Pinhole field of view.

[Grandpa Ron]

When taking a pinhole picture I have always wondered how much of the scene am I capturing? So, while setting up some experiments with my pinhole and view camera I noted the following results for an f 256 and f 500 pinhole setup.

The subject was an old oil well pump exhibit at the State Park on a sunny day with light winds. My reference photo was taken with a tripod mounted 4"x 5" cut film view camera, using a 127 mm lens. The distance to the pump was approximately 100 ft (30 meters). All these photos are uncropped, full frame 4x5.

Reference photo....... 127 mm lens at 30 meters.

Next, the lens was replaced with a .46 mm (.018") pinhole and the bellows extended to 117 mm (4.6") giving me a f 256 aperture. The image projected by the pinhole onto the 4x5 film has about the same field of view as the 127 mm lens. There does seem to be some vignetting of the leaves directly above the camera.

f 256 Aperture at 7 sec. with 200 ISO film.

Next the bellows were extended to 228 mm (9.0") with the same pinhole making an f 500 aperture. As you can see, with the pinhole projection being spread out over a larger circle, the 4x5 film captures far less of the total image. This gives a mock-telephoto image. Also, the smaller aperture does improve the sharpness. However the vignetting also appears to increase.

f 500 Aperture at 30 sec. with 200 ISO film.

The point of this post is to give the new comers an Idea of what it expect. In particular the advantage of larger format negatives. At this point I have reached the limit of my bellow extension so my next attempt will be to produce a .254 mm (.010") pinhole. I could buy a laser cut pinhole but that does no match my "home brewed" nature. Comments are always welcome.

 

[ic-racer]

The focal length of the pinhole is simply the distance to the film; it is a zoom not a telephoto.

 

[Grandpa Ron]

ic-racer,

You are correct. This point has been discussed before.

By definition Telephoto implies the use of a lens to magnify and object, making it look closer or larger than normal. Since a pinhole camera does not use a lens it cannot magnify an image.

Instead a pinhole projects an image. The farther the projection the larger the image. Zoom is probably more accurate as it implies a smooth transition from near to far and back, without a reference to a lens.

Unfortunately when looking up the definition of Zoom in today's dictionary parlance, when referring to image viewing; in many of the definitions, zoom has become synonymous with telephoto.

Hence I chose mock-telephoto to indicate a similar effect but zoom would be more accurate.

 

[MattKing]

By definition Telephoto implies the use of a lens to magnify and object, making it look closer or larger than normal.

Actually, telephoto refers to a lens whose nodal point is outside the body of the lens, thus allowing the lens to be physically shorter than its focal length.
A retro-focus lens is similar, in reverse. It allows a short focal length lens to have a nodal point that is farther away from the film plane or sensor.
Telephoto doesn't refer to magnification. Telephoto lenses may, however be useful in increasing the apparent magnification, because they permit you to have a longer focal length in a shorter lens body. But long lenses aren't always telephoto lenses.

 

[MattKing]

That being said, thanks for the illustrations of field of view. That field of view is, of course, entirely determined by the size of the film (or sensor) and the physical distance between the pinhole and the film (aka the focal length). The size of the pinhole doesn't affect the field of view.
My "manufactured" pinhole camera has raised bumps on the top surface that help me align the edges of the frame. You could draw your own with a ruler if you have a camera with a suitable flat surface.

 

[grahamp]

Make a frame the size of the film frame, and position it above the pinhole. Put a peep sight at the film plane. If you are using a bellows camera and rack it out, the frame will adjust and maintain the correct field of view. There will be a little parallax - maybe the width of the film frame. It becomes unwieldy when the pinhole to film distance gives you something wider than maybe 100 degrees because you cannot see all the frame at once. It does not have to be attached to the camera - just old it in place while you work out your frame.

This is just a variation on a viewing frame, but if you have a camera where the pinhole to film distance can be varied it can be useful.

 

[Grandpa Ron]

Matt,

Interesting discussion on lens nodal points. I learn something new every day. However, for the sake of this post, I simply wanted to indicate the apparently enlarged view.
Since the dictionary defined telephoto as; tel·e·pho·to /ˈteləˌfōdō/..noun...1. a lens with a longer focal length than standard, giving a narrow field of view and a magnified image.
I chose mock-telephoto to describe the effect of a narrower field of view and a larger projected image of the pinhole.

Your summery is spot on "That field of view is, of course, entirely determined by the size of the film (or sensor) and the physical distance between the pinhole and the film (aka the focal length). The size of the pinhole doesn't affect the field of view."

If I recall properly, I calculated a 2 f stop focal length change based on my .018" pinhole. I wanted to see the difference in sharpness of the photo. Since the projection is independent of pinhole size, I am curious how much larger the projected image would be at the longer focal length?

 

[MattKing]

Since the projection is independent of pinhole size, I am curious how much larger the projected image would be at the longer focal length?

