Landscape lens odyssey Part V - Divining MTF charts and cinematographers lens evaluation

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.

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

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. 

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.

Leica's MTF chart for the Vario Elmar 80-200mm f4 @ 135mm

Landscape lens odyssey part I - The benefits of stopping down the aperture

The first 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. 

There is a valid observation that photographers obsess over lens quality, viewing images at the pixel level and ultimately losing sight of the important factors that actually make a compelling photograph. Which is not to denigrate examining an image at pixel level, it can provide feedback on technique, information on the lens character and effect of atmospherics on capturing fine detail. How relevant pixel peeping is on a monitor when images are viewed by the public via a display, book or ideally a print,  I'm not so certain, given the effect of Jpeg compression, ink nozzle diameter and bleed.  Nonetheless, there is compelling evidence on gear forums, where web sized comparisons are posted of images with exif data stripped, from assorted high quality primes, kit zooms etc and the cognoscenti are asked to identify the mystery lenses.  When images are made with wide open apertures there's an impressive hit rate on identifying lenses, when lens apertures are stopped down embarrassment has resulted.  Simply put, many lens optical aberrations and phenomena become more problematic as the physical size of the aperture gets larger and angles of incident light become steeper for marginal and oblique rays of light gathered by the lens.

Optical designers can correct or minimise optical aberrations and phenomena through a combination and selection of optical glass, lens elements, physical size, coatings, tolerances, build etc A comparison of two contemporary lens designs is a perfect illustration of the trade offs in weight, size and cost, to achieve a high level of optical performance wide open.


Zeiss Otus 55mm F1.4 marketed as The best standard lens in the world 
Optical design : 12 lens elements in 10 groups, of which 6 lens elements are made of special glass with anomalous partial dispersion and 1 aspheric lens element.
Weight : 1 Kg
Dimensions : 92.4 mm in diameter and 127.3 mm long without caps.
Focus - manual
Retail price ~ £3,000

Zeiss Otus 55mm f1.4 @ Zeiss

Zeiss Planar T 50mm F1.4 marketed as Reveal the true character
Optical design : 7 lens elements in 6 groups
Weight : 0.38 Kg
Dimensions : 71.3 mm in diameter and 48 mm long without caps.
Focus - manual
Retail price ~ £560

By Tamasflex (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

There is a revealing test online of comparison images made with the Otus and Planar, taken at a series of apertures with a 36mp full frame Nikon DSLR. Scrutiny of full sized Jpegs, revealed to my subjective eyes, that at wide apertures the Otus demonstrates its high optical performance convincingly, whilst the nature of the optical aberrations in the Planar give it distinctive 'drawing style' or 'look'.  Stopped down to F8 and F11 the Planar's optical performance is very respectable in comparison to the Otus.  As the aperture reduces in size i.e is stopped down, the angles of incident light become shallower for marginal and oblique rays of light gathered by the lens and many optical aberrations cease to be an issue.  It emphasises that when considering a lens, landscape photographers need to consider the respective optical performance of a lens when it is stopped down against size, weight, build and price.