360* Pinhole camera

So, after a bit of searching around online, a fair bit of time reading

the forums, and a few minutes playing around with the Pinhole Designer

program that I've seen mentioned a few times here, I'm still left with

a few questions regarding the idea of making a 360* pinhole camera

that uses 120 film.

 

I'm planning on using a folger's coffee can (actually been drinking

the awful stuff just so I could make the camera), which measures 125

mm diameter. I'm not exactly sure how I got to the math of it, but it

seems like I should be using a 60 mm central shaft as the film plane -

both because it'll give me enough wiggle room to load the film and for

some strange sense of numerical aesthetics.

 

It seems like the first question I need to ask is:

 

What is the minimal focal length required to ensure proper coverage of

the negative? In other words, will a 65 mm focal length adequately

cover the 60 cm height of 120 film? If not, how do I figure out the

minimum focal length needed?

 

I would've thought that the Pinhole Designer would help decide this

with the Angle page, but it doesn't seem to help you choose based on

film format.

 

One I've figured that out, I guess it becomes time to figure out how

many holes I need to make to get 360*. Then comes the fun part of

devising the crank shaft to rotate the film, calculating the number of

exposures per roll, and how many rotations I crank to advance.

If properly made, a 65mm "focal" length should cover 120 film okay. They sell 4x5 cameras with a 2" focal length, if that helps. I assume you would need a thin pinhole for this, but evidently it's doable.

 

It's not clear from your description how this is going to work. I assume a series of pinholes will make a series of images on the film? Consider first off, that if you don't adjust the geometry right, you won't cover 360 degrees; that is, you'll have either gaps or overlaps in the coverage. With a 65mm focal length, one millimeter of film covers about 0.8815 degrees of view. For 360 degrees, you need 408 mm of film, or 130mm diameter. Now, with film wrapped around a 60mm central shaft, your total coverage will be slightly less than 50%.

 

Secondly, images made by adjacent pinholes will NOT line up properly to make a panoramic image, as you might expect. Each image is reversed, so an object at the dividing line between pinholes will be split into two pieces that are on the far sides of two adjacent negatives. In other words, you'd have to cut your image apart and paste it back together in reversed order to make a panoramic image of it.

 

Have you used pinhole cameras before? If not, I'd suggest you build or buy a simple one and try it a while before jumping into what looks like an exercise in frustration. Freestyle sells a cardboard 120 pinhole camera kit. You can buy lenscap adaptors for 35mm SLRs's. And you can make your own box-type without too much problem if you're willing to load it in a darkroom.

 

And if you're experienced at the pinhole cameras, I'd suggest a bit more thought on the layout and effect is in order here. If you're not expecting panoramic effect, you could perhaps just enlarge the central shaft diameter and get the effect you're after. I assume you need some sort of divider between the image areas, so they don't have a zone of double-exposure.

Illustration of why you don't get a panorama- two adjacent "cells", note that image on the dividing line gets separated to far sides of film, not the part that's touching.

I've seen pictures and drawings of a 360 degree pinhole camera using a round cookie tin, with smaller round insert. The film is wrapped, emulsion side out, around the perimeter of the inner circular insert.

 

There are six pinholes, equally spaced around the sides of the outer cookie tin, that produce an overlapping image effect upon the inner, circular film.

 

This may not be exactly what you're looking for in a panoramic image, however, as the resulting image has overlapping artifacts that are visually quite interesting, but not "traditional" panoramic in style.

 

In general, a camera with ~60 degree angle of view gives a nice image with little light falloff at the edges, so that's a good starting point.

 

If I recall correctly, light falloff with a flat film plane, using a circular pinhole aperture, is related to cos^4 function. There's formulas available for calculating how many stops of falloff between center and edge.

First off... the fewer holes you have the worse focus problems you will have... Consider:<br><br>

 

Focus is a spherical projection out from the aperature hole... points 65mm from your pinhole will be in focus... in a regular pinhole camera with a flat filmplane you see that only the dead center of the image is in perfect focus, with focus dropping off on the sides. Some builders use a curved film plane so that the in focus area will be a horizontal line through the center of the image. By wrapping your film around a cylindrical core you will have focus dropping off to the EXTREME away from the center of the image.

