Lens verses Pinhole field of view.

[Grandpa Ron]

I was working with my 4x5 view camera trying to mount a view finder. To do this I needed to know the field of view for the various lenses. Also, when working with a pinhole It a difficult to aim the camera accurately as there is not much light reaching the frosted viewing glass.

The results, were surprising to me,

• The 123 mm lens is a bit of a wide angle view.
• The 165 mm lens is a "standard" view based in the diagonal measure of the film sheet.
• The f 357 pin hole is projecting an even closer view. The focal length was about the same as for the 123mm lens.

The actual pinhole image diameter is about 2 1/4 " so what you see is about 2 time actual size. What surprised me was, I expected the pinhole to have projected a much wider field of view, so I though I would pass this information on.

All of the shots were tripod mounted and 40 feet from the swing which is about six feet wide. I used a light meter to calculate the exposure. The f 357 pinhole was shot at about 15 sec.

 

[grahamp]

That's a pinhole without lens, at 123mm from the film onto 5x4 format? I am surprised you get a circular image. Either the pinhole material is thick, or there is some physical vignetting involved. My 'cigar box' pinhole will illuminate the corners of 5x4 at about 43mm from the film.

If you create a frame the size of the film, and mount it above the pinhole (or lens board), and put a peephole sight at the film plane in the center of the frame, what you see should be what you get if the pinhole can illuminate the corners. Unless you use a retrofocus or telephoto lens, this film to optical center arrangement will work. You see it on technical cameras like the MPP.

 

[DWThomas]

Yes, I'm with grahamp, I have a homebrew 4x5 pinhole with pinhole to film plane distance of 62mm and it fills the frame. There is some light fall-off but no actual vignetting. I have found (the hard way naturally) that a pinhole plate doesn't have to be recessed very far into a mounting to start clipping off corners. I had to totally redo a fancy sheet metal shutter mechanism I built on a Bronica body cap after discovering the stacked up depth of the various components got in the way of light rays.

A conventional lens sort of collects light at the front element which is typically out ahead of much of the mount, and funnels those hapless light rays down through various contortions and projects them out of the rear element. With a pinhole, the mechanism is strictly straight line ray tracing. A pinhole plate mounted on the back of a 1/4 inch plywood "lens board" might need a 5/8 or 3/4 inch hole in the plywood to prevent picking up the front edge of the mounting.

All this depends on the specific camera geometry of course, but my two "best" cameras are rather wide angle, around 100º diagonal field of view. The other potential problem is literally drilling a pinhole in a relatively thick plate -- material with thickness several times the pinhole diameter. The pinhole, which is ideally cut through an infinitesimally thin plate, starts to become a tunnel and the edges cut off the light for relatively small off-axis angles even though the clear diameter meets the required f-number calculations. One could wade in with trigonometry (but no, I'm retired! ) or draw an enlarged scale proportional representation and trace lines/light rays to do thought experiments on this.

 

[MattKing]

Grandpa Ron,
I'm afraid your pinhole is more of a pin-tunnel.
What material is it drilled/puched/lasered through?

 

[Grandpa Ron]

I have to agree and there is no one more surprised than I was. People describe pin holes as having well over 100 degrees of coverage.The pinhole is quite simple, it is an aluminum pop can sanded smooth on both sides, pierced with a .36 mm needle, then the inner dimple sanded off. I doubt metal at the pin hole is even .08 mm thick.

However, grahamps and DWs comments on possible vignetting was a forehead slapping moment. My shutter assembly came from a toy camera and it sit about 6 or 7 mm behind the pinhole. So it would appear the size of the shutter hole, vignettes the wide angle image from the pin hole. While not an easy fix, I will reverse the situation and put the shutter in front of the pinhole. Thank for the information.

 

[ic-racer]

The pinhole angle of view on the film frame will be inversely proportional to the distance from the pinhole to the film.
For example if one wants a narrow angle of view, one places the pinhole far from the film plane and vice versa. Mechanical vignetting reduces the angle of view and larger film size increases the angle of view.

 

[MattKing]

My shutter assembly came from a toy camera and it sit about 6 or 7 mm behind the pinhole. So it would appear the size of the shutter hole, vignettes the wide angle image from the pin hole. While not an easy fix, I will reverse the situation and put the shutter in front of the pinhole.

Are you sure that this will solve anything.
If it vignettes when behind, it will probably vignette if in front.

 

[DWThomas]

Dredging back through some files on the box here, I found an example of a scaled layout I used with the Bronica body cap unit I mentioned (thus the 57x57mm film format). The technique would apply to any format with the appropriate numbers and line layout. It's not exactly a tutorial but I think you can see the technique. It's basically a ray tracing exercise. The larger you make the drawing, the more accuracy you can achieve. It is desirable to measure as accurately as possible the actual diameters and spacings of the mechanical gizmos around the pinhole plate area.

(Since the filename has "Apug" in it, I must have posted before ca. 2013!)

 

[Grandpa Ron]

Matt,

You are correct, I doubt simply switching the pin hole position would solve the problem. So I removed every thing from the lens board.

The lens board is 1/4 inch thick, so I drilled a 7/8" hole in the center, mounted a .016" pinhole in the to center. 7/8" should be large enough to prevent vignetting at a 1/4" thickness.

The shutter arrangement is a bit of a Rube Goldberg type invention. Since all I really needed was the spring return on the shutter lever, I mounted a 1 1/4" x 1 1/4" black paste board shutter directly to shutter lever. I push the shutter lever with a remote release.

My objective is to try to duplicate some the original pinhole scenery and stationary object type photos. So far I have found that at f 250 and f 360, reciprocity has not been much of an issue. With some luck I will be able to contact print my 4x5 negatives and eliminate the computer scanning issues.