Talk:Aperture

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Anyone know whether this can be applied to eyes? When one is in a bright area, can they focus more deeply? Just wondering... -Jeshii 02:09, May 2, 2004 (UTC)

Yes, it can. Ever tried squinting to focus? That's using the same trick ;). DodgeK 19:22, 3 August 2005 (UTC)

The eye is just a biological lens. Though, it'd be nice to be able to upgrade eyes like I can with my SLR... Cburnett 19:57, August 3, 2005 (UTC)

Contents 1 Not just photographic 2 depth of field 3 Wrong definition for Astronomical telescopes? 4 Problems with Aperture article 5 Aperture and aperture stop 6 Glossographia Anglicana Nova

[edit] Not just photographic

Where's antenna aperture, effective aperture, etc.? Ojw 13:38, 18 October 2005 (UTC)

Antenna aperture would deserve its own page. Not sure what "effective aperture is". See Aperture (disambiguation) for other apertures. Perhaps what you seek is there.--Srleffler 06:03, 16 November 2005 (UTC)

[edit] depth of field

There has been some reverting back and forth about stops and depth of field. So I added the following (hidden) comment in the text:

There is some confusion here. So let's be clear: Long depth of field occurs when the lens opening, and thus the stop, is small. However, a small opening equals a large f-stop number.

--Jeremy Butler 12:58, 27 February 2006 (UTC)

[edit] Wrong definition for Astronomical telescopes?

Astronomical telescopes for the most part do not have "aperture stops" that limit the light cone entering the system. In astronomical telescopes the word "aperture" is most commonly a synonym for "diameter" of the main optical element. Maybe that differnce should be noted in the article.(Halfblue 16:07, 11 March 2006 (UTC))

In optics, the aperture stop of any optical system is the aperture within the system that limits the system's ability to accept light. It doesn't have to be an adjustable iris. For a telescope such as you described, the edges of the main optical element are the aperture stop of the system.

The usage of the term in photography may be slightly different, leading to confusion.--Srleffler 16:22, 11 March 2006 (UTC)

P.S. Did you miss this line in the introduction: "The diameter of the aperture stop is sometimes simply referred to as the aperture of the system, especially when speaking of cameras and telescopes." If I understand what you are saying, I think that addresses your point. (But perhaps I'm misunderstanding you.)

Actually I was following the link "aperture" from a telescope article I was working on. Following that link leads the reader to this article that seems to be technically correct but does not give them a clear explanation. The specific definition that link needs to follow to is one like you find in Webster's Revised Unabridged Dictionary :

3. Aperture: (Opt.) The diameter of the exposed part of the object glass of a telescope or other optical instrument; as, a telescope of four-inch aperture.

This article starts by describing it as "something which restricts the diameter of the light path" and having the "most obvious function" of reducing the amount of light.

The "Application" part does not seem to refer to telescopes.

The "In photography" section by definition refers exclusivly to the photographic term.

This article could use another category explaining that in Astronomical Telescopes Aperture is a synonym for Maximum Diameter of the system. Either that or maybe a new page giving the clear astronomical telescope definition?(Halfblue 03:35, 13 March 2006 (UTC))

Hmmm. I think everything is already covered here, but perhaps not very clearly from the perspective of someone who is interested in telescopes. It can probably be improved. I don't think that a new page is a good solution, because the usage in telescopy is clearly related to the more general usage in optics. We're really talking about the same thing. The aperture of a telescope is important because the size of the aperture determines how much light the telescope collects. This is exactly the same as the aperture (as defined here) in a camera or other optical system. The only difference is whether aperture refers to the physical thing, or to its diameter. Note, by the way, that Wikipedia is not a dictionary. It would be inappropriate for a wikipedia page to contain only a simple definition like that given by Webster. Simple definitions belong in Wiktionary. Note that Wikipedia articles can contain links to Wiktionary, like this: aperture.

OK, I took a stab at clarifying it. You're certainly right, in that the article was too photography-oriented. A lot of what was said wasn't general enough to include telescopes. I've tried to make it more inclusive. See what you think.--Srleffler 01:47, 14 March 2006 (UTC)

Looks good although the photographic parts seemed ok before. Mixing astronomical uses of aperture may not be the best thing since astronomical telescope's aperture affects two qualities not as important to a photographer: total light gathering ability and Angular resolution. And astronomical telescope aperture is different from cameras and even terestrial telescopes since the astronomical telescope deals with point objects at infinity who's brightness is not affected by F-ratio, whereas with cameras F-5 is F-5 no matter how big the lens is. I would propose using Wikipedia’s Headings and Sub Headings method to move the astronomical telescope to a separate heading with a more concise definition. Have a look at my user page for an example of what I mean. The headings/categories may need to be clarified a bit.Halfblue 03:15, 15 March 2006 (UTC)

I'm not sure why you think that total light gathering ability is not important in photography. It certainly is. Telescopes are certainly affected by f-number, the same as any other optical system. The brightness of the image produced by a telescope is proportional to its f-number. This comes up less often with telescopes simply because you don't change lenses or (typically) apertures, the way you do with a camera, so the f-number is fixed. I don't fully understand your comment on this, though, so perhaps you are thinking of something different than what I am.

