If it has a focal length of 500mm, then it’s a telephoto lens, right? No, not necessarily …
Most modern long focal length lenses are indeed telephoto lenses, because they incorporate a special group of elements that extend the focal length while keeping the length of the lens short. But it is also possible to achieve high magnification by simply extending the length of the lens. Technically, it is only a telephoto lens if its physical length is shorter than the focal length.
Telephoto lenses were invented at the end of the nineteenth century, but there were problems such as chromatic aberration, especially in higher magnification telephoto lenses; and the techniques used to overcome that made them much more expensive than the simpler, longer lenses. This example was bought in the mid 1980’s, when it was available at the bargain price of £44, from J D Brown’s photography shop in Dundee. At that time, a 500mm telephoto lens would have cost several times that amount.
So what should we call the longer lenses to distinguish them from telephoto lenses? They have been known by various names. We could refer to them as single element lenses, but that’s not very descriptive or catchy is it?
It’s worth noting that this type of lens became popular with sports photographers and paparazzi, particularly just after the Second World War – a time when users would be familiar with the obvious resemblance to weaponry such as the 155 mm Long Tom, a world war two field gun, or the even more famous 420-mm howitzer known since the first world war as Big Bertha. So no surprise that popular names for the lenses were borrowed from those cannons – and even when bought in the 80’s this lens was still referred to as a Long Tom.
The lens needed a T2 mount to adapt it to different bayonet fittings – or as in this case, a 42mm screw fit, making it suitable for enthusiasts on a tight budget who had opted for East European SLR cameras such as the well-regarded East German Praktica models, or the less reliable Russian Zeniths. Here however, it is coupled with the historic Asahi Pentax Spotmatic, which in 1960 was the first SLR in the world to feature TTL – through the lens metering.