[ reflected 90deg away from the centre which is left unaffected ...
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.
Front surface mirrors - the thinner they are the closer you can get them to the 2 pinholes ...
Originally Posted by wildbillbugman
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:
I was looking through f295.org and I came across this.
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.
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.
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.
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?
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.
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?
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.
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?
Originally Posted by wildbillbugman