Is a lens necessary for producing focused images?

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luckis11
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luckis11 said:
There's blurness behind the lens except a particular distance behind the lens. This means that there's blurness in front of the lens, yes or no? And, why yes, or why no? Obviously no because seeing without an (outside the eye) lens, there's no blureness, but we need a lens to see and to photograph, so...?

DaveC426913 said:
Inasmuch as, if you placed an imaging plane there, it would not produce a focused image, yes. Because an image can only form when the rays falling on point X on the imaging plane all came from point X' in the scene (and no rays from points Y' or other - do). Nowhere does this occur except at the focus of the lens. If too many rays from disparate parts of the image fall on a given image point, that point will not decipherably represent the image.

But if this is so, then in these photographs:
http://en.wikipedia.org/wiki/Bubble_chamber
http://en.wikipedia.org/wiki/Cloud_chamber
the "particle track - line of bubbles" shouldn't be able to be photographed so defined, but blureness should be photographed instead, since-if no lens was used! Correct?

Was a lens used?From the most detailed discriptions of the experimental apparatuses, it seems that no lens was used, but actually in all such descriptions it is not clear if lens was used or not.
 
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HallsofIvy, I edited my post, correcting it and clarifiying what you asked me.
 
No lens, no picture. If there is a lens, there is a DOF which you can control with aperture.

That is, you can take a picture using a lensless pinhole camera, which - at least in theory - has infinite DOF. That would make whole discussion a moot. But pinhole cameras are probably way too dark for fast pictures.
 
You are guessing of what exactly happened in the bubble champer, aren't you? I made the same guess myself, so what, I still have to ask someone who's 100% certain.
 
luckis11 said:
You are guessing of what exactly happened in the bubble champer, aren't you? I made the same guess myself, so what, I still have to ask someone who's 100% certain.

No he is not guessing. You are looking at a photograph of a bubble-track .. it was taken with a camera. For a given f-stop, a camera will have a certain depth of field .. read the wiki on depth of field that Borek posted. It answers the question *I think* you were asking in your original post, although it wasn't exactly clear what you were asking ...

[MODERATOR] It doesn't seem like this thread belongs in Quantum Physics? Wouldn't General Physics be more appropriate?
 
SpectraCat said:
You are looking at a photograph of a bubble-track .. it was taken with a camera.

Yes, and because that photo dates from the 1960s, it was recorded on photographic film just as with a pre-digital-era still-photo or movie camera. When I was a grad student I spent some time "scanning" such film for possibly interesting events, using a projection viewer.

It's also possible to use the film itself as the target for the incoming particle beam, in which case the particles produce tracks directly in the emulsion, with no camera involved. The photograph that we're talking about here isn't of that type.
 
jtbell said:
When I was a grad student I spent some time "scanning" such film for possibly interesting events, using a projection viewer.

I'll never complain about debugging code again.
 
Well my question is clear here: Was a lens used or not? And since I doubt you are sure, what can I do? First I can ask you if you have used the champer yourself (Jtbbell seems to say he has). Second, I can claim you are wrong so that you show me a detailed discription of such an apparatus that says that a lens was used.

And if you are interested enough in my "not clear" question, think it like this: What would it mean if the photo was taken with no lens at all?
For example Bohm claims "were we to view the cosmos without the lenses that outfit our telescopes, the universe would appear to us as a hologram". That doesn't say anything in particular, but perhaps is particular enough to disagree with what ray optics say, because ray optics say that we would just see blurness, doesn't it? That's the reason I classified the question into quantum physics, as the analysis of such questions involves the explanations of the double slit experiments.
 
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The bubble chamber that my research group used when I was a grad student was the 15-footer at Fermilab. It had three cameras with fisheye lenses that could each capture a large part of the interior of the chamber. By digitizing tracks from three photographic views of the same event, we could reconstruct the tracks in three-dimensional space and extract their curvature, which is the most important variable because it and the magnetic field strength tell you the momentum.
 
You have been told several times that lenses are used, including by people who were there, which you were not. Yet you insist on believing otherwise. Not much purpose in continuing this thread, since it can only end up continuing in the "is not!" "is too!" "is not!" vein.
 
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