If its a Trigor it will be marked Trigor with a blue dot. It will also be a f11 lens. The largest Dagor I've seen is a 24". Their literature lists a 30 and 35". The 35" will cover a plate 34x44 sharp to the corners stopped down to f32. I have a 16 1/2" that the serial number dates back to 1903 before the name "Dagor" was used. Naturally it is uncoated and I prefer it that way. It takes great pics.