Sort of Strange Question about Pinhole Diameter

wildbillbugman · Dec 8, 2009

Hello to All,
It has been years since I made a pinhole image. My "specialty" is emulsion making,in-camera color separation and Platinum/gum on glass. But I have decided to push my practice to the limits by making Color Separations with a pinhole camera. Attached is a diagram of a Tri-color,one-shot camera, which I have. This is a 5x7 camera which contanes 2 pellicle mirrors. The light from the lens takes 3 paths and is filtered through one of three Red,Green or Blue cut-off filter. The distance from the lens to the red filter is 12 inches with the bellows totaly contracted.
My question is:What is the MAXIMUM pinhole diameter that can still produce an image. I have seen nice pinhole images where exposure time is measured in MONTHS. I am willing to do this, or use strong multiple strobes.
Regards,
Bill

keithwms · Dec 8, 2009

Bill, here is the big issue that comes to mind. As you know, a pinhole's optimum diameter for max sharpness is *very* wavelength dependent, and the 'effective focal length' is likewise very wavelength dependent. If you care about sharpness and want to explore the limits of that, then you might come up with a nifty way to get sharp colour pinhole images by colour sep; I've had some ideas along these lines. This would be interesting because it would not be possible with normal colour films e.g. multilayered films. You'd need to hold the film (or the pinhole) at different distances for the different sep wavelengths... or have different sized holes for the different colours. And then figure out how to bring the colours together in good registry (at an enlarger, I suppose).

Anyway, that nutty thought aside, there is no limit on the pinhole diam, but obviously the bellows or whatever starts to get very long. If you have a big diameter hole and you put the film close to it, you won't get much focus/collimation at all. I think if you just peruse the online pinhole calculators you'll see that big holes mean big path lengths.

wildbillbugman · Dec 8, 2009

Thank you Keith,
Sounds like I will need to do this using my monorail view camera. Not the "one-shot". I think that I will try the one-shot approach too. Just to see what happens.
Just a thought ,though. The cut-off filters on the "one-shot" are very close to the focal plain,not to the lens. Therefor, we are talking white light for most of the distance the beams have to travel.
Bill

DWThomas · Dec 8, 2009

I dunno, I love to analyze stuff to death, but this might be one of those "just do it" ideas. Maybe it's the irregularities of homemade pinholes, but my experience is that there is relatively minor variation with a fairly broad deviation from optimum with a pinhole. You might just try a few shots with a middle of the road sized hole and see what it looks like. I would think the location of the filters wouldn't be that important either since each piece of film ultimately only sees the cut off spectrum. This would seem to be an interesting project -- let us know what happens!

Denis K · Dec 8, 2009

keithwms said:
... the 'effective focal length' is likewise very wavelength dependent.

I could see the focal length of a zone plate camera being wavelength dependent as image formation is dependent on interference, but not a regular pinhole camera. I'm I missing something?

Denis K

keithwms · Dec 8, 2009

Denis, the pinhole diam that gives the best result has a factor of wavelength multiplied by focal length in it. There are a few different versions of the criteria; Ralph pointed out (there was a url link here which no longer exists) two particular cases, from which I quote:

Ralph said:
1. The smallest pinhole possible is based on the Airy disc to optimize image sharpness.

d = sqrt(2.44 * wave length * focal length)

2. The largest pinhole necessary satisfies the Rayleigh criterion to optimize image resolution.

d = sqrt(3.66 * wave length * focal length)

So if you pick a d and then collimate different wavelengths through it, the optimal FLs will be different. I.e. if you keep d constant across the wavelengths red, green, and blue, you'd need for the product wavelength * FL to be constant. Which means that a shorter (bluer) wavelength requires a longer FL, and a longer (redder) wavelengths requires a shorter FL.

These formulas also show that if you want a large d, you need to go to a large FL.

That is my (latest) understanding of it, and I'd welcome further clarification from the experts.

Denis K · Dec 8, 2009

keithwms said:
Denis, the pinhole diam that gives the best result has a factor of wavelength multiplied by focal length in it.

I can easily see the image quality being dependent on the pinhole diameter, wave length and selected focal length, but I would still think the focal length is dependent only on the distance between the pinhole and the film plane.

In other words, if you construct a pinhole camera without the ability to move the film plane relative to the pinhole, you will end up with a fixed focal length camera (i.e. a with a fixed angle of view for the image size of the camera.) I do believe you are correct in that for a fixed geometry pinhole camera you would need to adjust the pinhole size dependent on the wavelength of light you wish to emphasize, or else be willing to sacrifice some image quality.

Denis K

nick mulder · Dec 8, 2009

Why not have 3 pinholes very close to each other (optimized in all respects for each color) - L and R (top/bottom whatever) reflected 90deg away from the centre which is left unaffected ...

