Thinking about a 2000mm pinhole camera

[ZachInIsrael]

I have had the idea of taking pictures of the sun for some time. The problem is that the sun subtends 31minutes of arc, so a very long FL is needed. But its also very bright! So I figure a 2M sonotube "oatmeal box" camera should work. I just need to find 2m of sonotube. I can reuse the tube after for a telescope I want to build.

 

[Ray Heath]

wow great concept Zach

what format?

what size pinhole?

what is the exposure time likely to be?

what is a "sonotube"?

Ray

 

[Nige]

I was thinking aiming would be a problem, but actually it may not if you make it so you can load the 'negative' in once you've got it positioned by using something at the film plane to allow you to see the image is in the right place.

 

[ZachInIsrael]

4x5, Pinhole would probably be about 0.5- 1 mm
Sonotube is the cardboard tube that is used to pour concrete, folks have been building telescopes out of it for many years.

Not sure what exposure would be, start with 1s and adjust from there. In truth a 2m pinhole will give me a field of view that is 3.6 x 2.9 deg, so I can make 2-4 exposures on one sheet of film for testing, (1,2,4,16 s) Just hold the camera stable and let the sun drift across the film. The sun moves across its diameter in about 2minutes. So aim, move the camera ahead of the sun, expose for 1s, shutter, expose for 2s shutter etc.

I will put a piece of ground glass on the back to aim with.

 

[Murray@uptowngallery]

Jim Jones here has made long long pinhole cams.

If you have an f-number, can calculate exposure then nail down reciprocity failure correction within reasonable estimate.

I'll come back with some numbers. You can use 'em, modify 'em ,or use your own.

I have a piece of 6" PVC about 1.8 m? I painted the inside of for this purpose by bending a paint roller straight (used a vice). Never moved further, probably has cobwebs inside now - Paul Prober of PinPlus cams advises baffling long narrow pinhole cameras close to the pinhole and close to the film because the coverage of such a long f.l. causes alot of illumination of the side walls and reflections. At large angles even good flat paint can scatter some light.

 

[ZachInIsrael]

Assume no reciprocity failure, fuji Acros has very little up to 10 minutes I think. And in color Provia is similar.

Probably F2000 (wow) working with the fact that the sun is really bright.

 

[Lee L]

There are a number of options for magnifying or non-magnifying solar finders. See a collection here: http://www.dd1us.de/Downloads/a collection of solar finder designs 0v4.pdf

You could go with a longer baseline version of one of those designs for greater accuracy. If you're shooting several images on one piece of film, you might be able to make a finder with four offset aiming points arranged in a square or rectangle. I'd label them 1 through 4 so that I had a known sequence and didn't lose my place during the exposure sequence.

Lee

 

[Pinholemaster]

Butt two trash cans together and you can shoot 11x14!

 

[bwakel]

What are you hoping to actually photograph? Without a hydrogen alpha filter you'll just get a white blob which won't be very exciting!

 

[ZachInIsrael]

I should be able to get sunspots without much problem, at least if there are some larger groups.

To do 11x14 (and fill the slide) you would need an amazing focal length, of course you could just shoot multiple images onto one sheet of film.

 

[nicolai]

I'd strongly suggest doing the exposure math using an optimum pinhole size calculator... I wanted to build a pinhole that would shoot enough strips of 120 film to make a square (the length of a whole roll on either side), and once I'd done the math, I discovered that the shutter time was an impractical several days.

 

[ZachInIsrael]

Exposure time should be pretty short, I am trying to photograph the sun after all.

 

[cowanw]

I should be able to get sunspots without much problem, at least if there are some larger groups.

To do 11x14 (and fill the slide) you would need an amazing focal length, of course you could just shoot multiple images onto one sheet of film.

You probably have way more experience at this than I but I was always under the impression that the coverage of the film size was only limited to the size of film you put on the back (and of course the diameter of the camera). That is too say, a pinhole camera is an infinitely wide angle lens.
While you could get multiple images of the sun as it travels in its arc, the background would be increasingly exposed as for multiple exposure.
Regards
Bill

 

[Dan Fromm]

Bill, cos^4 kills quickly.

 

[DarkroomExperimente]

in Eric Renner's book "Pinhole Photography Rediscovering a Historic Technique" page 125 there's a photo and description of a solar eclipse camera made by Jim Jones similar to your project.

he used a ten foot long 3" diameter plastic pipe, 4x5 Kodalith film, 1/100 shutter speed, and a 0.070" pinhole

 

[ZachInIsrael]

Also you are talking about 1-4s at F2000. Anything not the sun is not going to expose the film. So doing 4 exposures with a space between them should work.

 

[JBrunner]

You probably have way more experience at this than I but I was always under the impression that the coverage of the film size was only limited to the size of film you put on the back (and of course the diameter of the camera). That is too say, a pinhole camera is an infinitely wide angle lens.
While you could get multiple images of the sun as it travels in its arc, the background would be increasingly exposed as for multiple exposure.
Regards
Bill

There is increasing fall off from the center of the image as the distance from the "lens" and the film plane increases. The film can be curved to negate some of this, but as the angle increases, fall off and distortion will still be evident as the apparent size and shape of the pinhole changes, the farther one moves off axis. Thin metals are used for pinholes to minimize this effect. Pinhole projections can be very wide, but not infinite ( although infinite isn't really the proper term, so I'm guessing you mean 180 degrees of a circle). You can use a pinhole to cover almost anything because focus isn't an issue, only focal length limited by practicality of exposure. For instance to cover 20x24 you can set the focal length at something you consider acceptable in terms of distortion and fall off, or longer, and you can increase the size of the pinhole to some degree because the larger format will be apparently sharper. In the OP's case he is building a camera that has a special intention, so he gets to "bend" the rules with an extremely long focal length. The camera may not be very practical for a "normal" exposure, because of the fall off factor involved in the extreme focal length. You can get wider than a pinhole through the use of more complex optics. (meaning in this case, a glass lens, or some other additional un-sinister machination.)

