Copal, Compur, Prontor, Ilex and Compound.
If you're hunting for a lens to fit your large format camera, you have likely come across this topic. Your desired optic comes mounted into one of the shutters mentioned above, but what diameter of hole will you need to mount it onto a lens board? Well, we're here to help.
What is a leaf shutter and why do I need a lens board for my camera?
Whether they are old, new, wide angle or telephoto; most large format lenses are comprised of two optical cells. These cells are made up of several different groups of individual glass elements. A leaf shutter is between the cells and controls the exposure by opening and closing a set of thin metal blades (or leaves) for a specific amount of time. The optical cells are threaded and screw into the shutter body.
These types of lens can be universally used with any make of camera - but must be mounted onto a metal or wood plate (the Lens Board) which then attaches to a particular camera. To mount a lens and shutter combination to a lens board, a hole of the correct size is required. Too big, it'll just go right through. Too small, and it won't fit.
Identification
Most shutters have the model or manufacturer printed or engraved into the shutter somewhere - usually on the front face or outer edge of the shutter.
But how do I know which size of hole I need?
There are five main brands of leaf shutters from over the years that you will find mounted between the glass of many large and medium format lenses. They are Copal, Compur, Prontor, Ilex and Compound.
The manufacturers produced different sized shutters depending on the size of the lens required. They are usually numbered sizes of 0 to 3, with 0 being the smallest and 3 being the largest. Ilex and Compound shutters begin at 3 and increase in size to 5.
Each type and size of shutter will need a different diameter of mounting hole for a lens board. Some sizes are the same between brands (As an example, Copal 1 and Compur 1 shutters require the same diameter hole at 41.6mm).
List of Shutter Sizes and Diameters
Here are the diameters of hole you will need to make into a lens board to mount a respective shutter. Of course, this is not an exhaustive list - and many shutters have been made, modified or adapted over the years. If you're in any doubt, measure yours carefully.
Copal
| Copal 0 | 34.6mm |
| Copal 1 | 41.6mm |
| Copal 3 | 65mm |
| Copal 3s | 64.5mm |
Compur
| Compur 00 | 26.3mm |
| Compur 0 | 34.6mm |
| Compur 1 | 41.6mm |
| Compur 2 | 52.5mm |
| Compur 3 | 65mm |
Prontor
| Prontor 0 | 34.6mm |
| Prontor 1 | 41.6mm |
| Prontor 3 | 65mm |
Prontor Pro
| Prontor Pro 0 | 34.6mm |
| Prontor Pro 1 | 41.6mm |
| Prontor Pro 3 | 65mm |
Ilex
| Ilex 3 | 50.42mm |
| Ilex 4 | 66.14mm |
| Ilex 5 | 85.47mm |
Compound
| Compound 3 | ~60mm |
| Compound 4-X 9 | ~65mm |
| Compound 4-X 10/11 | ~76.7mm |
| Compound 5-X 12/I/II | ~90mm |
Mounting a lens onto a board
Your lens should come with a retaining ring of the correct size for your shutter. Unscrew the rear cell, remove the retaining ring and watch out for any shims or washers.
Mount the rear of the lens through the board and install the retaining ring. You may need to use a special retaining ring spanner to torque it down tightly, but in most cases fingertight is enough.
Well, actually...
If you've spotted something not quite right in this article and are feeling particularly pedantic, feel free to Contact Us and let us know. Much like our shutters - we would like our advice to be accurate!
By Howard Parker