# Talk:Aperture

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## Eyes

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)

Shouldn't the pupil be the aperture stop? The pupil controls amount of light, not the iris. MonketDLuffy (talk) 06:43, 4 August 2011 (UTC)

## 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)

## 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)

Agreed - and in addition : Stopping down means reducing the aperture = increasing the f-number (or is it the other way round? ;). Redbobblehat (talk) 15:32, 29 August 2008 (UTC)

## 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)

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)

## 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)

## 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)

## 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)

## Zoom aperture range

bhphotovideo.com shows 58 lenses with aperture 6.3 at the tele end. I admit that 5.6 is more common (about 230 hits), and I'll stop arguing about it, but my objection was to uncommented changes without mentioning a reason or a source. Dicklyon 16:04, 20 May 2007 (UTC)

Okay, just next time try not to cite a source that is bias towards specific brands/lens mounts, and having f/6.3 as a max aperture would suck, AF is a pain and f/6.3 is the limit for most consumer SLR's AF systems (some pro bodies can AF as narrow as f/8); not to mention the amount of light needed. Ctrlfreak13 20:28, 20 May 2007 (UTC)

## Field of view

Why does 'field of view' link to Angle of view, when it has its own article, Field of view? In the first section, it says:

...a photographic lens may have one or more field stops, which limit the system's field of view.

I may be missing something, so I wanted to make sure on the talk page first. --iNkubusse? 06:28, 25 July 2008 (UTC)

I think the text should actually say "Angle of view". However I'm a bit confused by the section in general, particular what a "field stop" is as opposed to an aperture stop, so maybe the whole bit could do with a bit of rewriting. Tejastheory (talk) 07:20, 25 July 2008 (UTC)
Then, I think it's better this way, because it says 'system's field of view' which is practically the 'angle of view'.
Anyway, it says In addition to an aperture stop.... The field stop just limits the angle of view (the system's field of view), but it may become the aperture stop if it's outside the angle of view (that's how vignetting is achieved), so the image is darkened on the edges. But you're right, it is confusing, it took me a long time to decipher the text, and I'm still not sure what I'm talking about. I hope someone can simplify it. --iNkubusse? 20:06, 25 July 2008 (UTC)
The field stop is whatever acts as frame around the film plane, ie "In a film camera, the physical film gate performs the function of the field stop". The field stop's job is to crop the image at the film plane and is usually in physical contact with the film in order to give a nice crisp edge. The digital equivalent I suppose would be whatever delimits the "effective pixels" on the sensor (which could be "cropping" of data rather than light). By definition it's the last stop in the system and part of the camera rather than the lens. Also, by definition, vignetting cannot be caused by the field stop itself. The sentence :"Outside the angle of view, a field stop may become the aperture stop, causing vignetting; vignetting is only a problem if it happens inside the desired field of view." makes no sense to me at all. Field of view and Angle of view are not always interchangable, the angle of view is only one aspect of the field of view. I suggest redirecting the link to field of view. Redbobblehat (talk) 15:22, 29 August 2008 (UTC)
The wording was confusing. I rephrased it based on what I think they were trying to say. One can in principle have field stops in the lens, as well as the film gate. If a field stop in the lens limits the field of view to less than what the film gate allows, the image on the film will be smaller than the usual image size, and might be a different shape (e.g. circular). This cropping of the image is, technically, vignetting, but is not a problem. Vignetting is any change in the image due to rays being blocked by something other than the aperture stop.--Srleffler (talk) 21:34, 29 August 2008 (UTC)

## Actual, Effective and Relative aperture

According to Jacobson, Ralph (et al.) (1988). The Manual of Photography (8th ed. ed.). Focal Press. ISBN 0-240-51268-5. p.49.

