Large Format Camera Leaf Shutter

Introduction

This is a fully functional model of a leaf shutter for large format photography. It is completely mechanical and capable of exposures around 1/60 of a second (and probably a bit shorter). It achieves this by using two separate shutters. The front shutter opens with the shutter release, the rear shutter closes it. 

The basic shutter design draws heavily on this great model and enables a much faster shutter speed, and eliminates the need for programming a servo and shutter. 

If you want to read more about the design proces or using it for actual photography, a writeup can be fount on this 35mmc blog post. 

List of Materials and Printing

• c.a. 180 grams of Black PETG
• 4 x 30mm M4 nuts and bolts (M5 fit very tightly, slightly inconvenient)
• 2 x rubber hair bands (mine are non-descript, so please experiment)
• Glue (Pattex Repair Gel works well)
• 1 x 3x10mm screw or bolt (for cable release mount)
  
  Flash Sync
• 1 x micro switch with lever 12,80 x 6,50 x 5,80 mm (I think this is the one i used)
• 2 x 2x10mm screw or bolt 
• 2 x short piece of wiring
• 1 x PC socket (or solder flash sync wire directly to microswitch)
• Solder

I have printed the model with mostly basic settings on a prusa mini+. With a layer height of 0.2, 3 or 4 perimeters, and 4 bottom and top layers. I recommend printing the moving parts with a 100% infill. For the rest i have used 20%. Using multiple perimeters is especially useful for creating holes that are strong enough to hold a screw, and allow for drilling it slightly larger if necessary.

Description/Notes/Tips

The model itself consists of quite a number of parts. Most of which fit together by friction, screws or small nuts and bolts. This makes it easier to replace worn or broken parts. A few parts need to be glued together. This minimises the need for printing supports and ending up with rougher surfaces. The names of the different parts in the STEP file indicate the parts that need to be glued. 

The shutter has been developed and tested with black PETG. Black to minimise light leaks, PETG for its flexibility, printability and durability. Different printers might work with different tolerances, hopefully the STEP-file allows other users to make the small adjustments that might be needed to get it to work. 

The shutter leafs are not 100% light tight at the thickness in the model. Relative to the exposure the transmissions is negligible (for my purposes at least) but it is therefor recommended to remove the dark slide of your film holder just before the exposure and put it back soon after. 

The image gallery includes a GIF for quick reference on how all the parts need to be put together, and some photo's of the final product. Also the parts in the STEP file have been put together for reference. 

The micro switch used in the model for the flash sync is a bit non-descript and possibly hard to find. The dimensions of the micro switch can be found in the image gallery for finding a similar switch if necessary. The microswitch mount has been designed slightly larger then necessary to allow different switches to be used. I have wired it to a pc flash socket i harvested from a broken Zorki rangefinder; but  am sure that cutting up a cheap pc-extension cable and tying it to the loop will work just as well. 

The model includes a lens mount consisting of two parts. The small part needs to be made to fit the desired lens, and then be glued into the larger part. This hopefully makes it quite easy to adapt the model to different kinds and sizes of lenses. 

The model does not have a built in mechanism to open the shutter for framing and focussing. This requires the rear shutter to be cocked, and the front shutter to be released. In order for the rear shutter to stay in this position, the front shutter needs to be slightly held back to prevent it from releasing the rear shutter again. A toothpick or something similarly sized does that well enough, a picture with an example is included in the image library. 

Shortcomings and thoughts

The model is fully functional and reliable . But it is also tailored to the lower limits of my needs and a first version. Not all parts are equally refined and the model is  limited in its range of shutter speeds. I will try to keep track of a list of shortcomings and possible future improvements. 

I don't know if this model is useful to others in the analog photography community, but if it is i do encourage other to take what they need and develop it further. Feel free to ask questions.

1. Shutter releases are a bit sloppy, the whole mechanism could probably be designed more rigidly. The hooks on the front and rear releases are also slightly different from each other without reason, and they may wear over time. They could also be aligned better with the action levers with little compromise. 
2. The model is probably slightly heavier than necessary. Especially the front and rear shutter base may be unnecessarily thick.
3. The shutter is fundamentally flawed. This shutter relies for its exposure on the time it takes to open the front shutter and for the rear shutter to close. This means the shutter is always somewhere between open and closed. The degree to which this causes problems (vignetting) on the negative may depend on a couple of things. For example the diameter of the rear lens element and the imaging circle of the lens. Having a small rear element means the shutter blades spend relatively much time ‘out of view’. Having a larger then necessary imaging circle for the negative has the same effect. 
4. I have tested the shutter on a Tower Press camera with 4x5 film and an 8x10 barrel lens and to my mild surprise it has produced perfectly good results without noticeable vignetting. But please keep in mind that if significant vignetting would occur it would probably occur mostly outside of the 4x5 crop. 
5. The shutter has limited options for changing shutter speeds. Increasing the tension on the springs should result in higher shutter speeds, but there are probably limits to what the mechanism can reliably take, and the vibrations that would introduce. There are also clear limits on the slow side. If the tension is too low the shutter may fail to complete their motions, leaving the shutter (half) opened
6. The shutter would be able to facilitate slower shutter speeds, if there would be a delay between firing the front shutter, and releasing the rear shutter. I have not been able to come up with a convenient and reliable mechanical solution for this, also because I don't plan on using it. 
   A possible electronic and simple solution might be to use the microswitch for the flash sync with a delay and a relay to trigger a solenoid to release the rear shutter. The shutter base should offer enough possibilities to add a mount for something like that. 
7. To increase the light tightness of the shutter blades it may be possible to cover them with aluminium tape and/or paint them. I have not experimented with this. It may require printing the blades a bit thinner. 
8. I have considered developing the shutter for proper metal springs. But simple small rubber hair bands worked well enough for me and are much more widely available. The kind i have used does lose its tension pretty quickly and requires frequent replacement and calibration before using it again. If someone finds a cheap and widely available off-the-shelve spring that does the job that would be great, though it probably requires an adaptation of the spring mounts and the action levers. 
9. The addition of a small latch for keeping both shutters open at the same time is on the list of things. The toothpick works, but a better solution should exist. 

textual edit in title