TS-E 24mm f/3.5L II
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| Photo 1: TS-E 17mm f/4L | Photo 2: TS-E 24mm f/3.5L II |
Development objectives for the TS-E 17mm f/4L
and the TS-E 24mm f/3.5L II
The all-new ultra-wide-angle TS-E 17mm f/4L (Photo 1), and the completely redesigned wide-angle TS-E 24mm f/3.5L II (Photo 2), were developed to renew Canon's TS-E series of tilt-shift lenses.
Canon launched the TS-E lens series in 1991 with three models: the TS-E 24mm f/3.5L, the TS-E 45mm f/2.8, and the TS-E 90mm f/2.8. The TS-E 24mm f/3.5L, in particular, became a favorite among pro photographers for architectural photography. At the same time, many photographers wanted a broader angle of view than that afforded by a 24mm focal length. Moreover, over the past 18 years since the TS-E lenses were marketed, users have been demanding lenses with enhanced perspective controls and better image quality suitable for the digital age.
For these reasons, we decided to update the TS-E 24mm f/3.5L model and add a new TS-E 17mm f/4L model to the TS-E lens lineup.
Both lenses make use of aspherical and UD elements to deliver image quality worthy of the "L" lens designation. The new lenses also give better correction of the characteristic wide-angle distortion even at the edges of the image circle; improved tilting, shifting, and rotating operation; and a new tilt-shift (TS) rotation function, which allows independent rotation of the tilt and shift axes relative to each other. All told, these lenses represent a giant step forward in performance and functionality over previous models. The following sections explain these improvements in more detail.
Feature 1: SLR lenses equipped with tilt, shift,
and rotational functionality
Let's first run through the principles and benefits of tilt-shift lenses.
The tilt control tilts the lens at an angle to the optical axis, which is normally perpendicular to the image plane and object plane, and takes advantage of the physical phenomena produced by the tilt angle between the image plane and object plane. The photographer can judiciously apply tilt to obtain certain focusing effects that would be unobtainable otherwise. For example, when the object plane is at an angle to the image plane, the photographer can tilt the lens (without tilting the camera) until the entire object plane is in focus (Figure 1-1). Tilting in the opposite direction, the photographer can reduce the depth of field to a single point (Figure 1-2). This second effect is sometimes known as "miniature faking."
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| Figure: 1-1 | Figure: 1-2 |
With an ordinary lens, the photographer must move the camera to change the composition when facing a subject at right angles. This movement, however, will change the perspective of the subject. The same effect can be achieved without the moving the camera or changing the perspective by shifting the lens a slight amount from the camera's optical axis (figures 2-1 and 2-2).
keeping the image plane parallel to the subject
in the frame while the image plane remains parallel to the subject
Lens shift, then, is the movement of the lens perpendicular to the optical axis. Lens shift allows the photographer, shooting from ground level, to capture a tall building, for example, without introducing perspective distortion (photo 3).
Another example of where lens shift is useful is photographing a mirror without the photographer's reflection appearing in the photo (photo 4).
in the photo while remaining at right angles to the mirror.
To accommodate lens shift, TS-E lenses have a 67.2mm diameter image circle (the circle in which a lens renders a sharp image on the image plane when focused at infinity), opposed to the 43.2mm image circle, which encompasses a 24 x 36mm frame, of ordinary lenses. Furthermore, TS-E lenses have many optical design innovations to limit vignetting and resolution degradation caused by tilt-shift shooting (Figure 3).
To provide photographers with more creative control over their photos, the rack-and-pinion tilt/shift mechanism allows a ±8.5° tilt range and a ±12mm shift range on the TS-E 24mm f/3.5L II and a ±6.5° tilt range and a ±12mm shift range on the TS-E 17mm f/4L. (All three previous models had a ±8° tilt range and ±11mm shift range.)
Perhaps the biggest innovation we made is the ability to rotate the shift direction ±90° relative to the camera and independently rotate the tilt direction ±90° relative to the shift direction. This second rotation, called TS rotation, makes it possible to tilt or shift the lens in any direction as well as set the angle between the tilt and shift anywhere between orthogonal (perpendicular) and parallel.
