150mm lens distance to film plane

[Davidenglish]

I have a 4x5 Chamonix and I need to know how far from the film plane to situate the lens board.

[Leigh]

What you're asking is the "Flange Focal Length" (FFL) or "Flange Focal Distance" (FFD).
It varies for each lens. You need to consult the lens datasheet.

The FFL is the distance from the lensboard to the film plane.
It's always some reasonable number.

In contrast, the lens "optical focal length" is the distance from the rear node to the film.
This is the number by which the lens is known and identified in sales literature, i.e 150mm in your case.

The position of the rear node relative to the physical lens is not obvious.
For example, the rear node for a short FL lens may be quite a distance BEHIND the physical lens.
The rear node for a telephoto lens can be quite a distance IN FRONT of the physical lens.

Or just mount the lens and focus it at infinity.
That will be the correct distance.

- Leigh

[IanBarber]

I have a 4x5 Chamonix and I need to know how far from the film plane to situate the lens board.

For the 150mm I put it in the 3rd hole back from the front

[Dan Fromm]

I have a 4x5 Chamonix and I need to know how far from the film plane to situate the lens board.

Eh? Wot? Do you want to focus the lens?

If so, just slide the front standard forward from its rearmost position until the image on the GG is more-or-less in focus, then make fine adjustments. How far out you'll have to slide the standard forward from its rearmost position depends on how far away the subject is. There's no need to determine how far forward is far enough in advance, and no reason to mark the "in focus" distance on the bed unless you're going to shoot only at that distance.

[Davidenglish]

Thanks, I read somewhere that the mounting spot is approx. 6 inches from the film plane and that about is the third hole from the front.

[Dan Fromm]

That's for quick setting up for shooting at distance with a well-behaved 150 mm lens. It won't get good focus at most distances with any lens. There's no substitute for focusing on the GG.

[Bob Salomon]

That's for quick setting up for shooting at distance with a well-behaved 150 mm lens. It won't get good focus at most distances with any lens. There's no substitute for focusing on the GG.

Unless the camera has a properly calibrated rangefinder.

[Greg]

Even though 90% of the images I shoot with my 8x10 Chamonix are made with one lens, I do have other lenses that I occasionally use. Got tired of guessing which hole to mount my lenses into, so brought out the lenses and determined which hole to mount the lens in so that moving the front standard forward a tad bit gave me infinity focus, and labeled each of the holes. Makes life so much simpler in the field.

[David Lobato]

I have a 4x5 Chamonix and I need to know how far from the film plane to situate the lens board.

At infinity focus it's 150mm. for closer focus it will be more than 150mm. I'm not familiar with Chamonix cameras, but select the mount hole which will allow at least 150mm and to adjust for longer extension.

[Davidenglish]

Even though 90% of the images I shoot with my 8x10 Chamonix are made with one lens, I do have other lenses that I occasionally use. Got tired of guessing which hole to mount my lenses into, so brought out the lenses and determined which hole to mount the lens in so that moving the front standard forward a tad bit gave me infinity focus, and labeled each of the holes. Makes life so much simpler in the field.

good idea!