This post is duplicative of my post @ http://www.hasselbladdigitalforum.com and I thought I'd share my results here.
I've been testing the Hasselblad HTS over the past several months and I am extremely happy with the results. While I do not use it all the time, I find it to be a necessary part of my landscape gear. I've primarily used my HTS with the 28mm through 100mm lenses.
However, in my testing of the HTS, I attached it to my HC 300mm with the 1.7x in between (300mm + 1.7x + HTS). I did not think the results would be any good given the number of elements the light has to travel through.
However, I was quite surprised. My H3DII39 (and Phocus) shows the combination to be 800mm, and I did a series of additional tests to determine the quality of the combined glass. Below are samples from those tests at various f-stops (mind you these are not portfolio keepers or award winning shots - I specifically selected some random car for the words on the back and the sign on the left):
800mm @ f11
800mm @ f16
800mm @ f64
800mm @ f90
I saved these as 100% JPG to eliminate data loss from compression and the sharpness in Phocus was set to 300/2.0/0/10 - no changes were applied in Photoshop except my copyright, 16 bit to 8 bit, and the Save for Web (to JPG). There's a slight discoloration at the license plate in the f64 and f90 shots; I do not know why. The focusing is very tight and I needed to be precise since the slightest twist pulled me out of focus.
I will perform additional tests shortly by switching the order of the HTS and the 1.7x and check to see if the results are better, worse or how they differ. (PM me if you're interested). Again, I'm pleasantly surprised by these results and it's good to know I have 800mm with my Hasselblad gear. The HC[D] glass is quite good (and perhaps under rated by some).
PS: I did not feed the sheep.