Basic Pinhole Photography Concepts

� Basic Pinhole Photography Concepts��

�By Mark Hahn�

�

�Introduction� �

Although there are many good sites devoted to pinhole photography I felt it would be useful to outline the basic pinhole photography concepts that I have found to be important.

In a nutshell, a pinhole camera does not have a lens, but instead has a small pinhole that lets light into the camera to form an image on a piece of light sensitive material.� Pinhole images are much "softer" than images formed by cameras utilizing a quality system of lenses, but have nearly infinite depth of field.� Pinhole cameras can be made from anything that is light-tight and can hold film behind a pinhole.� Many pinhole cameras have been made from old cookie tins, oatmeal canisters or precision built large format cameras.� For many "pinholers" building their pinhole camera is part of the pinhole "art" and I must confess that there is something very satisfying about building such a low-tech apparatus that can actually be used to produce very pleasing images.

I require that all my pinhole cameras accept either cassette, roll-film or large format film backs so I can go out in the field and shoot pictures to my heart's content.� The easiest way to do this is to cannibalize an existing camera and install a pinhole in place of the lens.� Argus A's and Lubitels are good candidates for this because they are both practically worthless as actual cameras, but have all the features required for pinhole cameras; essentially a shutter with cable release fitting that has a bulb (B) setting.� The Argus has a time (T) as well which is very useful for long exposures.

�Technical Details� �

Once you have settled on a camera, you have to decide on the focal length that you plan on using; this is simply the distance from the pinhole to the film.� If you are after the sharpest images possible from your pinhole camera you have to use a pinhole that balances being as small as possible, but not being so small that diffraction starts to degrade your formed image.� Lord Rayleigh presented the following formula for the optimum pinhole diameter� (do):

do = 1.9 Sqrt[lamda*F]�� [Eq. 1]

where, F is the focal length of the "lens" and lamda is the wavelength of light that the camera is being optimized for.� Lamda is generally assumed to be .00055mm.

There are multitudes of equations for determining the optimum diameter for a pinhole, but for historical� reasons I feel that you should use Lord Rayleigh's formula (besides, his formula agrees well with most modern formulations anyway).

There are many ideas how to create a proper pinhole, but I will present my� approach because I have never had a problem easily producing very precise pinholes.� I first set my vernier calipers to the desired pinhole diameter and place it in my negative carrier (with my enlarger head as high as it will go) and focus the caliper gap onto a piece of paper held flat in my easel and then mark out the gap using a sharp pencil.� Without moving my enlarger head I next proceed to make my pinhole.� I use a common pushpin and poke a hole in my .001 inch brass shim-stock (available at Ace Hardware and hobby stores) with a rotating motion while it is held on a hard surface.� I then steel wool both sides of the shim-stock, blow it out with compressed air and then slide it into my negative carrier and check the hole diameter as compared to the marks on the paper below.� I do this several times until I get the pinhole just right.� You will be amazed at how perfectly round your pinhole will be using this method.� I see no need to purchase laser cut pinholes for use in experimental cameras.

Now that you have your pinhole made you have to attach it to your camera.� There are many ways to do it depending on your camera design, but never underestimate the usefulness of black electricians tape.

The next step is determining your camera's f-stop (f).� This is simply:

�f = F/d�� [Eq. 2]

where F is the camera's focal length and d is the pinhole diameter.

If you used my method for making the pinhole, this f number will be very accurate.� The only problem is that you probably don't have a light meter that goes past f-100 so the easiest method for determining outdoor exposures is to use the "sunny 16" rule.� This rule states that for general outdoor shots in "bright" sun your exposure time (t sec.) should be:

t = 1/ASA� @ f-16�� [Eq. 3]

were ASA is the ISO number of the film you are using.

Unfortunately, your pinhole camera will have a "lens" nowhere near f-16, so you have to do some side calculations to adjust the rule for your particular pinhole.� The first step is to determine how many stops (x) you are above f-16.� This is accomplished by solving the following equation for x:

16 Sqrt[2]^x = f�� [Eq.4]

where f is the calculated pinhole f-stop.��

It should be noted that each f-stop is Sqrt[2] times greater than the proceeding one.� This is because the f-stops are defined to represent a doubling of light entering the camera which comes from the area of the "lens" opening, where:

Area = Pi d^2 /4�� [Eq. 5]

Note that it only takes an increase in d of Sqrt[2] to double the Area and consequently the amount of light admitted in the camera.

