User talk:BoP

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Hello BoP, welcome to Wikipedia.

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Again, welcome! Chris Roy 01:26, 3 May 2004 (UTC)

[edit] Category:British Hills by Height

I saw you comments in Wikipedia:Village pump (proposals)#Automatically Generating Category-Lists from Categories and realised you may be interested in the categorys Category:British Hills by Height and Category:Mountains by Elevation (km). These appear (in my opinion) to be liked by the actual mountain contributors. Can I tempt you to make a contribution/comment here to save (or otherwise) these pages?: Wikipedia:Categories_for_deletion/Log/2005 September 1#Category:Mountains_by_Elevation_(km) and its subcategories

¢ NevilleDNZ 04:17, 4 September 2005 (UTC) ¢

[edit] Self-phase modulation

Hi BoP, I just did a rewrite of self-phase modulation, because I think the derivation you added isn't correct. In particular the frequency shift doesn't seem right. Please take a look and let me know if I'm missing something. --Bob Mellish 00:58, 4 November 2005 (UTC) - I agree that the new derivation is much more generic and looks quite O.K. to me! (I have only corrected the inst. phase \phi \rightarrow \phi(t))--BoP 08:24, 27 December 2005 (UTC)

[edit] Numerical aperture and focal length

Hi BoP. In Numerical aperture you wrote "The f-number therefore is independent of the object distance and is directly related with the focal length, while the numerical aperture is dependent on the particular imaging geometry." This is not really true. The f-number (as defined in the article) describes the imaging properties of the lens only when the object or the image is at infinity. It is no more independent of the imaging geometry than numerical aperture is. To describe imaging with the object and image a finite distance from the lens, one must use the "effective f-number", which is defined slightly differently. (I don't remember the formula offhand, and the book where I have it is at work.) Photographers simply ignore this. One could say that the use of f-number in photography involves an approximation, that the object distance is much greater than the image distance. I would expect that this approximation would become noticeably inadequate for closeups and macro photography, but unless someone is dealing with exposure very quantitatively one still might not notice.--Srleffler 00:47, 4 March 2007 (UTC) Agreed - the earlier definition was a bit misleading - The current version seems to take care of that! --BoP (talk) 21:44, 13 December 2007 (UTC)