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Tuesday, August 3, 2010

Low-Cost Lens Solutions

Think about using a lens adapter to get lower-cost specialty lenses

Labels: GearLens Adapters

This Article Features Photo Zoom

When using a lens adapter, also keep in mind the format for which the lens was designed. Lenses designed for Four Thirds System DSLRs, for example, would vignette on APS-C or full-frame DSLRs, or 35mm SLRs, because their 21.63mm image-circle diameter is too small to cover the larger image formats. For the most part, adapters aren’t available to attach smaller-format lenses to larger-format cameras, so this shouldn’t be a big problem.

Another consideration is electronic linkage. Canon EF lenses use electronic diaphragms, so you can’t change the aperture when an adapter ring disconnects the electronic linkage between lens and camera. This—and the EOS system’s flange back distance, which is slightly shorter than that of other DSLRs—is why you don’t see adapters to connect EOS lenses to other DSLRs.

All of these things make it a good idea to consult the adapter maker’s specs (or query the manufacturer/distributor) to make sure the adapter will work with the lens-and-camera combo you want to use.

How To Achieve Critical Focus With An Adapter
The focusing screens in AF SLRs were designed for autofocusing, not for manual focusing. The focusing screens in manual-focus DSLRs have focusing aids such as central split images and microprism collars on ground-glass focusing screens that make it easier to focus manually. Some hard-core lens-adapter fans will change to one of these screens if their AF DSLR accepts interchangeable focusing screens and such a screen is available for it. A better solution, if your DSLR offers Live View, is to focus manually using the magnified Live-View image.

Some adapters come with chips that activate an AF DSLR’s focus-assist system so the “in-focus” lamp in the viewfinder glows when you’ve achieved focus manually. You also can buy chips and install them on the adapters yourself. Some adapters from Novoflex incorporate an aperture-control ring so you can adjust apertures with lenses that lack one, such as Nikon’s G-series. With most adapters, you can use manual exposure control or aperture-priority AE, but focusing will be manual (an exception is adapters to attach autofocus Four Thirds System lenses to Micro Four Thirds System cameras—some adapters retain autofocusing capability with some of these lenses).

When you use a compatible lens, a modern DSLR will keep the aperture wide open for easy composing and focusing, regardless of the aperture you choose for the shot. The camera then will automatically stop down the lens to the selected aperture when you depress the shutter button to make the shot.


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