Quote Originally Posted by HDNitehawk View Post
By the charts it will not be close to the 300mm F/2.8 II with a 2x at 600mm.
The 300mm would be the better choice but the $4600 savings could take you on several cool trips with a cheaper lens.
Of course, that assumes that I have the extra $4,600 I doubt I do this year.

I am not even sure if super telephoto is where I am going to invest next. The 100-400L gets the job done, but I use it a lot less now that I mostly travel with the 70-200 II plus 2x TC. So, something different like the Tamron or this new Sigma, or eventually a Big White, would be very tempting.

Regarding its optics, all we have is the MTF chart. While, theoretically, these should be comparable, I have heard they do vary between manufacturers. So what I had done is compare the 150-600 MFT chart to the 120-300 f/2.8 sport. Their lines at 600 mm f/8 (150-600) and 300 mm f/8 (120-300) are comparable (slight edge to the 120-300). So then I looked at Bryan's test charts of the 120-300 @ 300 f/8 and was impressed. Here is a chart comparing the 120-300 @ 300 f/8 (assuming the 600 is similar) to the EF 300 f/2.8 +2xTC. I do give the edge to the Canon set up, but I am impressed by both. Then, compare it to the 100-400L +1.4xTC or even at the native at 400 mm. And finally the Tamron. Of course, the EF 600 f/4 II is better and has the aperture advantage.

So, if my assumption that the IQ of these two Sigma lenses is valid, the 150-600S may be good enough for a hacker photographer like myself. I am also thinking Sigma knows that it's lens is $1k better than the Tamron, otherwise it would have priced the 150-600S lower. So, as I mentioned before, I am very interested in the reviews, in particular of IQ and AF.