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# Thread: Pinhole size and distance

1. I assembled a 5x4 format camera a few weeks ago. The film to pinhole distance is ~39mm, and the pinhole is 0.3mm. To a certain extent the coverage is governed by the thickness of the material used for the pinhole. The thicker it is in proportion to the hole diameter, the smaller the coverage. Then there is also the amount of corner light fall off that you can accept as coverage.

My first pinhole was too thick, and I had a roughly circular image on the 5x4 film. The current one is much better and has (weak) detail in the corners. I'd say that there should be no coverage problems with a pinhole to film distance close to the 'normal' focal length for the format.

There's a negative scan of the first image with the camera here: http://grahampatterson.home.comcast....d-building.jpg The fall-off in a print is not quite as pronounced. You can see the darkslide being used as a shade in the top left corner 8-)

2. Originally Posted by Darkroom317
Ok, thanks. My guess is the numbers are off then

It gives a waring saying that the image circle will not cover the film. So,I moved the distance until it would.

Edit: The designer gave me a focal length of 50mm. I checked the distance in my plans an it comes out to 76mm. Which for 6 x 6 would be the same as 50mm on 35mm. The wizard is really confusing
So when you moved it so it would cover, you've changed your F to an arbitrary value. Then, you might as just poke a hole and see if it works, because you've invalidated the calculations. If it is supposed to be 76mm, that's the value of F regardless of whether it covers or not. Of course, if you change it to an arbitrary value and can accept the results, it's ok, but you will need to refigure your f/#.

I've often used the formula in the old Photo Lab Index since I started doing this before Eric published his data. That formula is sqrt( .00007 x F) all in inches. I suspect the formula cited above, by Lee, at .000055, would be as good or better. The difference in the various formulae stems from the specific wavelength of light that the individual chooses as a basis for the calculation. The result is always a compromise between the softening effects of diffraction (becomes more pronounced as the diameter decreases) and resolution (which becomes more pronounced as the diameter increases). Any diameter within the range between Lee's quotation from Eric and mine ought to be good. As for the wavelength of the light, I don't bother with it, although I suppose I ought to consider it.

The other factor which nobody seems ever to consider (although grahamp alludes to one aspect of it) is the quality of the physical hole. You can have a hole that agrees with the math and still produces crummy images because it has ragged junky edges and most likely forms a rough tube through metal that is too thick. A nice clean hole with sharp edges will give the best results.

3. Originally Posted by Darkroom317
I know this has likely been covered to death but what would be a good pinhole size for 120 (6 x 7). Also, what would be the distance needed between the pinhole and the film plane?
I can offer this information:

http://www.waybeyondmonochrome.com/W...ographyEd2.pdf

4. Originally Posted by Darkroom317
Ok, thanks. My guess is the numbers are off then

It gives a waring saying that the image circle will not cover the film. So,I moved the distance until it would.

Edit: The designer gave me a focal length of 50mm. I checked the distance in my plans an it comes out to 76mm. Which for 6 x 6 would be the same as 50mm on 35mm. The wizard is really confusing
for any given pinhole diameter there is a focal length, a .39 pinhole is suitable for your 76mm camera weather its 6x6, 35mm or 4x5. If you have a .3 pinhole then your correct pinhole to film plane is 45mm. As you use larger formats the light falloff at the edges is greater.

5. Originally Posted by SMBooth
for any given pinhole diameter there is a focal length
Poorly stated again to the point of falsehood. A pinhole has no focal length, as it doesn't focus. It has a pinhole-to-film distance.

For any given pinhole diameter, there is a range of pinhole-to-film distances that gives a reasonably good balance of point spread and diffraction. Theory also often assumes a perfectly made pinhole in an infinitely thin material.

See bowzart's post for other considerations that need to be taken into account.

Lee

6. OK, I ran through some numbers ...

Typically a focal length equal to the diagonal of the film frame is provides a "normal" lens field of view.

Using the square root of the height squared plus width squared for a 6 x 7 frame comes out to about 9.3 cm = 93 mm for the frame diagonal dimension. The angle of view is about 53º.

Going into Pinhole Designer with a focal (pinhole to film distance) length of 93 mm, using 1.9, Rayleigh's constant, in the calculation, I get a pinhole diameter of 0.43 mm, which results in an effective aperture of f216.
If I use the constant of 1.6, which some folks use, I get a pinhole of 0.36 mm for f258.

For a bit wider angle by using a focal length of 60 mm -- approx 75º angle of view, I get a 0.35 mm pinhole diameter (f171) with the 1.9 constant. And 0.29 mm pinhole, f207, with the 1.6 constant.

Even wider, using 50 mm focal length -- approx 85º angle, I see 0.315 mm pinhole diameter (f159) with the 1.9 constant, and a 0.265 mm pinhole (f189) using a 1.6 constant.

