 Judy A. Lawhon |
About a lens I have a Canon Digital Rebel 300D and was given a 500mm F/8 mirror lens. Can anyone tell me how or when to use this lens? It came with a skylight, ND2x and ND4x filters. What is a mirror lens and how do I use it, please. Thanks so much. Judy Lawhon
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Michael H. Cothran |
Mirror lenses have been around for decades. I actually owned a couple years ago. They incorporate mirrors in the optical design which keeps down the size, weight, and cost. Disadvantages include having only one f-stop (usually f8), and rather poor image quality. But for the price you paid for yours, put it on your camera (if it will mount), and have fun. I doubt that the lens has the electrical contacts to mate with your camera, although it may. If it doesn't, you won't be able to activate your camera meter, and will have to use an altenative method of metering. Before you take it out to conquer the world, here are three pieces of advice I can offer when using this fun lens - 1. Focus very, very carefully. 2. Hunker it down on a very strong tripod, not some wobbly WalMart special. 3. Don't even THINK about hand holding this lens if you want even a remote chance of obtaining a sharp image. Good luck, Michael H. Cothran www.mhcphoto.net
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Jon Close |
Mirror lens (also known as Reflex) use mirrors to "fold" the light path, making the lens very compact for its focal length. It is the same design used for reflecting telescopes. Light enters the large objective lens and hits a mirror at the other end of the lens. That mirror focuses the rays to another mirror glued to the backside of the objective lens, which passes the light back into the camera. Relatively light and economical, mirror lenses also can be very sharp as the mirrors do not impart the spherical and chromatic aberrations inherent in refracting glass lenses. The downside is the design dictates a non-adjustable aperture, out of focus highlights are rendered as doughnut shapes instead of blurred disks, the lens is manual focus only (though Minolta has an autofocus model for their Maxxum series) and build quality can vary widely. The lens may have an EF-mount (Canon's EOS lens mount), or some have a T-mount which requires a T- to EOS adapter. Either way, when mounted to your EOS there is no communication between the lens and camera. You will have manual focus only, and metering can be done only in Av (aperture priority) or Manual modes only. On the camera, set the aperture value to "00". Av will automatically choose the shutter speed, or you set it manually in M. The skylight filter is a UV filter with a pinkish tint for warming scenes that might be excessively blue (like open shade). More useful with film than with a digital camera where white balance is a more effective control. The ND2x and ND4x are neutral density filters. Because the lens has fixed aperture of f/8, these filters are used to give slower shutter speeds. For example, at ISO 400, your exposure may be 1/1000 at f/8. The ND2x cuts 1 stop of light, so using it you would get 1/500 @ f/8. ND4x cuts 2 stops of light, giving you 1/250 @ f/8. Again, these are not as necessary with a digital camera, where ISO can be changed on the fly to accomplish the same thing.
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