I feel it’s time for me to lay out a guide, of sorts, for how I review my lenses. This way, I can keep commentary centered towards how a lens actually performs, rather than explaining all the technical jargon each time. This post will be updated as new terminology/review sections are added. Currently, the NEX-7 is both my camera and review body of choice for its demanding 24MP APS-C sensor. If a lens performs well on it, it’s almost guaranteed to perform at least as good on less-megapixel-dense sensors. The order below will generally follow that of every review:
This section at the beginning of each review will summarize some basic characteristics of the lens, such as its intended usage, and my general thoughts on how useful a particular lens may be.
Full name, dimensions, close-focus, average price, and other miscellaneous specifications will be listed here.
One section I always love to write about, the “feel” of a lens describes how comfortable/uncomfortable a lens is to shoot with, as well as its overall operation.
My four pillars of “shootability” are analyzed here as well. For a lens to excel in all four is rare, the ones that do are always a joy to shoot with. These pillars are:
- Small size
- Light weight
- Smooth operation
- Generally favorable optical performance
An example of a lens which claims all four pillars would be the 50mm f/1.8 E, it is tiny, weighs next to nothing, functions very smoothly, and is optically great at most apertures.
One can read this to get an overall impression of how good or bad a lens performs. In a way, this can be a section to read if you do not want to bother with all the technical sections that follow. I rarely get into specifics in this section, but it sums up many of my thoughts on general performance.
Sharpness, a lens’ ability to resolve fine detail, is supposed to be only a small component in its performance, but there are many who feel it is the deciding factor between a good or bad optic. Personally, I fall somewhere in the middle. I love seeing pixel-level sharpness (especially with a 24MP sensor), but it isn’t terribly important that all my shots are sharp when viewing at 100% on screen. To assess sharpness, I use the pictured test chart below:
Sharpness tests (as well as most of the other tests), are performed on a tripod with an infrared remote release. Before each shot, I magnify the picture to 100% to ensure there is no residual camera shake after focusing. Speaking of focusing, each shot is focused manually to ensure there is no computer interference. 100% crops (meaning, clicking on them will not make them bigger) are taken from the center, as well as from one corner of the chart. For corners, I always refocus to help counteract possible field curvature (a lens’ inability to maintain a flat field of focus at certain distances). Focus shift, an anomaly in which focus is different at different apertures, is assessed by focusing wide-open, then shooting at each stopped-down aperture to observe different degrees of focus. Contrast is also analyzed in the sharpness section.
For an example of what to look for in sharpness and contrast, take a look at the following:
Though sharpness rarely affects the quality of a photograph (and contrast can always be helped in post-processing), this section can be useful for those curious how a lens will perform for critical work (printing at 12×18 inches or above).
Two sub-sections of sharpness, infinity and “macro” sharpness is assessed immediately following the test chart crops to see how consistent a lens’ performance is at different focusing distances. The subjects chosen for infinity sharpness testing varies with the lens, but for macro assessment, a classic Altoids tin box with fine dot print is used:
“Bokeh” is an artistic term of Japanese origin for the character of anything in the image that is not in focus. Typically, smooth bokeh, where out of focus objects and highlights seem to “melt” into the background, is favorable. For the most part, lenses with longer focal lengths are better suited to providing out-of-focus backgrounds than wide-angles, but at close-focus distances, even the 28mm E can throw some backgrounds out-of-focus. To assess bokeh smoothness I stagger 4 small and detailed russian dolls behind and in front of the altoids box:
In this section, how a lens handles out-of-focus highlights (or, bokeh highlights) is also analyzed. To do this, I shoot a sparkled decoration out-of-focus to get the most point sources of light as possible. Usually, bokeh highlights without artifacts or hard edges, are both pleasing and non-distracting. For example:
“Good” Bokeh Highlights
“Bad” Bokeh Highlights
Unless focusing very closely or printing 12×18 or larger, bokeh highlights (as actual light sources) themselves will rarely detract from an image. However, keep in mind that depending on the exposure, small objects such as hard edges or spots can appear as a highlight in a photograph.
Without getting into too much technical jargon, chromatic aberrations are caused by a lens not focusing all wavelengths of light to the same convergence point (a.k.a. each pixel on the sensor), or magnifying wavelengths differently. Most fast-aperture lenses are very prone to a CA called purple fringing. Usually it is present wide-open, with some remaining at a couple stops down. “Bokeh Fringing” is another type of CA that affects out-of focus areas: typically, foregrounds are tinged in magenta, and backgrounds shaded with green. For an example of how bad chromatic aberrations can be, take a look below:
However, with modern post-processing programs such as Adobe Lightroom 4, the chromatic aberrations sliders can help to rid many images of distracting aberrations. It’s been a lifesaver for my fast primes, and with a little trial-and-error, even the worst fringing can be remedied (albeit at the expense of detail lost):
The sun gives us light (and life, for that matter), but it can be a nuisance to photography, especially once it enters the frame. Flare is caused by internal reflections in the lens, usually due to the elements having an ineffective coating. How exactly the coating process works, I’m not sure, but it’s a safe assumption that multi-coated elements reflect less light than single-coated ones. Most Nikkors have multi-coating (with the newer ones sporting “nano coating”, whatever that means), while the Series-E’s are typically single-coated. There are two main types of flare, internal reflections and veiling flare. Some lenses have none, one or the other, or both. Let’s see some examples:
“Good” Handling of Flare Reflections
“Bad” Handling of Flare Reflections
Veiling flare, on the other hand, significantly reduces overall contrast when the sun is in the frame:
Vignetting is the appearance of darkened corners, usually seen at large apertures. Since the lenses I have used up to now have been those designed for a larger sensor (well…FILM, actually), I typically do not experience vignetting. Seeing as it is trivial to correct vignetting in LR 4, this performance attribute really only applies to those who do minimal post-processing. To assess vignetting, I simply shoot a wall at large apertures at infinity focus (where vignetting is typically worse), convert to black-and-white, and overlay that with a grey background to see how much I have to adjust to get vignetting to go away. Vignetting corrections of +10 or less at the wide-open aperture do not have a problem with vignetting, but lenses requiring +20 or more will have noticeable vignetting in photographs.
“Good” Vignetting Performance
“Bad” Vignetting Performance
Distortion is an effect where straight lines in photographs are slightly bent. Wide-angle lenses can give perspective distortion at close-focus distances, but a real-world test of distortion in a lens is if it distorts at normal focus distances. Most prime lenses tend to have little distortion due to their simple optical designs, while zooms with a short focal range also are less-likely to experience distortion. Distortion can range from “pincushion” to “barrel”, the former giving the effect of an image compressing in, the latter an image bulging out. So far, due to my tendency to shoot prime lenses, I have only had one lens with truly noticeable distortion. The 36-72mm E has noticeable barrel distortion at the wide end:
Pros and Cons
In this section I summarize a lens’ performance attributes and shortcomings in a simple list form.
The Bottom Line
My send off for the review, here I give my final thoughts on a lens, its usefulness, overal performance, and recommendation for different areas of photography. Accompanying this section are usually at least three additional photographic samples taken with the lens. Depending on how much I liked shooting with certain lenses, the amount of samples can be rather large. :)
As mentioned, this post will be updated as I add sections in the future to lens tests. For instance, when I start reviewing autofocus lenses, I have to see how fast and accurate it is at acquiring focus. Features such as optical stabilization will also be added for review, testing just how much of a shutter speed advantage the stabilization provides.
Now that you’ve read this, you should now understand my lens reviews a bit more. :D