I personally find it convenient to select film that results in a one second exposure for "bright sun" conditions.� This is because I can easily count out "one thousand one" for my exposure time and get fairly accurate exposures.� Longer exposures are not a problem, you simply count longer.� You can determine the required film speed to achieve this condition by using the following equation and solving for ASA:

2^x/ASA =� 1�� [Eq. 6]

where x is the number of f-stops your camera is above f-16.

Once you know how many f-stops your camera is from f-16 you can use any exposure meter to take precise exposure readings.� The easiest way to do this is to set your meter's ASA setting to that of your film and take a reading from you scene.� You can then just count how many f-stops the scene is from the sunny 16� prediction and adjust your cameras base sunny 16 exposure time by that many stops.� For instance, if you are using 125 ASA film and your meter suggests 1/30 at f-16, you are two stops away from the sunny 16 "bright sun" condition and have to increase your pinhole exposure by 2 stops.� As in f-stops, each "stop" increase in exposure is a doubling of the previous "exposure stop," hence the adjusted exposure (E) is determined from:

E = 2^z Es�� [Eq. 7]

where Es is the shutter speed at sunny 16 conditions and z is how many stops the scene is away from sunny 16 conditions.� For my cameras with a base sunny 16 exposure time of 1 second, my exposure times are:

Ei = 1, 2, 4, 8, 16, . . .

where Ei = 1 sec. for bright sun, 4 sec. for cloudy bright (no shadows) and 8 sec. for heavy overcast.� Past this you really need a meter for any accuracy.� Note too that this is for an average subject and further adjustments might be required to make a proper exposure; with some practice you get very good at shooting without a meter.� Below I present an exposure chart [Figure 1] for my pinhole camera.

�� Pinhole Exposure Chart

Figure 1.� Exposure chart for my pinhole cameras.

You can simply scale my exposure time by the your base exposure time, for example, if your base exposure time is 1/2 second and you are shooting a scene that requires 4 additional stops you read my required time for 4 stops to be a 16 second exposure which you then scale by your base exposure time of 1/2 and you know that your required exposure time is 8 seconds.

�Conclusion� �

We have discussed all the relevant aspects of building and using a pinhole camera while keeping the discussion completely general.� I suggest that anyone planning on building a pinhole camera contemplate what would make the camera a pleasure to use and then put the effort into building one the way you like.� I show a couple of examples of my pinhole cameras along with images that I have produced from these cameras on other pages to give you a possible starting point.� As I said at the beginning of this page, there are many other sites devoted to pinhole photography and I suggest that you search out some of the better ones for more in depth information and other people's ideas.� My aim was to present a concise overview of all the concepts, theories and practical steps required to understand fully how to make and use a pinhole camera, now the rest is up to you.

�Postscript� �

While we have discussed how to make and use a pinhole camera we have completely avoided the question, "why?"� There is of course no really good answer to this question, but as you research the subject you will find that there are many people involved with pinhole photography, there is obviously some some draw to the process if people keep returning to it.� My theory is that pinhole photography puts you back in touch with an original technological form of magic that is very refreshing in this age of impressive auto-everything cameras capable of producing super-sharp detailed images of reality with the push of a button.� From a practical standpoint, we could take "good" photos and just mess them up in Photoshop to produce the same images that we get from pinhole cameras, but then there is no magic.� Further, it has been said that the problem with photography and why it isn't generally considered "art" in the traditional sense is that it just contains too much detail.� Pinhole photography randomly drops detail and gives the feeling of being more artistic; there is plenty of room for the viewer's imagination to wander and fill in the unstated boundaries of a pinhole print.� Pinhole images are also unpredictable, though all your traditional photography skills greatly improve your chances of producing really good pinhole images.� We are still just capturing light to record an image in front of us, but the unpredictability gives the practitioner a feeling that they are somehow conjuring images out of the air.

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