Talk:F-number

message: Is a F-stop basically a camera's spatial filter?  That is it is an iris positioned at the focal point between the lens system of the camera?Waxsin (talk) 16:10, 2 February 2016 (UTC)
replies: text: It is not intended as a spatial filter, and it is not at the focus of the lens. It does in some way behave as a low-pass filter, at small apertures, when sharpness is limited by diffraction. — Edgar.bonet (talk) 18:29, 2 February 2016 (UTC)
thread_title:  A Spatial Filter 

message: I'm in favor of using entrance pupil instead of aperture in the definition of f-number, because entrance pupil is more precisely defined.  There are multiple types of apertures, which are not all the same.  The aperture formed by a lens's diaphragm, for example, is usually not the same as the entrance pupil and not what the f-number is defined in terms of.  But we must recognize that in common photography speak, people say aperture when they really mean entrance pupil.  So I wrote in the first sentence of the Notation section that the entrance pupil is often called the aperture.  I'd be fine to move that statement up into the definition also, but I think we should maintain a distinction between aperture and entrance pupil, and not turn them into synonyms.  Lens design textbooks are pretty consistent about using entrance pupil or clear aperture, and never just aperture. Balazer (talk) 04:30, 19 January 2013 (UTC)
replies: text: I suppose, but for the early cameras, when f-number was being defined, with fairly simple lenses and the aperture very close to the lens, it would have been close enough. With modern retrofocus lenses, it is much less obvious, so entrance pupil is better. But unless someone actually takes the lens apart, they won't know the actual size of the aperture! Gah4 (talk) 20:38, 7 February 2013 (UTC)
replies: text: But there are common real-world examples where the the distinction really matters and the difference is easy to see.  Take most any video zoom lens, or any other zoom lens with an f-number that is constant across the zoom range.  The physical aperture is unchanged as you zoom, but the entrance pupil gets larger as you zoom in.  It's quite obvious if you look into the front of the lens as you increase the focal length:  the image of the aperture becomes increasingly magnified.  Balazer (talk) 04:59, 10 March 2013 (UTC)
replies: text: Seems to me, though, that aperture is the WP:COMMONNAME used by photographers, even though it is technically wrong.  As you note the physical aperture can change, such as in zoom lenses, but photographers never say "physical aperture", just "aperture". It seems that "effective aperture" is used for antennas, and from Webster, also used in place of entrance pupil in photography. Gah4 (talk) 16:04, 13 September 2018 (UTC)

text: I would suggest using the term 'objective lens,' or just 'objective' rather than the term 'entrance pupil,' as pupils generally have a (biologic and common) definition that includes adjusting in size to adapt the eye to the amount of light entering. 'Objective lens,' or 'Objective' are both used for microscopes and telescopes, which relates nicely to camera lenses. DocKrin (talk) 18:07, 11 August 2019 (UTC)
replies: text: Sorry, but you don't seem to understand what is being discussed here. The entrance pupil of an optical system is the image of the system's aperture stop, formed by whatever optics are in front of the stop. The system's f-number is the ratio of its focal length to the diameter of the entrance pupil. When you look into someone's eye, the image of their pupil that you see is in fact the entrance pupil of the eye; the terminology is not a coincidence.--Srleffler (talk) 22:43, 11 August 2019 (UTC)
thread_title: Aperture vs. Entrance Pupil in the definition of f-number

message: Nanette L. Salvaggio  Basic Photographic Materials and Processes
 Sidney F. Ray  Applied Photographic Optics: Lenses and Optical Systems for Photography 
Nanette Salvaggio makes the mistake of saying "effective aperture" instead of "relative aperture" - a common mistake as Sidney F. Ray points out. 
RPSM (talk) 08:44, 12 January 2014 (UTC)
thread_title: Two references (google books) after searching for ''effective aperture'' and ''relative aperture'' (f/ number) 

message: On a camera, the aperture setting is usually adjusted in discrete steps, known as f-stops.  This was usually true from the rangefinder days through the manual focus SLR days. Though there are detents at full stops, the aperture changes continuously. The later electronic SLRs, and continuing into digital SLRs, normally allow steps of 1/2 or 1/3 stop. The settings are electronic, and not continuous.  Seems like we should at least take out the usually.   Gah4 (talk) 07:55, 20 July 2016 (UTC)
thread_title:  step sizes 

