Talk:Numerical aperture

message: The two definitions should be merged into a single page, replacing this disambiguation page. The definitions are all fundamentally the same--the NA formula for a fiber in terms of the indices of refraction theoretically should be the same as the NA as defined by the acceptance angle of the fiber (which would be the "correct" optical definition). Unfortunately, it seems that the federal government has confused this in their standards, making the approximate theoretical formula the definition of NA for optical fibers. This ambiguity could all be addressed in a single page.--Srleffler 06:48, 16 November 2005 (UTC)
thread_title: Merge proposal

message: "Lenses with larger numerical apertures also collect more light and will generally provide a brighter image." - and, moreover, a better signal-to-noise ratio. I'd like to know a bit more about this - how exactly does light-gathering vary with NA? This is of increasing interest in microscopy, where we've recently seen improvements in NA at the top end from 1.40, the state of the art 5-10 years ago, to 1.45, now common although far from standard, and recently 1.49, at sell-a-graduate-student-into-slavery prices. The improvement in resolution is small, about 6%, but people reckon the better lenses make a significant difference, so i assume it's to do with light-gathering capacity. Or it's a big con.
The 1.49 lenses are marketed specifically for Total internal reflection fluorescence microscopes; i don't know if that's because the TIRF physics is especially sensitive to NA, or because TIRF microscopes are just such bastards generally that you need a great lens to get useful data.
-- Tom Anderson  —Preceding unsigned comment added by 128.40.81.185 (talk) 16:04, 26 October 2007 (UTC)
replies: text: TIRF lenses must have a high NA to achieve the critical angle required for total internal reflection of the excitation light. An added bonus is you collect more of the fluorescence emisson from a fluorophore because of the high NA. Objective-based TIRF requires high NA lenses but prism-based TIRF can be used with whatever lens you've got, although it will affect your light collecting abilities. I have been investigating the geometry behind light collection with a microscope (using glass coverslips) and, interestingly, I do not think that two lenses with the same NA means that they must collect the same amount of light from a fluorophore. The resolution of course will be the same, but my opinion, based on my inspection of the geometry, is that the light collecting could be different depending on the medium in which the fluorophore is located relative to the medium in which the lens is working. Also, there are weird effects when the fluorophore is very close to the surface of an interface (see Fluorescence Microscopy of Living Cells Axelrod Chapter 15: Emission Of Fluorescence At An Interface) which will change the results drastically. 
132.239.25.220 (talk) 02:52, 22 August 2011 (UTC)
thread_title:  Light gathering capacity 

message: The article doesn't mention this distinction. It should. —Ben FrantzDale (talk) 00:02, 29 September 2010 (UTC)
replies: text: Actually, the distinction between object and image NA is mentioned, in the section "Working" or "effective" f-number. --Srleffler (talk) 02:27, 29 September 2010 (UTC)
thread_title:  Subject NA versus image NA 

message: I changed the symbol "D" to "w0" in the definition of NA in the laser physics heading, since D is used previously in the article and I believe a simple change of symbol avoids confusion/ambiguity, especially to those who do not read the page in it's entirety. I may have caused someone offence by doing so since they swiftly returned the equation to it's previous form (inside 40mins of my edit, well played that man). Is my suggestion really that bad?Dtlloyd (talk) 22:16, 20 April 2011 (UTC)
replies: text: I reverted your edit because D is equal to 2×w0, so your edit made the equation incorrect (if one uses the conventional meaning of w0). I didn't notice that D was already in use in the article for something else.  That would clearly make it necessary to change one of the variables.--Srleffler (talk) 02:34, 21 April 2011 (UTC)

text: My mistake. Thank you for clearing this up.Dtlloyd (talk) 08:29, 21 April 2011 (UTC)
thread_title:  Just a small change 

message: When stating errors the objective approach gives the error in an estimate relative to that of the true value.  --Jbergquist (talk) 00:16, 22 March 2012 (UTC)
replies: text: It turns out in this case that the "true" value is not so true, and for many lenses the "approximate" value presented is more accurate than the value presented as "true". I've amended the text to reflect this better.--Srleffler (talk) 04:10, 22 March 2012 (UTC)
thread_title:  A Note on Objectivity 

message: N=f/D is unreliable as a definition of f-number and most often only an approximation.  For instance N is not equal to f/D in the typical thin lens diagram shown in the article, as explained by Kingslake in the quoted paragraph.  N is on the other hand always equal to 1/[2nsin(theta)] for a practical photographic lens, per Kingslake and othersImage Sensors and Signal Processing for Digital Still Cameras. That's the definition that should be used at the beginning of the section.  It follows that N = 1/2NA exactly, which should shorten the section considerably, increasing clarity and removing uncertainty.  Can page admins make the relative changes?  I will make similar comments to the f-number pageJack Hogan (talk) 16:09, 3 March 2016 (UTC)
replies: text: There is indeed an unreliable approximation here, but it's not , it's the thin lens. See the discussion on f-number page, and continue the discussion there rather than here if necessary. — Edgar.bonet (talk) 10:02, 4 March 2016 (UTC)
thread_title:  NA vs f-number 

message: Could someone rewrite the 'General Optics' preface? It is very unclear. I couldn't understand it.
Specifically, "maximal half-angle of the cone of light that can enter or exit the lens". What does it mean? Say, we have an object that touches the lens at the center. (Let us assume the lens is thin.) Then this half-cone is 90°. Clearly this is not what is intended.
Lockywolf (talk) 03:29, 7 September 2017 (UTC)
replies: text: You missed the line in the second paragraph, "The NA is generally measured with respect to a particular object or image point and will vary as that point is moved.". So, yes if your object is touching the lens the half-cone is 90°. That's not a particularly interesting case, since the lens isn't going to form an image there.--Srleffler (talk) 05:00, 7 September 2017 (UTC)
thread_title:  Improvement request 

message: Under-maintained stub without enough content to keep as a standalone article. Topic is closely related to the proposed target. –LaundryPizza03 (dc̄) 23:16, 7 April 2021 (UTC)
replies: text: I don't think this article is a good merge target for that topic. Perhaps it belongs in a microscopy article somewhere?--Srleffler (talk) 17:30, 10 April 2021 (UTC)
replies: text: Diffraction-limited system might be a better target. Optical unit is rather in need of improvement too (even if merged). Klbrain (talk) 11:27, 13 September 2021 (UTC)

text: I cleaned up Optical unit to the best of my ability, but there's not a lot of sourcing.  Added a discussion on the talk page of that article to discuss what should be done with it. PianoDan (talk) 21:08, 9 December 2021 (UTC)
replies: text: Without further discussion, I am closing the merge request, and leaving Optical unit where it is. PianoDan (talk) 17:12, 15 December 2021 (UTC)
thread_title:  Proposed merge of [[Optical unit]] into [[Numerical aperture]]