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Heres an idea that might work... Instead of wrapping your film around an insert core in the center of the can... use mirrors to reflect the image down from the pinholes to the filmplane wrapped around the inside of the can below the holes. Im thinking about a 10 degree tilt on the mirrors is enough to translate the image but not cause serious distortion. You will need to use some kind off light baffle between the film and the pinhole so the top edge of your film doesnt get fried. I would build the camera... then measure the angular distance from the pinhole to the center of the film and call that your focal length, and make a pinhole the coresponding size. Because the mirrors will reverse the already reversed pinhole images you SHOULD be able to get a fairly well overlapped continuous image.... that all depends on how well you position the mirrors... i would glue those onto some kind of wooden frame and insert that into the "camera".

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Heres a drawing if my description sucks. Granted, Ive never built a camera like this and its just an idea....<br>

 

<img src="http://i16.photobucket.com/albums/b15/patrickjdempsey/Cameras/coffeecan360.jpg">

Note, because of the displacement between the pinhole and the film, this camera would only shoot things above it... so if you put it on the ground it would only see buildings and trees and cars above its level.

I don't think the mirrors would reverse the image in the desired way. Try looking at that arrangement from the top.

Yup, you are right, the only way to do it with mirrors, is to use 2 per pinhole... and thats alot of aligning and whatnot.

Patrick,

 

That was my original idea. I gave up on it because it seemed overly complex (I had forgotten about image reversal. There's a variety of places that sell mirrorlike material that is reshapable, so the idea has some appeal. I think it's fair to say that I'm more interested in building a 360* camera than a pinhole.

 

This is my first attempt at a pinhole camera. Perhaps I should follow the other advice posted here about just using the can to build a basic one before getting complex. I really would prefer to build one that takes roll film and includes some kind of film-advance mechanism.

I'm a tinkerer. And I'm not a machinist. So I run into similar problems- I have neat ideas that are difficult to pull off.

 

The idea of advancing 120 film is very simple. Building a working 120 film advancement with common home tools would be moderately difficult. You'll notice even on a lot of factory-made cameras, the "film transport" becomes a problem area. You want to make a film-transport system that does not scratch the film, allows even film spacing, is absolutely light tight, and is easy to load and unload. Those are difficult goals from scratch.

 

One option is to buy some old 35mm or 120 film body and use it. Just remove the lens and replace with a pinhole of your choice. On some of the foldable 120 cameras, you could possible remove the entire folding mechanism and seal up the front- seems like I have seen this done. I just bought an Ansco Shur-Flash camera off ebay for $5, and it is one that would be easy to convert (although I don't plan to). You can pay $15 or so for a Holga and make it into a pinhole. It's not ideal due to light construction and lack of a tripod screw, but can be done.

 

You can buy the cardboard pinhole kit I mentioned above. It might be possible to build a wooden version of that, I'm not sure of the details of construction. You can buy a couple of 120 roll film pinhole cameras, for that matter.

 

Some time back, I built a 4x5 pinhole camera. I didn't make it for filmholders, just load and unload it in the darkroom. What I discovered is that I'm just too lazy to take it out somewhere, take one picture, come back, change film, then go take another, etc. So I've used it a total of 4 times now. Roll film is definitely the way to go! (Or film holders, at least).

Stephen,

 

Actually, I had planned on using those clockwork lego pieces to construct the film advance mechanism, for sheer cool factor. Something for you to consider.

Amul, if you are more interested in building a functioning 360 camera and are willing to use a lens, heres a concept for a very simple one using the lens/shutter assembly off of a bellows camera...

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<img src="http://i16.photobucket.com/albums/b15/patrickjdempsey/Cameras/360camera1.jpg">

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You would have to find two metal cookie tins, one slightly smaller than the other, and both tall enough to fit 120 film and a little extra space. The inside tin is pretty simple... it has the film running around inside it, and a long bolt coming up from the bottom. This bolt is your fulcrum that the upper part will rotate on.