• Actual Aperture is the mean diameter of the actual aperture formed by the diaphragm opening (this is not necessarily circular). Ie it's the physical hole inside the aperture stop.
• Relative Aperture is represented by a number N (f-number), which is defined as the equivalent focal length of the lens divided by the diameter EN of the entrance pupil; N=f/EN.
• Effective Aperture (sometimes used erroneously to refer to the entrance pupil) properly refers to the relative aperture corrected for a lens that is not focussed at infinity. Redbobblehat (talk) 15:56, 29 August 2008 (UTC)
Those seem like sensible definitions. I'm not sure they are used universally, however. In optical engineering, what he calls the "effective aperture" is typically called the "working f-number". (Relative aperture is the f-number.)--Srleffler (talk) 21:38, 29 August 2008 (UTC)
Nailing down synonyms seems like a good use of wikipedia! "Working f-number" is certainly less ambiguous than "effective aperture". Jacobson seems very keen to avoid confusing the "effective aperture" with "entrance pupil", which is contradictory to at least 3 out of the 4 uses of "effective aperture" in the current article. Perhaps entrance pupil and exit pupil should be added to this context/list of specific photography/optics aperture terminology, so that their differences and relationships can be explained explicitly ? Redbobblehat (talk) 12:33, 30 August 2008 (UTC)

## Article target audience

This article needs to be rewritten to a beginning target audience, and another article written for advanced readers. One for a beginner who's trying to figure out how to read the numbers showing on their camera? One for an advanced photographer, astronomer, or physics student.

Article would benefit greatly from two or three simple diagrams showing a cutaway side view of lens elements.

Terminology is inconsistent. I.e., is it a "prime lens", "a fixed focal length lens", an "FFL" or a non-zoom lens? The article uses all four terms in a single sentence without actually ever explaining what what it is! In places the article reads "film" as focus of a lens, in another "film or image sensor". In another, it uses "image/film plane"! Make it clear at the beginning of the article that a lens can focus on film, an electronic sensor, the back of the eye, or even a wall. Then use the same term throughout the article. Using "professional lenses" when "expensive" or "specialty lenses" is meant is imprecise, and unhelpful.

There is considerable original research. My understanding is that most professional photographers now prefer zoom lenses in most shooting situations. Kubrick's lens in Barry Lyndon may have had the largest aperture 20 years ago, but is that still true? Citation? Piano non troppo (talk) 20:29, 15 October 2008 (UTC)

These are nits, not major rewrite issues. I'll take the tag off. Feel free to work on or point out specific issues that still need attention. Dicklyon (talk) 01:02, 16 February 2009 (UTC)

## Aperture control

Several months ago, I added a section on aperture control to the article Perspective control lens to explain why Nikon's inclusion of automatic aperture in its recent PC-E lenses was important. I don't think that article is the right place for a detailed explanation, and I don't think the topic merits a separate article. If there's no objection, I'd like to move the bulk of that section here, with only a brief description remaining in the Perspective control lens article. JeffConrad (talk) 07:34, 11 December 2008 (UTC)

Sounds reasonable, but I hope you'll cite some sources on automatic aperture control facts. Dicklyon (talk) 17:59, 11 December 2008 (UTC)
Just like the rest of this article ;-)? I'm not quite sure which items count as “automatic aperture control”. The only specifics I mention relate to Canon and Nikon tilt/shift lenses; for those, the source is Canon and Nikon literature. Good sources on the transition from manual to auto may be harder to come by, though Sidney Ray has several paragraphs on it in The Manual of Photography, 9th ed. (136–137). I think Moose Peterson briefly covers this as well, but I'll need to check. Anything else may need to be flagged; full-aperture metering and automatic diaphragm control have been the norm for so long that the topic isn't even mentioned in most photographic books written in the last 40 years. And it's not even mentioned in this article, either.
I'll add it as a new subsection under In photography; first, though, I suppose I should make sure that no one objects to having it removed from the current article. JeffConrad (talk) 00:08, 12 December 2008 (UTC)

## Aperture area

Have I got this right : the aperture area described in the article is the same as the area of the entrance pupil because it is 'reverse engineering' the f-number (as effective focal length/entrance pupil diameter) ? --Redbobblehat (talk) 20:14, 2 March 2009 (UTC)

I think so. This article needs updating to either clarify that most of what it is talking about is actually the entrance pupil, or clarify that in some fields "aperture" is used to mean "entrance pupil". —Ben FrantzDale (talk) 14:05, 5 December 2011 (UTC)