What I was saying is that they are not as important to photographers since given good equipment they have no need to build ever larger objectives. They need a certain level of performance for their task, going "bigger" gets into diminishing returns as far as their ability to do that task. This is not true for astronomical telescopes....bigger is always better. It was an equivocation of application.. sorry if it was confusing.

Judging by the time stamp you may have read my comments before I finished typing them...my bad for editing online. What I was pointing out re: f-ratio is that telescopes used for astronomy do behave differently from the same type of system used with terrestrial photography.... and F-numbers do not have the same affect for each application. Whereas increasing the objective aperture of an F/5 system has no affect for a photographer (in that the image of an illuminated terrestrial (extended) object stays at the same brightness per given square centimeter at the focal plane) aiming the same larger F/5 system at a self illuminating point source (stars) has a big difference over a smaller F/5 system - the objects becomes brighter as the size of the overall objective aperture increases... and changing the F-ratio has little affect to the brightness when imaging this class of objects.Halfblue 17:36, 16 March 2006 (UTC)

Ah, I see. I had the right equation but was reading it wrong. Yes, the brightness of the image of a point source does not scale with f-number the way that of an extended source does. I didn't realize that before.--Srleffler 01:54, 17 March 2006 (UTC)

Looking at the text on your page, I don't think your changes to the introduction work. I'm not willing to accept an introduction that doesn't deal first with the usage of this term in optics. Other uses are secondary, and need to be addressed, but without interfering with a clear definition of the optical term. Also, the paragraph on aperture stop needs to stay in the introduction, because that term redirects to this page. Moving it into a subsection will lead to confusion, especially since the terminology overlaps (photographers and astronomers call the diameter of the aperture stop the "aperture", contrary to both the optics terminology and common English usage.) As far as separating the optics, photography, and telescopy usages, I think you are creating a completely artificial division. The concepts involved are all fundamentally the same. The only difference is a slight difference in usage, that to an optical designer or scientist an "aperture" is a physical object with a hole in it, while to an astronomer the "aperture" is the diameter of that hole. The math, physics, and optical design criteria are all the same. The specific constraints are different because a telescope and a camera have different applications, but the principles are identical, and are the same in the design of microscopes, binoculars, etc.--Srleffler 03:59, 15 March 2006 (UTC)

P.S. Note that the size of the Airy disk, which determines the resolution of a telescope, is proportional to the telescope's f-number. Reference: The Encyclopedia of Astrobiology, Astronomy & Spaceflight--Srleffler 04:06, 15 March 2006 (UTC)

I think the problem I am seeing is that this may be what I said originally “a wrong definition for astronomical telescopes” I am not saying this article is wrong. Your link to Wiktionary helps me out. There are three definitions there. This article is, as you say, about the noun “aperture” 2. (Optics) Something which restricts the diameter of the light path through one plane in an optical system. But the term amateur astronomers are using rightly or wrongly is “aperture” referring to definition 1. An opening; an open space; a gap, cleft, or chasm; a passage perforated; a hole; as, an aperture in a wall…… and actualy the quality of that opening…. it's size. This article does cover those aspects technicaly.... but since this is an Encyclopedia.... clarity to the readers is also a consideration. So the article is not wrong….. it may just be wrong to link the astronomical telescope term to this article and instead link it to the Wiktionary as you suggested.Halfblue 17:36, 16 March 2006 (UTC)

Actually, as I see it the astronomers are not referring to definition 1, but to definition 2. The diameter of your objective lens restricts how much light you can get into your telescope. When you talk about the "aperture" of a telescope, you are talking about the diameter of what an optical engineer would call the aperture stop of the telescope. And no, I don't think it's wrong for astronomers to use different terminology. I think it's important to address both together here because it may help astronomers understand better the optics of their telescopes. Where this article goes wrong is then in its comments about the effect of aperture on an optical system, some of which are not correct for a telescope.--Srleffler 01:54, 17 March 2006 (UTC)

[edit] Problems with Aperture article

This was posted on the SA Forums and has a couple criticisms of this article. Could an expert review these and fix the article as they see fit?

"Just out of curiosity, I decided to look at the first thing I could think of that I have a fair degree of confidence in my knowledge. So, I went to Wikipedia and searched for 'Aperture' (as it relates to Photography).

A criticism:

"Aperture is usually measured in f-numbers. A lens will have a set of "f-stops" that represent doublings in the amount of light let through the aperture."

