Large aperture lenses already have a large diameter, and this tends to increase even further when equipped with image stabilisation, so the rearward positioning of the diaphragm is important. Since the diaphragm is located relatively far from the mount, the diameter of the rear lens group has to be larger. (Lens front) Diaphragm - Image stabilisation unit - Rear lens group (Camera) On the other hand, as mentioned earlier, since the image stabilisation unit is also positioned on the mount side, the components must be arranged in the following order: Iwamoto: Due to the nature of optical design, the further the diaphragm (EMD unit) is from the rear of the optical system (i.e., the mount side), the larger the rear lens diameter must be.

This is possible because of the large diameter EF mount, which provides a maximum aperture of f/1.4. The optical arrangement makes the best use of the large diameter EF mountĮOS 5D Mark IV/ EF85mm f/1.4L IS USM/ FL: 85mm/ Manual exposure(f/1.4, 1/2500sec)/ ISO 200/ WB: AutoĪn image that is not only in sharp focus, but also carries a beautiful bokeh in the background. In the 2nd part of our interviews with the developers of Canon’s new EF85mm f/1.4L IS USM lens ( Part 1 here), we learn more about the unique features in the optical and mechanical design of an L-series lens.

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