Originally posted by gerax You are damn right...I didn't multiply aperture X2...
In that case I'm not sure...I'd get less of a FL for the same aperture than with the 150-500, and I seem to remember that stacking TCs gives lots of vignetting...isn't it?
L.
Depends on the combo. When I stack the 1.4 and 1.7 on the DA*200 I use the K-3 so no vignetting. I also have tried the same stack on my Tamron 300 2.8 and it seriously degrades IQ. There are variables in lens design and construction which affect the use of TC and Tamron actually says you shouldn't use stacked TCs on the 300, and they're right.
So, you do need some knowledge to make this work. In my case I already owned both the 1.4 and the 1.7x so, it was no sweat. I'd hate to buy a TC and have it not work. So my recommendation would be, it you don't already own the TCs, don't buy one hoping it will work. In the case of the Sigma, it's a matched TC and it works great.
To my mind, 400 or 500 for wildlife is not that great a difference, especially since I frequently shoot at considerable less than 500. But 2.8 for wildlife with so many images shot in the mroning or evening 2.8 is really useful.
280mm ƒ5.6
250 mm ƒ5.6
420mm ƒ8
198mm ƒ9
88mm ƒ5.6, shot with the 60-250.
Of the 16 images in my flickr wildlife album only one is shot at 500mm.
Only one was taken at 500mm. And it wouldn't have hurt to have been able to back that out a bit for a bit more context. Tamron 300 ƒ2.8 with F 1.7x AF adapter) (510mm)
Where i do always use the longest glass possible is birds. DA*200 with F 1.7x TC, (340mm) and even then, I don't always use maximum reach.
I frequently use the Tamron 300 and 1.4 TC because I get to keep my auto-focus. I could use the 1.7 for 510, but I rarely suffer IQ wise.