These are issues I'm thinking about:
* Can I make a simple shutter meganism to operate 4 shutters at the same time?
Yes.  the shutter can pivot at the center of the camera front, or it can slide.
* Should I make a division inside (like a cross) to avoid the 4 images to overlap?
Try a removable divider so you can experiment with images that overlap or don't overlap.

Curzon, several people here on f295 have built multi-aperture cameras where the images overlap. These do not require internal dividers, and can produce some very interesting images.

Myself, I've built several multi-aperture cameras with internal dividers, what I call "grid-cams".

This camera: http://www.f295.org/gallery/main.php?g2_itemId=116 has internal dividers made from masonite that divide an 8"x10"sheet of photo paper into 9 seperate compartments, with a large, central image and smaller, satellite images surrounding it. Each compartment has to be individually exposed, because its virtually impossible to operate all 9 lens caps at the same time. I also have to individually calibrate each compartment to its own, unique exposure time, such that the 9 seperate exposures will be the same density, for a group contact print.

This camera: http://www.f295.org/gallery/main.php?g2_itemId=683 is a tiny, brass, 9-cell grid cam that takes a 35mm-sized piece of film or paper. The front plate of the camera is made of steel, and I use tiny squares of flexible magnets as individual shutters. The compartments are divided by pieces of sheet brass, with interlocking slots cut into them, and all the brass pieces are assembled using a soldering iron.

For a wooden camera like you suggest building, model aircraft plywood or masonite can be easily cut with hand-tools to make the internal dividers. Use interlocking slots, and use wood glue to fillet the joints. Be sure to paint over the filletted corners, as well as the interior, with flat black paint.

If you really want to operate all 4 shutters at the same time, you could fashion a large, rotating disc, whose rotation axis is on the middle of the front face. There could be 4 shutter apertures in the disc, located around the edge. When you rotate the disc, all 4 shutter openings will overlap the pinholes simultaneously. This will only work providing your individual cells are square in shape, so that the corresponding pinholes are arranged in a square configuration.

Good luck. These types of cameras are easily built of wooden materials and simple hand tools.

I think I'll make an internal divider, that I can remove. I'll make the front panel (with the pinhole(s) in it) removable also. This way I can use it as a 4eyes or even a 9eyes camera.
This is a drawing of what the devider would look like (probably).

Quoted from Joe_VanCleave

If you really want to operate all 4 shutters at the same time, you could fashion a large, rotating disc, whose rotation axis is on the middle of the front face.

Hello Joe and Jim,
Thanks for the help. I'll use your suggestion of a rotating disc as a shutter. All the four image fields are squarre so the 4 pinholes are spread evenly on the front.
By rotating the disc, the 4 openings in it will fall before the 4 pinholes and the film is exposed. So simple, why didn't I think of it myself?

One question, though: How do I prevent light leaking between the disc and the body of the camera? If the disc is in direct contact with the body, it won't be able to rotate proparly??

Quoted from curzon

One question, though: How do I prevent light leaking between the disc and the body of the camera? If the disc is in direct contact with the body, it won't be able to rotate proparly??

You can line the camera side of the disk with black craft felt, and tighten the rotational axis hardware (machine screw, nut and washers) until the disk is "snug", but still rotates. There's a brand of stiff craft felt, available here in the US at Hobby Lobby, that has a peel-off, adhesive backing that's ideal for this application. I've also used this to line the inside surfaces of cameras. Its ideal for absorbing stray light. I'd also recommend using a "nylok" nut on the center axis machine screw, so it won't easily unthread or otherwise make the disk come loose upon repeated rotations.

If you get fancy with the shutter, you could have 2 notches cut in the edge of the shutter disk, with some sort of metal engagement leaf spring, that keeps the disk from rotating on its own until you bend the spring out of the way. One notch is for the 'closed' position, the other for the 'open' position. Or, an eccentric wooden cam, made from a section cut from a wooden dowel would also function to lock the disk from inadvertently rotating.

Sorry, Bert, but I'm missing the sense of this camera. If you don't shoot macros but landscapes or architecture with a distance of more then 1 or 2 meters, with the intended division of the film plane without overlapping and a shutter working them all at (more or less) the same time, you'll get 4 times exactly the same negative  

Quoted from taco

Sorry, Bert, but I'm missing the sense of this camera. If you don't shoot macros but landscapes or architecture with a distance of more then 1 or 2 meters, with the intended division of the film plane without overlapping and a shutter working them all at (more or less) the same time, you'll get 4 times exactly the same negative  

You're right about that, but by taping off one or three of the openings I can expose each part seperately or all at once. For example, making 4 different portrets of a person onto just one negative and use it for Gum printing or ... Or I can simply remove the divider and install the front pannel with just one pinhole for landscape images on 400 x 400 mm negatives.
Mostly - for now - the sense is just the fun of thinking about it, planning and building it (I guess).
But to be honest, you raised a good point.  I didn't think of this yet.

Just one question: is the mentioned focussing distance of 1 or 2 meters an educated guess or can I calculate this somehow? With an angle of view of 90 degrees it will be much shorter than with lets say 40 degrees.

Thinking about this, I've got an other idea: what if I make the focal length of each pinhole different? Four simultanious shots varying from wide angle to tele? A bit more trouble to build, but it could give a nice image??

The same camera but with different focal lengths could look like this drawing (below). I need to calculate how tall it can be before I get the "lens" with the bigger focal length on the image from the smaller focal length. Maybe if I made the bigger "lens" like a piramide with the top only 30 x 30 mm instead of the square 100 x 100 mm.
I should also not forget to give it extra exposure. With a longer focal length the f-number gets bigger and so will the required shutter speed. But this can easily be calculated.

It might be easier and take less wood if you made a cross instead of a disk.
By the way, have you considered making making the longest fl pinholes extend with bellows? That way they don't come in sight of the other pinholes.

Hello eternauta3k,
Keeping the side of the longest focal length out of the angle of view of the smallest focal length is a serious danger, I agree. It would take some math to calculate this properly, but it is a serious limitation.

How would a bellows avoid this problem? Do you mean to make it retractable (seems difficult)? Or just by making the end with the lensboard smaller?

I never made a bellows myself, but I need to cross that bridge sometimes....

BTW: Making a cross instead of a disc is a veeeery good suggestion. Thanks for the help!!

Bert:  I'm not sure if this will be any help to you, but I thought I'd show it anyway.  Last October, after seeing Joe Van Cleave's 9-cell grid camera, I was inspired to build this camera.  The camera is 10x15 inches with three 5x5 inch cells and two 5x7.5 inch cells.  All cells are 90mm f260.  The dividers are made from 5mm plywood and are not removable.  Tripod mounts on all four sides.  The front and back are held together with strong rubber bands cut from a truck tire tube.

Hello Ralph,
Thanks very much. This is a big help. Good to see how a camera like this looks like. Helps me making up my mind about the design.
Thanks

What a great idea.  I think having the removeable deviders is a useful feature.  That way you can have overlapping images too.  Can't wait to see how it turns out.

Scott

It's going to take a little while to make this one, because I'm building an all 295 camera at the moment.
See http://www.f295.org/Pinholeforum/forum/Blah.pl/Blah.pl?m-1153211462/
And I'm going on holidays to Luxembourg next Friday. But after that, I'll build it and post the images here.