Focal Flange Distance

[Vallantho]

Hello there, just a quick question. Where is the focal flange distance measured from? Is it from the shutter or the lens board? Sorry I'm sure this question has been asked many times before. Thank you

[Tin Can]

I just did this. I measured from the actual flange rear to the GG front when focused on infinity

MY NOS mystery barrel lens is marked 360 mm and the flange back was exactly that on 4X5 Horseman Optical Bench camera

I was surprised it was exact...

https://briansmith.com/flange-focal-distance-guide/