Well, a year has now passed, and we are about 3 months out from our trip. Here's where I've ended up:
Nikon released a new 70-200 f/2.8 that is getting stellar performance reviews, so I took the plunge and bought one a few months ago. I haven't had a whole lot of opportunities to use it yet, but I've been very impressed with what I've seen so far. It will definitely be my primary lens on the gorilla treks. In the bigger picture, I also think that it will nicely compliment my primary wildlife lens, which is the 200-500, so I've at least convinced myself that this is a good long-term investment.
I wish I could have so easily resolved the question of whether I should buy a full-frame camera. We both shoot with the Nikon D7200, and we have a spare D7200 that we use for incidental wide-angle shots and as a back-up should we ever encounter problems. Birds are a frequent and favorite subject, so the extra "reach" we get from a crop sensor camera is a very important consideration for us. I've been able to push the D7200 to ISO 3200 in rainforest settings with decent success fairly consistently (though not always).
With that in mind, I have considered buying a full frame D750. Its controls are almost identical to those of the D7200, so switching between the two would be pretty seamless. The D750 reportedly provides at least a 1-stop improvement in ISO performance over the D7200. Being able to make acceptable photos at ISO 6400 would really open up some opportunities for me.
But therein lies the rub. Just how many opportunities would there be?
The reason I've held off is that I have doubts about how often we'd actually use a full frame camera after this trip concludes. Except on those all-too-infrequent occasions when we are fortunate enough to be riding around in a jeep on safari in Africa, we're on foot, and I don't want to carry a lot of gear.
That means, other than in very unusual situations (like a gorilla trek, and with a porter at that), we're taking our crop sensor cameras on the hike in order to maximize our chances with birds, smaller mammals, and the like. And even when we have been in a jeep on safari, I've rarely lamented having the extra reach we enjoy with the crop sensor.
Still, the noticeably better ISO performance of the D750 tugs at me. While the new f/2.8 lens will certainly be of use to me in low light, J. will still have the 80-400 f/4.5-5.6 (newest version). This nagging voice in the back of my mind keeps telling me it would be great to pair it with a D750. This trip may very well be the only opportunity we ever have to see gorillas in the wild, and it's important to me that our photos be the best that we can reasonably manage. (Emphasis on the word "reasonably").
My brain tells me I shouldn't do it, and that a better long-term plan would be to save the money and apply it some day in the future toward a new generation of DX cameras with improved ISO performance.
We'll see if I have the willpower......
P.S. I did consider renting a D750, but the rental for the duration of our trip would be close to $700. For $1800, I could buy a bread-new one. Sure, that's more money, but at least I'd end up with the camera in my kit.
Edited by Alexander33, 06 April 2017 - 12:36 AM.