Lens Reviews - Find Out How We Review Lenses

Lens Reviews - Find Out How We Review Lenses - This is a summary of how lens reviews are undertaken and hopefully should help to explain and expand so that the greatest benefit can be gained from the information they contain.

|  Nikon AF-S NIKKOR 58mm f/1.4G in Interchangeable Lenses
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Some time has elapsed since the publication of the first article on this subject and many things have changed in that time. This is a summary of how lens reviews are undertaken and hopefully should help to explain and expand so that the greatest benefit can be gained from the information they contain.

Nikon Nikkor AF S 58mm F1 4G (9)
Nikon Nikkor AF-S 58mm F1.4G

 

Lenses arrive via courier, with a suitable body to use them with if necessary. We do have a small stock of suitable cameras, but cannot possibly keep all marques in our cupboards.

The first thing to note is that lenses cannot always be tested using the same camera body/sensor and so the results are always pitched against the theoretical perfect result for any combination. The maximum potential LW/PH figures change with different mega pixel counts, so descriptions such as “excellent”, “very good” and so on are retained to summarise how different lenses compare. These descriptions have been made to tally, as closely as possible, with the same descriptions used in previous reviews. The LW/PH figures are now shown in the graphs to help you more clearly compare sharpness between lenses reviewed from late 2015 onwards, and descriptions are used in the text, so that you can compare with reviews made before this. 

 

Some time is allowed to give the lenses time to acclimatise, as when they arrive they can be very cold. To prevent internal condensation they are left for a couple of hours, time that can be spent researching what the manufacturer claims about the new optic.

 

Imatest - Camera in front of chart

 

Technical tests use a very large Imatest slanted-type test target, which has been mounted on what is effectively a small portable wall. Lenses up to around 200mm can be accommodated in the studio, after which we have to move outside. When outside, a dry, bright overcast time is chosen to make lighting as consistent as possible. Any focal length can be tackled in this way, the biggest challenge in the winter being snatching a suitable break in the weather.

The camera/lens combination is mounted securely on a Manfrotto 055 tripod with Manfrotto 115 three-way head and aligned very carefully on the target. All lens corrections in camera are switched off and the highest resolution possible chosen. The base ISO is used, often ISO 100, but sometimes ISO 200, depending on camera. No in camera sharpening is allowed. The self-timer is used to make the exposures, to avoid all possibility of shake, but any in-camera or in-lens shake reduction is switched off.

AF lenses are focused using Live View and for prime lenses, three runs are recorded, shooting at every aperture. For MF lenses extreme care is taken to focus accurately using whatever aids the camera offers, plus magnifiers on the screen if necessary. MF lenses are given at least four runs, and up to seven might be used if a lens proves tricky to focus accurately.

 

Canon EF 24-105mm MTF at 24mm

MTF Chart shows central and edge sharpness at different apertures.

 

Zoom lenses are tested at several zoom settings, with each zoom setting being treated as if were a prime lens as detailed above. Typically, four points in the range will be measured.

Canon EF 24-105mm CA at 24mm

Chromatic Aberration Chart shows the level of chromatic aberration in the centre and edges, at different apertures.

 

The images obtained of the lens chart are then processed through Imatest 3.7 Master, which gives resolution figures, CA (Chromatic Aberration) figures, distortion levels, and falloff (or vignetting). These start to build up a picture of the lens performance. This is summarised in the form of graphs and text. In the case of resolution (sharpness) results are offered using the MTF50 figures and measuring at the centre and edges of the image field, really quite a demanding standard.

 

Taking product shots with LED lighting

 

The product shots used in the reviews are also shot in-house, currently using a Pentax K-3 II body plus a variety of lenses, after which it remains to take the lens out in the field to see how it performs and handles in real life shooting. As wide a selection of shots as possible is aimed for, including portraits, architecture, close up/macro, landscape, wildlife, reportage and sport. Whatever speciality the lens is intended for is, where possible, is explored with extra shots. Images are also taken that demonstrate CA (Chromatic Aberration), flare resistance and the ever more important bokeh, the quality or smoothness of the out of focus areas in an image. Different locations are used for the test images, to give some variety to the reviews, although many will be revisited on a regular basis. Bokeh shots are made at all apertures whilst on location to give a realistic feel of the “look” or aesthetic qualities of a lens.

All this material is then assembled on the PC and the text of the review written. Sample images are not cropped, nor are they sharpened in any way. The idea is that they can be downloaded and put through whatever processing desired, to see exactly how the files handle and give the best possible indication of whether or not a lens will suit an individual. Ratings are given as a guide, and these of course represent a band of performance, with very few lenses achieving the coveted assessment of Editor's Choice.

Being published on the internet allows anyone interested to post comments on the reviews, ask questions and seek clarifications. Wherever possible these will be answered and there can be a continuing discourse not possible with traditional printed publications.


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