Thanks to all for such well-considered advice.

Regarding another camera, I already have the Nikon 1 AW1 with WP lenses: I started this adventure out with this astonishing little camera & it took most of the pics I've posted here. I was gifted the D7200 when a very encouraging & published Japanese photographer insisted I needed to upgrade for the Alaska stage. I use the AW1 whenever it's damp or when we are in the dinghy or hiking up creeks to booming waterfalls. It's spent 3 years in severe tropical heat & humidity, and been underwater or in pouring rain (I made a hood for it) many times & still shoots flawlessly after 3 years of significant abuse. But it has limits.

I have been avoiding the 70-300 for 2 reasons: I already have the Nikkor 55-300 VR - so close, yet so far from what I need so I'd be accumulating over-lapping gear; plus I find it hard to tell which of the 5 versions is being offered on various sites. The 18-400 is a little like this: I already have a Nikkor 18-140 VR and an 11-16 f/2.8 Tokina, but I'll read up more on it.

I will not be returning to the US so unless I buy through UHH used is more risky than new. At least with new (non-gray) I may have time to claim warranty & send for repair etc when I can.

After 4 months solid learning & research I was seriously considering the Tamron 100-400 f/4.5-6.3 Di VC USD. The aperture starts out at 4.5 & doesn't ratchet up as early as any of the comparable lenses; it's light; I already have filters to fit it & I can get it for $599 new with 12 mths warranty. It doesn't get slammed in any review I've found although it is rated slower for tracking speed sports than others. That seems OK as I'm not interested in shooting fast action sports (except the one-off Iditarod - but no lighting fast motor sports!!).

BUT - I will take another look at the 18-400, as then maybe I don't need to change lenses too often.

The thing is, I'm a novice with an outstanding camera: maybe with a few more years experience I will get better results without such heavy reliance on gear (& you guys!). But this voyage is full of one-off experiences - we will never come this way again. Plus I never expected anyone would be interested in my story or pics, it all just sort of grew & I was unprepared - so, for now, it seems like having the right gear will help.

Thanks all so much again. I will let you know how it all goes!

I bought the fresnel lens to get a hand held 300mm lens. I planned to test it against what I had been using at 300mm - the 28~300 3.5~5.6 @ 300mm. I am at a stage where I tend to forget things; I forgot that I had attached a 1,4 telextender to the fresnel lens. OK so this test turned out to be the fresnel 300 with a 1.4 telextender (420mm) vs 28~300 @ 300mm.
I ran the test twice to be sure I was getting correct results.
The fresnel lens with a 1.4 telextender outperformed the 28~300 @ 300mm by quite a margin.
It surprised me.
All shots were at f8 camera setting / tripod mounted with appropriate tripod settings.
Since the 1.4 telextender does not seem to bother the fresnel lens, I intend to leave it on permanently. Now I can walk around with a 420mm and take hand held shots with it. I'm happy.

I took up the hobby of astrophotography several years ago and over that time I have learned many things about star or moon pictures using a DSLR camera that I can share here. The problem of a tripod mounted camera that can't point straight up is only the first of many problems that have to be solved. Luckily that is the easy one. A ball mounted tripod head will allow the camera to point straight up. I use a MeFoto tripod that comes with a ball mount or a ball mount can be purchased separately for most tripods.

The second problem is that the stars and moon etc are all moving due to the earths rotation. Depending on the focal length of your lens, you are limited as to how long an exposure you can make without getting into star trail (blurring) issues. This problem can be solved by using an astro tracking setup that rotates the camera about the polar axis in the opposite direction to the earths rotation. I use the Optron SkyTracker but there are others. Using this device and properly polar aligning it, the moon will essentially stay in one place so that you can take much longer exposures. This isn't normally needed for the moon since it is so bright. 1/500 exposures work fine for a full moon but during a lunar eclipse the other day, I had to use 1.3 second exposures at ISO200, f6.7 with a 300mm lens to capture the red color. These would have been blurred pictures if mounted on a stationary tripod. I'll include a picture of my setup below. I've added a few 3D printed parts to make things a bit better but they aren't needed for a basic setup.

I like to take a series of pictures of events like the lunar eclipse so that I can have individual pictures or make them into a movie. Luckily, my Panasonic GX7 has a time lapse mode where I can tell it to take pictures repeatedly at a given interval. So for the lunar eclipse I took about 1200 pictures at a 6 second interval and over a 2 hour period. This way, I could stay inside where it was warm while my camera did all the work. I should add that my GX7 has a tiltable LCD screen and also a tiltable viewfinder that makes pointing the camera straight up super simple. The GX7 has been replaced with the GX9 which has the same features. Great little camera.

I'll include a link to my moon video here:

https://www.facebook.com/mike.leemhuis/videos/10216829080815261/UzpfSTExMTA5Njc3NDQ6MzA2MDYxMTI5NDk5NDE0OjEwOjA6MTU0OTAwNzk5OTo2MTM2OTk0NTMzNzY0MDc3Njg3/

The final thing I'll mention is that you must use manual focus to get a good sharp picture of stars or the moon during an eclipse. There just isn't enough light typically for a camera to autofocus properly.

I hope this helps.

Mike

It's my favorite travel lens. As others have said here, it's a little short on the telephoto end, but it provides a great balance of weight, sharpness, and zoom range. If I need to travel light, I use my 18-55, but the 18-140 is a bit faster at focal lengths longer than 18mm, and of course it has the greater reach.

I'd say its greatest weakness is distortion. You can see how the steps at the bottom of my attached photo appear curved. It's easy enough to fix in post, but it's still a weakness.