How to eliminate vignetting in pinhole photos?

[Kuenp]

How to eliminate vignetting in pinhole photos?

The diameter of the pinhole is approx 0.4mm, in aluminum foil.
The pinhole is approx 1.5~2mm from the camera's lens mount.
The size of the image is about that of 22~23mm wide angle.
The issue:
1.Vegnitting on both sides of the image.
2.Fade greysh tone on top and bottom side.

How to eliminate the vignetting, please?

Thanks.
Kuenp

 

[loccdor]

You can buy a laser-cut pinhole if you want more predictable optical effects. But vignetting is a normal and expectable effect in pinhole photography. Think of a circle drawn on a piece of paper. Now turn that paper 45 degrees. The circle now has less area in your 2-dimensional optical view and as a result will pass less light. This is what happens in the corners of a pinhole image that causes vignetting.

Since this appears to be in the wrong forum and is a question about digital photography, I'll also provide a digital answer: use the pinhole to take a picture of a perfectly illuminated white image like a white TV. Then, in image editing software, use this layer on the "Divide" blending mode on your pinhole images. This will counteract the vignetting.

 

[Dustin McAmera]

Once you've set the geometry of the camera and pinhole, I don't think you can change the vignetting (except by post-processing).
The vignette happens for a number of reasons:
* at the edges, the light has travelled further, so has spread out more
*the light at the edges is also arriving on the sensor/film at a more acute angle
*the light is also passing through the pinhole at that acute angle, so the hole is effectively smaller for the edge areas.

You get less vignetting by moving the pinhole further from the sensor/film, so you just don't use the light that comes through at very acute angles. But then you then don't get such a wide-angle view, and those views are sometimes interesting.
If you are still at the stage of designing your camera, and if you use film, you can lessen the vignetting by passing the film in a curved path, so the light arrives at a right angle.

 

[Kuenp]

How to eliminate vignetting in pinhole photos?

The diameter of the pinhole is approx 0.4mm, in aluminum foil.
The pinhole is approx 1.5~2mm from the camera's lens mount.
The size of the image is about that of 22~23mm wide angle.
The issue:
1.Vegnitting on both sides of the image.
2.Fade greysh tone on top and bottom side.

How to eliminate the vignetting, please?

Thanks.
Kuenp

 

[koraks]

I've merged two threads on the same issue, hence the redundancy between some of the posts.

 

[koraks]

How to eliminate the vignetting, please?

By making the film plane curved, so the angle of incidence of the light is perpendicular all across the image. Since you're shooting digital, this isn't possible. The only thing you can do is correct it in digital post production.

 

[grain elevator]

Everything written above is true. Just two additional considerations: with such a wide angle of view, it really matters that the pinhole is cleanly made, i.e. no burrs and if it's thick material, angled or thinned out edges, as otherwise more light coming in at an obligue angle will be blocked.
Then there's also the remote possibility of mechanical vignetting, i.e. some part of the camera, lens hood etc. being in the image. But it doesn't look that way.
Edit: I just re-read your post. Since it's aluminium foil, burrs could really be an issue if you just poked the hole with a pin.

 

[DWThomas]

Edit: I just re-read your post. Since it's aluminium foil, burrs could really be an issue if you just poked the hole with a pin.

This is an important point. A pinhole should be a clean round hole with a knife-like edge, no burrs or upset, for best results. My best homemade pinholes have been in 0.002 inch (.05 mm) brass shim stock using the "dimple and sand" method with #400 wet-or-dry sandpaper used wet.

I have only shot film for pinhole, but I vaguely recall that in the past digital sensors had some quirks related to the angle of incidence of light rays. Not sure what that situation is these days, but it could compound the simple and inevitable fall-off at wide angles. In my film pinhole cameras I find a diagonal angle of view can get up to 90 to 100 degrees without becoming too bad. (But at 180º it would go to total blackness, so it has to end somewhere!)

 

[Kuenp]

By making the film plane curved, so the angle of incidence of the light is perpendicular all across the image. Since you're shooting digital, this isn't possible. The only thing you can do is correct it in digital post production.

