antennaboy Posted June 11, 2012 Share #1 Posted June 11, 2012 Advertisement (gone after registration) Hello Forum, it is said that in the case of a converging lens, the field of view is determined by the focal length f of the lens and the size of the film: the smaller f and the larger the film size the larger the FOV.... Does the diameter of the lens not play a role? In the case of mirrors (like a flat mirror) I "think" the FOV depends on the size of the mirror, correct? thanks, antennaboy Quote Link to post Share on other sites More sharing options...
Advertisement Posted June 11, 2012 Posted June 11, 2012 Hi antennaboy, Take a look here field of view FOV.... I'm sure you'll find what you were looking for!
01af Posted June 11, 2012 Share #2 Posted June 11, 2012 ... the field of view is determined by the focal length f of the lens and the size of the film: the smaller f and the larger the film size the larger the FOV ... As a first-order approximation—which is accurate enough for most intents and purposes (but not all)—this is correct. Does the diameter of the lens not play a role? Sure it does. The lens must be wide enough to cover the film (or sensor). That's why a 500 mm for 35-mm format is long and thin. A 500 mm lens with the same aperture that is supposed the cover the same angle-of-view as a 50 mm lens on 35-mm format would also be long but not thin. It would look like, say, an Elmar-M 50 mm lens but ten times longer and ten times wider ... and it would cover a film area 100× the size of 35-mm film (ten times wider and ten times higher). In the case of mirrors (like a flat mirror) I "think" the FOV depends on the size of the mirror, correct? Sure—and on the distance to the mirror, too. And in case of a window, it's the same again: the field-of-view that you can see through also it depends on your distance to the window as well as the size thereof. Quote Link to post Share on other sites More sharing options...
luigi bertolotti Posted June 11, 2012 Share #3 Posted June 11, 2012 (edited) As a first-order approximation—which is accurate enough for most intents and purposes (but not all)—this is correct. To complete this excellent answer, I'd say that the "but not all" can be taken into account in macro photography, which is a rather common though specialized field : in this case, the dependancy of FOV from distance of focus (almost negligible at "normal" distances) becomes significant : a 50mm lens (on 35mm sensor/film) mounted on a bellows at a significant extension has the FOV of a light tele like 80-100 mm... and for microphotography (always on 35mm) lenses do exist with focal 25mm, which by no way are wideangles... they are designed to be used at very very short distances, with great bellows extension, and neither can be used at infinity or even 1 meter - they wouldn't cover the frame. Edited June 11, 2012 by luigi bertolotti Quote Link to post Share on other sites More sharing options...
antennaboy Posted June 18, 2012 Author Share #4 Posted June 18, 2012 thanks everyone. So, in summary, for a single, positive lens, the field of view (leaving approximations out), depends on the distance from the lens to the objects (large distance --> small FOV); the focal length of the lens (large f --> larger FOV) the film size (large film --> large FOV) the lens diameter (large D --> large FOV) A flat mirror field of view has a similar dependence of the above parameters (size, object distance, etc....) The FOV is given an the angular extent of the scene that gets images by the lens. There are the vertical, horizontal, diagonal angles to characterize the FOV... If a lens has a FOV horizontal angle that is different from the FOV vertical angle, does it automatically mean that the shape of the lens is asymmetric? I believe a symmetric lens would a have a field of view that is a perfect conical region of space... thanks antennaboy Quote Link to post Share on other sites More sharing options...