We also took steps to improve the usability of the lenses' knobs and locks. Larger tilt and tilt-lock knobs and shift and shift-lock knobs were used so the photographer can tilt or shift the lens with just a gentle touch. We also lengthened the rotation-lock release levers. And for finer shift adjustments, we included a cap that fits on the shift knob. Finally, we added an extra tilt lock, which securely locks the tilt mechanism (and the corresponding optics) in the neutral position so the photographer can enjoy the lens's full ultra-wide-angle optical performance.
Feature 2: Outstanding optical performance
and special anti-reflective coatings
The first design problem was to improve the lenses' image rendering across the entire large image circle while keeping distortion to an absolute minimum. To do this, we incorporated large-aperture molded glass aspherical elements. We were able to maximize the distortion correction of aspherical elements by using molded glass aspherical elements for G2 element on the TS-E 17mm f/4L and for G1 element on the TS-E 24mm f/3.5L II. And by using multiple UD elements we virtually eliminated the problematic chromatic aberrations of wide-angle lenses as well as achieving high MTF even at the edges of the lens (figures 4, 5, 6, and 7).
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[How to read MTF charts] Bold lines: 10 lp/mm, fine lines: 30 lp/mm. Black lines are the MTF at full aperture; the blue lines at f/8. Solid lines represent sagittal (tangential) MTF and the broken lines represent meridional (radial) MTF. | ||
| Figure 6: TS-E 17mm f/4L MTF characteristics | Figure 7: TS-E 24mm f/3.5L II MTF characteristics |
We also concentrated on reducing the minimum focusing distance. We selected a floating design on the TS-E 17mm f/4L for superior optical performance at all focusing distances while shortening the minimum focusing distance to 0.25m. For the TS-E 24mm f/3.5L II, we chose a rear-focus design that reduced the minimum focusing distance to 0.21m.
Finally, we cut ghost and flare dramatically with super spectra coating and a Sub-Wavelength structure Coating (SWC), which are used as the second and third TS-E models.
Additional features
To keep the lenses light and to achieve the ruggedness and durability professionals demand, extra-strength diecast aluminum was used for the TS and rotation units and aluminum for the main components of the focusing assembly.
The lenses feature an electro-magnetic diaphragm with a circular aperture that creates spectacular bokeh even when tilting the lens for selective focus or when using the lenses as an ordinary high-performance lens.
Naturally, these lenses use only lead-free glass in consideration of the environment.
Usage tips
As we have seen, the TS-E 17mm f/4L and TS-E 24mm f/3.5L II have special features and characteristics. Below are some of the necessary tips to use these lenses. There is no hood available for the TS-E 17mm f/4L, since a hood is incompatible with covering the full tilt range. The TS-E 24mm f/3.5L II uses the cylindrical EW-88B hood, which attaches with a two-pronged bayonet mount. Although the hood's inner wall has flocking for better anti-reflective performance, it cannot completely prevent harmful light from reaching some parts of the large image circle. When harmful light that may lead to ghosting enters the lens, other methods must be improvised to block the light.
The special Lens Cap 17 is provided with the TS-E 17mm f/4L to protect the surface of the front element from handling and scratches since the front element extends well beyond the lens barrel. The lens cap attaches to the lens with a bayonet mount and has a locking mechanism to ensure it remains fastened. Be sure to lock the lens cap so it doesn't get lost while on a shoot. Remember that it is not safe to carry the lens by the lens cap's strap because the lens could be damaged if the strap breaks.
The shift knob cap may come in contact with the built-flash on some EOS cameras when mounting the lens on the camera. To avoid this, set the shift and rotation to their center positions before attaching or removing the lens. The shift knob cap poses no problems on EOS-1Ds/EOS-1D/EOS-1 series cameras or on EOS 5D series cameras.
This concludes our look at the special features of the TS-E 17mm f/4L and TS-E 24mm f/3.5L II lenses. Table 1 compares the specifications of the two lenses with the original TS-E 24mm f/3.5L.
The world of tilt-shift photography is truly remarkable. Why not experience it for yourself with the superb images from these lenses.