In all, I used the PD default of 0.00055 mm for the light wavelength (green == mid-spectrum). Note that anything using numbers between those pairs of results will work, and indeed numbers some distance outside will also work to some extent. It's not a real tightly defined situation.

7. Originally Posted by DWThomas
OK, I ran through some numbers ...

Typically a focal length equal to the diagonal of the film frame is provides a "normal" lens field of view.

Using the square root of the height squared plus width squared for a 6 x 7 frame comes out to about 9.3 cm = 93 mm for the frame diagonal dimension. The angle of view is about 53º.

Going into Pinhole Designer with a focal (pinhole to film distance) length of 93 mm, using 1.9, Rayleigh's constant, in the calculation, I get a pinhole diameter of 0.43 mm, which results in an effective aperture of f216.
If I use the constant of 1.6, which some folks use, I get a pinhole of 0.36 mm for f258...
I agree with your calculations, but have a couple remarks:

There is such a thing as a Raleigh's constant, but it has nothing to do with Pinhole photography:
http://hal.archives-ouvertes.fr/docs...97132C1135.pdf
I think what you're referring to is simply the square root of the Airy disc's diameter (square root of 2.44 or 3.66, respectively). One maximizes sharpness (2.44). The other maximizes resolution (3.66).

You correctly referred to the angle of view, which is calculated from the negative-format diagonal and the focal length, but we need to make sure that we are not confusing it with the 'actual' angle of view, which is highly dependent on the thickness of the pinhole material and responsible for the image circle? (see attachment)

8. Originally Posted by RalphLambrecht
You correctly referred to the angle of view, which is calculated from the negative-format diagonal and the focal length, but we need to make sure that we are not confusing it with the 'actual' angle of view, which is highly dependent on the thickness of the pinhole material and responsible for the image circle? (see attachment)
I would agree with you that DWThomas correctly describes 'angle of view' as a product of film size and pinhole-to-film distance.

I think it's misleading and confusing to also call the restriction of the light path by the thickness of the pinhole material the 'angle of view'. Why use the same term for two entirely different effects? In my view the effect of the pinhole material thickness would much more accurately be described as 'angle of coverage' if we're choosing terms analogous to lenses.

Lee

9. Originally Posted by Lee L
I would agree with you that DWThomas correctly describes 'angle of view' as a product of film size and pinhole-to-film distance.

I think it's misleading and confusing to also call the restriction of the light path by the thickness of the pinhole material the 'angle of view'. Why use the same term for two entirely different effects? In my view the effect of the pinhole material thickness would much more accurately be described as 'angle of coverage' if we're choosing terms analogous to lenses.

Lee
Yes, I agree with that. That's more consistent. I will change my notes accordingly.

10. Originally Posted by RalphLambrecht
I agree with your calculations, but have a couple remarks:

There is such a thing as a Raleigh's constant, but it has nothing to do with Pinhole photography:
http://hal.archives-ouvertes.fr/docs...97132C1135.pdf
I think what you're referring to is simply the square root of the Airy disc's diameter (square root of 2.44 or 3.66, respectively). One maximizes sharpness (2.44). The other maximizes resolution (3.66).

You correctly referred to the angle of view, which is calculated from the negative-format diagonal and the focal length, but we need to make sure that we are not confusing it with the 'actual' angle of view, which is highly dependent on the thickness of the pinhole material and responsible for the image circle? (see attachment)
Enh, this is how the world works .... maybe another decade or two of instant worldwide communications will clear some stuff up. In Pinhole Designer, there is a pull-down for that constant value. One of the choices is "1.9 Lord Rayleigh." I was under the impression that he gets credit for the number, but can't say I've ever delved into it at any detail and may have misspoken. Anyway, perhaps I should say:
One popular magic constant is 1.9
That is a good point about the angle of view business. The numbers I posted were from using Pinhole Designer, but I'm sure it is based on the "perfect pinhole," an infinitesimally thick sheet of absolutely opaque non-reflective material with a perfectly round hole (since it's infinitesimally thick, it's got a knife edge for sure. As anyone who has tried it well knows, the ideal is only a goal and some of us don't get anywhere close to it. And at the minimum, the light fall-off is an issue of the hole becoming a narrower and narrower ellipse viewed from an angle off the pinhole to film axis, eventually a (closed) line at 90º. But that too can be complicated by the actual fabrication.

Anyway, the calculations I suggested above were to illustrate my approach to the original poster's question. You have to pick some basic parameter(s) and work out the rest. When I did my pinhole body cap for the SQ-A, the film format and film to pinhole spacing were pretty much fixed, so there was no point in agonizing over angle of view calculations, other than to learn what it was.

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