## Variable relative aperture

JeffConrad, you changed "a variable relative aperture" to "a variable maximum aperture". Probably it should be "a variable maximum relative aperture." You can get by without "relative" when saying the aperture is f/2 etc., but when f is changing, you need to be more explicit; in the sentence in question, how can it make the intended point without saying relative? Dicklyon (talk) 02:29, 8 February 2011 (UTC)

I guess I implicitly posed the question, “Can we informally take ‘maximum aperture’ as equivalent to ‘maximum relative aperture’ in this context”, as typically is done in the photographic vernacular. “Variable relative aperture” strikes me as a bit vague, seemingly implying that the relative aperture changes with focal length whether or not it’s set to the maximum value. For some zooms this is true; for others it is not. If it’s felt that we must say “variable maximum relative aperture”, I don’t have a problem.
I just don't think it's right to use "maximum aperture" both for "maximum aperture diameter" (implied by the use of "aperture" to mean "aperture diameter" in calling f/2 an aperture value), and "maximum relative aperture" in the same article. Find a way to disambiguate. Dicklyon (talk) 00:21, 9 February 2011 (UTC)

Same problem with "largest maximum aperture in film history". How can that make sense when you intend to say lowest f-number in film history? Dicklyon (talk) 02:31, 8 February 2011 (UTC)

No disagreement on what’s formally correct—I’d first thought of saying “lowest minimum f-number”, but I thought it would confuse most readers—so instead I posed the question (apparently the answer is “No”). I’d much prefer “largest maximum relative aperture”, as it was before. Another alternative would be to use the photographic vernacular and just say “fastest lens”.
Fastest works for me. Dicklyon (talk) 00:21, 9 February 2011 (UTC)

I’ve added relative in a few places where it seems appropriate. Though “variable maximum relative aperture” may be strictly correct, it seems to have an awkwardly long string of modifiers. The only means of avoiding it I can think of is to refer to the aperture f/# (rather than the f-number) in all places, and doing so might introduce its own awkwardness in some places. To be honest, the entire section is marginal as well as essentially unsourced, and some of the claims are mighty questionable, especially in the last paragraph.

I replaced the ref for the f/0.7 lens with the original English-language article; however, like the gizmodo source, this article seems marginal with regard to WP:RS.

## Merger proposal

I propose that Entrance pupil and Exit pupil be merged into Aperture. The message of the pupil articles is mostly already contained within the Aperture article. Any missing information could be easily transferred, staying entirely within the context of Aperture, given that they are referring to the same thing. The Aperture article is more robust. Aperture is the more common term. Some of the content of the pupil articles is more technical in nature and would be beneficial to add to the Aperture article regardless. JimsMaher (talk) 19:26, 14 January 2013 (UTC)

• Oppose. Entrance pupil, exit pupil, and aperture are three distinct things. The topics are related, but not identical. Merging the articles would probably make the distinction between these concepts less clear. There is enough material for three articles. Entrance and exit pupil are extremely important concepts in optics.--Srleffler (talk) 02:53, 15 January 2013 (UTC)
• Comment – the pupils could be well covered in one article. Not aperture. Dicklyon (talk) 04:17, 15 January 2013 (UTC)

Let me add that Aperture stop redirects to this article. How is that difference, between the aperture and the aperture stop, significantly less than the difference (in theory or practice) between aperture and the entrance and exit pupils, enough to support their own independent articles? Moreover, the aperture article is lacking in an understanding of the full process that is light traveling through aperture, without exit and entrance pupil being more involved with the explanation than they currently are. JimsMaher (talk) 17:25, 31 January 2013 (UTC)

I don't see why aperture stop redirecting to aperture is a problem. I don't doubt that the aperture article could be improved, but I do not see merging the other two articles here as helpful. This article can and should discuss the relationships between these concepts. This does not require a merge.
Because this conversation is stale, I have removed the merge tags.--Srleffler (talk) 16:43, 21 July 2013 (UTC)