Parallax issues could be smaller than the effects of the pinhole size/wavelength issues ?

keithwms · Dec 8, 2009

Denis, what I am saying is that if one wishes to do colour sep with a pinhole and get optimal sharpness or resolution, you cannot not have optimal results for all three colours at the same d and FL. So you'd have to vary them in concert to get optimal results. Does it really matter? Maybe not :rolleyes: I was just relating a nutty idea I had at one point.

For fun, consider an apo-corrected lens as a counterexample: it has the same FL across the wavelengths, so no refocus is required for UV through near-IR. The foci at relevant wavelengths coincide. So in some sense, a pinhole is kinda anti-apo

P.S. That is an interesting idea, Nick. I had more in mind to have a pinhole mount and then three different discs with three diameters, and you'd just swap them out as you do your colour sep exposures.

lxdude · Dec 9, 2009

nick mulder said:
Why not have 3 pinholes very close to each other (optimized in all respects for each color) - L and R (top/bottom whatever) reflected 90deg away from the centre which is left unaffected ...

Parallax issues could be smaller than the effects of the pinhole size/wavelength issues ?

Let's see...

Hole size could be optimized for each color.
It would require much shorter exposures, be easier to make, would be cheaper and easier to source materials with no need to acquire 1/3 reflectance pellicles.

Hmmm... I'm likin' it.

wildbillbugman · Dec 9, 2009

[ reflected 90deg away from the centre which is left unaffected ...

Pa

Nick,
I don't understand what you mean by"reflected 90 degrees from center. Reflected off of what?

I think that the first thing that I will do is to measure the distance from a single pinhole to each separate focal plain. Then use a pinhole diameter around the average of optimum for each. Then take some images with the separation filters removed (I am speaking of the "one shot tri-color camera). Then put the filters back in, Take more shots and examine how the different colors affect the images.
I am glad that my question has sparked some interest.
Bill

nick mulder · Dec 10, 2009

wildbillbugman said:
"reflected 90deg away from the centre which is left unaffected ..."

Nick,
Reflected off of what?

Bill

Front surface mirrors - the thinner they are the closer you can get them to the 2 pinholes ...

Thinking about it now you wouldn't have them lined up - better to have them forming the 3 points of equilateral triangle so the distances between any two arbitrary holes were always equal.

Maybe you'd want to use 3 mirrors - the camera would end up looking kind of 3-way symmetrical (what is the correct term for that?) - sci-fi ! :munch:

willrea · Dec 13, 2009

I was looking through f295.org and I came across this.

Jim Jones · Dec 14, 2009

It's true that pinholes exhibit moderate chromatic abberation. That may be less a problem than trying to make tri-color negatives with three pinholes precisely positioned at the same focal distance for the three colors. Anyone desiring the sharpest possible images should use lenses, not pinholes.

wildbillbugman · Dec 15, 2009

Jim,
You are correct. I know that I will never get pinhole images as sharp as what I can get with a lens. But I have seen some images that wre taken with pinholes that are amazing as long as the viewer takes their origin into consideration.
For Evrybody,
I have been working with some of the online pinhole calculators, But their are signifigant diffrences in the "optimal" pinhole diameter for each wavelength, given a constant focal length.

Kirk Keyes · Dec 19, 2009

Bill - isn't there just a difference of a factor of about 2 going from red to blue?

Anyway, make something big (a couple mm) and try it, and see what it looks like.

Are you testing with commercial film, or your own emulsion?

Larry Bullis · Dec 19, 2009

Wow! Three pinholes would certain increase the amount of fooling around. I guess if you are into research primarily, it would be worth it, but if you are planning to make images, you'll make a lot less of 'm. In my experience, for practical purposes, I really doubt that even the most discerning viewer - i.e. anyone who isn't looking at your work through an electron microscope - would ever notice the difference between three color images made with a pinhole calibrated to a middle value. That's usually in the green part of the spectrum... I'm sure I could dredge up a wavelength if someone really needs it, in my collection of Pinhole Journal.

Usually, pinholes aren't made to sufficient quality standards where wavelength variation would be the main source of degradation. Most people seem to be using (if I'm not wrong) laser drilled pinholes. In these, only the center has the nominal diameter. As you move away from the center of the image, not only the size of the opening changes, but its aspect as well, and additional diffraction elements would enter into the picture.

