11-02-2012, 09:01 PM
Hi BC,
[quote name='Brightcolours' timestamp='1351863455' post='20785']
Those calculations mean nothing, Wim.
I have before already pointed out that what is important to the photographer is not focal length, but field of view.
What is problematic (for some) about the Nikon (and Sigma) 70-200mm f2.8 VR II (OS) is that the field of view gets a lot wider when focusing closer.
You do not get that with the canon or this new Nikon. In fact, the field of view gets more narrow with my Canon 70-200mm f4 when focussing closer.
So to all intends and purposes, the Nikon 70-200mm f2.8 VR II shows strong focus breathing, resulting in very evident wider field of view. The new nikon 70-200mm f4 VR does not show strong focus breathing, and will NOT show a wider field of view when focusing closer. Like the Canon(s), it will show a slightly more narrow field of view when focusing closer (if the published specs are reliable).
Or did you think that the calculated 174mm meant a wider field of view? I assure you, it does not. Again, it is not the rather theoretical focal length number that matters for us (photographers), but the widening field of view. Not many realize that focal length numbers are not fixed with a field of view figure.
As example the Canon 70-200mm f4 L USM focussed at MFD and infinity, Sigma 18-50mm f2.8 EX DC focussed at MFD and infinity.
Both are IF lenses, one (70-200mm f4) shows a narrowing of field of view, the other (18-50mm) a clear widening of field of view.
According to the specs, the new Nikon 70-200mm f4 is similar to the Canon.
[ATTACHMENT NOT FOUND]
[/quote]
By definition, with old fashioned focusing lenses, i.e., with extension of the distance between optical node(s) and camera, closer focusing makes the FoV narrower - AoV should stay the same, but now we have a crop essentially of the image circle at infinity, so we only see part of what the lens is capable of displaying. If the FL goes down while focusing closer, this automatically means that the AoV gets wider, and we therefore will see a larger part of the original image circle, however, at reduced magnification, because the FL is getting shorter after all.
The question now really becomes what is meant with focus breathing, and to be very honest, I have seen too many contradictory definitions to be too bothered by it myself. From an optical POV, it is impossible to have the same relations between fore- and background while focusing closer or further away if the FL changes. However, that is neither the case if the FoV stays exactly the same, because in that case the FL MUST change. The same FoV at a short distance means that the FL must be shorter due to the fact that we can only see part of the image circle at infinity, hence AoV must get wider, and hence FL must get shorter. That changes the way the relationship between foreground and background objects are imaged rather drastically. At shorter FLs the background disappears more quickly into the background than at larger FLs, just look at the difference between a WA and a tele lens. This effect may not be very drastic at relatively long, i.e., non-macro distances, let's say 1 m or further away, and be hidden by the effect of large apertures and the unsharpness and potential bokeh that come with that, but at shorter distances this really is almost unavoidable (when shifting focus from something up close to something much further away).
Personally, I prefer lenses which keep the original AoV, hence show a smaller FoV at close distances. This is entirely natural, because it also is the way the human eye works. This makes for exactly the same relationships, magnification wise, in fore- and background, whether in focus or not. And this is one of the definitions of focus breathing I have seen - no change in original, or true AOV, hence no change in FL while focusing. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />
I think for stills it is a bit of a moot point anyway, other than that we cannot achieve maximum magnification factors according to "official" FLs at the indicated focus distances. With video and film it makes for a less stable image when shifting focus from foreground to background or vice versa.
Kind regards, Wim
[quote name='Brightcolours' timestamp='1351863455' post='20785']
Those calculations mean nothing, Wim.
I have before already pointed out that what is important to the photographer is not focal length, but field of view.
What is problematic (for some) about the Nikon (and Sigma) 70-200mm f2.8 VR II (OS) is that the field of view gets a lot wider when focusing closer.
You do not get that with the canon or this new Nikon. In fact, the field of view gets more narrow with my Canon 70-200mm f4 when focussing closer.
So to all intends and purposes, the Nikon 70-200mm f2.8 VR II shows strong focus breathing, resulting in very evident wider field of view. The new nikon 70-200mm f4 VR does not show strong focus breathing, and will NOT show a wider field of view when focusing closer. Like the Canon(s), it will show a slightly more narrow field of view when focusing closer (if the published specs are reliable).
Or did you think that the calculated 174mm meant a wider field of view? I assure you, it does not. Again, it is not the rather theoretical focal length number that matters for us (photographers), but the widening field of view. Not many realize that focal length numbers are not fixed with a field of view figure.
As example the Canon 70-200mm f4 L USM focussed at MFD and infinity, Sigma 18-50mm f2.8 EX DC focussed at MFD and infinity.
Both are IF lenses, one (70-200mm f4) shows a narrowing of field of view, the other (18-50mm) a clear widening of field of view.
According to the specs, the new Nikon 70-200mm f4 is similar to the Canon.
[ATTACHMENT NOT FOUND]
[/quote]
By definition, with old fashioned focusing lenses, i.e., with extension of the distance between optical node(s) and camera, closer focusing makes the FoV narrower - AoV should stay the same, but now we have a crop essentially of the image circle at infinity, so we only see part of what the lens is capable of displaying. If the FL goes down while focusing closer, this automatically means that the AoV gets wider, and we therefore will see a larger part of the original image circle, however, at reduced magnification, because the FL is getting shorter after all.
The question now really becomes what is meant with focus breathing, and to be very honest, I have seen too many contradictory definitions to be too bothered by it myself. From an optical POV, it is impossible to have the same relations between fore- and background while focusing closer or further away if the FL changes. However, that is neither the case if the FoV stays exactly the same, because in that case the FL MUST change. The same FoV at a short distance means that the FL must be shorter due to the fact that we can only see part of the image circle at infinity, hence AoV must get wider, and hence FL must get shorter. That changes the way the relationship between foreground and background objects are imaged rather drastically. At shorter FLs the background disappears more quickly into the background than at larger FLs, just look at the difference between a WA and a tele lens. This effect may not be very drastic at relatively long, i.e., non-macro distances, let's say 1 m or further away, and be hidden by the effect of large apertures and the unsharpness and potential bokeh that come with that, but at shorter distances this really is almost unavoidable (when shifting focus from something up close to something much further away).
Personally, I prefer lenses which keep the original AoV, hence show a smaller FoV at close distances. This is entirely natural, because it also is the way the human eye works. This makes for exactly the same relationships, magnification wise, in fore- and background, whether in focus or not. And this is one of the definitions of focus breathing I have seen - no change in original, or true AOV, hence no change in FL while focusing. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />I think for stills it is a bit of a moot point anyway, other than that we cannot achieve maximum magnification factors according to "official" FLs at the indicated focus distances. With video and film it makes for a less stable image when shifting focus from foreground to background or vice versa.
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 ....