Talk:Focal length

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Contents 1 Diagram 2 herschel telescope of the 1700's 3 EFL 4 Convex & concave 5 Too Technical

[edit] Diagram

I only started learning about focal length today, so if the diagram is wrong or can be improved let me know. - Redjar 01:36, 14 Oct 2004 (UTC)

[edit] herschel telescope of the 1700's

Has anybody any idea where I can find a picture of the early telescope by Herschel ?

send to malcolm.bennett@ntlworld.com thanks

[edit] EFL

In my own experience, the term "EFL" is used to express the equivalent size of a digital lens in 35mm terms. For example, on some Olympus cameras, since the size of the sensor is smaller, a 150mm lens will have the same angle of view as a 300mm lens would on a 35mm camera. That lens would be described as having an EFL of 300mm.

I'm an amateur photographer and have been working in laboratory optics for the last four years and have never heard of this. EFL has a very well-defined meaning in terms of both traditional optics as well as consumer camera optics—it's the distance from the focal point to the first principle point. I strongly doubt an optically-saavy company like Olympus would deviate from the accepted standard on this...although I admit that I have been wrong in the past. --Milkmandan July 6, 2005 18:46 (UTC)

[edit] Convex & concave

I've re-generalized things a bit. It's important to note that convex and concave lenses are examples of converging and diverging lenses, not definitions of them. It's fine saying that in the picture caption, because the picture actually shows convex and concave lenses. But generally things are more complex. For example:

The third lens in this picture is a converging lens, but is both convex and concave. Therefore it's incorrect to define converging lenses as purely convex. --Bob Mellish 17:00, 25 October 2005 (UTC)

[edit] Too Technical

I find this article very heavy on the technical side, and it doesn't give an explaination in simple terms. Other photography terms have good basic descriptions, followed by more in-depth information.

This is not a photography article. It is an optics article that happens to be of interest to photographers (at least those who want to know more about how their cameras work.)--Srleffler 00:40, 8 November 2006 (UTC)

Agreed. It's great that we have the knitty-gritty of focal length here, but how about the simple description that it is, for practical purposes, quantified zoom? --User:RobertM525 00:26, 8 November 2006 (UTC)

Part of the problem is that we have several communities intersecting in this article. Focal length is an extremely important concept in optics, and deserves a full explanation. If all photographers care about is that it is "quantified zoom", that's fine, but then there is little need for them to read this article.--Srleffler 00:40, 8 November 2006 (UTC)