Tokina SZ Pro: I put three mirror lenses through their paces
As the name would suggest, mirror lenses use mirrors to direct light to a camera’s sensor. So, what do I need them for? The short answer: practically nothing. I can, however, use them to create fun effects.
Tokina has released three new mirror lenses for APS-C cameras. They’re super telephoto lenses with focal lengths of 300, 600 and 900 millimetres, compatible with Fujifilm, Sony E and Canon EF-M systems. The latter seems a little strange to me given the EF-M is unlikely to be developed further. Not only that, but Canon is using RF-S as a new APS-C format instead. We don’t even have the Canon versions in our range at the moment. I put the Sony versions through their paces.
Until this review, I didn’t even know what a mirror lens was. I suspect I’m not the only one, so I’ll start off with a short explainer.
What are mirror lenses?
As the name suggests, these lenses contain not only glass, but also two mirrors – one at the very back and one at the very front. On the left-hand side of the diagram below, you’ll see the front of the lens, with light coming through the blue glass elements below and above it. Light reaches the mirrors on the right i.e. the back of the lens, where it’s directed forward towards the centre, then back to the sensor from there. This means the light covers a distance greater than the length of the lens itself.
Source: Tokina
Consequently, the lens is much shorter than the focal length, keeping even powerful telephoto lenses compact. On the left of this photo, you can see a 70–300 mm lens, set to 300 millimetres. On the right, there’s a lens with the same focal length. In the interest of fairness, I should mention that the «regular» lens is designed for full frame. It’d be a little less bulky if it were solely an APS-C lens. Nevertheless, it’s much larger than the mirror lens.
Source: David Lee
The mirror lenses with a focal length of 600 and 900 millimetres are significantly larger, but still much more compact than their mirrorless super telephoto equivalents. Here’s a comparison with the Canon RF 800 mm F11 when extended. The Canon lens is also designed for full frame. However, as far as I know, there are no APS-C lenses out there with such a long focal length.
Source: David Lee
Given their focal length, the lenses are also lightweight. This lightness and modest size are probably why mirror technology is only used in telephoto lenses – that’s where these benefits have the most impact.
A travel lens? Absolument pas
My first thought was that having such a petite lens would be great on the go, including on vacation. So is a dinky 300-millimetre telephoto lens like this one the perfect travel lens?
As the gentleman in this video puts it when asked if he’s ever heard of Galaxus, absolument pas.
As practical as the dimensions of a mirror lens are, certain other features are impractical.
Drawback 1: no autofocus
Like almost all mirror lenses, the Tokina trio don’t have autofocus. This means you need to focus manually. The focus ring is tight, so you can’t move it quickly. Almost a full turn is needed to get it from the shortest to the longest distance. Tokina says it’s a 270-degree turn, but it’s actually just short of 360 degrees. Although this allows for very precise adjustment, it’s impossible to focus quickly.
As a result, photographing wild animals – probably the most common subject for strong telephoto lenses – is a non-starter. A mirror lens won’t be much use to you on a safari. Even on a walk or hike, manual focus isn’t ideal. Stopping to take a quick snap before catching up with your buddies is simply out of the question. Portraits are likely to be difficult too, even discounting the fact that you can only take portraits with a super telephoto lens at long distances.
Drawback 2: no image stabilisation
These mirror lenses don’t have image stabilisation. The stronger a telephoto lens is, the more acute the impact of even the smallest hand movements. Even at 300 millimetres, you need to keep exposure times snappy to avoid camera shake. Without resting the camera on something, it’s difficult to keep the subject in frame at all. The three Tokina SZ Pro are no exception. They’re all shaky.
A camera with a built-in image stabiliser minimises the problem. I tried out the lenses on the Sony Alpha 6400 and 6500. The Alpha 6500 has an image stabiliser, the 6400 doesn’t. I notice the difference when taking pictures. However, having a stabiliser in the lens would be much more useful. The longer the focal length, the more important stabilisation in the lens becomes in comparison to stabilisation in the camera.
When using the Sony cameras, I have to specify the focal length in the camera menu for the stabilisation to work correctly. The camera can’t detect the focal length of these lenses automatically. Not only that, but there’s no option to set it to 900 millimetres, meaning I have to switch to 800 or 1000 mm.
I can’t shoot freehand at 900 millimetres anyway, failing even to keep the subject in the frame. At 600 millimetres, it’s manageable if you prop up the camera and use camera stabilisation – as long as you don’t expose longer than 1/125 of a second. However, even at this focal length, a tripod is a must.
