Or, well, the fastest Thornton-Pickard “Time&Instantanious” in any case.
Natively, that one has shutter speeds from 1/15s to 1/80s. It’s a very simple curtain shutter – the width of the gap is not adjustable, only the spring tension.
I made a new curtain for it. I made it out of a pretty thin IKEA blackout curtain – they are not all 100% light tight, but this one is. I don’t know if it would fit more modern shutters with their considerably tighter tolerances, but for this one it’s pretty ideal.
I made the gap a fourth of the original size, so nominally that should be a top speed of 1/320s. I measured it and it’s more like 1/150s but that’s alright – it’s possible it could go faster than that but I don’t want to over-wind the spring in it either.