Lens Survey And Subjective Evaluations

By Bjørn Rørslett

Introduction
During my many years conducting Nature and Scientific photography, I have had the opportunity to use a veritable arsenal of 35 mm and large-format lenses. Many of these I do own personally, a current total of some 100 lenses. Not all lenses are created equal, that's for sure. Price is a putative indication of optical quality, but can equally well be misleading.

People have repeatedly asked me to provide an overview of these and other lenses to show their image-producing potential. True, a number of excellent resources for evaluating lenses are found on the Net. Many are based upon subjective evaluation of the items in question, but only a few sites can provide a truly encompassing overview based on a single person's experience. On the other hand, sites exist that overwhelm you with MTF plots purportedly providing indisputable facts. MTF methodology has a genuine scientific foundation and there is nothing "wrong" with MTF as such. I even understand the mathematical equations. However, such statistics basically are as helpful as knowing the mass of a lens - on its own, MFT testing cannot predict the pictorial outcome of any lens. Thus, MTF tests will not show all problems from field curvature, colour fringing, flare and ghosting, the variability in performance that arises from near or distant focus, the subjective 'feel' of the images and in particular the out-of-focus rendition (given the buzz word of 'bokeh'), the way a lens handles under actual use, and so on. MTF data can just indicate there is a problem with a lens, or that a particular lens might be an excellent piece of glass. All of this information can be obtained as easy (but likely not as fast) just by shooting pictures with the lens. Averaging MTF numbers to arrive at a single value in order to rank lens quality is simply impossible and largely a waste of time.

The final verdict of any lens must come from using it for taking pictures. Hands-on experience isn't entirely random and unpredictable: by and large, a fair number of equipment reviews (or reviewers, for that matter) will coincide on the merits, or lack of such, for many lenses. Clearly, differences of opinions are found and indeed are to be expected, but a major pattern usually will emerge. I think it's important that the review is open-minded, comprehensive and detailed. This will give the users a possibility to make up their own mind. I haven't an axe to grind with other reviewers, I do respect their evaluations and regard some of the reviewers highly, but shall assert my right to form my own conclusions. These are published here.

Because I aim to publish my photos, I am quite concerned about optical quality of the equipment I use, and test each and every lens before it is put to actual use. Such tests involve shooting test rolls of targets with known properties, and evaluating the pictures under high magnification (10-40X) afterwards. I prefer using brick walls as targets, because these feature patterns and details on a number of scales, and readily show geometric distortion (pincushion or barrel), colour fringing, field curvature, colour saturation and more. It's also easy to vary shooting distances, important for evaluating wide-angle lenses with close-focusing correction (CRC) and 'macro' lenses. Furthermore, exact parallel alignment of the camera with the target plane is easily achieved. I run each lens through all aperture setting three times independently, and use fine-grained film (mostly Fuji Velvia) to realise the inherent sharpness of the test lens. The camera, either Nikon F4 or F5, is carefully mounted and levelled on a sturdy tripod using my massive 'L'-brackets. The test films are scrutinised under my Nikon Stereomicroscope at 10 to 40 X magnification using a diffuse cold-light source.

My Rating Criteria are as follows:

It should be kept in mind that these ratings are purely subjective. However, it is even more important that they result from actually using the lens for shooting real-world images. Scrutinising slides under a 40X Binocular Microscope can tell the trained eye quite a lot about the optical quality of the lens. I have added comments on each and every lens to underscore the good and weak points of each item. Please read these comments carefully together with the ratings themselves. There isn't such a thing as a perfect lens capable of delivering top results at all apertures. Hence I have stated the optimum aperture range for each lens. The propensity for flare and ghosts (those ugly reflections of the diaphragm) is another important information that is given. These problem areas can only be found while doing actual shooting in the field.

I have come to the conclusion that many modern lenses, during their computer-optimised design stage, have had certain performance criteria maximised to the disadvantage of other parameters. The optimised parameters aren't necessarily optimal for a specific end user, however. For example, the clever trick of making lenses focus very close by shortening their actual focal length, a principle frequently applied to 'macro' lenses, will give a short working distance as an undesirable side-effect. When a lens changes its focal length, it becomes awkward to work from a fixed position, such as from a tripod. Sooner or later the tripod has to be moved because it becomes impossible to get sharp focus without changing image magnification and thereby altering the picture composition. This is the very reason I won't touch some recent 60-105 'macro' designs with a ten-foot pole. Other examples: central area sharpness can be extremely good, but corner softness can be evident either from field curvature (very common for short zooms or wide-angle lenses) or residual spherical aberration, or from visible colour fringing in the peripheral areas of the image. The presence of colour fringing is in fact typical for most modern designs, since elimination of chromatic aberrations evidently is given fairly low priority. Hopefully, the coming digital era will alter the priorities here since digital cameras do need better chromatic correction than contemporary models.

The internal focusing (IF) principle may unfortunately also introduce some colour fringing outside the plane of sharp detail. This can give rise to disturbing red, green, or purplish fringing of unsharp highlights. Lack of concurrent focus for the primary colours also leads to a certain fuzziness in the depth-of-field (DOF) zone. In the focused plane, colours may coincide more or less perfectly to diverge in front or back of that plane of maximum sharpness. Thus, many wide-angles will never attain anything like the theoretical DOF due to their residual colour aberration. Even very expensive lenses clearly exhibit such problems. I often find older lenses to behave much better in this respect - although their peak sharpness may be lower than the modern designs, they more than make up for this with improved rendition of the out-of-focus areas.