I suspect one of the ingredients in Nicolai's calculations were not correct, or he was perhaps looking for acceptable sharpness based on the 120mm format rather than the overall exposure area of his mosaic, which would have a greater apparent sharpness as a whole and therefore could use a somewhat larger pinhole.

For an example of just how large a pinhole camera can be, see:


http://www.legacyphotoproject.com/

 

[ZachInIsrael]

Also remember that the sun subtends 1/2 degree of arc (about) so even at 2m FL the image will be pretty small.

I tend to think about building a custom camera when I want to do something strange. I am also working on plans for a F4.5 Astrocam.

 

[nicolai]

IIRC the image circle of a pinhole is about 3.5x the pinhole-to-film distance.

My calculations could well have been off, but reciprocity correction of a few stops based on a "metered" shutter time of several hours quickly gets into days.

 

[Lee L]

With filters made from thin metal films on a plastic base (Solar Skreen or Astro Baader types), and optical densities of about 6.0 (a filter factor of 1,000,000), recommended exposure for f:200 and ISO 400 film is about 2 seconds. Without a filter, exposure length with an f:200 pinhole and ISO 25 film would be about 32 millionths of a second, into the complement of LIRF (low intensity reciprocity failure) known as HIRF (high intensity reciprocity failure) where exposures are extremely short. To capture sunspots you may need some neutral density along with the pinhole unless you've got an unusual shutter that goes to 1/31250 second.

With the sun's photosphere properly exposed, the background sky will be well below the threshold of exposure.

With a focal length of 2 m, the image of the sun would be approximately 18 mm diameter on the film.

Lee

Exposure adjustments calculated in my head. Please correct my adjustments if I'm wrong.

 

[Jim Jones]

in Eric Renner's book "Pinhole Photography Rediscovering a Historic Technique" page 125 there's a photo and description of a solar eclipse camera made by Jim Jones similar to your project.

he used a ten foot long 3" diameter plastic pipe, 4x5 Kodalith film, 1/100 shutter speed, and a 0.070" pinhole

After the above camera I tried another solar eclipse with 24 feet of 8 inch black drain pipe. I can't find the negatives now, and don't remember the type of film, but all were overexposed at the top shutter speed available, probably about 1/125 second. Aiming the camera was simple. The top end of the camera was supported from a pole, and the shadow of that end was centered on the film end. For somewhat shorter tubes, the film end could be rested on the ground and the upper end moved by hand until its shadow is centered on the lower end. With long tubes a string attached to a self-cocking shutter and running the length of the tube can trip the shutter. Although holding everything steady is difficult, it isn't absolutely necessary. The low resolution of a pinhole and the high speed of the shutter tend to mask any movement. I did try a 32 foot tube, but it was too difficult to manage. High contrast negatives work better than ordinary film. When the exposure is right, the limb effect darkens the edges of the sun so that it appears spherical instead of a white disk. This exposure should also capture large sunspots.

Pinhole images of the moon are much more difficult. I tried a tube maybe 7 feet long on an SLR and Kodak T-Max P3200 film for two seconds with push developing. Little detail was recorded.

Plastic pipe has several advantages for solar pinhole cameras. It is fairly rigid. Shutters and film holders can be mounted on caps for interchangeability. Focal length can be adjusted by cutting the tube or extending it with couplers. Bracing may be needed when long lengths are joined with couplers. If black pipe is unavailable, the pipe can be painted inside. One way of doing this is by capping one end of the pipe, pouring some black paint inside, capping the other end, and spreading the paint by moving the pipe.

 

[DarkroomExperimente]

I was using google to find more about your cameras...and here you are!

This discussion has got me thinking about a lunar pinhole I had considered a while back. I have a tripod for a Celestron telescope that has a motor drive. Although the power cord has been lost, I can probably still bring it back to life.

 

[copake_ham]

I should be able to get sunspots without much problem, at least if there are some larger groups.

To do 11x14 (and fill the slide) you would need an amazing focal length, of course you could just shoot multiple images onto one sheet of film.

We are presently at, or maybe beginning to slightly upswing from a sunspot minimum.

It's an 11 +/- year cycle.

So if you were to shoot right now - you'd likely just get a white blob.

But your project may take a few years which could bring you around to the sunspot maximum period.

The cycles are very unpredictable as to intensity of sunspots (i.e. solar storms). The last one was very active, and also it was a "double hump" with two peaks separated by a slight trough between them. Unfortunately, this suggests that the upcoming cycle may be disappointing.

You can get weekly updates regarding sunspot activity at:
http://www.arrl.org/news/stories/2007/11/26/100/?nc=1

Have fun. And who said ham radio and photography don't mix!

 

[ZachInIsrael]

Well the first version should take a few hours to build (at most) plus time for the paint to dry. I'm planning to make it out of cardboard .