Talk:Normal lens

Why?
I would like a bit more why? on this article. Will try to add it, but I cant find any good sources so far. Photographers tend to be not very technical alas. Why is this true about the human eye? And is the whole thing about the diagonal a myth? I cant see that 6x6 and 6x9 say dont project the same view, just more of it. Or am I wrong? Justinc 00:01, 15 December 2005 (UTC)

definition of normal
I have a doubt on the definition of "normal" as the natural visual perception. It's a matter of culture: five hundred years of Perspective (graphical) in painting makes us think it is the way we se things, but our eye is more a Fisheye lens-like which our brain remap to let us think straight lines are straight. The 45° angle of view is perhaps only the easiest way to make Photographic lenses, and we are so used to it we came to think of it as the natural perspective of our visual system, around 180° wide with a 2° fovea. Is there any authoritative source for those claims? --Marc Lacoste 23:54, 17 December 2006 (UTC)

You're right IMO there is no normal perpective. I think the current wording of the article "generally held to have a "natural" perspective" is rather neutral about this, but there's is matter for expanding the article. Ericd 19:43, 20 March 2007 (UTC)


 * I have read in a couple of (still) photography books that the term 'normal' as referring to a 50mm lens is not because it gives the same FOV as a human as is commonly stated but rather because it was the lens that was normally sold with an SLR. --Stujoe (talk) 00:28, 4 May 2008 (UTC)


 * I read somewhere that a "normal lens" is defined as one where the focal length = image circle diameter (giving a diagonal AOV of 53&deg;). This makes more sense to me because I always find a 50mm lens a bit 'cramped' compared to my human field of view. The word "normal" (rather than "standard", etc) suggests an origin in optical design rather than photographic usefulness, and may be more concerned with what goes on behind the lens than in front of it, so perhaps the 53&deg; AOV is just a by-product of an obscure lens-design optimisation.


 * 1: What is so special about a 53.13010235&deg; Angle of View? Well, one thing stands out if you describe the angle as a ratio of object frame to working distance rather than a fraction of a circle. The Field of View formula for a normal lens is o/d = i/f = 1/1 which simplifies to o = d. In other words, for a normal lens the diagonal of the object frame (o) - aka diagonal field of view - will be exactly the same as distance from lens to object (d). From knowing your normal lens FOV you can use f/n = o*n as a quick focal length FOV calculator; eg when the focal length (f) is half normal, n=2, which doubles the FOV (o). This is quite a handy thing to know for setting up a shot without the help of a viewfinder.


 * 2: Thus for 36x24 SLR film, a normal lens should be 43.3mm ... so where does the 50mm normal lens come from ? Here's one theory: a 36x24 image frame has and aspect ratio of 3:2, but an image circle has an aspect ratio of 1:1. If the 135 film was a 1:1 plate it would be 35x35mm - and have a diagonal of 49.5mm ... coincidence ? Square plates/film formats seem to have been more popular in earlier photography, so perhaps this legacy might explain the 43-50 normal lens discrepancy ? Another "pre Kodak 135" legacy theory is observes that a 2" (50.8mm) image circle covers a square 1.3/8" (34.925mm) film sheet.


 * 3: Photographers usually use the camera's Horizontal Field of View for composition, as it's easier to visualize than the diagonal. A 36mm lens on a 36x24 frame gives a horizontal field of view equal to the working distance (AOVh=53&deg;). Perhaps that's why wide angle lenses (for 135 format) are traditionally thought of as having focal lengths shorter than 36mm (ie >1:1)? It's tempting to dub the 36mm a "horizontal normal lens" or even a "normal landscape lens" ...?


 * 4: Curiously, a 43mm lens on a 36x24mm (3:2) frame gives a horizontal angle of view of 45.1&deg;, or 1/8th of the horizon, whereas a 50mm frames 39.6&deg; or 1/9th of the horizon.


