Sinar DB shutter - recessed lens boards?

[LF_rookie_to_be]

Which lens boards, apart from DB boards with aperture, can be used with Sinar shutter (first generation, black)? I reckon the hole in front of the blades is about 78mm dia. Is it possible to use a recessed Sinar lens board for a barrel 210mm lens that has the threaded mount "flat", at the very end of the lens? Shutter manual recommends to get the rear lens element as close to the blades as possible. Also, flat Sinar 0 and 1 boards I have bear the warning at the back "not for use with sinar shutter". Is it simply for the usual protruding of the back element of lenses in Copal/Compur/etc shutters that interferes with the shutter blades?

[Leonard Robertson]

With the Sinar Copal shutter installed on my Norma front standard, from the rear face of a flat Sinar lens board to just in front of the shutter blades measures approximately 3/4" or 19mm. A couple of lenses I happen to have mounted on flat boards, a 150mm Berlin Dagor mounted in shutter, and a 16 1/2" Goerz Artar mounted in an Ilex No. 4 shutter, both clear the shutter blades. I've seen charts from lens manufacturers of measurement from the lens mounting face to the rear element, but I don't have a link handy. There are Sinar boards similar to the DB boards, often referred to as "top hat" boards, with a raised "bump" in front of the flat part of the board. This moves the lens mounting face forward to give more clearance for the rear element to the Sinar shutter blades. I guess these boards are like a DB board only without the DB aperture mechanism. The hole in my Sinar shutter with the blades open is very close to 75mm.

I don't know if that helps answer your questions. I also don't know if the newer Sinar F and P front standards have the same distance from the board to the Sinar shutter as the Norma standard.

Len

[LF_rookie_to_be]

Leonard, the boards I'm referring to are, obviously, reverse of top-hat, so what I'm wondering is if the outer diameter of that "back-hat" will fit into the hole in front of the blades. All of this in order to have the rear element of a 210mm barrel lens as close to the blades as possible. Oh, and it's also a Norma I have.

[Sevo]

Shutter manual recommends to get the rear lens element as close to the blades as possible.

Don't bother about that - I have never encountered issues due to extra space there. Tight spacing is supposed to reduce vignetting (due to the shutter spending relevant parts of its run time half open or closed) when shooting at 1/60, with short lenses where the lens-shutter distance can be a relevant part of the focal length. At longer times it is no issue, each step halves the vignetting as the open/close time grows into a increasingly insignificant sub-component of the total shutter run pattern. And it will only affect decidedly short lenses.