The 5th post in a series looking at how I arrived at a stable of lenses for my landscape photography as a Canon 1Ds3 owner and dedicated tripod user.
Canon produces a publication titled 'Lens Work' with a chapter on Optical Terminology and MTF Characteristics, which unusually for texts on optical matters is remarkably lucid in describing what a layman needs to know and one of the few publications that refers to a lens Colour Contribution Index. An ideal MTF chart illustrates the measurements of contrast of an actual lens optical performance under a test environment and can potentially indicate areas of the lens strengths and weaknesses. MTF charts provide no information on colour rendition, flare, distortion and build quality.
A little knowledge is dangerous, as I could appraise Canon's calculated mtf charts with images made by the lenses I owned and observe how the optical performance indicated by the 30 line pairs per millimetre (lp/mm) of the sagittal and meridional curves appeared to correlate with the resolution of fine detail in an image, with the difference between the sagittal and meridional curves indicating astigmatism and a nod to field curvature, astigmatism, chromatic aberration and an assumption my technique was adequate.
It was an exercise that provided an insight into correlating actual performance with theoretical, I'd be lying if I said, I didn't try and visualise what the image might look like if the 30 lp/mm curves were closer together, higher up the %contrast scale and flatter across the image. My eyes also suggested that my copy of the 17-40 was better away from the ends and not that bad focused in the corners and stopped down at 20mm, performance at the tele end was also visibly better when stopped down to f11, which for landscape photography is not a bad thing at all.
Every article I have read on divining mtf charts has a caveat that charts shouldn't be compared with other manufacturers nor across different focal length lenses. It appears that some manufacturers charts are not tests of actual lenses, but are calculated curves; some manufacturers calculated measurements, may be more theoretical than others and may or may not, include design tolerances, assembly tolerances, geometric losses etc. Some knowledgeable commentators hint that a lens could be designed to produce a respectable mtf characteristic that wouldn't necessarily be reflected in actual performance. So ideally, it would be good if someone independent had the wit to test and measure real lenses and correlate manufacturers MTF charts with reality. It just so happens that a photography website once did just that http://www.photodo.com/browse-lenses/sort-mtf-score-desc and graded lenses to some criteria and also published the actual MTF charts of lenses tested by Hasselblad and the 10, 20 and 40 lpm spatial frequencies at full aperture and f8, at infinity focus. The downside was that the lens tests dated back to 1990's/early 2000's, but they did highlight, to my eyes, some potentially high performing lenses that could be adapted to the EF mount. Just an observation from analysing the photodo MTF's, but if the 40 lp/mm sagittal and meridional curves are above 60% contrast across the image width at f8, there's a high probability the lens is highly regarded in the photography community.
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| Leica's MTF chart for the Macro Elmarit R 60mm f2.8 |
Back in late 2011, despite Canon's extensive lens line up, the future in my eyes suggested more image stabilised lenses, faster autofocus motors and a suspicion Canon was focusing on video cameras and cine lenses. So, I decided to look elsewhere for lenses to meet my desired angle of view and optical performance. For a few years EF mount landscape photographers had migrated to Carl Zeiss ZE lenses, legacy 35mm and medium format film lenses that could be mounted on the EF mount by using adaptors. In my opinion there's an entrenched tribalism to photography brands and gear, which unfortunately manifests itself on photography gear forums, as highly subjective opinion based on pseudo science/delusion/personal agendas/prejudice and anecdotal evidence. There are some genuinely useful opinions, but it is a dispiriting search for pearls of wisdom
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| Leica's MTF chart for the APO Macro Elmarit R 100mm f2.8 |
Cinematographers were also starting to seriously test and evaluate legacy manual focus 35mm lenses for their needs, their incentive was driven by the price of cinematography lenses and the fact that 35mm DSLR's were incorporating video and increasing capability. The evaluation of legacy and current lenses by the cinematographer community was insightful and informative for its transparency and reliance on characterising a lens performance on actual images under varying subject and lighting scenarios.
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| Leica's MTF chart for the Vario Elmarit R 28-90mm f2.8-4.5 @ 70mm |
Based upon the manufacturers published MTF correlation with photodo's actual MTF testing and the insights gained from the cinematographer community evaluation, the surprising upshot was that Leica's R lenses would be the ones to further investigate.
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| Leica's MTF chart for the Vario Elmar 80-200mm f4 @ 135mm |
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