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Sometimes people say that a lens has bad vignetting but it looks very similar to the effect of pinhole (darkened edges).

What's the difference?

If someone asked to have a vignetting effect (in PP) and someone else asked for a pinhole effect, what would you do different?

Also, if you look at a photo, can you tell if it was due to pinhole or vignetting?

Is it simply that vignetting happens at open apertures and pin-hole happens in closed apertures? (Thus resulting in quite different shutter speeds)?

EDIT: Great, thanks for your answers guys! But I'd like to add something. If I was to draw a graph of Vignetting versus Aperture (in general terms), would it look like a reversed bell curve?

eg:

Rough graph

If so, why?

Example:

Taken from Lenstip

From Lenstip.

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why would it go up? The open aperture allow light to reach the sensor that is partially occluded by the edge of the front element, and stopping it down will remove these rays of light. Stopping down further won't allow you to see those edges suddenly as it doesn't increase your FOV. The equivalent pinhole size doesnt decrease, because the front element where the light enters is still as large as it was wide open. Wide FOV increases the probability of seeing the edges. If you add a filter on a lens you increase the equivalent "pinhole thickness" and can see more vignetting, esp. on wide lenses. –  Michael Nielsen Jan 25 '13 at 10:06
    
Another vignet you can get is sensor vignetting as the pixels (e.g. with microlenses) also have en optimal incident angle, and if the light reaches the sensor from a larger angle, you will see vignetting. –  Michael Nielsen Jan 25 '13 at 10:08
    
@michael Why would it go up where? At the open aperture or closed, pinhole sized aperture? I have no idea. That's why I'm asking. And I'm happy to be told that my graph is not the case. I perfectly understand why a pinhole creates vignetting, it's obstructing light, but why does a wide angle lens and wide aperture create it? I think I kinda get it by your wording, but diagrams would be great! :) –  BBking Jan 25 '13 at 11:20
    
It doesnt go up when stopping down. The wide angle lens also obstruct the light in a more complex manner (internally in the lens), where only the rays that hit somewhat straight pass through unobstructed, and rays that hit at a wide angle only partially make it to the sensor. The "objective" (the correct term for a lens) is a complex set of lenses where the light rays bounce around internally, collected by the large front element and redirected to hit a smaller image circle in the camera body. The construction of these many lenses it what defines the final results in contrast, fringing, ... –  Michael Nielsen Jan 25 '13 at 13:10
    
...sharpness, vignetting and what not. So the optical vignetting is not really different than mechanical vignetting, just the complexity in the route the rays take before getting obstructed. the-digital-picture.com/Canon-Lenses/Canon-Lens-Vignetting.aspx –  Michael Nielsen Jan 25 '13 at 13:12

4 Answers 4

up vote 1 down vote accepted

There are multiple causes for the light falloff which we call vignetting. In lenses, the primary causes are:

  • Poor response to light rays hitting the sensor at a strong angle. That's normal for wide angle lenses, and is fundamentally more of a problem at wider apertures. It's also significantly more problematic in digital sensors than in film, which is why the Four Thirds standard emphasizes telecentric lens design.
  • Physical obstructions like lens hoods, filter rings, or even internal lens elements. This reduces the effective image circle size, and again is more problematic at wide angles and wide apertures. (Sometimes people make a distinction between external and internal obstructions, but it really comes down to the same thing.)

As you stop down or zoom out, you get to the point where these factors have zero impact inside the area captured by the sensor.

The vignetting associated with pinhole lenses occurs for a different reason: it happens when the size of the aperture approaches the thickness of the aperture material itself. That doesn't happen in normal lenses because: A) the aperture blades are quite thin and B) even the smallest apertures are much bigger than the f/200 and smaller common to pinhole lenses.

(This may be related to Do rounded edges on aperture blades improve image sharpness, and how?, but I can't make any promises on that score.)

It's also really a special case of physical obstruction — rays from too wide of an angle hit the side of the aperture material — but one which occurs in a different case from what we see in typical lenses.

So, for your chart, we'd be looking at a less symmetrical curve, where the effects of the first causes disappear at smaller apertures used in normal lenses, and the pinhole cause doesn't appear until much later. (I've entirely made up the numbers and the particular curve here; they're for illustration, and don't take into account any actual lens or aperture material.)

chart

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is the side after your chop "f/256" where the aperture approaches the thickness of the aperture blades? –  Michael Nielsen Jan 25 '13 at 18:47
    
@MichaelNielsen Yes, exactly. Again, the actual numbers and curves are not necessarily to scale; they're just meant to be illustrative. –  mattdm Jan 25 '13 at 18:54
    
Great! Thank you. What I also learnt is that yes, vignetting is vignetting, but there are different types. Optical, where the graph would be on the left and Mechanical, which would be the right side. So overall vignetting would be your graph, but different graphs for different types. Thanks again! –  BBking Jan 28 '13 at 23:19
    
Well, some sorts of physical vignetting would be on the left — a lens hood or filter would work that way. The distinction between that and "optical" vignetting is generally whether or not the obstruction is inside the lens, and by that rule the pinhole vignetting is optical. I think it's more useful to call it something distinct, though. –  mattdm Jan 29 '13 at 0:03

Vignetting is vignetting. And vignetting can occur with a pinhole camera for the same reason it happens with a fancy lens. When thickness of the material is close to the pinhole diameter the rays are cut off in the Field of View.

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Thickness of what material? –  BBking Jan 23 '13 at 23:00
    
Thickness of the material in which the pinhole is made. –  Bart Arondson Jan 23 '13 at 23:04
4  
Correct. Punch a hole in a thin paper and your FOV is huge, punch it into a thick MDF sheet and you have a telepinhole in the middle of your photopaper, if you get a magnification glass to see it. –  Michael Nielsen Jan 24 '13 at 8:04
    
Hah, I like that...telepinhole. :D –  jrista Jan 25 '13 at 6:44

I believe with a pinhole, the vignetting is largely due to light falloff (inverse square law). The distance from the pinhole to the edges of the sensor/film is longer than to the middle of the sensor/film.

With lenses, the rear element is of a similar size to the sensor (compared with a pinhole) so the light falloff is not a big factor. Vignetting can occur due to obstructions like lens hoods or by the lens elements themselves ( as the Wikipedia article states

Rear elements are shaded by elements in front of them, which reduces the effective lens opening for off-axis incident light

As far as your question - can you tell the difference - I would imagine lens vignetting is typically a subtle effect mainly occuring in the corners, whereas the pinhole effect would be more noticeable even towards the center of the image. So to me in PP if you wanted to do a "pinhole" effect you'd make it more pronounced with perhaps a sharper transition.

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Every lens, whether made of glass or a tiny hole in card, creates an image circle, which fades to black towards the edges. When you close down the aperture in lens based cameras, the soft edge of the image circle hardens, matching the increased depth of field (it's basically an out-of-focus image of the physical edge of the lens). Hence, with wider apertures, vignetting is more common when you take photographs with lens-based cameras.

With a pinhole camera, the image circle is theoretically infinite in size, as light passes through the hole at all angles. However in practice, there is a physical thickness to the medium in which the hole is made, which results in light fall-off towards the edges as the effective size of the hole decreases with the greater angle of incidence.

The net result is that the type of vignetting you see from pinhole cameras is of a different character to that from lens based cameras. Vignetting is often added in post-production for aesthetic reasons (it's not always seen as a bad thing) and how it is applied will determine whether the image looks like it was taken with a pinhole camera.

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