The new Tokina SZX SUPER TELE 400mm F8 Reflex MF sounds like a blast from the past, but mirror lenses like this one could stage a comeback, thanks to advances in digital cameras and sensor design.
Telephoto lenses use a 'refracting' principle – a series of lenses which bend the light to form the image on the sensor. Mirror lenses use a radically different design, with a parabolic mirror at the back of the lens to focus the image on a mirror mounted centrally at the front, which bounces the light back down the lens to the camera sensor.
In photography this is called a 'catadioptric' lens, but astronomers will immediately recognise this as a Cassegrain design. Because the light is 'bounced' up and down the barrel, it produces a much shorter, lighter lens for any given focal length.
What's wrong with mirror lenses?
Back in the 1980's, mirror lenses had a brief popularity as an inexpensive super-telephoto design, but so-so optical performance and a fixed aperture of f/8 (typically) limited their appeal at a time when high ISO/sensitivity settings were for emergencies only and there was no such thing as image stabilisation.
Two things have changed since mirror lenses had their heyday. One is that modern digital cameras can deliver great results at ISO settings simply not available back in the days of film. F/8? Not a problem! For outdoor photography at least, you can simply wind up the ISO to get the shutter speeds you need.
And for those situations where you don't want to use a higher ISO, there's always in-body image stabilization, now close to being a standard feature on all but a handful of full frame mirrorless cameras.
We can't comment on image quality until we've seen a sample lens, and we don't know the price either – though historically, mirror lenses have tended to be budget alternatives to 'real' telephotos.
The Tokina SZX Super Tele 400mm F8 Reflex MF is not just a couple of mirrors in a tube, as its optical design is a hybrid combination of mirrors and lenses.
However, as well as lacking an aperture mechanism, like other mirror lenses it's also manual focus only.
Mirror lenses never quite went away, incidentally. Samyang has been quietly marketing its 300mm F6.3 ED UMC CS for some time now, and we've also spotted an Opteka 500mm f/8 HD Telephoto Mirror Lens for T Mount which is designed around the same principles.
Will it fit your camera?
The Tokina SZX SUPER TELE 400mm F8 Reflex MF uses the old T2 mount, based around adaptors for a whole series of different camera bodies. Adaptors will be available for Nikon F, Canon EF, Sony E, Fujifilm X and Micro Four Thirds cameras, either sold as a kit with the lens or available separately.
Interestingly, although lens makers have adapted the Cassegrain telescope design for lenses, we haven't seen one based around a Newtonian reflector yet. We can't think why!