>>2671342I'm not rich enough for a 500/4, but I own an old manual-focus 300/4 and an old teleconverter to make it into a 600/8, or 900mm equivalent on the DSLR shown here. It's not razor pinpoint sharp but I still found it to be better than cropping from a shorter focal length.
The stock is from an old .22LR rifle found in a relative's house that was useless as a firearm thanks to a corroded barrel and action. The little button I used to fire the shutter came unglued from the trigger guard at some point in the year or so since I used it. Also note the tacticool laser I put in it - not because it's useful, just for kicks. It works just by shorting wires from a cut-up $10 Chinese remote shutter release. The tripod plate was generic, I whittled off a bit of the stock to get it to sit right, and then epoxied it on with JB Weld.
I am not a trained marksman, so I could believe that someone who was could get more out of this than I could. I'd say it was good for an extra stop, on top of the two that my camera's sensor stabilization generally gives. Maybe one more if I could rest it on a fence or a stump or something. needless to say, manual focus made things difficult, I tried it with an autofocus 300mm and it was more useful.
Also that lens only weighs maybe three pounds. I bet it'd be more useful with an 11-lb hunk of glass. If you do that, use a more substantial tripod plate than I did.
