Patent: Very small large aperture zoom lens optical formulas

Canon Rumors Guy

Canon EOS 40D
CR Pro
Jul 20, 2010
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www.canonrumors.com
Canon has published a pretty interesting optical design patent for large aperture zoom lenses. The two designs in this patent are pretty interesting.
Canon’s goal in this patent
To provide a zoom lens having a short total length and a small size but having high optical performance, and an image pickup apparatus having the same.
As you can see, these lens designs use the “reverse” zoom design like the original EF 24-70mm f/2.8L USM. This probably helps in reducing the length and size of the lens. As you can see, the image height changes when zooming in and out.
Overall length is quite impressive at 105.42mm (about 4″) at the wide end. Keep in mind that those measurements are from the image sensor to the front element of the lens design.
Example 1

Focal length: 28.84mm – 67.90mm
F-number: 2.91
Half angle of view: 32.68° – 17.67°
Image height: 18.50mm – 21.64mm
Overall length: 138.40mm – 105.42mm
Back focus: 10.97mm – 21.12mm

Example 2

Focal length: 28.84mm – 60.00mm...

Continue reading...


 

bbasiaga

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Nov 15, 2011
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If the image height doesn't cover the full frame sensor, how does Canon propose to accomplish a full image?
I'm guessing that it'll be heavily vignetted without correction in the corners at the wide end. The 24-240 lens, for example, has an image height of ~19mm at 24mm (there were a number of similar patents for that range, all in the upper 18s to lower 19s). It works very well with digital correction, as these likely would.

-Brian
 
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I really liked that the original EF 24-70 L started of at the right end then you could zoom out. It was counter intuitive at first, but for me I used it most frequently at the long end.
The advantage to that 'reverse' zoom is that the lens hood is effective throughout the zoom range, instead of only at the wide end.
 
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If the image height doesn't cover the full frame sensor, how does Canon propose to accomplish a full image?
By stretching the image. The geometric distortion at the wide end is substantial, and correcting that distortion results in the 'missing' (mechanically vignetted) corners being filled in. That geometric correction is forced (in-camera and in DPP) for lenses like the RF 16/2.8, RF 24-240 and RF 14-35/4L.

There was a recent front page post claiming a new set of patents were APS-C 'pancake' primes, based on an image height of 18.2mm. It turns out that the patented 16/2.8 in that post is not a new APS-C pancake lens, but rather is the existing RF 16mm f/2.8 lens that you can buy today (which isn't a pancake, but the length in the patent is consistent with the length of the production lens).

Simple as it is: The image height corresponds with APS sensor size.
The closest is actually APS-H, not APS-C. These are full frame RF lens designs. Consider what we know of Canon – is it more likely they'd make a lens with a larger image circle than necessary, or a smaller image circle than necessary that gets corrected by software (along with forcing that correction in-camera and in DPP)? The latter, of course.
 
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If image height == radius, it needs to be half that, or 23.6 mm, to cover FF.
Your math is wrong. The diameter of the FF image circle is ~43.2mm, and the image height for a FF image circle is ~21.6mm (not coincidentally, the image height at the longer focal lengths of the lenses in these patents is 21.64mm).
 
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