It's challenging to describe these subtle differences, but 800E bokeh is sublime
It's advantages stand out in lowlight, backlit conditions etc
The extremely high New prices of exotic telephotos buys significantly more than the best of Nikon's proprietary lens coatings to control flare and maximize light transmission. The advantages of the E FL and S Line TC-Telephotos extend quite possibly to the undisclosed chemical formulae (thus refractive properties) of what are effectively bespoke optical elements specified in the design.
Nikon does not need to disclose its proprietary secrets, particularly considering the optical engineers can order specific types of Hikari glass, besides fluorite and ExtraLow Dispersion. In fact, the NeoNoct patent confirms what marketing copy calls "ED" might represent 2 or more different types of optical glass, but these differences aren't shown in official lens cross sections (Links below)
So
@wotan1 one buys into the stratosphere of optical quality owning a 800mm f5.6E FL Nikkor + TC125
Of course each the 800E has its bespoke TC125 with matching serial #, and a skilled craftsman assembled and checked each copy.
It seems to me that we can get caught up in reviews and second guess the performance of a lens we love. We are looking for the affirmation the we made a smart purchase. I see that in a lot of forums. At this point I find reviews interesting and informative but I usually try to read those before...
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