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The Big Eye: A DIY Large Format Camera

What have I gotten myself into? These are my thoughts after completing another project today. Do I really need this? Was this a project for the project's sake? Or perhaps I found myself enthralled by the romance of a truly large camera. Well anyway this is how I got here...

I had managed to collect a number of cheap components and a couple of weeks ago I realized I was close to having a large format camera. I had bought a 300mm f5.6 Rodenstock Rodagon lens for £18.60+£6.00 shipping because I couldn't pass it up about a year and a half ago when I was thinking of making my own 4x5 enlarger (I know way too big a lens for 4x5). I also bought a 5x5" bellows in good condition for £18.00 for the same project. Finally I saw a few weeks ago three 8x10 dark slide film holders for £75. The seller threw in a fourth decrepit one which was fortunate.

A subconscious plan had developed with this third purchase. Build a large format camera.

I spent a two weekends putting it together. I had decided to do this quickly and cheaply. I like to build finer woodworking projects but couldn't see myself putting in the time and collecting the materials for this. Instead I would use material I had laying around in the garage. Mostly plywood.

I did do a little planning but not enough to avoid some minor mistakes. I did some reading and Jon Grepstad's Camera Builders site is the most comprehensive I found. This got me started on the basic idea (though I already own and use a 4x5 so have a pretty good idea of how they work.) This would be a flatbed design.

I started out making a frame to hold the film holders. I made it from three layers of plywood which made for a slot to guide the film holder. The final strips of plywood would be tightened with some knobs I salvaged from an old enlarger. Tightening these knobs would press the film holder tight against the frame keeping it light tight.
Back of camera with slot for film holder. Knobs are used to tighten it. Note groove just below screws to fit light seal in film holders.

Top view showing film holder slot. The sides are attached at the bottom and flex out at the top to accommodate the film holder. 

The frame I then mounted vertically to a piece of plywood (the flatbed portion). I then put another piece in front of this at a distance that was about 12" (300mm focal length) minus the collapsed bellows thickness. In this front piece I made a 5x5" hole and mounted one end of the bellows using thin strips of wood and screws.

The front of the camera with lensboard and dovetail slide. This is the fully retracted position. 

Side view showing bellows fully retracted. Camera box is on the left in block.
In the flatbed I made a sliding dovetail trough where my focus adjustment would slide. A matching dovetailed board was made to fit this so the whole thing slides forward and back.

Bellows fully extended.

At the other end of the bellows I mounted yet another piece of plywood that would also mount my lens. This had a hole for the lens sawn in it and a square slot at the back to accept the end of the bellows. Again more wood strips were used to secure the bellows and make it light tight. The lens was screwed to the front. Two strips of plywood were attached to the sliding board to accept this lens-board.

The bellows are not tapered and this created  an aspect of the design where there is a large camera box. This was to make sure I could maximize the extension of the bellows before the film end of the bellows would obscure the image from the lens. In fact the full extension is determined by this problem. I laid a straight edge from the edge of the inside end of lens to the edge of the film holder  and move the lens away from the film holder until the line of the straight edge indicated it would cross the edge of the bellows on the side. This was my maximum extension. Since bellows extension is used for less than infinity focusing this would probably be alright. Testing revealed this left the minimum focus at about 2ft.

Then I used foam board to enclose the camera box. These were glued to the tops and sides carefully to ensure no gaps for light to leak through. This would make it lighter (and besides I had the material. It will not be very rugged however.)

Next I took a thin sheet of clear acrylic and sanded it using 600 grit sandpaper to make a focusing screen. This is not ideal as the scratches are too visible as long scratches and while it works the focus is still difficult.

The focusing screen was fitted to the fourth decrepit film holder and the weak joints glued together again. I was careful to try and make sure the distance from the front of the frame to the focusing screen was the same as the film in the film holder.

Finally I loaded the film holders with 4 sheets of Ilford MGIV C paper to use as paper negatives. I took 3 exposures that I metered at ASA 3 at f11 at 8 seconds. I took one exposure at 8 seconds, another at 16 and another at 32. These I timed by counting out the seconds and using the lens cap as a shutter. The fourth paper I used to test light tightness. For this I left the lens cap on and opened the dark slide and left the camera in daylight for 5 minutes. I then returned the dark slide.

The results are encouraging. The first exposure at the metered setting was recognizable. The subsequent ones were much too dark. The image was very contrasty but this is expected with unfiltered VC paper and I did not have large enough filter to put in from of the lens.

The light leak test sheet developed completely white which is great news.

Here is the first negative.

Paper Negative
Inverted image

Basically the image is recognizable. It suffers from too much contrast. It is also not well focused. The right side of the image is in focus (the bricks in the house). Traveling further left across the house and beyond it is increasingly out of focus. I set the focus using the near roof line as it was easy to focus on. I set f11 to make a countable number of seconds. Unfortunately large format DOF is very narrow even at f11. Using an online calculator I found that 300mm at f11 only gives 3.74m of focus behind the subject and 2.2m in front. I would have to go to f45 to get to infinite behind the subject. I have learned my first lesson!

I will need to further check the film and focus screen distances are the same and check on parallelism in the lens to film plane.

Anyway the adventure awaits. What have I gotten myself in for?