This unique lens will surprise you firstly by tiny size and light weight. The secret is in its optical construction. Kenko Mirror lens 400mm F8 is designed according to mirror-lens or catadioptric system, developed by famous soviet physician Dmitriy Maksutov. The same optical structure is applied in big (up to 2 meters in length) telescopes.
What is specific thing in this lens? First, is the central part of the tube fulfilled with second mirror. This effects the speed of the lens. Second, the lens does not have aperture unit. So the control of the light volume coming to the camera through the lens can be controlled either by shutter speed, or 67mm neutral density filters. If we indicate the speed of Kenko Mirror lens 400mm as F number, it would be F8, that is not so speedy.
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