70d and tamron 150-600mm

Started Feb 19, 2014 | Discussions thread
Mark B. Forum Pro • Posts: 22,664
Re: 70d and tamron 150-600mm

bill hansen wrote:

I think we're saying the same thing. To bring the 100-400 up to (somewhere near) the 600mm max range of the Tamron, you'd have to add at least the 1.4X TC. That takes the 100-400mm to 560mm, almost to the max 600mm of the tamron. The question might be - okay, how would the two compare at those max focal lengths? Without a series of test images it's impossible to tell for sure - so I proposed comparing effective MTF numbers. If my thinking is correct, the Tamron would do significantly better.

I'd bet on it.  The Tamron benefits from not having to use a converter, which always reduces IQ.  There really isn't much point in doing such a comparison.

There would be no point at all, IMO, in putting a TC on the Tamron, to bring its focal length out to 600X1.4=840mm, and then comparing that IQ to the Canon at 560mm.

If you think about other considerations, the Tamron still is the less expensive lens. The Canon, with the TC, probably weighs the same as the Tammy (without the TC it's 1 lb less), and has just about the same length from lens mount to filter adapter. The Tamron, with its huge 95mm objective lens, would have the greater light gathering ability, even at the same apertures.

I've used the Canon with a Kenko 1.4TC which allowed all the necessary communications between lens and camera body, including autofocus. In good light it worked very well. In poor light I had to focus manually. As you know, the Canon 1.4 TC can also communicate with the camera body if you tape the pins. Just tape the pins between lens and adapter, not between adapter and camera as I did once, and very nearly lost a piece of tape into the mirror box !.

I haven't tried it, but after seeing the IQ loss with the converter I had no interest in any further attempts.

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