01af Posted June 18, 2012 Share #5 Posted June 18, 2012 ... for a single, positive lens, the field of view [...] depends on: the distance from the lens to the objects (large distance --> small FOV) ... No. ... the focal length of the lens (large f --> larger FOV) ... No. ... the film size (large film --> large FOV) ... Basically, yes—provided the lens can cover the film's (or sensor's) area. ... the lens diameter (large D --> large FOV). Basically, yes—provided the film (or sensor) is large enough to capture the image coming from the lens. In other words, the lens' circle of coverage and the film's (or sensor's) size must match each other. Larger film won't help when the lens cannot serve it, and a wider circle of coverage won't help when the film (or sensor) cannot capture it. The FOV is given an the angular extent of the scene that gets images by the lens. There are the vertical, horizontal, diagonal angles to characterize the FOV ... No. That's the angle-of-view. Do not confuse this with field-of-view. These two are closely correlated but not the same thing. If a lens has a FOV horizontal angle that is different from the FOV vertical angle, does it automatically mean that the shape of the lens is asymmetric? No. The symmetry (or asymmetry) of the lens has absolutely nothing to do with the image's aspect ratio. The lens always casts a circular image; the film (or sensor) crops an rectangle out of that. I believe a symmetric lens would a have a field of view that is a perfect conical region of space ... That's right—but that's true for any lens, not only symmetric ones ... well, with the exception of anamorphic lenses used in cinematography but let's keep these out of this discussion. Quote Link to post Share on other sites More sharing options...
120 Posted June 18, 2012 Share #6 Posted June 18, 2012 No. That's the angle-of-view. Do not confuse this with field-of-view. These two are closely correlated but not the same thing. depends on the author; there is no standardization of these terms Quote Link to post Share on other sites More sharing options...
01af Posted June 18, 2012 Share #7 Posted June 18, 2012 Advertisement (gone after registration) Depends on the author ... No, it doesn't. ... there is no standardization of these terms. Yes, there is. Quote Link to post Share on other sites More sharing options...
120 Posted June 18, 2012 Share #8 Posted June 18, 2012 Angle of field, angle of view, field of view, etc. are all used variously in the literature. Sorry, but that's just the way it is. Quote Link to post Share on other sites More sharing options...
jaapv Posted June 18, 2012 Share #9 Posted June 18, 2012 No it its not the way it is. Sloppy use does not set the norm. Quote Link to post Share on other sites More sharing options...
120 Posted June 18, 2012 Share #10 Posted June 18, 2012 No it its not the way it is. Sloppy use does not set the norm. Has nothing to do with sloppiness, just these are old terms and have been used variously for a hundred years or more. Quote Link to post Share on other sites More sharing options...
01af Posted June 18, 2012 Share #11 Posted June 18, 2012 Sloppy use does not set the norm. Even less does sloppy reading. Quote Link to post Share on other sites More sharing options...
120 Posted June 19, 2012 Share #12 Posted June 19, 2012 Even less does sloppy reading. so I should be reading what, exactly? Quote Link to post Share on other sites More sharing options...
01af Posted June 19, 2012 Share #13 Posted June 19, 2012 So I should be reading what, exactly? Any decent textbook about elementary geometry, optics, or photography. Maybe a dictionary will help, too. English is not my first language but still I'm absolutely sure that the difference between angle and field is as obvious in English as it is in my native language (which happens to be German). Field has several meanings but none might possibly be confused with angle. In particular, for a given lens, field-of-view depends on the subject-to-lens distance (wider at longer distances), angle-of-view does not (unless we're nit-picking). By the way, I didn't mean to say you were reading sloppily. I just wanted to generally point out that not only sloppy writing but also sloppy reading possibly can lead to misconceptions. Quote Link to post Share on other sites More sharing options...
120 Posted June 19, 2012 Share #14 Posted June 19, 2012 Any decent textbook about elementary geometry, optics, or photography. Maybe a dictionary will help, too. English is not my first language but still I'm absolutely sure that the difference between angle and field is as obvious in English as it is in my native language (which happens to be German). Field has several meanings but none might possibly be confused with angle. In particular, for a given lens, field-of-view depends on the subject-to-lens distance (wider at longer distances), angle-of-view does not (unless we're nit-picking). By the way, I didn't mean to say you were reading sloppily. I just wanted to generally point out that not only sloppy writing but also sloppy reading possibly can lead to misconceptions. I appreciate the distinction... but I don't find these two used consistently in textbooks. And I checked about fifteen. For example, one of the best has "field angle of view" used for your "angle of view" with the abbreviation FOV; a few have angle of view used for field of view; a couple suggest the terms are interchangeable. I would always check the context to be sure. Quote Link to post Share on other sites More sharing options...
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