There are four different ways to change focal lengths for a camera. You can switch lenses, use a zoom lens, use a modular system, or attach teleconverters. The first has a fixed number of elements in a fixed grouping, moving only to change focus. This is called a prime lens and offers one field of view. A zoom lens has a fixed number of elements, but can shift one or more of them to offer different magnifications between a set range that can be varied infinitely within that range at either a set or varied maximum aperture. The third is a modular system where different numbers of elements are pieced together to give a number of specific focal lengths and apertures. Teleconverters are very different than a modular system. The teleconverter is an magnifier that essentially crops the image circle of the lens which increases magnification but also increases the lens’ flaws at the same time. Teleconverters always degrade the image quality of the photograph, while a modular system will not. The advantage is that a teleconverter is much smaller and less expensive so is an easy way to increase reach in a pinch.
The Modular system is rather rare in photography. Nikon had a system in the 1960s and 70’s for their super-telephotos which consisted on a single focusing unit and then various heads that plugged into the focus unit to offer fixed focal lengths. This system suffered from among other things, excessive length and long minimum focusing distances. The APO Telyt system solves these problems to use five pieces to make four different focal lengths and three different maximum apertures. In addition, you can chose apertures for both the 400 and 560mm lengths based on weight and expected light conditions.
The APO Telyt system consists of three different focusing modules and two lens heads. They are connected via a locking bayonet fitting to ensure proper alignment. Using the smaller head, you can use the focus modules to make a 280 f2.8, 400 f4, and 560 f5.6. Using the larger head you can make a 400 f2.8, 560 f4, and 800 f5.6. Of course if you have the entire set, you can make up two lenses. I would think that the most popular configurations would be 280 f2.8 and 560 f4, while leaving the 2x f5.6 module in the bag.
Construction is up to Leica standards; meaning that it is made to last. The lens heads are metal, as is the focusing module’s barrel. There is some plastic in the bayonet ring, but it is of little consequence as it merely acts as the actuator for the metal interior fittings. The lens is ROM so that the R8/R9 cameras can use focus distance in the metering algorithms. There is also a slide in Series 6 filter holder that comes standard with a ND1 filter. A special holder can be bought to be used with a circular polarizer filter which has an externally activated wheel for spinning the filter. This is the same filter arrangement as the 180mm Summicron.
The top of each head is fitted with a handle and opposite of this is the tripod foot. This is both a blessing and curse compared to other vendor’s offerings. Most other vendors combine the tripod foot with the handle so that the camera is carried upside down. The trouble with this design is that it is tough to make a tripod support for super-tele’s so that they can double as a handle without also reducing their ability to dampen lens vibration. Leica circumvents this problem by having a very nice and sturdy tripod foot on the underside of the lens, and having a handle at the top for strictly carrying. Unfortunately there is now a large hook on the top of the camera assembly when it is mounted on a tripod of monopod. This is just begging to catch on something and cause a disaster. So while the lenses offer excellent tripod performance, be wary of the handle. Another issue with the handle in practice is that it will start to hurt your hands in no short amount of time. The handle has ridges that conform to your fingers, but there is no padding so it can cause your hand to cramp. A bit of foam rubber over the handle helps a bit with this problem.
The small head offers an integral telescoping hood. The front of the hood is rubberized to reduce wear on the lens hood when the camera assembly is placed hood down as is often the case with super-teles. The large head, on the other hand, offers a more standard accessory hood that has a bayonet fitting so as to twist onto the front of the lens. To store this hood, merely reverse it, and it locks on. Both heads offer rubber front lens caps that fit over the hoods. The design of both the shades and hoods is a step up to the Nikon system for lenses of this caliber. In addition to the front caps, each head has a rear cap, and each focusing module has a front and rear cap as well. The sheer number of caps makes the lens pieces more difficult to deal with in the bag, but is the price you pay to have a modular system.