Thank you.
"The only thing you can do is correct it in digital post production."
Yes, Photoshop can lighten up the vignetting edges a little bit, but very hard to eliminate it.

 

[Kuenp]

Everything written above is true. Just two additional considerations: with such a wide angle of view, it really matters that the pinhole is cleanly made, i.e. no burrs and if it's thick material, angled or thinned out edges, as otherwise more light coming in at an obligue angle will be blocked.
Then there's also the remote possibility of mechanical vignetting, i.e. some part of the camera, lens hood etc. being in the image. But it doesn't look that way.
Edit: I just re-read your post. Since it's aluminium foil, burrs could really be an issue if you just poked the hole with a pin.

Thank you.
"it really matters that the pinhole is cleanly made, i.e. no burrs and if it's thick material, angled or thinned out edges,"
Cleaned the edge of pinhole both sides with a very fine abrasive stick (stone). The best I could do. The material is a piece of aluminum foil, medical quality, thin and fine.

 

[Kuenp]

This is an important point. A pinhole should be a clean round hole with a knife-like edge, no burrs or upset, for best results. My best homemade pinholes have been in 0.002 inch (.05 mm) brass shim stock using the "dimple and sand" method with #400 wet-or-dry sandpaper used wet.

I have only shot film for pinhole, but I vaguely recall that in the past digital sensors had some quirks related to the angle of incidence of light rays. Not sure what that situation is these days, but it could compound the simple and inevitable fall-off at wide angles. In my film pinhole cameras I find a diagonal angle of view can get up to 90 to 100 degrees without becoming too bad. (But at 180º it would go to total blackness, so it has to end somewhere!)

Thank you.
"My best homemade pinholes have been in 0.002 inch (.05 mm) brass shim stock using the "dimple and sand" method with #400 wet-or-dry sandpaper used wet."
Wonder if you used a precision-machine to achieve the size and shape of the hole.

 

[Kuenp]

You can buy a laser-cut pinhole if you want more predictable optical effects. But vignetting is a normal and expectable effect in pinhole photography. Think of a circle drawn on a piece of paper. Now turn that paper 45 degrees. The circle now has less area in your 2-dimensional optical view and as a result will pass less light. This is what happens in the corners of a pinhole image that causes vignetting.

Since this appears to be in the wrong forum and is a question about digital photography, I'll also provide a digital answer: use the pinhole to take a picture of a perfectly illuminated white image like a white TV. Then, in image editing software, use this layer on the "Divide" blending mode on your pinhole images. This will counteract the vignetting.

Thank you.
"But vignetting is a normal and expectable effect in pinhole photography."
A great comfort to me. Thanks.
"Since this appears to be in the wrong forum..."
Sorry for this. My mistake.
"... take a picture of a perfectly illuminated white image..."
Thank you very much for the valuable instruction.

 

[Kuenp]

Once you've set the geometry of the camera and pinhole, I don't think you can change the vignetting (except by post-processing).
The vignette happens for a number of reasons:
* at the edges, the light has travelled further, so has spread out more
*the light at the edges is also arriving on the sensor/film at a more acute angle
*the light is also passing through the pinhole at that acute angle, so the hole is effectively smaller for the edge areas.

You get less vignetting by moving the pinhole further from the sensor/film, so you just don't use the light that comes through at very acute angles. But then you then don't get such a wide-angle view, and those views are sometimes interesting.
If you are still at the stage of designing your camera, and if you use film, you can lessen the vignetting by passing the film in a curved path, so the light arrives at a right angle.

Thank you.
"I don't think you can change the vignetting (except by post-processing)."
Tried in Photoshop to to reduce the dark shape of the vignetting. Yes, it helps but not eliminates the whole vignetting. And, by the way, I do not want the vignetting be removed completely because that would lose the flavour of home made pinhole image.
"You get less vignetting by moving the pinhole further from the sensor/film,"
I want to use this home made pinhole camera, with a field of view of an ultra-wide angle, around 21~23mm, for some street shootings of people in close range yet not showing their faces.

