I have been looking to replace my Nikon 200-500 lens which I use for birding. I have been both researching and looking at some options available for sale. I have both F and Z bodies, and the two that I primarily use for BIF are the D500, and now the Z6iii. I am trying to use the latter as my main body as I prefer the AF system, but I have not made any decisions about the future of the D500. I never warmed up to the D500/200-500 combo and while that lens performed better on the Z6iii, I would still like to see about other options that will not completely break my wallet.
I have been considering a trade up to a180-600, but that would leave me with just the Z6iii and its 24MP sensor. I recently had a line on a used 500PF, which I thought would be a good solution as it can be used with both bodies, but it was literally sold while I was in the midst of responding. Now, an opportunity has also come up for a used 400/4.5 S lens at a good price and that got me to thinking about a future1.4TC purchase to give me a bit more reach with the Z6iii. I previously found the 500mm FL of the 200-500 on a DX body to be a good fit for the birding opportunities generally available to me.
Having used the TC14ii and TC 20iii in the F-mount, I am very familiar with giving up IQ for reach, and never found either TC to be of great value when it comes to IQ. But almost everything I have read or watched about the Z-mount TC's seems to indicate that they are much better at minimizing any IQ loss. And, there are a decent number of reviews here, in other forums and by folks who have YT channels that do not try to sell any and everything they post about, that the 400/4.5 with the 1.4TC produces images about equal in IQ to the 500PF and the 180-600.
But what I do not fully understand is that after praising this combination and displaying images that look quite good, many will go on to say that if you are going to primarily shoot at a focal length of, or around, 560mm, then it is better to buy a lens that can hit that focal length without a TC. I could understand this advice if we are talking about F-mount lenses, or a known bad combination of lens and TC, but why say this right after elaborating about how this specific combination loses little to no IQ as well as showing sample images that seem to support these statements? After all, we are discussing a specific combination and not talking in generalities.
Apologies if I sound a bit frustrated, but if the IQ is supposedly there, and assuming the lens/TC combination is not expected to be hammered daily and/or used in harsh conditions, what are the reservations about this combination? If it is the exception to the rule, then say so. But to say that it is a great combination, and then say that you would still recommend otherwise seems to send conflicting messages. Did I miss the elephant in the room?
--Ken