Major manufacturers Canon

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Many astrophotographers have settled on the Canon Digital Rebel, XT, XTi (EOS 300D, 350D, and 400D) and their successors. These are low-priced, highperformance cameras. One reason Canon leads the market is that Canon is the only DSLR maker that has specifically addressed astrophotography, first with tutorials published in Japan1 and then, briefly, by marketing a special DSLR for astrophotography (the EOS 20Da).

Also, because Canon SLR bodies are relatively compact, you can use other brands of lenses on them, including Nikon, Olympus OM, Leicaflex, Contax/ Yashica, and Pentax-Praktica M42 screw mount. For more about lens adapters, see p. 80. Of course, with an adapter, there is no autofocus, but with Canon DSLRs, you can use the exposure meter and aperture-priority auto exposure (useful for eclipses) with any lens or telescope.

So far, there have been three generations of Canon DSLRs suitable for as-trophotography. The EOS 10D and Digital Rebel (300D) used the original Canon DIGIC image processor and CRW raw file format. With the EOS 20D, Canon moved to a new system, DIGIC II, with the CR2 raw file format; this is used in the Digital Rebel XT (350D), XTi (400D), 20D, 20Da, 30D, and their successors. The third generation, DIGIC III, began with the EOS 1D Mark III in 2007. Each of these has its own raw file format, and software that supports one will not necessarily support another.

Canon's nomenclature can confuse you. The EOS Digital Rebel, EOS Kiss, and EOS 300D are the same camera, but the EOS 300 and EOS Rebel are film cameras from an earlier era. The EOS 30D is an excellent recent-model DSLR, but the EOS D30 is an early DSLR from before Canon developed sensors suitable for astronomy. And so on. If you want to buy a secondhand camera, study the nomenclature carefully.

1 On the Web at http://web.canvn.jp/Imaging/astro/index-eMml.

Nikon

Nikon also has a loyal following. At present, Nikon DSLRs are a bit awkward to use for astronomy because of a quirk called the "star eater" (p. 17). This is a problem that could disappear at any moment if Nikon made a change in the firmware, but so far, the D40, D50, D70, D70s, D80, and D200 (among others) are all afflicted. Also, it's harder to build your own electrical accessories for Nikons because several models rely on an infrared remote control rather than a plug-in cable release.

Another Nikon drawback is that if the lens contains no electronics, the DSLR cannot use its exposure meter and cannot autoexpose. You can attach Nikon AI-mount manual-focus lenses to a Nikon DSLR, but the exposure meter is disabled. Of course, for astrophotography this is usually not a concern.

Nonetheless, Nikon cameras are easy to use for daytime photography, they are widely available, and some astrophotographers report that the sensor in the D40, D50, and D80 is more sensitive to stars than the competing Canon sensor -possibly because a Mode 3 image (p. 17) is "rawer" than Canon's raw images. Nikon CCD sensors are reportedly made by Sony, but I cannot confirm this.

Others

Using modified Nikon bodies, Fuji makes DSLRs for general and scientific photography. The Fujifilm S3 Pro and S5 Pro have special sensors designed for high dynamic range; each pixel actually has two sensors, one for normal exposure and one to deal with overexposed highlights. Both cameras offer live focusing, and there is a version (the S3 Pro UVIR) that is not filtered to exclude infrared light. These cameras are relatively large and heavy.

Pentax, Sony, Olympus, and other DSLR makers are highly respected but have not achieved a large following among astrophotographers, and I have not tested their products. It is widely rumored that most other manufacturers use Sony CCD sensors similar to Nikon's, although of course the firmware and internal image processing are different. Before buying any camera, you should search the Web and get astrophotographers' opinions of it; also make sure its file formats are supported by astrophotography software.

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