 

[MattKing]

Ultra wide angle imaging will inevitably show darkening on the edges and at the corners if you are using either a flat sensor or a flat piece of film.
The simplest way to think of/visualize this is that the edges and corners are farther from the pinhole or lens than the centre is, so the light is spread out more, and is therefore less bright. This is more properly referred to as the cosine effect, and the mechanism is more complex than the picture drawn by my explanation, but that way of thinking of it makes it easy to understand.
People who do this with large format film cameras and ultra-wide lenses either accept the darkening, or employ a centre filter that dims the centre of the image, in order to make it come close to matching the intensity of the edges.

 

[DWThomas]

Thank you.
"My best homemade pinholes have been in 0.002 inch (.05 mm) brass shim stock using the "dimple and sand" method with #400 wet-or-dry sandpaper used wet."
Wonder if you used a precision-machine to achieve the size and shape of the hole.

What I have done is lay the brass shim stock on a piece of 4-ply mat board, or super smooth wood surface, so the sheet is supported but the support allows a bit of give. I then carefully push a needle against the shim stock to produce a sort of dimple (as viewed from above -- looks more like a pimple from the underside). It is not necessary to puncture the brass sheet, just create the bump. This means almost any sized sewing needle will work. Then I sand using #400 or #600 sandpaper with some water on the brass.

Use light pressure and small circular motion until a hole opens in the bump. Start small and work up to the desired size. The original needle can be put in a pin vise and gently spun in the hole to burnish the edges, keep the hole circular, and perhaps open it up a little. Do this in increments until you get the desired hole size. Sanding the bump down to the sheet surface produces a knife edge which is desirable.

A miracle! I found a quick sketch posted long ago ...

For measurement I happen to have a small 50x hand microscope that has an etched reticle for direct measurement, but I know others scan the plates and count pixel widths or something. With a magnifying loop and a fine machinist's scale you can "guestimate" an approximation. What constitutes optimum is a rather broad curve anyway (in my opinion).

A couple of earlier articles on the topic:
Article 1
Article 2

Years back I made some with 0.001 inch stock, but it is very hard to handle, and in the case of my big 8x10 camera the plate developed a crack from stress, perhaps the wood expanding with humidity. Sanding on something that thin can impair the robustness of the plate. I chemically blacken the plate using some mysterious goop used to blacken or "weather" brass model railroad locomotives, but some say sulfide toner works also.

 

[Nick Dvoracek]

As mentioned earlier, vignetting is an inevitable effect of short distances to the pinhole because f increases toward the edge (on my 30mm camera the corner of the frame is 45mm from the pinhole - f=distance/aperture) and because the pinhole gets foreshortened into an oval which has a smaller area.
The way I deal with it, in Photoshop, but also in the darkroom if I was going to do it that way, is burning and dodging, adjusting the range and exposure of the tools constantly for that particular spot in the image since exposure is going to vary quite bit.

 

[xkaes]

What is shown in the image is light fall-off, not vignetting. To use the same label for both phenomenon -- which many people do -- simply confuses the conversation.

Also, the pin hole is not the correct size for the focal distance. If it were, the image would be more clear -- especially in the center of the image. Here's a page to compute the size of the pinhole:

http://www.subclub.org/fujinon/pinmath1.htm

 

[NedL]

Ultra wide angle imaging will inevitably show darkening on the edges and at the corners if you are using either a flat sensor or a flat piece of film.
The simplest way to think of/visualize this is that the edges and corners are farther from the pinhole or lens than the centre is, so the light is spread out more, and is therefore less bright. This is more properly referred to as the cosine effect, and the mechanism is more complex than the picture drawn by my explanation, but that way of thinking of it makes it easy to understand.
People who do this with large format film cameras and ultra-wide lenses either accept the darkening, or employ a centre filter that dims the centre of the image, in order to make it come close to matching the intensity of the edges.

I do think this is the main effect until you get close to the edges. "Squint" is also a factor, and angle may matter more with a digital sensor.