Ron – I hope this helps
Shutters
All LF Lenses are split somewhere near the middle and so have a front and a rear portion.
The front portion sits outside the front of the camera and the rear portion sits inside the camera nestling in the bellows.
Almost all LF lenses have a shutter built in and this mounts to the front portion of the lens.
The Lens (both front and rear portions) and the Shutter start life as a matched assembly – to give accurate aperture scales.
The Lens/Shutter is a standard piece of info supplied with each lens – eg
http://www.badgergraphic.com/store/cart.php?m=product_detail&p=165
Here is info is shown as “SHUTTER: C-O” = Copal (most common shutter manufacturer – in size 0 )
The front portion of the Lens and the Shutter are pushed through a mounting plate and secured by a retaining ring.
The rear Lens assembly then screws onto the rear of the whole assembly.
In order to not restrict the maximum aperture of the lens, a range of standard shutter internal diameter sizes are available – 0, 1 & 3
O is the smallest and 3 is the largest.
You therefore need to match a Lens/Shutter combination with a suitable Lens Board – hence the 0, 1 & 3 sized Lens Boards – to match the 0, 1 & 3 sized Shutters.
Typically short LF (less than say 150mm) use a Copal 0 shutter.
Intermediate lenses (say 180mm to 250mm) use a Copal1 and the big long lenses use a Copal3.
As a potential 5x4 user – most of the lenses you would use are likely to be Copal0 & 1.
Recessed Lens Boards
All things being equal, the distance between the Nodal Point (usually close to the shutter – and thence the Lens Board) and the Film Plane is the same as the Focal Length of the Lens – when focused at infinity.
LF cameras facilitate a range of Focal Length Lenses by Bellows extension.
However, Bellows have a physical minimal and maximum length – you can only scrunch them up and pull them out so far
This is also true for View Cameras and so they tend to be biased to what they do – cameras that can cope with very short lenses tend to have a shortish maximum extension.
Cameras with a large maximum extension tend to have a longer minimum extension.
(These two pieces of information are some of the most vital statistics you need to know when buying a LF Camera)
To assist with a long minimum extension, Camera manufacturers came up with the trick of recessing the position of the Shutter (hence Nodal Point) inside the body of the Camera Bellows.
They do this with a Lens Board with a stepped recess.
They come in different amounts of recess.
The problem with using a Recessed Lens Board is that the Lens Controls are mounted on the Shutter – which is tucked away inside the recess – hence difficult to reach and see clearly – particularly is you have thick fingers
The reverse is also available – where the Lens Board is stepped outwards – normally known as a “Top Hat”.
Lens Manufacturers also play their part.
Very short Focal Length Lenses (say 90mm & less) are designed to have their Nodal Position rearwards of the shutter in the lens – so the Cameras and Bellows don’t have to scrunch up as much.
This is in effect the opposite of a Telephoto Lens.
The information is given by Lens Manufacturers as the Flange Focal Distance (or flange back) – the distance between the rear surface of the lens shutter (the front surface of the lens board) to the Film Plane (Focal Plane)
When buying very short Focal Length lenses you need to know this distance – as you may otherwise not be able to focus such a lens at infinity with the LF Camera you own.
If you are buying second-hand and need to know will Lens A fit onto Camera X – just start a new thread here – APUG is a real mine of info
Sorry it is such a long reply, but as Frank said, “the only dumb question is the one you don’t ask” – and this wasn’t a dumb question.
Good luck
Martin
