In the last couple of posts I have been talking about the large format pinhole camera that I am building. I started with the film holder made from thick card which was looking good and only needs a couple of tweaks to get it perfect for it's use. The decision had been made to make the first incarnation of the camera out of card too so I got started.
I divided the build into three parts - the rear standard, the bellows, and the front standard. In large format camera terms, this refers to the rear section that houses the film holder and viewing glass, and the front section that houses the lens. Between the two of them you have the bellows bridging the gap. That is a very simple way to look at it - the sections do more than that but those are the basics you need to know.
With a pinhole camera, things are even simpler. There is no viewing glass so you only need to house the film holder and there is technically no lens either.
The structure of the camera would be built from thick cardboard and I would then cover all the visible surfaces in nice white card that would help with the rigidity but also make it prettier.
The Rear Standard
I started by building a tray that the film holder would slot into from one side. I left plenty of room for it to slide in and out of as the plan was to have a second piece of card slide in behind the film holder once it was in place and pin it to the top of the opening. That along with a soft light seal along that edge would make the opening light tight. This method would give the cardboard structure of the camera an easier time - creating an opening that was perfect in size would eventually weaken the film holder and camera, and would be at risk of falling out when being moved.
Pinhole cameras don't need bellows for focusing as everything from right in front of the camera to infinity is in focus. This meant I could just build out the camera to the focal length I had decided on and leave it there. That said, I had originally designed it to have a tapering effect from the rear to the front. It's an effect that would have been quite obvious in thicker wood but not to much with the thinner card. It looks good though and I'm glad I stuck with it.
The distance between the front and the rear plays a big part in what the final images will look like. Close together and the image will be very very wide. Further apart and the image will be zoomed in. I'm a big fan of my 50mm lens on my SLRs so I wanted this camera to have the equivilant size - that was 300mm. Once I started building I saw some images of shorter focal lengths and changed it to 240mm and then again to 210mm which I've stuck with.
The Front Standard
The front standard needed to do two things - house the pinhole and also a shutter. The design for this is very similar to the Holga 120WPC that I have - a shutter that slides back and forth in front of the pinhole. To do this I made two square pieces of card, one bigger that the other, stacked on the front. The lower square had the middle cut out of it horizontally to allow another longer piece of card to take it's place. When I say longer, I mean long enough to span the width of the camera and then some. This would let me press in either side to open and close the shutter. I cut a square into the shutter to allow an open state when pressed in from one direction.
The size of the pinhole is determined by the focal length. There is a website that is superb for determining the size you need by the focal length you've decided on and vise versa called Mr Pinhole. By entering the focal length it will give you the diameter of the pinhole you need. It also gives you the f/stop that will help to meter your compositions.
For a focal length of 204mm I needed a diameter of 0.6mm. The first needle I found in the house gave me a diameter of 0.588mm which was close enough for me. At this diameter I would have an f/stop of 347. This is a very high f/stop and would result is extremely long exposures - in my first meter reading on a bright sunny day I was told 2mins 30secs. Inside in a bright room it would take 45mins to 1hr.
Because I would mainly be using photo paper with this camera, I needed to cut down the contrast that happens when doing this. There are a number of ways of doing this - pre-flashing the paper can do it of some kind of filter. I opted for the filter method and taped my 00 multigrade filter from my darkroom enlarger to the rear of the frot standard. I use this filter in the darkroom for exactly the same reason as I needed it now - to give an even exposure with normal contrast.
The Finished Result
I took two tests when I'd finished the camera. The first one from our balcony which I didn't expose for long enough. The second was towards our local football team's stadium when there was a match on. This was was far better.
Overall the result was good. There is a slight light leak from the film holder which I expected but nothing like what I thought it was going to be. It's an easy fix.
I've really enjoyed myself with this project and I'm looking forward to tweaking the design and taking it out into the field. I'll keep you posted.