[davidmanze]

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@ Dave M., "....is the 500D really any better?...Well finally something I have experience with.  I owned the 500D for 4 years in the Santa Cruz mountains where it is extremely wet!  I never had even the hint of a problem!  I also had the 350D, and the 400D in much wetter conditions.  They were fine.  The battery door doesn't bother me, it is not likely to get wet and there is nothing to really short there anyway.  The battery contacts are on top of the battery.  Compare that to TWO recent xxD cameras that had a few tiny droplets land on the camera and they power down.  I cant really accuse Canon of lowering the build quality of their cameras, other than to say my own experience is that the rebels, in more ways than on out preformed my more recent.  70D and 90D.  I may have take 500,000 photos with the 500D.  Standing in creeks, on the banks of creeks, and muddy, rainy, windy weather.  If I think it is better quality than a two camera's that did not even make it one year before acting up before one year is up, can you blame me.  There.  I've said it.  The build quality does not compare as far as I am concerned.  Sorry, but you did ask.

I really didn't want to end up in Sony's camp, but there do seem to be a lot to recommend them.  Their APSC Models may just be the dark horse here!  Take care,

-Mac

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Sorry Dave, you said D500, not 500D!  But still, the D500 is considered a professional camera, is it not.  I expect that it pretty well sealed, although I am just guessing.

The D500 and Nikon's 200-500 are really widely used in birding.  But you favored the 150-600mm G2.  That actually tells me a lot!  I've seen your photos, as you know.  I guess following your lead would not be the worst thing to do!

And reasonable to predict that the same thing would apply to the APS-C Canon's.  But that's another story.


-Mac

   Hi Mac ....... I can't say enough about the D500 ...... it's the best birding APSc DSLR ever !! ....... it's designed expressly for rapidity in focus acquisition with an instant choice of four focusing modes at the touch of a button ..... great viewfinder and excellent rear tilting screen ....... it's super fast and never ever leaves you waiting ........ never ever !!
  I'm going to shoot for the rest of my days with it   ... simply !!  

Following MLCs is just a side interest for me ....... like keeping up with SpaceX  ...
   
Seriously Mac ...... I don't think you would go far wrong with the G2 on the 90D ...... both IQ wise and financially !!

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There is very little difference with higher ISO performance between the latest Sony APS-C camera (A6600), the Canon EOS 90D, and the Nikon D500.
If you want the best higher ISO performance, you need to look at the new and very expensive Pentax K3 III. It outperforms the rest by very smart noise reduction in the electronics themselves.

But you could also look at better noise reduction in post processing.

FF gives better high ISO performance in general, because the sensor is bigger. This also means you get less reach (no sensor based crop) and more shallow DOF at the same aperture.

MTF performs less than APS-C.

You do not need the best rain protection for bird images, as you do not go out to photograph them in the rain. And while transporting equipment in the rain, the camera bag is the protection. And yes, the Tamron 150-600mm G2 also works the same on a Canon 90D, for example.

   

Those are the basic rules, and you seem to over complicate things a lot, resulting in running around in circles.

  I've been following the results from the K3 III BC ..... and unfortunately it's not quite living up to the expectations that many were counting on ..... certainly the BIF images I've seen don't ! ..... however, the BIF lenses are just not there excepting the 150-450mm zoom lens .....
  In DSLR land for BIF nothing's changed, it's still between Canon and Nikon !!




Rainfall in Costa Rica:

https://jameskaiser.com/costa-rica-guide...ny-season/


they get up to 260 inches of rain a year !! ........ that's way above chest height .......

That will put any weather proofing to the test !!