With the currently available high-quality digital cameras, it may be possible to perform efficient correction of colour defects in the digital domain. Several raw format converters have this capability (for example, ACR in PhotoShop CS2, or Bibble Pro). However, if you have tons and tons of images to process, digital colour correction - even when feasible - does add yet another step in the workflow.

It is an often neglected fact that some old lenses can have merits that simply are unrivalled by the modern lenses. Progress in itself doesn't guarantee better lenses - they may be cheaper, cover greater zooming ranges or whatever. Still, I sometimes am amazed by what the optical wizards are able to develop, so several of the new phantom lenses are now added to my favourite list. Shows that I'm not entirely conservative. And modern, fast telephoto lenses do tend to perform better than the old warhorses, at least when only optics are concerned.

Complex multi-element designs generally are much more prone to flare and can exhibit quite nasty ghosting despite advanced multi-coating on the glass surfaces. Prime lenses tend to alleviate these problems to a greater extent. Only a very few lenses are truly comfortable when they are used for shooting into the sun.

An issue frequently left out from reviews is the variation found in optical products. All manufacturers gloss over this and say that their products are "quality tested" before shipping. Take it with a pinch of salt. This statement is virtually always true for long lenses, often true for medium long lenses, and more commonly false than you would like to care about for short lenses and zooms. The fact is that you run a real risk of getting a lemon sample even of highly expensive professional lenses, in particular zoom lenses. From a reviewer's point of view, the basic problem isn't sample variability, but the non-feasibility of testing it. Usually it is difficult enough just to secure one single lens for testing! The variability shows itself by the partly contradicting evaluations of some lenses. The highly complex optical designs of today's most advanced lenses exacerbates the situation because the production needs cutting-edge technology and very small production tolerances. A typical example is the exciting AFS 17-35 mm f/2.8 Nikkor, which incidentally is a lens that I literally had available by dozens. I found in early production runs of this very expensive lens samples that showed mild degrees of optical decentering, or focus shifts within the zooming range. So, the basic lesson is that you should test your multi-$$$ lens before plunking down the money, preferably by using it for shooting brick walls. If in any doubt, return it or have it replaced. Just remember that your camera's front- and film-plane alignment must be perfect for such tests to be valid, and misaligned cameras are no less rare than are badly assembled lenses.

The recent breed of high-quality digital cameras, exemplified by Nikon D1X and even more D2X and the new D3, has brought forward a novel issue: a number of lenses simply have insufficient resolution to give a truly sharp image at the sensor surface. Moreover, residual chromatic aberrations may become annoyingly visible. The arrival of D3 certainly will stress this issue and thus I will continuously update my reviews bearing this in mind. The entries will be annotated accordingly.

Interspersed in the reviews are comments upon tripod collars. I'm a big fan of shooting from tripods so pay much emphasis on the quality and handling of tripod mounts. Many lenses, and Nikkors are no exception here, turn in a disappointing performance when they are mounted on tripods because their collars are too small, too weak, or both. My demands in this respect may be stricter than those of many other people, yet they are realistic in terms of what the gear should offer, but disappointingly often doesn't.

Sometimes people ask me why most lenses are rated "above average". This is a perfectly valid question and the answer is simple: because the lenses included in the reviews are not a random sample of all kinds of lenses available to the public. On the contrary, in most cases I have selected lenses that I anticipate would be of interest to a keen amateur or professional user. So the "sample" is as such quite biased. Just in case anyone still should wonder.

NOTE: The lens survey will be continuously updated to reflect new insights. Thus, with the arrival of new digital cameras, re-rating sometimes is required. The same applies when a lens is used for shooting outside the visible range, in UV or IR. Since the UV or IR rendition also will depend on the camera, one really has to create a matrix of dimension Lenses * Cameras. Obviously, this should be presented as a "sparse" matrix because most entries will be undefined for practical reasons.

For the time being, the lens survey is in its infancy and is mainly textual. I'm happy to receive any comments or criticism of my survey. Just drop me a mail.

And for all of you mailing me and complaining about the lack of reviews of brand XX 20-300 mm f/5.6-f/nothing lenses, consider my situation. I'm not paid to do review work, and in fact, am not interested to conduct testing on a consultant basis either, because that might encroach on my professional integrity. Thus, I do test equipment which should hold at least vestiges of professional interest, and try to stay away from most darkish "consumer" zoom lenses. Sometimes, like on a field trip, I exchange lenses with other people and thus can have access to less expensive items. I do not "cherry pick" any lens, and fresh samples are loaned me for testing with the express understanding that I'm going to report any finding, be it positive or negative. These are my firmly established guide lines underlying any review published on my web site.

My reviews can be freely cited, provided a reference link or site URL is presented. However, make sure you don't quote out of context, unfortunately I see this happen not infrequently. The same holds for using the text on eBay and similar sites. You can use it only if the source is given.

I have firm views on many lenses, but these points of view are never an universal truth, thus the actual needs and shooting habits of the user should be factored into the equation as well. For example, if a lens is downrated because it doesn't perform well for a given task (which may be important to me) and you intend to use it otherwise, that of course can override any objection of mine. My intention is to provide means for any user to draw his or hers own conclusions and make the appropriate decisions based thereon.

TIP: If you click the link "Lens Survey" (found at the end of each review page), you'll return directly here ready to select another review.

Lenses For Nikon 'F' Bayonet

When applicable, ratings are given for different cameras (film, digital) or uses, such as UV or IR. Since behaviour may differ on digital systems and formats (DX, FX, etc.), I continuously retest and indicate specific rates if applicable.

If no indication of use is presented, the description is for visible light only. If the camera kind isn't shown, the description applies to silver-halide systems.

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