Patent: Canon EF 28-560mm f/2.8-5.6
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neuroanatomist said:
Interesting, and thanks for the actual measurement.
Which leads us to conclude that either Canon have broken the laws of optics and kept it very quiet, or the MP-E65 isn't a true 65mm and f2.8.
Personally I believe the latter
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privatebydesign said:
Can you see an elephant while you're wearing glasses? The whole elephant at once through 30mm diameter lenses?
You can see an entrance pupil appearing 92mm in diameter through a 60mm front element if you depart from the thin lens assumption so you are able to place the aperture somewhere in-between the front element and the sensor and place yourself close enough to the front element.
So yes, the MP-E 65 can have a 19.5mm front element through which an entrance pupil seemingly 23.2mm wide can be seen, as long as you place your eye rather close to the front element and the aperture is placed some distance from the front element.
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privatebydesign said:neuroanatomist said:
Interesting, and thanks for the actual measurement.
Which leads us to conclude that either Canon have broken the laws of optics and kept it very quiet, or the MP-E65 isn't a true 65mm and f2.8.
Personally I believe the latter
Haha, if there's one lens guaranteed to muddy the waters... I'm sure you're right though
I rather wonder what 65mm really means for a lens like this. I mean, normal lenses you can compare in terms of focal length and have an idea of field of view, and for macro lenses that still focus to infinity, the working distance at 1:1 . But this one is so odd, it seems redundant giving it a focal length designation (to me).
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hne said:
Ironic that your analogy much more closely approximates a thin lens.
It's not relevant, though, given the position of eyeglasses in relation to the biological optics. In this case, scyrene is looking in the right place – 'focal length' is the distance from the image plane to the apparent position of the entrance pupil when the lens is focused at infinity. The design of the MP-E precludes infinity focus, so the 65mm focal length is a theoretical not a real measurement, i.e. the FL would be 65mm if the lens could focus at infinity. It can't, so the actual focal length is shorter. Ignoring rounding of the aperture value, f/2.8 with a 19.5mm front element would be a max FL of 55mm. In fact, the actual FL with the focus racked out as far as possible is probably even shorter. As an example, the FL of the 100/2.8 Macro is 100mm focused at infinity, but ~67mm at 1:1.
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neuroanatomist said:hne said:
Ironic that your analogy much more closely approximates a thin lens.
In this case, scyrene is looking in the right place – 'focal length' is the distance from the image plane to the apparent position of the entrance pupil when the lens is focused at infinity. The design of the MP-E precludes infinity focus, so the 65mm focal length is a theoretical not a real measurement, i.e. the FL would be 65mm if the lens could focus at infinity. It can't, so the actual focal length is shorter. Ignoring rounding of the aperture value, f/2.8 with a 19.5mm front element would be a max FL of 55mm. In fact, the actual FL with the focus racked out as far as possible is probably even shorter. As an example, the FL of the 100/2.8 Macro is 100mm focused at infinity, but ~67mm at 1:1.
Eureka! This is very well explained, thanks
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neuroanatomist said:scyrene said:Eureka! This is very well explained, thanks
Well, you know, it'd still be cool if Canon had figured out how to get around the laws of physics.
They are trying with all of that blue stuff in the mix. I hear they are tinkering with dynamic lens elements that can change shape and FL when an electrical signal is applied.
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neuroanatomist said:hne said:
Ironic that your analogy much more closely approximates a thin lens.
In this case, scyrene is looking in the right place – 'focal length' is the distance from the image plane to the apparent position of the entrance pupil when the lens is focused at infinity. The design of the MP-E precludes infinity focus, so the 65mm focal length is a theoretical not a real measurement, i.e. the FL would be 65mm if the lens could focus at infinity. It can't, so the actual focal length is shorter. Ignoring rounding of the aperture value, f/2.8 with a 19.5mm front element would be a max FL of 55mm. In fact, the actual FL with the focus racked out as far as possible is probably even shorter. As an example, the FL of the 100/2.8 Macro is 100mm focused at infinity, but ~67mm at 1:1.
How do you have measured the FL of the 100mm or do you have some source of people who measured the FL?
My internal conflict is: The EF 100 (non-IS) needs a 4 times increase of the exposure time between infinitity and 1:1 which is conformal to a lens(group) of 100mm FL over the whole focusing range. While the MP-E 65 is sth. like a zoom where zooming is used to focus.
I alway thought the EF 100 Macro and EF-S 60 Macro are lenses which shift principal planes optically to simulate the shifting of a 100mm lens (having a fixed lens arrangement).
Would be great to have some additional info about that - Best, Michael
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