Monday, August 28, 2017

A moderately telephoto pinhole camera

A couple things got me thinking about a camera with a longer pinhole to film distance (I refuse to use the refractionist term focal length) in the moderately telephoto range.

The first was the eclipse. I toyed with the idea of trying to directly image it with a pinhole camera. With a 24 inch camera you'd get an image of the sun almost a half inch wide. I didn't do it but I thought about it. 

The other was the problems I've been having making exposures short enough to not overexpose Tri-X on a sunny day.  The thought crossed my mind that a longer camera with a higher f ratio would require longer exposures that would be easier to time accurately.

I didn't do it for either of these reasons, it just got me thinking about it.

Nobody makes telephoto pinhole cameras.  Probably because of the high f ratios which leads to even more extreme exposure times than we're used to. The other thing is Lord Rayleigh's equations tell us the longer the camera, the bigger the "optimum" pinhole is, and although we repeatedly tell ourselves sharpness isn't a primary objective, the size of the pinhole is really what determines the resolution of a pinhole image, and most of us want a reasonably clear picture.

I have done this sort of thing before. In the 90's when I was doing my Guide for Teachers, I made 4x5 cameras 3, 5 and 10 inches long to show how that affected the angle of view and the effect on exposure times.

In my 4x5, black and white period in the early 2000's I made a 10 inch camera out of foam core.

One afternoon last week I decided to make one for 120 film. 

I had a 6x6 cm, 60mm long camera laying around that was the first prototype for the 10th anniversary Populists. (I used it for the Snowy Day pictures and the pinhole comparison post).

I cut a hole in the front of it, made a 60mm long box and a new shutter, and taped it on to make a 6x6cm camera, 120mm long.

The "optimum" pinhole for a camera this length is .462mm.  I don't mean to be too disrespectful of physics, but I decided to use a .3mm pinhole.  That sounds crazy, but I had some evidence that it wouldn't be too bad.  All the pictures above were made with the same size pinhole, .5mm, which is only optimal for the middle one, the 5 inch camera. I also did this with the foam core camera. Some of the pictures I did with that camera seemed as sharp as any pinhole image I've ever done, despite being 75% of optimum for that distance.

This 120mm long 6x6cm camera is roughly the same angle of view as those 10 inch 4x5 cameras, about 28°.

I had a .3mm pinhole in my box, probably from the bunch I made working on the pinhole comparison post. That makes the camera f400. Even using ISO 100 film, exposures are just 10 seconds or so on a sunny day. Once you start getting into reciprocity failure territory, they do get pretty long, but you can just open the shutter and go do something else.

I loaded the camera with 100 because it's inexpensive and I wasn't that confident I would like the results.

So what's a moderately telephoto camera good for.

Most obviously, you don't have to get as close to things.  One of the problems I've been encountering is that to shoot some architectural pictures with my wider angle cameras, I'd have to be standing in the middle of the street. Kind of embarrassing to be in the lane of traffic when somebody in an SUV comes around the corner while you're standing there with a tripod.  This is the side door of the Masonic Temple, a formerly very elegant structure which is now in need of a little restoration. It drew my attention because if Trump starts a nuclear war, I know where to find a fallout shelter. I wonder if they still have the cases of crackers in the basement.

The telephoto compression of space is well known effect.  When I'm using the wide angle Populist and I fill the foreground with these trees on the shore, the trees on the causeway which encloses Miller's Bay are hardly noticeable on the horizon. (If you're remembering the shot from the recent post about panoramas, remember that cropping out a small portion of a wide angle shot will recreate all the effects of a telephoto - it's the angle of view that creates the perception of space.)

Probably the most common use of this effect is in "portrait" lenses, to reduce the impact of a large schnozzola.

Very often, I'll see some abstract composition of lights and shadows and if a wide camera is close enough, the expansion of space will change the relationships of elements, and include background which detract from the design. A narrow angle makes it easier to exclude extraneous distractions.

If you do want to get a close-up, you don't have be so close you can't get your fingers in the front of the camera to open the shutter.

And you can get really close if you want to.

Another advantage with architecture is you can get as close as necessary to compose the shot the way you want to without having the camera tilted up so the building looks like it's falling backward.  In order to do this shot with a wide angle, I'd have to be about 20 feet in the air.  By the way, there's also no vignetting since the distance to the center of the shot isn't that much different than to the edge.

I have to admit that these pictures are little softer than I was hoping, and I forgot that this early prototype, made by adding flaps to the original template made the film chambers a little small, so it's a bit of a struggle to advance the film.

I think I'm going to make one from scratch.  I spent part of the afternoon extending the template to this length.  I think I'll probably drill another pinhole a little bit bigger to see if those equations really make a difference.

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