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The upper part of the fulcrum could be simply a wooden block with a hole drilled in it... it would actually be better if the thing didnt spin freely. The upper tin would have to have a hole cut in it to let the light pass though, and you would have to build some kind of box to contain the mirrors, and sheild coming down from the upper tin to mask the unexposed film. Building the box for the mirrors would be the most difficult part, as each mirror would need to be set at 45` and you would need to measure your focal length from the lens and reflecting off the center of each mirror to the center of the film, to insure focus... (making sure to measure focus to the infinity mark for the Lens) If you built your assembly tight enough, you would be able to test focus on a peice of ground glass held against the mirror box.

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Also, in order to take 360` pics, you would need a template that would show the distance between "frames". Taking the image would be pretty slow, but very simple. You would have to use a cable release and take each shot, and then rotate the lens the correct distance to the next "frame". The number of shots would of course be determined by the diameter of the pie tins and the width of the mask on the mirror box. <br><br>

Well, I have no idea if this thing would actually work, but it seems like it would be fun and easy to build, and very cheap. Plus, thats alot of cookies... and cookies are MUCH better for you than coffee as anyone knows, and should be pretty easy to find this time of year. ;)

Joe VanCleave just about has it. But try 36 pinholes, not six. With baffles about 3/4 the distance from the pinhole cylinder to the film cylinder (this number may not be exact, I'd have to simulate it to try different "blend" effects). This will decrease the artifacts substantially.

 

And the decreased spacing betwen the pinholes will substantially reduce the perspective distortions in the image blend areas. For much the same reason a WideLux rotates the lens around its rear nodal point, or a modern panoramic bracket rotates a camera around the lens's entrance pupil.

 

The curvature difference between a 36 sided polygon and a circle isn't that much. So I'd solve the pinhole design by simular triangles. That makes the radius of the pinhole cylinder twice that of the film cylinder. This means you can have pretty much any cylinder diameters, as long as you maintain a 2:1 ration.

 

So you choose a diameter to accomodate a particular vertical coverage. Using 120 film, you'll have images 56mm high. Let's say we want a 60 degree by 360 degree panorama. I've always found 60 vertical degrees to be "comfortable" for 360 degree panos. That means the focal length of the pinholes, and the film cylinder radius, is 56mm/2/tan(60deg/2) = 48.5mm. The film length is 305mm.

 

The pinhole cylinder diameter is 194mm so it shouldn't be hard to find or fabriate something close...

 

And the pinholes are spaced 16.9mm apart on the cylinder.

But wouldnt each of these slices still be a reflection, so they wouldnt line up?

Ok.... this is how you get a true 360` panoramic pinhole camera... A coffee can upsidedown with a cylindrical mirror which would fit inside .. Amul, you mentioned being able to buy flexible mirrored material? that would probably work perfect for this!

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<img src="http://i16.photobucket.com/albums/b15/patrickjdempsey/Cameras/360camerapinhole1.jpg">

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Ive just sketched this out with 4 pinholes, but obviously it could be made with as many as need be.... however, i THINK that the curved mirror and the curved surface of the can will create an area of focus across the entire horizonal center of the photograph. Also, because the curved mirror is reversing the images, all of the scenes would butt together on the film.

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Again, the difficult part of building this camera would be aligning the two flat mirrors which bring the image into the main curved mirror. I was thinking if you mounted these on blocks of wood suspended from screws, you could adjust the position of the mirrors with the screws. You could test the alignment by taping a darkcloth around the can and using a peice of white paper where the film would normally be; with the "top" (on the bottom) of the can removed so you could see in.

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The orange squares in the crosssection are light baffles which i was thinking could be made from that 1/2 inch foam weather stipping you can buy for sealing your windows... its self adhering so it would go on quickly and easily.

Unfortunately, the main drawback to this camera is its roughly 260mm focal length.... projected onto the full height of 120 film, this is only about 20 degrees vertical veiw. It would be great in the desert.... where everything is nice and flat. heheheh. ;)

I was thinking today, a possible material to use to make the curved mirror would be reflective mylar ribbon... im guessing its pretty cheap and you could probably find it at any party supply store. It would already be an appropriate hieght... 1 or 2 inches.