message: Thanks, page useful. Will read in detail, but at this point just trying to help daughter into using the loaned camera.
THe split image showing effect of f-number - great.
Below a just as useful image with caption.
"Shallow focus with a wide open lens" - if this just said (high f-number) or (low f-number) it would be great, much easier to grasp by those reading the page to learn.
I totally, understand that if I already knew this all, read the page thoroughly, it would be redundant infromation, but that's why I'm reading it.
As a wonderfully informative page, it would be even easier with this consistency of comment in the caption as well.  — Preceding unsigned comment added by 122.60.105.241 (talk) 23:53, 25 August 2018 (UTC)
replies: text: As the comments above indicate, photographers pretty much never say high or low, or increase, or decrease, the f-number. Expressions like wide open, open up, or stop down are common, and everyone very quickly learns that open up is a smaller number written on the lens, and stop down is a larger number.  Even more, though, photographers pretty much always write it in the f/(number) fraction form, such that increasing (number) decreases the fraction. There just isn't enough room for the f/ on the lens barrel. Gah4 (talk) 16:26, 13 September 2018 (UTC)
thread_title:  Shallow focus with a wide open lens - Just a comment 

message: Can someone rewrite this section? I understand many aspects of photography, but I did not understand this section. Could someone please write it in layperson language, clarify what is being said, and expand it a bit to make it more useful? because it looks like it has the potential of being a very useful section! Misty MH (talk) 03:43, 10 November 2018 (UTC)
replies: text: Doesn't look so bad to me.  f/number is defined as the focal length divided by the (effective) lens diameter.  (Entrance pupil in more complicated lenses.)  That gives the appropriate amount of light when the lens is focused (and the object is at) infinity (or close enough).  But as you focus closer, and the lens moves farther from the image plane, the light gathering ability reduces.   It is, pretty much, based on the new lens to image plane distance.  Most of the time it can be ignored, but with extension tubes or bellows, the lens can be much farther away, and the correction gets more important.  That is why it is commonly the bellows correction factor.  Gah4 (talk) 04:31, 10 November 2018 (UTC)
replies: text: It doesn't look so bad because I edited it between when he posted and when you replied.--Srleffler (talk) 16:08, 10 November 2018 (UTC)
thread_title:  Working f-number rewrite? 

message: Regarding the correction for objects not at infinity, with TTL (through the lens) metering systems, this will automatically be corrected. Should this be mentioned? Gah4 (talk) 04:33, 10 November 2018 (UTC)
thread_title:  TTL 

message: The article says Most old cameras had a continuously variable aperture scale.  I suppose this depends on how old you mean by old. Many box cameras from the early 1900's have a sliding metal tab, or rotating metal disk, with holes in it.  The continuous aperture might have been from about the 1930's or so. Many cheaper cameras only offer one aperture setting. With electronic aperture control, the continuous scale went away. Gah4 (talk) 04:46, 27 March 2019 (UTC)
replies: text: Actually, even modern electronically controlled lenses have an essentially continuously variable aperture setting.  I don't recall the details, but I seem to recall the increments are tiny; it's just the camera UI that quantizes them coarsely. But more generally, you're right, there has always been a mix.  But for cameras with iris diaphragms, they were usually continuous. Dicklyon (talk) 04:34, 12 August 2019 (UTC)
thread_title:  ''Most old cameras had a continuously variable aperture scale,'' 

message: A recent change removes photography as the use of f/number.  As well as I know, optics other than photography, uses Numerical Aperture, symbolized as N.A.  In most cases, N.A. is twice the denominator of the f/number.  (That is, if you think of it as a fraction.)   Is there a WP:RS that shows it widely used in optics, other than photography, or I suppose when photographic lenses are used in non-photographic applications. Gah4 (talk) 01:22, 9 August 2020 (UTC)
replies: text: Any of the first three references in the article suffice. Note that it's not a "recent change", but rather a partial revert. The implication that f number is only used in photography was inserted yesterday. --Srleffler (talk) 16:41, 9 August 2020 (UTC)
thread_title:  photography