All right: it's not hard to see why you might need "spectacles" versions of both 35mm and 135mm lenses, and then there are the vanishingly rare (and non-Leica-built) "spectacles" 21mm lenses that call up the 35mm frame on everything except an M3 (which hasn't got one) and convert it to a 21mm field of view. But why on earth would you need "spectacles" on a 50mm lens? Why was the 50mm f/2 Summicron offered both in conventional form and in "spectacles" guise, also unofficially known as "close focus" and officially as "Dual Range"?

"Spectacles" Summicron, with the spectacles off and on. There's no positive lock, just a spring-loaded ball, so it is possible to lose the spectacles without noticing. Aaargh!

This time, the answer lies in the close-focusing ability of rangefinder lenses. Few 50mm lenses focus much closer than about one meter, or 40". It makes the rangefinder coupling more difficult (though not insurmountable) but what really makes life interesting is the difference between the field of view of the lens and the field of view of the viewfinder. This is not just a question of parallax--the separation between the lens and the viewfinder--but also of the reduction in the field of view as the lens focuses closer.

Hey, presto! Spectacles! These allow the rangefinder and viewfinder to work down to about half the usual viewing distance: in fact, in the range from 90cm (35") to 50cm (19"). There's a no-focus gap between one meter and 90cm, but at the closest focusing distance, you are down to about 1/7 life size instead of about 1/17. It's still not exactly macro, but it can be very useful. Unlike the "spectacles" versions of the 35mm and 135mm lenses, where the "spectacles" are fixed, the "spectacles" on a 50mm f/2 "spectacles" or close-focusing Summicron are removable, and are added only for close focusing, when they are clipped on to the top of the lens like high-precision pince-nez spectacles.

Once again, "spectacles" added significantly to the price: about 25 percent, this time. "Spectacles" Summicrons are significantly less common than non-"spectacles" versions, but equally, they are far from rare.

Understandably, the spectacles sometimes get lost, which is why you occasionally see advertisements for "50mm close-focusing Summicron, no spectacles." The lens is still perfectly usable in the normal range: it just looks a bit lonely, and it doesn't feel quite right. When I say "feel," I don't mean the tactile sensation: I mean something much more abstract, the sort of feeling you get when a picture isn't hanging straight on a wall.

Values (or at least prices) are very difficult to give. Among the 35mm lenses, "spectacles" versions should logically command either more or less money than their non-bespectacled cousins, depending on whether the photographer needs them or not. Personally, I'd pay less for a 35mm "spectacles" lens than for a non-"spectacles" version--not least because I couldn't use the "spectacles" lens on my Voigtländers.

"Spectacles" Summicron, with the spectacles off and on. There's no positive lock, just a spring-loaded ball, so it is possible to lose the spectacles without noticing. Aaargh!

But of course, we are talking about Leica collectors here, which means we are not talking about wholly rational people (I know; I used to collect Leicas). Summiluxes (f/1.4) which are relatively rarely encountered in "spectacles" form, tend to go for more of a premium as compared with their non-"spectacles" sistren, so look in the $1000-$2000 region.

A Summicron (f/2) should be around 1/2 or at most 2/3 the price of a Summilux, and a Summaron (f/3.5 or f/2.8), 1/2 to 2/3 the price of a Summicron. Everything depends on condition: a mint, boxed lens might be worth two or three times as much as a decent "user" lens, and that in turn might be worth twice as much as a really rough, ugly lens.

The 135mm f/2.8, recently discontinued, likewise covers an immense range: anything from $300 or so for a good "user" to $1000 or more for one that is mint and boxed.

A 50mm f/2 "spectacles" Summicron generally goes at a modest premium compared with a contemporary non-spectacles version: a maximum of about $450 provided it has its spectacles. Without them, it is generally worth rather less than a non-spectacles lens--despite being every bit as usable. So if you want a Summicron to use, look for one of these!