Reflex or mirror lenses

Ken Rockwell reviews the Nikon Reflex-Nikkor 500mm f/8 lens, one of several mirror-based telephoto lenses Nikon once made. These are catadioptric lenses, which use a combination of mirrors and lenses. It’s an optical type familiar to astronomers: the popular Schmidt-Cassegrain and Maksutov telescopes are catadioptric systems. (It doesn’t look like Reflex-Nikkors are either Schmidts or Maksutovs, though.)

Catadioptrics achieve very long focal lengths in a compact space, and, because they use mirrors, there’s no chromatic aberration. But their focal ratio is fixed and, at those long focal lengths, depth of field is very shallow even at f/8 or f/11 — and because of the central obstruction, bokeh is horrible: out-of-focus elements appear as donuts. This isn’t a problem in astronomy, where focus is always at infinity — I’ve taken plenty of shots through my Schmidt-Cassegrain — but it’s distracting in terrestrial telephoto photography. (Three examples on Flickr here, here and here.)

This page compares a Tamron mirror lens with a Canon telephoto: the Canon is the clear winner in quality, but the mirror lens is considerably cheaper (another advantage). Only one reflex lens — Sony’s 500mm f/8, still available — has ever had autofocus; the rest are manual lenses.

There’s a mirror reflex lens group on Flickr, and an (inactive) blog about mirror lenses.

Colour photos of Imperial Russia

Emir of Bukhara (Prokudin-Gorskii collection)

In 1948, the Library of Congress purchased a collection of colour images taken by Russian photographer Sergei Mikhailovich Prokudin-Gorskii (1863-1944). Taken during a series of surveys of the Russian Empire on behalf of the Tsar prior to World War I, these photos were produced by taking a series of black-and-white photos through red, green and blue colour filters; Prokudin-Gorskii created colour images by combining the images with a special projector using the same filters. (This method is still used by astrophotographers, who use specialized monochrome CCDs to take a series of images through special filters.) The result, when processed with modern-day tools (hello, Photoshop), is a series of stunningly vibrant colour photos from a period otherwise remembered in sepia, and from a part of the world not often seen in the West, even at the time. A total of 2,607 images are available in the LOC’s Prokudin-Gorskii Collection; an online exhibition from the LOC and The Big Picture offer some of the more stunning examples. Above: a portrait of the Emir of Bukhara.

First impressions: Nikon 105mm macro lens

Nikon macro lens Last week I bought another new lens — Nikon’s 105mm macro lens. (That makes seven, in case you’re wondering.) I took advantage of the Henry’s eBay channel and got it for more than $200 less than it would have normally cost, but it’s still the most expensive lens I’ve ever bought. (I have another lens that costs more new, but I bought it used.) It’s also the heaviest: at 750 grams, it weighs more than the camera it’s attached to. The thing is a tank — no surprise there, it’s a professional, full-frame lens.

I’ve had a chance to run it through its paces a bit; here are my test shots. I bought this lens for four purposes: as a macro lens (natch), as a portrait lens, as a fast telephoto prime, and for astrophotography. I haven’t gotten good results using it for macro photography: a fast macro lens isn’t much good, because there’s absolutely no depth of field at f/3, so I need to stop it down and throw some more light at my target (one of these will probably be necessary at some point). There’s a lot of focus travel, so it can be a bit challenging keeping moving snakes in focus; I imagine I’ll be suffering some frustrations there. But as a portrait lens and telephoto prime, it’s fantastic — so scary-sharp that I can crop like crazy and still end up with a great image. I haven’t tested it for wide-field astrophotography yet, but I’m betting the ED glass will yield good results.

I expect to use this lens a lot — a good thing considering how expensive it is. Probably the last lens I buy for a while. (Yes, you can point to this blog entry later on if I backtrack on that statement.)

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