As large as your film.
If you had 8x10 film the same distance from the pinhole, the image would have filled that as well. The size of any element in the scene will be the same on either film - its just that the 8x10 film will have a lot more of the scene outside of the edges of what shows on the 4x5 film - you would see more of the park than what you see on the 4x5.
All subject of course to the limitations of any physical vignetting, as well as cosign falloff of light intensity.
The "magnification" - the ratio between the size of the subject and the size of the image on the film - is purely a function of the focal length.

Since the dictionary defined telephoto as; tel·e·pho·to /ˈteləˌfōdō/..noun...1. a lens with a longer focal length than standard, giving a narrow field of view and a magnified image.

That definition is wrong - but it does reflect a common misunderstanding.
The thing about pinholes, in contrast to lenses, is that no light is bent by a pinhole. Everything just goes straight through that tiny hole, and continues straight to the film.
Excluding the role of diffraction, which only affects clarity and resolution.
Draw a line from the corner of the film, through the pinhole, and then straight out to the scene in front of you. It will cross the scene at the corner of what will show on the film.

 

[MattKing]

And it is really important to understand that the size and subject content of your image is not in any way affected by the size of the pinhole - the size of the pinhole only affects the clarity and resolution of the result.
If you have a pre-existing pinhole, it makes sense to design a camera with a focal length that goes well with that size. The actual image you obtain will depend on the size of the film you put at that distance away from the pinhole. A piece of 35mm film will show just a little bit of the scene in front of the pinhole; a 6x9 piece of film will show more of the scene in front of the pinhole; a 4"x5" piece of film will show even more of the scene in front of the pinhole and if you should be so crazy as to try to use an 11"x14" piece of film it will show vastly more of the scene in front of the pinhole than the smaller options - subject to any physical vignetting and cosign fall-off concerns.
Typically, you work the other way.
You start with the film size you want to work with.
Then you decide which angle of view you want to obtain with your camera.
That determines what focal length you are working with.
And then you use the calculator to determine what pinhole size you need to optimize the clarity and resolution of your images.

 

[RalphLambrecht]

As large as your film.
If you had 8x10 film the same distance from the pinhole, the image would have filled that as well. The size of any element in the scene will be the same on either film - its just that the 8x10 film will have a lot more of the scene outside of the edges of what shows on the 4x5 film - you would see more of the park than what you see on the 4x5.
All subject of course to the limitations of any physical vignetting, as well as cosign falloff of light intensity.
The "magnification" - the ratio between the size of the subject and the size of the image on the film - is purely a function of the focal length.

That definition is wrong - but it does reflect a common misunderstanding.
The thing about pinholes, in contrast to lenses, is that no light is bent by a pinhole. Everything just goes straight through that tiny hole, and continues straight to the film.
Excluding the role of diffraction, which only affects clarity and resolution.
Draw a line from the corner of the film, through the pinhole, and then straight out to the scene in front of you. It will cross the scene at the corner of what will show on the film.

that's how I see it too.This way simple trigonometry should give you your field of view.

 

[DWThomas]

I generally begin with the film format (as in mask dimensions) and then look at angle of view for various pinhole to film distances. Even there one may choose between horizontal, vertical, or diagonal angle of view. In the case where I made a body cap pinhole attachment for an SLR, that pretty much set the pinhole to film plane, so there the angle of view is what it is.

Once that's nailed down I look at the pinhole diameter. Even that has some variables that may be of interest -- the wavelength of the light which might be important for some ortho film or when using a filter. In the typical equation there's also a magic constant that can be tweaked which can possibly affect center vs edge sharpness. In general the process is tiptoeing around the question of diffraction at very small apertures. So far my efforts have been from 6x6 cm to 8x10 inches for which optimum hole diameters run between f/200 and f/350

At very wide angles, even if the pinhole is "perfect," assuming a flat film plane, the further you get from the central axis, the longer the pinhole to film distance becomes, effectively making the f-stop even smaller. Also as we move further off-axis, the pinhole opening appears as a narrower and narrower ellipse, further reducing the light. The compounding of these effects will be a noticeable light fall-off in very wide implementations. (But it should be a gradient not any sudden change.) My two widest beasties are about 92 to 104º diagonal angle of view. That begins to show some fall-off, but isn't terrible.

I've tried a frame viewfinder on one camera but found, as described upthread, it was very difficult to use. My latest wide cameras have some little dowel pegs on the top and side that can be sighted along to get an idea of coverage. They aren't quite NASA precision, but help. My first pinhole camera in this millennium used a custom lensboard in a B&J 4x5 Press. The camera has a wireframe finder on the front standard and a flip-up rear sight on the back of the camera so it actually adjusts for various pinhole to film spacing.

I suppose I could really dive down the rabbit hole with spreadsheets and all -- I have some background for it -- but I tend to treat pinholery as an opportunity to be loose -- like in baking bread without a recipe! It's always fun to see what happens. (And yeah, every now and then you get something good for a doorstop but it looks pretty.)