For discussions on Bob's article on aperture, which can be found here: www.the-photo.org/aperture.html
Aug. 14, 2024
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I just think the articles need listing or have an expanded title in some way on the front page, as "Bob's Articles" in a bit too vague.
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You could pin current article thread globally. When there becomes more of them, you could create listing (pinned, locked thread), linking to articles and discussion threads.
Also you could copy-paste some excerpt of article here (with Bobs permission of course) - this may help to start discussion. Currently it is harder to comment or ask about article contents. -
I found the phrase "Bob's article on aperture" quite understandable.
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I like Bob's treatment of Depth of Field relative to aperture size which is much like Merklinger's and avoids intense discussion of the "CoC" red herring which, as we know, is whatever Chuck Norris say it is.
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No No No. I was talking about the way it is presented on the front page! Not the article
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I was mainly thinking about sombody who lands on the page via a search engine.
It is pretty good recourse to revive this forum.
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Yes Yes Yes. I did find the phrase "Bob's article on aperture" quite understandable.
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- By ArvoJ on Aug. 20, 2024, 2:51 p.m..
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Ted, NCV means home page of current forum:
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Yes, exactly. Thanks for clearing up the misinterpretation of what I wrote.
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Enough of discussion about how to make Bob articles more visible, let's continue with the article itself :)
Very good introductory article about lens (optical system) aperture, more devoted to optical properties (depth of field and bokeh), less to exposure control. But there is more to aperture...
Once upon a time I was schoolboy in our beloved country, at this time located on the territory of former USSR. In one summer I worked two hard weeks on local farm and earned my first money, about 15 rubles - and bought me my first camera, Smena 8M. (There were about four types of cameras available then - simple plasticky Smena, Leica-cloned rangefinder FED, I don't know from what cloned family of Zenit SLRs and few MF cameras too.)
How is this related to aperture? Directly - on Smena 8M there were two sets of markings for aperture, shutter speed and focus distance (see linked page above). Focus distance was doubled with pictograms of face, people, buildings and so on; shutter speed was doubled with icons for sun, partially clody, cloudy and some more - and aperture had alternate scale with GOST/ISO/ASA/DIN speeds :) Sure this is related to exposure, but I could call that just ISO speed control.
Taking images was pretty straightforward - you set aperture by film ISO (common were GOST65 films, GOST = ISO), shutter speed by weather conditions, focus by object size and hit shutter button - and those pictograms guaranteed pretty good result for most of the time.
Some time later I bought me a light meter and started set aperture and shutter speed in more usual way, but this is already another story.
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Bob's article uses the following diagram:
The article says: "The rays describe a cone of light based on the aperture with its apex on the focus point. Now let's consider what happens to rays coming from a point ‘A’ half way to the focus point."
Why not show the rays from point ‘A’ instead of the rays from the focus point? It is the rays from point A that produce the blur, not those from the focus point.
How is this diagram intended to help the beginner?
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Bob does say the blur is from rays coming from point A which seems pretty clear.
The rays are not coming from the focus point as you suggest. What the article says is the rays coming from a point the lens is focussed on will all converge onto a single point on the sensor.
From Bob's article:
"A lens is focused on a particular point and all the rays from that point passing through the aperture of the lens will be focused to a single point on the sensor (assuming a perfect lens). The rays describe a cone of light based on the aperture with its apex on the focus point. Now lets consider what happens to rays coming from a point ‘A’ half way to the focus point. Rays from this point travel to the aperture, but instead of being focused on a point on the sensor converge somewhere behind. Because the rays travel in straight lines, the shape of cone that the sensor intercepts corresponds to the shape of the image, and its size corresponds to the image of an object the same size as the light cone in front of the lens at point A".
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It's the terminology that is confusing, not the diagram which is clear and common enough. 'A' is a line, not a point, and rays do not emanate from it. Rays only "come from" from the point of focus in 2D object space. Having said that, the terminology is good enough for the intended readership, i.e. novices.
Not unlike the infamous Exposure Triangle when we are told in many if not most tutorials that the ISO setting changes the sensor's sensitivity when really it does not.
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The diagram and explanation are clear to me.
Sure, it might not be clear to everyone but then any explanation and diagram might not be clear to everyone.
Perhaps you or Tom could post a diagram and explanation you believe will be clear to everyone.
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It is intersting. I think I know quite well how lens and aperture work and how blur is produced, but I just can't understand neither this image nor explanation. I know it is just my personal problem, but anyway :)
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In well over a dozen years on photographic fora, I have yet to post a technical diagram or explanation for anything that will be clear to everyone.
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That is the point I was making as well.
The diagram and explanation are clear to me.
