as cross points, for example.

[drdroad]

I'll close this out by saying I talked to Tamron and they assured me that the lens should focus with the 70D, they tested it. I'm sending my lens to them for repair.