On most converted DSLR's the metering is not measuring IR at all. Metering usually being done by a separate sensor by the prism. I've never heard of a conversion adjusting the metering wavelength but no doubt it's possible.
Mirrorless cameras & some in liveview mode will meter from the main sensor and will be measuring the same wavelengths the image gets recorded from.

PM sent re OGPS

You obviously missed the first art of Davids post, where he specified tubes with contacts! The contacts allow the camera to adjust the aperture when there's no ring.

I've been tempted by drone photography as well, but wouldn't give up IR for it!
There are now drones with low resolution cameras available for under £50.
Perhaps one of these could be enough to scratch your itch without costing you your IR kit.

I've had an expensive year in non-photographic ways so I'm compelled to resist the urge to try another converted camera (or any sort of drone).

Exactly, with the exception of any UV influence, I can do any of the standard conversion types. UV might be relevant for the 'superblue' conversion, at least in some situations, but for landscapes my results seem broadly comparable.

I can also use a range of technical filters such as U330 (deep blue & some IR) , some less well known filters such as a 'variable wavelength IR' (actually a red filter stacked with crossed polarisers - standard polarisers typically transmit IR untouched. This allows the ratio of reds to IR to be changed with a twist, roughly 590 to 720nm in effect.) and even old photographic filters which mainly transmit IR... It gives me loads of options to play with!

A long focal length macro lens will give 1:1 from a greater distance than a short one. In either case extension tubes will make the point of focus closer, and so the magnification greater. The degree of extension needed for an magnification is a function of the lenses focal length, so short focal lengths are easier to get high magnifications with by adding extension, but the working distances can be impractical - especially for insects!

Yes, several.

With a filter fitted to the lens the viewfinder still shows the scene - my camera is full spectrum converted, so I usually have a filter fitted many of which you can't see through.

AF works from the picture taking sensor so is automatically the same wavelengths as used in the shot. (No focus shift needed)

Exposure readings are also taken from the main sensor & so are relevant for the filtered image.

There's no chance of stray light leaking in via the viewfinder - a real issue on non-converted DSLRs doing long exposures...

IMO these aspects make using a DSLR considerably more awkward than mirrorless. For visual action shooting I still find a DSLR preferable, but when you can't see through the viewfinder, or focus accurately any advantage they had is gone.

I got mine pre-converted with some cosmetic body damage, for less than any conversion charges I've seen.
In hind sight a different model would have been preferable for me. It turns out MFT has a very thick sensor stack which limits it's UV sensitivity drastically, I'd have liked to dabble in UV photography too...

John you missed out one important step - Bracketing exposures with this approach is very important!
As you say the ratio of IR & visible varies significantly (rather like trying to measure the red light by looking at the green) I've known the ratio of the two to vary by more than 2 stops in sunlight.

IIRC I just used Av with the filter mounted for my shots with an unconverted K100d, and adjusted the EC to give improved exposures, though these days my IR is nearly all on a converted mirrorless camera.

As usual a well formed set.
My favorite would be the shot of 'Flash' (No 7) though no 8 is also particularly good IMO.

No, it's due to shooting through more atmosphere.
Near the horizon light from the moon has to pass through about 10 times as much air, getting distorted by any turbulence. Even when the moon is directly overhead turbulence will frequently have a significant effect on image sharpness.