Extinction meter

This year's "CHRISTMAS LECTURE" (ha!) is about extinction meters, because I love them.
Why? Because this is not measuring the light, but looking at it. You can measure weight, but what tells that about beauty? And to me photography is about light and beauty.

And now, nevertheless, the science. Extinction meters can roughly be divided in 2 X 2. Built-in, and loose; and with or without eye-adaptation. Let's have an example of each of them.

The (Tönnies?) Practos pre-WWII from Germany. You should adapt, "standardize" your time. Nothing to calculate: it gives the time/diaphragm combination. Detail: it uses not only Europ.Scheiner, but also the modern DIN/ASA (so: 21 DIN = 100 ASA).

The 1950 Nebro Visual, British Made. Hold it like a digicam, so you can't adapt (well - I do keep a hand above it, to block the sky). And shouldn't, because it's the only one also for indoors! Scale 1-6, and a lot of calculating, weather, filters, Weston, Scheiner, B.S. but no DIN: that was not so "norm" at the time (21 DIN = 80 ASA!).

The built-in 1950 Made in England Agifold meter looks Nebro-made. The calculator turns the other way, only 16-125 Br.Std. (btw this is not the BSI or BS Log) the weather is different and no interior.

The built-in 1950 Made in Germany Paxette meter: Scale 1-12! and you must adapt 20 secs. while looking through it like a viewfinder. No weather, maybe indoors usable. The calculator is on the leather camera-case (which I have not). I printed a few for different film-speeds; easier: scale 8 is f8 at 1/100 on 400ASA film.

Of course there are more, the Diaphot, or that flip-over-the-lens Voigtlaender. I keep looking; still much to learn.

Do I use them? Yes: when used carefully they are remarkably good! But I even want to go a step further: the Johnson Standard Exposure Meter which I use to learn the ultimate: just looking, and knowing what t/d I should use.

Further information from you, dear visitor, will be much appreciated. Happy New Year!