The 500 PF remains a formidable optic in a commando kit for wildlife. A Used copy is a wise investment, particularly on a budget.
Photography Life have updated their review of the 500mm f5.6E PF with Imatest data. These include both Teleconverters. The results with TC14 III corroborate the high quality of the images obtainable with this combination. And the review compares the older 500 f4G...
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The Z AF gives its a new lease of life,
particularly with the TC14 III as a 700 f8. For my needs, the 400 f4.5S is better for larger mammals than smaller birds. Besides backup and for DSLRs, I keep my 500 PF on hikes, and with a TC14 for birds.
The other advantage of the Z telephoto Nikkors is their improved on barrel functions, particularly Recall Focus Position (although Fn1 button is in the wrong position when handholding on all these lens ).
Recalling Focus Position with a 500 PF, and its kin, one has to change the 3-position switch from AFL to Memory. The Lens-Fn buttons do not work in this configuration.