 * I'm not sure where this is going, but it seems to have a 'handy logic' which might have appealed to the founding fathers of photography and given rise to popular use of terms like "normal lens", "wide-angle" etc. 87.102.83.121 (talk) 19:51, 19 August 2008 (UTC)


 * This article offers a fuller explanation of the "optimum viewing perspective" theory of the "normal lens". The key point is that whilst the total human FOV is large, only a portion of it can be comfortably scanned for detailed information. If well founded, the "normal angle of view" should crop up in microscope/telescope eyepiece design, in ophthalmic lenses -especially Corrective_lens-, and maybe even architects deciding the size of a window! But I'm still not convinced this is the source of the term "normal lens" ;) Redbobblehat (talk) 15:53, 2 September 2008 (UTC)


 * Mike Johnston of Luminous Landscape points out that 42mm would be the "true normal" taking the diagonal of 35mm, which is exactly a 28mm lens on a APS-C digital sensor. ... posted anonymously to article and then removed, but of interest to discussion --Redbobblehat (talk) 23:10, 17 March 2009 (UTC)


 * I took it out for several problems:
 * 1. Duplicative; the 43 mm diagonal and relation of normal to diagonal is already noted above.
 * 2. No definition of "true normal" or why he said 42 instead of 43.
 * 3. No clear indication of why this random opinion needs to be considered.
 * 4. Misquote "which is exactly a 28mm lens on a APS-C digital sensor" where he had said "Using the diagonal of the format as the standard, the true normal would be about 42mm (curiously, that's about exactly a 28mm lens on an APS-C digital sensor)." Your "which" has no clear refferent; should refer to "the diagonal of the format" or "the true normal", which it does not appear to in your version.
 * You should know I'm not going to condone such sloppy reporting.
 * Dicklyon (talk) 23:18, 17 March 2009 (UTC)


 * I agree it was misplaced in the article page, but interesting enough for the discussion page. So I moved it. That's all :-) The referenced article makes me think of "normal perspective" (ie not too flat, not too steep) rather than normal AOV ... if that makes sense ? --Redbobblehat (talk) 00:15, 18 March 2009 (UTC)


 * "Normal perspective" means viewing a print at a distance of focal length time enlargement factor. In the case of a normal lens, that's equivalent to "normal viewing distance" equal to print diagonal.  So, yes, they're closely related concepts. Dicklyon (talk) 01:44, 18 March 2009 (UTC)

Digital photography section
Definitely needs a split between TV lenses (were movie standards works) and digital still phototography. Ericd 20:15, 10 April 2007 (UTC)

Link to olypedia.de
Sorry, but olypedia.de is not spam, promotion or any other (we say in german) "Quatsch". It is THE german free wiki about olympus - nothing to do with olympus co! You find here many informations about olympus, that you can not find in en.wikipedia.org or other wikis. The most of the autors came from germany, for many of them (also my person) is english not a favorite language.

I try again....

Sorry - my english is for runaways...

Best regards from the lower rhine in germany rudolfo42 (http://olypedia.de/Benutzer:Rudolfo4)

Diagram
This page could do with a diagram showing a regular-sized picture held at a regular viewing distance taken with a normal lens with the scene of which it is a picture behind it. This would show that it approximately subtends the same angle of view as the image itself and hence approximates the view. —Ben FrantzDale (talk) 15:13, 8 March 2011 (UTC)
 * ✅JamesMcArdle 05:30, 8 June 2016 (UTC)

Then, undone, because of copyright issues. Jamesmcardle(talk) 06:15, 22 August 2016 (UTC)

Film still section
It is stated that "50mm is the simplest optical design possible for a lens". Can we have a reference for this? I don't know anything about lens design, but it seems like a pretty broad assertion. Markwads (talk) 14:51, 24 July 2011 (UTC)
 * Indeed, it's lame, though probably has roots in something true, like that a slightly long normal lens is pretty easy to design. I'll take it out. Dicklyon (talk) 15:32, 24 July 2011 (UTC)

Sections and query about relevance of the image circle
I have introduced new section headings and rearranged things for clarity, adding more detail on why matching the vision of the human eye with a manufactured lens is problematic and pointing to some useful references. However I have separated text that has no references, and that confusingly contradicts the rest of the article, into its own section "The image circle". Its argument seems to be a red herring and the text was inserted by an anonymous editor 70.55.205.168 around 3 September 2017. Unless someone can track down the relevance and authority of this passage, I suggest it be removed. While it remains I don't think the article should be classed as anything but a 'Start'. What do other editors think? Thank you, Jamesmcardle(talk) 07:46, 28 July 2018 (UTC)

Explanation for "why"
A better explanation for "why these focal lengths" can be found in [this paper](https://jov.arvojournals.org/article.aspx?articleid=2192052): distortion seems to go away when viewers view pictures at/near the center-of-projection, and these focal lengths match viewers' preferred viewing distances. I think this should be added to the article. That paper also lists problems with the conventional explanations. Aaronh (talk) 19:10, 7 March 2024 (UTC)