03-22-2012, 07:05 PM
[quote name='Brightcolours' timestamp='1332415622' post='16918']
Indeed, that is what I wrote in my post. It very much depends on your usage of the lens.
My 70-200mm f4 L USM has no focus breathing either, depending on how one calculates it. Just like the 70-200mm f2.8 L IS USM II or others.
Interestingly, when one calculates it with the correct node whatsitcalled, you get a shorter focal length. When you calculate it without, just ignoring it, you get a longer focal length.
That on its own is not interesting. But what is interesting is that in field of view, you see it getting narrower when focussing closer.
So... that makes me wonder about the relationship of focal length and field of view... they do not seem to be fixed together. The relationship seems to change with focus distance.[/quote]
Focal length and field of view are linked together, actually, just that there is a non-linear relationship with magnification, close focusing IOW, and FoV.
The closer one focuses, the narrower the imaged FoV: This is caused by the image circle widening when focusing closer, just like it happens when doing macro shots. It is also the reason for losing light, relatively, when focusing closer than infinity. As you know, at 1:1 the image circle has twice the diameter of the image circle at infinity (which is why one loses effectively 2 stops at 1:1). Since the sensor and VF are only looking at the central part of the image, in principle one should therefore get a seemingly narrower FoV.
That's for lenses which focus normally, however, by extending the focusing barrel whilst keeping the configuration of the lens elements the same (like in most primes). With zoom lenses and IF lenses it gets more complicated, because both use internal lens movements for focusing, which generally tend to diminish the FL when focusing closer.
I did work out the FL of the Canon EOS 70-200 F/2.8L IS II a while ago, when someone claimed it got longer.at close focusing distances. Based on a few shots of a tape measure I could calculate actual FLs at different distances. Here is the final post on this, which also shows the formulas used:
[url="http://photography-on-the.net/forum/showpost.php?p=13599514&postcount=16"]http://photography-o...14&postcount=16[/url]
Effectively at MFD the FL at 200 mm zoom position is about 170 mm, which is approximately the same as it was with the older version. Some focus breathing, but not as large a difference as with the Nikon 70-200 F/2.8. Similarly, the IF EF-S 60 F/2.8 becomes a 50 mm lens at 1:1, and the EF 100 F/2.8 Macro USM becomes a 72.5 mm lens at 1:1.
Yes, essentially because the decrease in magnification due to the shortening of the FL is less than the increase in magnification caused by focusing more closely.
Kind regards, Wim
Indeed, that is what I wrote in my post. It very much depends on your usage of the lens.
My 70-200mm f4 L USM has no focus breathing either, depending on how one calculates it. Just like the 70-200mm f2.8 L IS USM II or others.
Interestingly, when one calculates it with the correct node whatsitcalled, you get a shorter focal length. When you calculate it without, just ignoring it, you get a longer focal length.
That on its own is not interesting. But what is interesting is that in field of view, you see it getting narrower when focussing closer.
So... that makes me wonder about the relationship of focal length and field of view... they do not seem to be fixed together. The relationship seems to change with focus distance.[/quote]
Focal length and field of view are linked together, actually, just that there is a non-linear relationship with magnification, close focusing IOW, and FoV.
The closer one focuses, the narrower the imaged FoV: This is caused by the image circle widening when focusing closer, just like it happens when doing macro shots. It is also the reason for losing light, relatively, when focusing closer than infinity. As you know, at 1:1 the image circle has twice the diameter of the image circle at infinity (which is why one loses effectively 2 stops at 1:1). Since the sensor and VF are only looking at the central part of the image, in principle one should therefore get a seemingly narrower FoV.
That's for lenses which focus normally, however, by extending the focusing barrel whilst keeping the configuration of the lens elements the same (like in most primes). With zoom lenses and IF lenses it gets more complicated, because both use internal lens movements for focusing, which generally tend to diminish the FL when focusing closer.
I did work out the FL of the Canon EOS 70-200 F/2.8L IS II a while ago, when someone claimed it got longer.at close focusing distances. Based on a few shots of a tape measure I could calculate actual FLs at different distances. Here is the final post on this, which also shows the formulas used:
[url="http://photography-on-the.net/forum/showpost.php?p=13599514&postcount=16"]http://photography-o...14&postcount=16[/url]
Effectively at MFD the FL at 200 mm zoom position is about 170 mm, which is approximately the same as it was with the older version. Some focus breathing, but not as large a difference as with the Nikon 70-200 F/2.8. Similarly, the IF EF-S 60 F/2.8 becomes a 50 mm lens at 1:1, and the EF 100 F/2.8 Macro USM becomes a 72.5 mm lens at 1:1.
Quote:To make it more clear: Correctly calculating the focal length shows the focal length going down slightly towards MFD with the Canons. But you see the field of view actually getting more narrow.
Yes, essentially because the decrease in magnification due to the shortening of the FL is less than the increase in magnification caused by focusing more closely.
Quote:The Nikon VR II and the Sigma OS show a strong widening of the field of view towards MFD.
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 ....