(04-10-2021, 01:25 AM)Klaus Wrote: With just a single 600mm f/4 or 400mm f/2.8 per lineup, it's a little pointless to test them. As a buyer, you simply have no choice - take them or leave them.
Yep... plus, you can expect superior performance from any brand offering such lenses. Technically, there is also the Sigma 500/4, but given its fairly high price (and from experience: sub-average resale-value) most potential buyers would probably rather go for a earlier generation Canon or Nikon lens instead.
Within one system, it's rather a question if you need (or can afford) the latest generation lens or if portability and/or flexibility is high on your priority list. In the latter case, the x00-200/4 zoom lenses would be an option, or the DO/PF lenses.
In any case: from the investment required alone (no matter if we'd rent or buy/resell such lenses), such reviews are fairly unlikely to happen.
(04-10-2021, 01:25 AM)Klaus Wrote: I'd absolutely LOVE to get my hands on the Voigtlander APO Lanthars but accepting thousands in losses just for the enjoyment of a few days is something different.
Similar feelings here. With the difference, that I'd be very tempted to get and keep one with M-mount. When the 50/2 APO Lanthar was announced, it took me some debates with myself to eventually come to the conclusion (again) that 50mm simply is not my focal length and even a stellar APO lens is unlikely to change that. But then they announced the 35/2 APO...
(04-10-2021, 01:13 AM)Rover Wrote: Though one might have probably done well as a reference lens if you were ever in need of another.
Not really, I'm afraid. Testing long lenses comes with all kinds of challenges regarding a stable setup already, testing a fast long lens (usually with a short focus throw) adds some extra annoyances on top.
For most systems, either 50s or mild tele lenses turned out to be the reference. For Fuji it's still the XF 90, for example, for Nikon F the AF-S 105/1.4 and for Nikon Z the 50/1.8 S.