The potential angle of coverage of the pinhole is not the same for all of them; it depends upon the method of making the hole. Any drilled hole is in fact a tube, albeit a small one. Let's take a ludicrous example. Say that you have a wall that is 1 meter thick and you make a pinhole in it, at the aforementioned "optimum" diameter, and that that is calculated to correspond to the inside diameter of a typical pipe as is used for plumbing a bathroom. So, the hole could be the optimum diameter, alright, but you could only see through it looking dead straight down through it. Moving this way, or that way, so much as 1 or 2 cm, there might not even be a hole visible, at least to transmit light.
Originally Posted by Dave Wooten
For the widest angle, it would be necessary to use the thinnest material possible and the edges of the inside of the hole would need to be knife sharp. This is a big order for the maker. While it is possible, it is not something most people would go to the trouble to make. This is the kind of pinholes that I use myself, and I make them using pure silver beginning with .003 inch thick and then I use jewelers' repoussÚ technique to dome the area where the hole is, pounding the metal thinner and thinner, and adjusting the size of the hole both larger and smaller using a needle and jeweler's files, the polished peen hammer and anvil, and a projection microscope. Then I finish them using a fine sharpening stone and blacken them chemically (NOT WITH PAINT). They have an amazingly wide angle and are as I've been told by a master pinhole photographer who shall go unnamed, "too damn sharp!". Granted that this is an unusual camera design, also, but I think it might give you an idea:
Here's a link to the design of the camera that produced this image:
I just checked (Eric Renner) Pinhole Resource's site, and found that the pinhole sets they sell are made in .001 inch hard stainless steel and are micro drilled. I'm sure that the reason they are made in this material is that it will stand up to the mechanical stress of the drilling. While a .001 inch tube is pretty thin, it is still a tube, and the field will be limited accordingly. Eric is well aware of this, and has adopted this particular compromise because making them as I do (which he knows about, although I really need to send him one of my latest samples) would be prohibitive in cost to the purchaser, and he's in business to make money as most people have to be. He told me that he doubted that he could sell more than a couple of mine per year, if that; now it would be even fewer, because they are so labor intensive and my eyes are getting older every day. The compromise he's using is a very good one; it is hard to imagine one that could work better and still be practical, but if you are a fanatic, it might just not quite do. For myself, it is definitely not adequate.
Use of filters with pinhole is not really practical. Eric R had asked me to write an article on that subject for the first edition of his book, but my research with it proved so disappointing that I declined to do it. Do you shoot in a clean room? Any dust at all will appear as a very ugly spot on your image. I was shooting in the desert in Eastern Washington. I ruined far too many sheets of 8x10 film to make my camping a happy experience!
Larry that has to be one of the most impressive pinhole photos I have seen! Thanks for posting.
I was thinking, perhaps incorrectly, that removing color with a filter, and shooting black and white might make a "sharper" image.
Have you found that for each focal length there is an optimum pin hole diameter size ? Also the lens being optimal as you construct them, what coverage can one expect in relation to focal length?
Originally Posted by Dave Wooten
There is very little argument about how to find the optimum size, except for myself. I like to think that diffraction is an expressive tool, and that while the optimum as calculated by the equation "sqrt(.oooo7*f) where f="focal length" (pinholes don't focus so we use the term "focal length" for convenience) it seems to me that if one wishes to have more diffraction one ought use a smaller diameter. However, for most of my work, I use the formula. It is calculated for that particular green band that we see the best, I believe, and it produces a really versatile and great pinhole. If making a pinhole for someone else, I'd have to have a signed waiver not to use this value.
As for coverage, you simply won't believe it. I really haven't measured the angle, but if you want, you could calculate and construct a pinhole of a very short "focal length", say on the order of 1", and tape it into the middle of a 4x5 film box. Then shoot something with it, measure the image circle, and figure from that. It will not be 180░, but it will be much closer to that than to 90░, depending upon your skill in making the hole.
Good luck. Please report what you try and what you get when you do.
