I picked up a Tamron-F 1.4x to use with a DA*300 I am renting for the month. For grins, I dropped it in with the Rokinon 800mm giving me a handy 1120mm lens. I will be using it from now on. If there is enough light for the Rok, there is enough to use the TC also even though it chews up a stop. I have a pic of a cat on someone's deck that is about 1/4 mile away but could not get a comparison shot w/o the TC.
Here is a pier post only 70m away so a couple of screw heads are visible for pixel peeping. 100% crops and I had to play with lighting on both to get them to match for comparison as the one w/o the TC (on the right) did not meter well and was a little dark, thus the noise evident. Draw your own conclusions. Of course, now I wonder if a 1.7x would work well with normal lighting.
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