Superzoom Lenses Benefits and Disadvantages
I'm sure that many of you reading this are likely to own, or have owned in the past what is commonly described as a ‘superzoom’ lens. These lenses typically cover a very wide focal range. The most popular super zooms are wide to long telephoto lenses and most of the leading camera and lens manufacturers will produce them. Then there are ‘telezoom’ lenses which typically start at around 70mm or 100mm, commonly ending at 300 to 400mm. There are both advantages and disadvantages in owning these lenses.
Superzooms have always had something of a poor reputation. They're generally regarded as a jack of all trades and master of none. This is because they are inherently compromised by their ambitious design. It's difficult (and expensive) to optimise a lens for sharpness when the glass elements have to cover a wide range. For this reason the longer the focal range, the more likely it is that the lens will suffer from softness and chromatic aberrations particularly at the long extremity. And for the same reason consumer graded superzooms and tele-zooms are more likely to suffer from copy variance. But these lenses offer so much convenience. They can be a viable (and valuable) all in one solution to recreational photography and travel photography and they save us from endlessly swapping lenses when we’re out and about. Providing we set our expectations accordingly.
What is a ‘Superzoom’ Lens?
A classic superzoom range would be something in the region of 18-200mm in APS-C terms. Or 14-140 in Micro 4/3 terms. Longer superzoom lenses also exist, around 300 mm at the long end is fairly common. The new Tamron 18-400 f3.5-f6.3 VC is the longest superzoom currently available.
With telezoom lenses the entire range lies in the more extreme telephoto part of the spectrum. These are very much geared towards nature and wildlife photographers. Examples might include the Canon and Sony 100-400 lenses, and Pana Leica 100-400 lenses. There are a raft of consumer grade 70-300 lenses, and the excellent Canon 70-300L lens which suffers from none of the limitations of its cheaper cousins. The optical performance of a broad-spectrum lens usually depends on its price point. The more expensive superzoom and telezoom lenses aimed squarely at professionals and advanced amateurs benefit from a higher level of engineering and better calibration. This means they are optically superior to their consumer counterparts, but at a price. They will also very likely have weather sealing and a more rugged build.
I've encountered quite a few superzoom and telezoom lenses over the years and my experiences have been mixed. One of my favourites was the Panasonic 14-140ii which was a fixture on my various micro 4/3 bodies for a number of years when on personal outings. This is a great little lens, very small and light, and very sharp throughout its range - falling off only slightly at the extremity (although it does suffer from purple fringing at the long end). I've won many awards for images taken with this lens and by their nature those images need to stand up to close scrutiny. This only offers a maximum of 280mm in 35mm terms, and many super zoom users want more reach than that. But with more reach comes more compromises, unless you're prepared to spend a great deal.
Staying with Micro 4/3 for a moment, a ‘super telezoom’ lens I use frequently reach for is the stellar Leica 100-400. This offers an effective focal range of 200-800mm in FX terms, making this lens quite unique. It is also gloriously sharp, right through to the extremity. There is no chromatic aberration to speak of and its stabilization system is incredible. It is a lens which has, in many ways, ruined me for every other lens I'll ever use. It's fairly expensive at around £1200, but it's worth every penny. As a professional it's easier for me to justify this kind of outlay but it may be a little rich for the average hobbyist. Because it's designed for a Micro 4/3 sensor, the Leica 100-400 is remarkably small and light for the range it covers. Because I own this lens, there is a horrible (and at times painful) tendency for me to compare all other lenses to it. That is completely unrealistic when it comes to consumer oriented superzooms and telezooms, but more on that later.
A smaller and less costly alternative to the Leica 100-400 is the Panasonic 100-300 which I owned up to a couple of years ago. This is a nice little lens and if you can get a good copy (it does suffer from copy variance) it's a worthwhile purchase. It's soft in the last 20 mm but that isn't a big deal given how well it performs otherwise. Some examples can be seen here:
Another superzoom lens which I was impressed by was the Sony SEL 18-200 - this is the original Sony super zoom (the chubby silver version) designed for the Sony e-mount APSC bodies. This lens is extremely sharp throughout its entire range but like many super zoom lenses it suffers from slow autofocus at the extremity in anything other than perfect light. But in terms of sharpness in good light it was up there with some of my pro glass. Prior to owning that lens I tried the Tamron equivalent, which was very good up to around 100mm but pretty much failed to focus on anything more than 15 feet away.
