The Sony 18-70mm DT f/3.5-5.6 Lens is actually the Konica Minolta 18-70mm lens moved over when Sony bought the product line from the last of the
Konica Minolta Maxxum Minolta Maxxum series DSLRs and renamed them the "Alpha." This lens is the successor to a less successful general purpose zoom, and this second generation product started with a clean sheet of paper to succeed where the first did not; and it does. This lens is smooth, fast, and sharp. All in all, it is a tremendous value. Sony Alpha owners should consider getting it under the "Konica Minolta" brand simply because it can now be had at about half the price, with the main difference being a helical shaped grip on the zoom instead of the straight lines on the Sony.
Background
The back history on APS format's legacy for the Digital SLR is included in my review of the
Konica Minolta Maxxum 7D, so I will not repeat it here. The main thing relevant to the Sony incarnation of this lens is it came with over 25 years of development on autofocus SLR lenses, and over 10 years of work on an SLR lens tailored to the smaller format of APS film, and the APS sized CCDs which have become the norm in the Digital SLR. Given the exponential difficulty in making sensors get larger than this size combined with the diminishing returns for increasing size, it would appear this will be a standard configuration for the foreseeable future.
The current crop of detectors for Digital SLRs have converged to a configuration where the 50mm focal length of 35mm film SLRs has been supplanted with the 35mm focal length of APS sized lenses. This isn't so convenient for doing the math in your head, but in essence it is like every lens has a 1.4X multiplier for magnification. So, the 18mm-70mm Soy telephoto has performance of 1/2X to 2X magnification. In 35mm terms, this would be a 24mm-100mm telephoto, a very healthy zoom range. If you have old Minolta Maxxum lenses from film cameras, all of these are compatible with the new cameras, and their electronics will faithfully report the correct parameters to be recorded in the data files.
Unlike the Zeiss Vario-Sonnar fixed focal length lenses Sony offers with an f/ratio as low as f/1.4, the 18-70mm zoom bottoms out at f/3.5 to f/5.6. The price for this lens' versatility is the glass can't correct light to as wide a portion of the glass. So, instead of having false color and optical defects plague the lens at low f/ratio, this lens has a stop on the iris, and even the $700 Sony Zeiss 16-80mm zoom stops at f/3.5.
Description and Usage
The 18-70mm Alpha mount zoom is a compact lens with the main barrel at minimum length near unity power around 35mm. The front end has a modest focusing ring, which is much easier to use if the small glare shield is installed. This component latches on to a groove on the outside of the lens, and is clearly meant to be left on since it does not interfere with filters and the lens cap has "Pinch" type grips so it is easy to remove with the glare shield in place. Since this component is no larger than the barrel of the lens and doesn't significantly change the length with the lens cap on, I recommend leaving it installed since it is a perfect bump guard.
The zoom mechanism on this lens is extremely smooth and responsive. With a two-handed grip on the camera, zoom is an organic part of using it with no significant adjustment time required. No detectable backlash is present in the mechanism, so it goes from forward to reverse without having a dead space in between. As a result, this lens has become my overwhelming preference when situations where quickly re-framing the shot is needed.
Photographs taken through the lens generally do not show false color on the edges of large changes in contrast. The only place I have seen this occur has been on dark metal parts of a building silhouetted against a brighter sky near dusk. In this case, they were at the edge of the frame at wide field with the lowest focal ratio available. No other photo has showed this effect, but that is where the limit is. This effect may become more signicant in the future when the sensors for these cameras push to 20 megapixels and higher (And I plan to not worry about it until it happens).
Unlike the
Sigma 28-300mm zoom, this lens has a completely successful relationship with the camera's autofocus system, where I find focus is effortless for conventional objects. The lens moves to focus quickly and with authority (e.g. it overwhelmingly will pick the right focus with little input from the photographer). This combined with the effortless zoom makes this lens a joy to use in rapidly changing shooting situations. For example, I have used it for photos from moving vehicles where the shot must be framed, focused, and taken in seconds. Conversely, the lens has worked well for taking photos of rapidly moving and changing subjects with complex backgrounds. This is a photo of a large flock of swallows I took in Agrigento, Sicily:
http://www.buytelescopes.com/gallery/view_photo.asp?pid=11462&c=35913
Here the flock was rapidly moving and changing as the birds quickly changed direction [how
do they do that, anyway?].
That photo is useful for another reason, since it also shows the largest weakness of this lens- the relatively high minimum f/stop. Like all Maxxum/Sony Alpha mount lenses, this one is also compatible with the camera's anti-shake system, which moves the detector to keep it under the image. Like many photographers, I am far more interested in using the natural light to get the right look for a place, so long exposures have wound up being common. The fact I tend to be mobile and tripod carrying-adverse does make this a bit more challenging. Here are some tips for dealing with this situation and how the anti-shake system can help:
(1) Use the anti-shake system on YOURSELF. The bars on the right side of the viewfinder telling you how hard the anti-shake are using are also bio-feedback- calm yourself until you see the bars drop. I have been able to train myself to get exposures up to 1/4 second this way.
(2) Brace- just putting an elbow against a hard object can be a major improvement in getting hard focus images at long exposure times.
(3) Look for alignment devices around you- for example, leaning against a wall behind you and pulling the camera against your head can yield a rock steady result. A small jog in a wall or a door frame can be a perfect spot to push the camera's base against and yield perfectly still shots.
(4) Try! Remember, this is the digital era- if you end up not liking the result, that's OK- it doesn't cost anything.
Conclusion
The Sony 18-70mm DT f/3.5-5.6 lens is a fantastic value as a general purpose lens for quick reaction photography with either the Sony Alpha or older Maxxum Digital SLRs. The lens flat-out works well, and is easily a match to 90% or better of everyday shooting situations. If fault is to be found, then it is with the limits to low-light performance for this lens. But even there, a lot can be done with these modern cameras to overcome lens shake. Keep in mind, if you want to save some money on accessories for a Sony Alpha, the Minolta Maxxum lenses work, and this lens was originally developed under that brand name.
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