Using a constant d and varying the "focal length" (misnomer, but you get what I mean) would probably not be what Bill has in mind, because each color image would have a slightly different angle of view and objects rendered in different scales. Changing out the pinholes would produce consistency at the cost of adding a great deal of trouble (IMHO). Bill asked about "maximum" ph size. I have used diameters ranging between about 5/1000's of an inch to about 1 inch, depending upon how big the camera is. The 1" hole was used in a room set up as a camera. In one of his books, Ansel Adams suggested making a viewing pinhole of about 1/8" which would be replaced with a working pinhole of much smaller size. Of course, the 1/8" hole would be big blurry, but would allow recognition of general shapes. What this might mean for you, Bill, is that you could use any size hole you want, depending upon your quality requirements. You could use a hole so big that you'd have a great shutter speed, but might sacrifice a recognizable image in achieving that.

wildbillbugman · Dec 19, 2009

Hello to All,
After reading all of these opinions, I think that what I will try first is to use the tri-color camera. I already have brand new pellical mirrors for it. So,as far as expense is concerned, the damage is already done. ($500 per mrror,BTW)
I will just choose a mid point wavelength, say 550. Then,, each film plain will be a diffrent distance from the single pinhole, so I will choose the longest for exposure calculation. I know the R/T vallues for my pellicals, so I will factor these into the exposure. I can see myself useing ND filters on the two shortest exposure calculations. Then I can have one optimum exposure for all three film plains.
I have no idea if this will work. But most of my work is experemental. Most of my time is dedicated to emulsion making and I am doing well to get one realy good piece of work in a year.
Also, if laser drilled pinholes are of mediocer quality, what would be a higher quality. Can anyone reccomend a source? Or are these carefully home-made, by experienced pinhole guys?
Regards,
Bill

Larry Bullis · Dec 19, 2009

Home poked. Commercially available pinholes are made for convenience. Hardly anyone can afford a really good one. Most people doing pinhole don't know what's possible.

Mine are made using a needle in a pin vise in .003" pure silver. First I make the hole too big, then I hammer it to make it too small, enlarge it with the needle again, hammer it again, enlarge it, rehammer, you get the idea. I have polished a ball peen hammer and anvil for this purpose. I don't know the resultant thickness, but it is very thin, and the hole is basically knife edged. At each stage, I file any burr with a very fine jeweler's file. The metal is domed, with the hole in the middle of the dome. I use a projection microscope, and I don't stop the process until it is perfectly round and absolutely clean. This is a very laborious process, and since my eyes aren't what they once were, it's getting more difficult all the time.

A long time ago, I used feeler guages (automotive) to set the diameter I wanted into a fly tying vise, and used that to set the needle's depth of penetration. Those were great, but the ones I make now are better. You can probably find the fly tying method online somewhere. It was published in Pinhole Journal back in the mid 1980's.

There you go. The secret is out. Make one like that, you won't believe the quality of the image you get. My pinholes have been criticized as being "too damn sharp" by pinhole nutcases.

With different distances from the hole to the film, you will most likely see fringing. Is that what you want? It might be very interesting. If I were doing it, I'd make the distances the same.

Larry

Jim Jones · Dec 20, 2009

wildbillbugman said:
. . . I have been working with some of the online pinhole calculators, But their are signifigant diffrences in the "optimal" pinhole diameter for each wavelength, given a constant focal length.

Pinhole Designer lets one choose Lord Rayleigh's constant, first Fresnel zone constant, or a user constant. The first two yield pinholes rather larger than optimum for on-axis sharpness. Many of us prefer a 1.5 or 1.4 user constant. The larger constants may sacrifice a little on-axis sharpness for improved off-axis sharpness, and reduce exposure time slightly. This has often been discussed on http://www.f295.org/Pinholeforum/forum/Blah.pl?

polka · Dec 26, 2009

I will just choose a mid point wavelength, say 550.

This is right, because it's exactly what one does when one uses a regular color film with a pinhole camera (and does not notice any sharpness difference in different colors). And moreover, one has no concerns either when using B&W panchromatic film.

Then,, each film plain will be a diffrent distance from the single pinhole, so I will choose the longest for exposure calculation

This I don't quite understand : isn't your camera designed to have the same optical paths in the three colors ? if it's so with a lens (to get three views of the same size and same focusing) then it's so also with a pinhole ?

Paul

wildbillbugman · Dec 26, 2009

isn't your camera designed to have the same optical paths in the three colors ?

Paul[/QUOTE]

Polka,
Of course, you correct. The diagram attached to my opening post in this thread clearly shows this,as dose the camera itself. So I am clearly working with one distance. If I eliminate consideration of 3 different wavelenghts I need only consider a pinhole of optimum diameter for 12 inches. This is the distance from the lensboard to film planes with bellows totaly contracted. But I will also get some pinhole sizes acurate fore some bellows extention.
I have decided to get some specialy prepared pinhole for this project. And to not use readily availible laser-drilled ones. I wish to do everything right for this project.
Bill

Sort of Strange Question about Pinhole Diameter

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