Well David, it probably depends to personal taste and experience since many of us do actually use different ratios. I thin my Tamiya paints with Tamiya's Lacquer Thinner (bottle with yellow cap) or with Gunzes Mr. Levelling Thinner and like the paint to be very thin. 50/50 isn't thin enough for me personally, I do it a bit more like 60/40 or even 70/40. This of course that you need more layers of paint to cover but you can obtain great results. The good thing about this is that the paint pretty much never dries at the needle tip of your AB.
Mind though, those thinners are nasty stuff, so use a good paint mask with filters.
A last thing: try your paints on a piece of scrap with different paint thinner ratios and see what you prefer
I agree with Wouter. I also like fairly thin paint. You can get great results using Tamiya X-20A thinner which is more user friendly than the lacquer thinner. I do prefer the lacquer thinner though.
One other point about thinning ratios is it depends on the state of the paint in the jar. Some colours are thicker than others and generally a new jar will be thinner than an old, half full jar.
Approximately fifty:fifty here, mostly using Mr Color levelling thinner and a good mask. Some of this will need to be done by feel as it can depend on relative humidity and air temperature. You will know when you get it right because the paint sprays like liquid silk and you get no tip drying. If you are after something to measure the paint and thinner get some disposable pipettes from Amazon for a couple of quid. I would also caution against mixing in the paint cup on the airbrush as I find you can’t adequately disperse the paint and get lumpy spraying...
Lastly, what pressure? I use 15-20 psi with my Iwatta, but it’s a side cup feed and a top feed brush may need less....
I agree do what have been said. I mainly use Mr Color levelling thinner and either Tamika, Mr color or (recently)AK Real collars. All eyeball thinned between 50 to 60/50-40, but sometime even thinner. I adapt my thinner to the needle I am using, If I use a 0,2 I go thinner. I try to keep my PSI very low, approx 15