Canon extender with Tamron lens question

[Pauly_6_String]

Hi all.  I just picked up a used Canon EF 1.4x II extender and attached it to a Tamron G2 70-200 f/2.8 lens.  

The camera displays f/5.6 to f/45????   Exactly two stops high on each end.  Is that a compatibility/communication issue between the two brands?

Also was disappointed to find that it won't fit my EF 17-40 or my EF 24-105 lenses.  

thanks

[Pauly_6_String]

"Question, why would anyone want to put a tel-con on a WA lens like the 17-40mm? It seems that concept is contrary."

Thanks for th e reply.  I tried to put it on those lenses because I wanted to see if the same thing happened (aperture display issue) with a Canon lens.  Also I though maybe for traveling using it on the 24-105 may lighten the load, THEN I went to their website and found which lenses it is compatible with.

I was unaware of the proprietary nature of the extenders.  I did get a Tamron lens for a Canon camera and figured (wrongly) that extenders were compatible in the same way. 

[kvbarkley]

You have to be especially careful with Canon Extenders. Sometimes the elements protrude a bit and can rub against the elements of the target lens.

[ebiggs1]

"I did get a Tamron lens for a Canon camera and figured (wrongly) that extenders were compatible in the same way."

I know that seems logical but even Canon tel-cons are not compatible with most Canon lenses. Buy yourself a Tamron extender.