[quote name='Brightcolours' timestamp='1351894274' post='20797']
Since when are Angle of View and Field of View not the same?
[url="http://en.wikipedia.org/wiki/Angle_of_view"]http://en.wikipedia....i/Angle_of_view[/url]
"In photography, angle of view describes the angular extent of a given scene that is imaged by a camera. It is used interchangeably with the more general term field of view." <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/blink.gif' class='bbc_emoticon' alt=':blink:' />
Anyway... as you see from my samples, the Angle of view gets more narrow when focussing closer with my Canon EF 70-200mm f4 L USM. Same will be the case with the Nikon AF-S 70-200mm f4 VR, as its published specs predict. Not too surprising, seeing just how smilar most of the lens's construction is.
The f2.8 VR II has a very clear angle of view widening. That is why people complain about its focus breathing.
Anyway... focal length and Angle of View are not linked 1:1. When the focal length stays the same at different focus distances, the Angle of view (Field of view) will change (get more narrow). This means that what you said earlier, about lenses for film, will have to change focal length to keep the same angel of view/field of view. And this then means, if those lenses have no focus breathing, that focus breathing is about keeping the same field of view/angle of view through their focus range, and that it is not about the focal length figure of the optics.
[/quote]
AoV and FoV are not the same actually. FoV, as I implied in my earlier post, is determined by FL and focusing distance, and obviously depends on imaging receptor. AoV depends on the image circle at infinity. It stays the same if the FL doesn't chaneg during focusing, but th eimage circle gets larger when focusing closer.What is referred to in the Wiki article as "angle of coverage", is what really the angle of view is. If FoV and AoV were exchangeable, there would really only be one anyway. Field of view is ablout the frame one can see, AoV is always about the lens in a particular situation, i.e., the image circle it is designed for. And AoV is always expressed as the AoV at infinity, just like FL is. That is where the link between FL and AoV lies.
FoV changes with focusing distance, normally, provided FL and AoV stay the same. It is thinkable that FoV stays the same while focusing, but that means that FL and AoV must change. If AoV really would change with FoV, we wouldn't have a loss of light when focusing closer. If FoV = AoV, we would have the same shutter speed as if we would focus at infinity, at the same aperture under the same lighting conditions. However, we don't, because the AoV stays the same, and therefore the image circle increases, of which we see less, IOW, a smaller or narrower FoV, of the actual image projected.
BTW, whether a certain term is used interchangeably with another, doesn't mean that that is the correct use. At least not 20-30 years ago <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />. And if a lens shows the same FoV at any focusing distance, it does mean one has to define at what distance this FoV is determined. It also means by definition that FL and therefore AoV must change when focusing, and it requires some kind of "zooming" mechanism to achieve this. The only way to increase the FoV when focusing closer to the same FoV as it was at larger distances, is to enlarge the AoV, IOW, go wider, whether that is only a little or not.
It is really about definitions in this case. AoV is defined as the angle the lens uses to create its image circle, at infinity. FoV is just what the camera/lens combination happens to see at a certain focusing distance within that AoV.
Kind regards, Wim
Since when are Angle of View and Field of View not the same?
[url="http://en.wikipedia.org/wiki/Angle_of_view"]http://en.wikipedia....i/Angle_of_view[/url]
"In photography, angle of view describes the angular extent of a given scene that is imaged by a camera. It is used interchangeably with the more general term field of view." <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/blink.gif' class='bbc_emoticon' alt=':blink:' />
Anyway... as you see from my samples, the Angle of view gets more narrow when focussing closer with my Canon EF 70-200mm f4 L USM. Same will be the case with the Nikon AF-S 70-200mm f4 VR, as its published specs predict. Not too surprising, seeing just how smilar most of the lens's construction is.
The f2.8 VR II has a very clear angle of view widening. That is why people complain about its focus breathing.
Anyway... focal length and Angle of View are not linked 1:1. When the focal length stays the same at different focus distances, the Angle of view (Field of view) will change (get more narrow). This means that what you said earlier, about lenses for film, will have to change focal length to keep the same angel of view/field of view. And this then means, if those lenses have no focus breathing, that focus breathing is about keeping the same field of view/angle of view through their focus range, and that it is not about the focal length figure of the optics.
[/quote]
AoV and FoV are not the same actually. FoV, as I implied in my earlier post, is determined by FL and focusing distance, and obviously depends on imaging receptor. AoV depends on the image circle at infinity. It stays the same if the FL doesn't chaneg during focusing, but th eimage circle gets larger when focusing closer.What is referred to in the Wiki article as "angle of coverage", is what really the angle of view is. If FoV and AoV were exchangeable, there would really only be one anyway. Field of view is ablout the frame one can see, AoV is always about the lens in a particular situation, i.e., the image circle it is designed for. And AoV is always expressed as the AoV at infinity, just like FL is. That is where the link between FL and AoV lies.
FoV changes with focusing distance, normally, provided FL and AoV stay the same. It is thinkable that FoV stays the same while focusing, but that means that FL and AoV must change. If AoV really would change with FoV, we wouldn't have a loss of light when focusing closer. If FoV = AoV, we would have the same shutter speed as if we would focus at infinity, at the same aperture under the same lighting conditions. However, we don't, because the AoV stays the same, and therefore the image circle increases, of which we see less, IOW, a smaller or narrower FoV, of the actual image projected.
BTW, whether a certain term is used interchangeably with another, doesn't mean that that is the correct use. At least not 20-30 years ago <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />. And if a lens shows the same FoV at any focusing distance, it does mean one has to define at what distance this FoV is determined. It also means by definition that FL and therefore AoV must change when focusing, and it requires some kind of "zooming" mechanism to achieve this. The only way to increase the FoV when focusing closer to the same FoV as it was at larger distances, is to enlarge the AoV, IOW, go wider, whether that is only a little or not.It is really about definitions in this case. AoV is defined as the angle the lens uses to create its image circle, at infinity. FoV is just what the camera/lens combination happens to see at a certain focusing distance within that AoV.
Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....