Just recently I purchased a little Canon DSLR destined to become my ‘general personal use friends and family camera’. This is a tiny little machine, extremely simple and intuitive to use, and so far everyone who has tried it loves it. It's very basic compared to my mirrorless bodies, but that falls in its favour when handing it to an inexperienced relative or buddy. General use cameras for walkabout and travel photography are the cameras most likely to attract a superzoom lens, or at least the more consumer oriented zooms.
A couple of weeks ago I purchased the much lauded Canon 55-250 STM lens for lightweight wildlife photography. This didn't entirely live up to the rave reviews you might see on forums and suchlike (nor should we expect it to) where it's been compared to its professional counterparts in terms of sharpness. It is fairly sharp, but it doesn't match a professionally specified equivalent. But it is cheap and light and it is a very good choice nonetheless – you can’t go wrong with it. I'm pretty sure mine had a front focusing problem and for that reason I returned it - a different copy may well have performed better.
The good people at Tamron UK sent me an 16-300 lens to try a few weeks ago (while I was waiting for the new 18-400 to become available). This proved to be the softest lens I’ve yet encountered. It’s possible I may have received a poor copy or a lens which has been dropped by a previous user. It was soft at all focal lengths and aperture values, and in fact none of the images in my field tests met my standards for acceptable superzoom performance, even for low resolution web use.
Therefore I waited for the new (and quite expensive) Tamron 18-400 f3.5-6.3 VC version with some trepidation, and that is the lens I'll be discussing and reviewing shortly in more depth.
How do we verify the performance of our lenses?
There are countless approaches to this from rigourous bench testing using special test targets, through to simple field use under the conditions we would normally shoot in. I have done both but I tend to start with field testing because for me at least that is the best way to ascertain if the lens suits my purpose. I'll visit familiar locations and I'll take the same photographs I've been taking for years with most of the optics I would normally use in those situations. This will involve static targets, targets in both bright light and dull light, and targets which are both near and far. This enables me to evaluate how well a lens can lock focus at distance (often a weak point of super zoom lenses) and whether or not it struggles in less than optimal conditions.
What I'm about to say now is crucial however. Sharpness depends on so many factors and when evaluating a lens it’s a given that the camera operator has the requisite skills and knowledge with which to carry out that evaluation. That means an understanding of the many factors which determine overall resolution. It isn't just about your lens’s optics. Assuming you start with testing static targets you need a shutter speed relevant to your focal length or crucially a shutter speed which is relevant to whichever image stabilisation (or not) your camera body or lens utilises. It's this very factor which I find limiting when switching to a small Canon DSLR from my Micro 4/3 cameras. The latter have excellent in body stabilisation mechanisms otherwise known as IBIS. Depending on the camera this will allow you around 5 stops stabilisation.
Certain lenses will also work in tandem with the stabilisation in the u4/3 camera, and can leverage both that and the lens-based stabilisation. My Leica 100-400 when mounted on my GX8 is a case in point. At the long end (800 mm equivalent field of view) I can successfully gain sharp images at around 1/60 of a second. Yet when I use my Canon 200D (which has no in body stabilisation and depends on lens OIS) I’ll be at the mercy of whatever stabilization the lens offers. At around 300mm on my Canon (480mm effective FX field of view) results at 1/200 can be hit and miss (see contributing factors below). A long super zoom lens on a DSLR camera can be more limiting than a similar lens on a Micro 4/3 camera (when hand held) which offers enhanced or dual stability. Therefore I recommend that your initial sharpness field tests are undertaken in very good light and you work backwards from there.
All of this assumes you have excellent handholding technique (and a static target). Even so, the shape of your camera and the balance of your lens is yet another factor in image sharpness as it relates to stability. I struggle somewhat to hold a small DSLR still, I can't seem to brace it against my face as easily as I can a rangefinder style mirrorless camera. Add a long lens to the mix, particularly if that lens is lightweight, and it becomes harder still (for me at least) to get a sharp and clear photograph in anything other than abundant light. This is an area where bench testing the lens can be useful, as it rules out the human factor.
For some general tips about gaining sharp images see this blog post: How to Get Sharp Photographs
My initial field review of the new Tamron 18-400 lens will appear on the blog soon. Until then, here’s a look at the relative size of the Tamron 18-400, which is an APS-C lens weighing 710 grams and is 12.4 cm long (72mm filter size). On the left is the Sony 70-400 f4G (a full frame lens), then the Tamron 18-400 and on the right the very lightweight (and optically impressive) Canon 18-55 STM kit lens.