By the way, I should have mentioned that the image will not be limited simply by the image circle, but by the "useful" image circle. Falloff, from the center to the edges can be fairly extreme. This is because we are subject to the famous "cosine". That is, the center of the field is the closest to the hole, and will be the brightest. As you move away from the center, the distance from the hole increases. As the distance increases from 1 unit to 1.4 (actually, the value of the sqrt(2), 1.414etc.) you've lost one stop, from 1 unit to 2 units, two stops, from one unit to 2.8 units, three stops, etc. (Don't know if you understand f/stop math, but this is a great start).
Furthermore, as you view the hole off axis, its aspect ratio narrows, and the difference between the elipse that results and a full circle amounts to a further loss of light. For this reason, too, the resolution of the image at every point on the filmplane is different, greater in one dimension than every other. Every point is unique in its peculiar resolution. Wild, huh?
As I understand it, if the pinhole-to-projection distance is at the Rayleigh limit (i.e. is 'optimized'), then the resolution will be the same regardless of whether a glass lens is used along with the pinhole. Thus, if you can see improvement by combining a glass lens with the pinhole, then the pinhole wasn't optimal for that projection distance.
Last edited by Joe VanCleave; 05-29-2008 at 11:39 AM. Click to view previous post history.
Reason: eye kant schpelle
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Just throw that lens away!
I believe that is correct. The lens is superfluous.
Originally Posted by Joe VanCleave
It does, but the improvement is slight. Pinhole photographs do have modest chromatic aberration. I've confirmed this through experiments. Some formulae and programs for calculating optimum pinhole diameters include the wavelength of light. As an aside, wide angle pinhole cameras also have astigmatism.
Originally Posted by Dave Wooten
More and more holy all the time.
Great observations, Jim.
Originally Posted by Jim Jones
I don't know that the terms that apply to lens characteristics such as chromatic aberration and astigmatism are really appropriate, but you are right that effects analogous to these are visible. Maybe someone knows for sure whether there are accepted terms for these effects, but I don't. Anyway, they can be quite interesting.
The chromatic event is related to diffraction. I have my doubts that it would affect the sharpness much, but again somebody may be able to explain it. The light is diffracted when it contacts the edge of the pinhole and since the various wavelengths bend different amounts, the light is separated into a color spectrum. This can be quite pronounced if the pinhole is sharp. It can be seen clearly in images when the light from the sun falls directly on the edge of the pinhole, as in this example:
As in light separated by a prism, the red end of the spectrum bends less sharply, the blue end, more. From this I suppose we might be right in expecting greater sharpness due to less pronounced diffraction using a sharp cutting red filter or even more using infrared. The use of a color filter with pinhole isn't really practical though, even if it might be sharper to use one color rather than the whole spectrum; the filter factor alone will extend the exposure out to the edges of the earth, and any dust or other accidental markings on the filter are extremely damaging to the image. I ruined a bunch of images and 8x10 film testing this. If you only shoot in a clean room, it might be ok. It sure didn't work on the desert in Central Washington.
The analog to astigmatism is due to another property of the pinhole image, to the appearance of the hole which does not look circular to any point on the film except at the very center on the axis of the hole. As the hole is seen at any other angle, the circle appears as an ellipse. The ellipse becomes narrower the farther away from the center you get, and so the axis is always perpendicular to the line going toward the center. Thus, the "astigmatism" is not aligned as astigmatism appears in a lens, but radially. It is different at every point on the film plane.
You can introduce an effect that is more like lens astigmatism by using a slit instead of a round hole. Then the "astigmatism" will be aligned (i.e. north and south) as it is in lenses. I used the eye of a needle as a pinhole once and got this effect; I photographed a camel with it -- duh. The resolution differs according to the aspect ratio of the hole. Of course that radial "astigmatism" will be present overlaid on the aligned "astigmatism".
Usually calculations for optimal pinhole size would be done for I think it's 550 nm. That is the yellow green color that our eyes see the best, and it is sort of an average of the visible colors. I guess if you were going to filter, the use of a filter that was the same color the hole is figured at would be the best combination.
Pretty weird stuff and fun to play with.