This is not quite true. While it is true that the standard f-stop progression used in photography does represent doublings of light per step along the progression, very few (if any) modern cameras work at this imprecise a level of granularity. Pretty much all cameras work in either 1/3 stop or 1/2 stop steps. So, telling people that each number in the set represents a doubling will quite likely confuse someone not familiar with the concept. They will be led to believe that if they increase the aperture by 1 "step" on a camera, they are doubling the amount of light being let in, and on the majority of modern cameras, that is not the case.

In short, they are confusing two concepts: the standard f-stop progression, and the f-stop scale as it is represented on modern cameras and lenses.

While it may be trivial, it took me all of 1 minute to look and find something that looks true enough, but is wrong in a subtle and meaningful way that might easily mislead someone who was using Wikipedia to find out about a new subject.

This doesn't even address the fact that the rest of that particular section is poorly worded in ways that tend to make things sound more or less absolute than they really are.

"A very fast zoom lens will be constant f/2.8, which means the aperture will stay the same throughout the zoom range.".

There are two concepts at work here: the existence of constant maximum aperture zoom lenses, and an example of such a lens with a particular quality (speed). As worded, this is a confusing mess. Will a very fast zoom lens always be a constant f/2.8? Is it possible a fast zoom lens exists that is a constant f/2.5? Why not explain the difference between constant max aperture and variable max aperture first, and why they exist, and then give examples, instead of throwing out examples mixed with terminology that the examples use?

Again, small things, but this was the first article I pulled up. Do you really think this kind of thing is isolated, and that I just got lucky?"

--Liface 18:43, 9 May 2006 (UTC)

I find the problem is pretty widespread, and I've been working on fixing such things, little by little; see my contributions to see what I mean. It's a big job to turn lots of amateur articles into serious professional-looking encyclopedia articles, but I see steady progress in that direction. Just jump in and help. Dicklyon 19:38, 9 May 2006 (UTC)

[edit] Aperture and aperture stop

There seems to be some confusion of terminology between different fields. In optics, an "aperture" is any opening through which the light passes. In an optical system, such as a camera lens, the edges of each lens element or its fixture is an "aperture". The aperture stop is a special aperture: the one aperture within the system that limits the size of the axial cone of rays that can pass through the system to form an image. Usage of the terms in other fields (such as photography) may vary, and the article needs to deal with both usages clearly and distinctly.--Srleffler 06:45, 10 May 2006 (UTC)

Your changes so far are great, but it's unclear what more you are saying we need to do. I'd disagree on one fine point: I'd say the aperture stop is a special stop, not a special aperture. I'll check some books... Dicklyon 14:46, 10 May 2006 (UTC)

My best authoritative book here is Hardy and Perrin, 1932, The Principles of Optics, ch. 5 p. 68 "The Limitation of Rays by Apertures". This chapter title is already somewhat inverted from how I conceptualize it, which is that the "stop" provides the limitation, the "aperture" being the open part. But let's see what they say... First off "...the aperture of the system, which is determined by the diameters of the lenses and the stops that it contains" sounds good to me; no circular use of aperture to define aperture. "The theory of stops was first developed by Abbe, and it constitutes one of the most useful concepts in the theory of optical instruments". So far so good. Then "...element II is the stop or diaphragm that such a system normally contains"; sounds good -- a stop is a physical blocking element, usually a diaphragm, that is a thin structure supported around its edges, and with a hole in it. "image-forming pencil (of rays)...in the image space...has a half-angle θ′". and "It is clear from the figure that the value of θ is determined by the diameter of the diaphragm II, which is therefore called the aperture stop in the terminology developed by Abbe. Later, "it is obvious that the rim of either lens I or lens III (or both) might become the aperture stop if the diameters of these were decreased sufficiently." Now, he never says there are multiple apertures, or that an aperture is a hole, or that a lens diameter is an aperture; he only applies the term aperture or aperture stop to the whole system. He goes on "In rare cases, two stops may be equally effective, ..." so now he has multiple stops, but still only one aperture. And "The fact that stop II is the aperture stop..." makes it clear that an aperture stop is a type of a stop, not a type of an aperture. And "The field stop is the real diaphragm of which the entrance window is an image" talks about another type of stop, not a type of aperture. So, I think I'll reword the article as I noted above. Citations supporting other points of view are of course welcome. Dicklyon 20:26, 19 May 2006 (UTC)

[edit] Glossographia Anglicana Nova

Well, thanks to a recent edit we now have the picture of the Glossographia Anglicana Nova quote right next to the quote itself, as text. This is not acceptable. Options:

1. move the picture somewhere else in the article
2. delete the picture
3. delete the text quote (less desirable due to accessibility concerns.)
4. nuke the whole history section but keep the picture.

I mention the last option because the history section is really just two huge quotes with little explanation or discussion of the history. While the quotes are interesting, this is not an effective presentation of the history of aperture, and may violate WP:NOT#Wikipedia is not an indiscriminate collection of information.--Srleffler 12:47, 27 October 2006 (UTC)