# Talk:Pinhole camera

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## Calculating the f-stop & required exposure

"The f-stop of the camera may be calculated by dividing the diameter of the pinhole into the focal length of the camera" The f-stop is the aperture, isn't it? shouldn't it say exposure time? Shouldn't it be "focal length"/"diameter"="exposure time"?

The f-stop is not just the aperture size, but rather the ratio between aperture size and focal length, if I remember right. 128.163.235.175 (talk)

== DOF clarif

The article states: The depth of field is basically infinite, but this does not mean everything will definitely be in focus. Depending on the distance from the aperture to the film plane, the infinite depth of field means everything is either in or out of focus to the same degree.

It's not clear to me why infinite depth of field doesn't put everything in focus. The depth of field page did not help on this matter. Maybe I'm dense, but perhaps this article could explain this non-intuitive concept a bit more explicitly, at least as it applies to pinholes. --Ds13 03:03, 21 April 2006 (UTC)

A pinhole camera has a optimum distance between the pinhole and the imaging plane, which is the focal length. (Although that concept doesn't really make sense for pinhole cameras, as pinholes don't actually focus light.) All infinite depth of field means is that the focus is independent of distance (every distance is equally sharp), but the image can still be fuzzy if you deviate from the optimum distance (equally sharp does not imply sharp). --69.108.112.130 19:04, 9 November 2006 (UTC)

I'm pretty sure that a pinhole camera does not have an optimum distance between the pinhole and the imaging plane. As the imaging plane is moved further from the pinhole (i.e. "focal length" increased), the image gets larger, dimmer, and sharper. A user might choose an optimum image distance that suits their needs; say some distance where the image is both sharp enough for them and bright enough for them. But I don't think this is the same thing that the above commenter wanted to mean by optimal "focal length." I think user Ds13's question is a good one, and I'm going to delete the text that lead to the confusion. 128.163.235.175 (talk)

I think my earlier comment is basically wrong, and is perhaps disproved by the formula in this section of the article, that defines the optimal pinhole size in relationship to the "focal length" (distance from image plane to pinhole, in this case). I'm assuming that this formula gives the sharpest image? So that a larger pinhole increases blur due to plain old geometry, and a smaller pinhole increases blur due to diffraction? I still think that this part of the article is not as clear as it should be. If anyone agrees with me and knows how to improve it, go ahead; I'm not sure that I'll have the time to get to the bottom of this. 128.163.235.175 (talk) —Preceding comment was added at 16:18, 25 April 2008 (UTC)

I agree. Larger pinhole diameter will increase geometric blurring and decrease diffractive blurring. I found this page while investigating how those two effects work together, and I still haven't found a complete answer. There should be some reference in here about Airy disks, the Rayleigh Criterion, and the Circle of confusion. And the explanations could use some general clean up. The fact that the focal length is just the distance from the hole any image plane should be made prominent. I think the detailed mechanics of how a pin hole camera works should get a lot of attention in this article, since pinhole cameras are more interesting for demonstrating basic optics than they are as a practical camera. Pulu (talk) 22:12, 19 February 2009 (UTC)