Drawback 3: fixed aperture
You can’t change the aperture on mirror lenses. The speed of Tokina’s 300-millimetre mirror lens is f/7.1 – not particularly fast, but I’m glad it isn’t faster. After all, without an adjustable aperture, you can’t change the depth of field, which is already super low with a 300-millimetre lens at f/7.1.
The depth of field is even shallower with the 600-millimetre lens; it only has a marginally smaller aperture at f/8, with twice as much focal length. A lot of the time, it’s impossible to get everything in focus.
Source: David Lee
Big distances, big problems
The 900-millimetre lens allows you to photograph very faraway objects in close-up. The quality of these snaps, however, is rarely good. At a distance of several hundred metres or even more, the colours fade. This isn’t because of the lens; instead, it’s down to the air, which is noticeably hazy. What’s more, temperature differences cause the air to shimmer. Here’s a shot of the Glarus Alps from approximately 60 kilometres away. Despite decent visibility, my 15 tripod-supported, self-timer attempts to take a sharp photo proved fruitless.
Source: David Lee
Source: David Lee
Pointing the camera skywards on a starry night gets you better results. With the 900-millimetre lens, the moon fills a good part of the image and becomes sharp. As a result, many of its details are recognisable.
Source: David Lee
Bokeh
There’s a special feature of mirror lenses that I haven’t mentioned yet: bokeh. This refers to spots of light that aren’t in focus, which appear as rings. Shot with a regular lens, they show up as circles or, at best, polygons, if the aperture blades aren’t rounded.
Let’s say some dew drops in backlighting create bright light spots. A glass lens makes them look like this:
Source: David Lee
A mirror lens makes them look like this:
Source: David Lee
This is due to the aperture’s ring-shaped appearance. The second mirror is attached to the back of the black circle in the middle. This reflects light from the first mirror to the sensor.
Source: David Lee
These distinct rings might bug you if you don’t want them, but they do pave the way for creative ideas.
Source: David Lee
The rings look especially good in videos when you slowly change the focus. However, even with a tripod, snaps taken with a super telephoto lens will be a bit blurry if you turn the ring. The issue is already apparent at 300 mm, and is exacerbated at 600 and 900 mm.
Image quality
Since these mirror lenses have numerous special features, image quality has played a secondary role in my review. Let’s say, however, you manage to take a sharp photo despite the shallow depth of field, haze in the air and susceptibility to camera shake. What will the quality of that image be like?
One advantage of mirror lenses is that they have virtually no chromatic aberration. Glass lenses, such as the Nikon 70–300 mm used to take the image below, on the other hand, create colour fringes on the contours. These fringes are easy to spot on the arm in the far left of the picture. However, since these blemishes can easily be removed using editing software, the advantage provided by mirror lenses is of little consequence.
Source: David Lee
Source: David Lee
The sharpness, tested with the 300 mm lens, is mostly good, only falling short slightly at the corners. While you can increase the sharpness of an ordinary lens by stopping down, you can’t do this on the Tokina SZ Pro.
To allow for a direct comparison with the Nikkor 70–300 mm mentioned above, I’ll only show you areas well inside the image. Seeing as it’s a full-frame lens, it’d be unfair to look at the edges. On an APS-C camera, full-frame lenses tend not to display any edge blur because the real edge of the image circle isn’t captured by the sensor at all.
Verdict: only for special purposes
The compactness of mirror lenses is advantageous, but this plus point is offset by some serious drawbacks. With no autofocus or adjustable aperture, they’re very inflexible and therefore make for unsuitable travel buddies. Sport and action photography are out of the question as it is, and I don’t recommend the lenses for portraits either.
Playing with the unique bokeh appeals to me – it’s a little different. However, I wouldn’t buy a lens especially for it; the novelty of the effect wears off quickly if it suddenly appears on every picture.
Of the three lenses I tested, I like the 300 millimetre one best. It’s very small, and it’s just about still possible to shoot with it hands-free. The 900-millimetre lens is strong enough to capture the moon, but besides this, it’s difficult to take sharp photos at long distances. Even using the 600-millimetre version, handling is anything but easy.
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David Lee
Senior Editor
David.Lee@digitecgalaxus.chMy interest in IT and writing landed me in tech journalism early on (2000). I want to know how we can use technology without being used. Outside of the office, I’m a keen musician who makes up for lacking talent with excessive enthusiasm.