The controls are very simple. There is a focus ring with a adjustable lock that allows the user to set a minimum focus distance. This can also be used as a hindered pre-focus point. Unlike some systems that use a knob to set a dent in the focus range, this knob will prevent you to from focusing any closer than the set distance. The scale is only in meters, but there are two sets of numbers on each module. Most lenses show the focus distance in feet and meters, but this one shows the focus distance depending on the configuration. For example, the 1x module shows the focus distance with the 280mm configuration and 400mm configuration, but only in meters. There is no DOF scales or IR marking (no need for an IR mark). Neither of these issues cause problems in practical use unless you really need a distance measurement for some reason.
The other control is the aperture ring, which is a step up from the Nikon focus unit because each module has a set number of apertures so there is no need to remember to convert based on the head it is paired with. The 1x module will always offer a range between f2.8 and f22 and so on.
In practice, this system is fairly easy to use and versatile. I typically know the kind of lighting I am expecting and where I am going. I also need to decide if I will need faster lenses and more distance, or if I can get away with shorter focal length and slightly slower speed. I will typically not bring both heads with me, but rather choose one head and then select the focus modules I may need. Typically for me, this means one head or another, and then carrying the f2.8 and f4 modules. I tend not to bring the f5.6 module unless I know I am going to need a long lens. I am less apt to use the small head with this module as 600 f5.6 is difficult to use with film, despite it’s relatively long range and light package.
The smaller head is much easier to handle so unless I need the extra length or speed, I will usually opt for the smaller head. There is a significant difference in both weight and handling between the heads. The differences in the modules deal mostly with length and aren’t too cumbersome to pack in a bag (typically 1 or 2 in a bag and the other mounted on the lens with camera attached)
I use this system on a heavy-duty carbon fiber tripod and gimbaled head. This allows for good stability, and a wide range of motions. The tripod mount is nearly ideally placed on both heads, so getting the balance doesn’t require an extremely long plate. Focus with the f2.8 and f4 modules is easy and the MF nature of the lens isn’t much of a hindrance for my wildlife photography. The f5.6 module with the standard screen starts to darken the rangefinder and micro prisms unless your eye is directly in line with the center of the screen. Leica and other users recommend a plain ground glass screen for this module. I don’t like switching screens, so I stick with the standard screen.
The greatest single advantage of this system is that it offers a great range of focal lengths and speed in a compact package. The only zoom that covers this range is a fixed f5.6 aperture, so is much smaller, but much slower, especially at the lower end of the focal range. A set of primes offers the same speed and focal length, but is much larger and more difficult to carry. The telyt system fits in a fairly large case, a set of 6 primes requires much more room to store, weighs more, and is much more cumbersome.
What about optical quality? The best images of the system are made by the 400mm f4 configuration, but is excellent with any configuration. The biggest weakness is probably distortion which is usually between 1-1.5% in most configurations which is larger than most other brand’s offerings. Vignette is minimal and sharpness is equal to most film and the DMR so that should not be an issue. Since these are APO lenses, color fringing is minimal and contrast is excellent, as with all modern Leica optics. MTF graphs are still available on the Leica website, but considering this is an orphaned system, they may be removed at any time.
The final issue is the slightly different focal lengths available in the Leica system compared to the major Japanese makers. For example, you will find many more options of 300mm lenses rather than 280mm. The same goes with 560mm instead of 600mm. People tend to obsess about these types of things, but what is that actual change in field of view between these two focal lengths? Fortunately, the longer the lens, the smaller the change of view angle per millimeter of focal length. Twenty or forty millimeters matters a great deal in shorter lengths, but not nearly as much in the super-telephoto range. For example, the difference between 280mm and 300mm is 0.6 degrees of view diagonally. At the longer focal length, the difference between 560 and 600mm is 0.2 degrees diagonally. Will this matter in the field? While there is a certain amount of framing changing, in practice, the slightly shorter focal length will not affect us too greatly and is certainly not enough to totally dismiss the system.