Moore's Law and Telephoto Imaging

Kopp, Carlo

Last Updated: Mon Jan 27 11:18:09 UTC 2014

Moore's Law and Telephoto Imaging

Technical Report APA-TR-2012-0302

by Dr Carlo Kopp, AFAIAA, SMIEEE, PEng
March 2012
Updated November, 2012
Text, Line Art © 2009 - 2012 Carlo Kopp

Introduction
Moore's Law and its Impact on Digital Imaging
- Photographic Technique to Maximise Sharpness
- Comparing Lens Sharpness
- Reading/Sites:
Comparative 300-400 mm Lens Peak Centre Resolution Performance
Comparative Imaging Sampling Density Performance
Representative Telephoto Imagery
Representative Telephoto Lenses
Twenty Empirical Observations on Telephoto Lens Performance and Use
Medium Format Lenses and DSLR Bodies
Nikkor 70-300 mm f/4-5.6D ED Imagery Examples
Notes on “Superzoom” Cameras

Introduction

The telephoto lens has been widely used in handheld military and civilian applications for decades, in the former role widely used to document operations in peacetime and war, as well as a supplementary tool for intelligence collection. Mostly the equipment used has been standard professional grade commercial equipment developed for sports and wildlife photography, and built for performance and robustness in field operations.

The advent of very affordable and reasonable semi-professional grade telephoto lenses has seen strong growth in the use of this technology outside of traditional professional applications.

Modern DSLR (Digital Single Lens Reflex) and better consumer grade compact cameras with long focal lengths have become a major source of good and often high quality imagery used for OSINT (Open Source INTelligence) analysis. Much of the detailed imagery of modern Russian and Chinese equipment currently in use has been produced by semi-professional and professional grade DSLR cameras and semi-professional grade telephoto lenses.

Until the last decade, sharpness and other optical quality limitations in lenses were constrained by the performance of film media, be it grain or resolution. Beyond some point, there was little benefit in improving lens optical performance, due to the basic limitations in the wet film optical capture medium.

Until recently, the performance of the digital medium has mostly been at best comparable to wet film media, but with Moore's Law driving photosite imaging density, the point has now been reached where the digital medium will outperform the wet film medium. In turn this has major implications for the industry, and for end users of professional and semi-professional equipment.

Moore's Law and its Impact on Digital Imaging

Moore's Law is an acknowledged reality in the computer and digital communications industries, and is reflected in the exponential growth of chip densities, with a “doubling period” of 18 to 24 months. This “law” will persist until either basic physics limits are encountered in further shrinking semiconductor switches, or the high profitability in further density improvement ceases.

Imaging chips in camera equipment, manufactured using the same MOS technology processes, also exhibit exponential growth. However, imaging chips, whether CCDs or CMOS imagers, have to also meet challenging optical performance requirements, mostly in the ability to capture photons. The result of this is that the doubling period in imaging chips is much greater, in fact empirical data suggesting 2-3 times slower density growth than in computing chips manufactured in the same technology.

Until recently, Moore's Law was seen mostly as a good thing in the photographic equipment and end user communities, as more pixels means better definition and better detail in pictures, and thus all else being equal, better quality.

This is contingent upon one condition, which is that the lens can capture spatial frequencies in the picture which are equal to or higher than the spatial frequency limit determined by the pixel count in the imaging chip, and the effects of Bayer pattern colour sampling and anti-aliasing filters.

What happens if the lens does not have adequate “bandwidth” to match the Megapixel count and thus imaging photosite density of the camera's imaging chip?

To any experienced photographer, this is simply a rhetorical question. The result, inevitably, is that the picture is “soft” or lacks sharpness and thus fine detail is lost.

The subject of sharpness in lenses has been debated and argued in the photographic community ad nauseum, and has been the cause of many a techno-religious war or schism between advocates of various lenses or manufacturers.

In the era of wet film cameras, the spatial frequency limits of the film imaging medium were essentially determined by the grain size in the film, which has improved progressively over the decades, but never exponentially. Exponential growth is not a feature of the processes used in producing fine grained optical films.

In the “digital age”, exponential growth is for the immediately foreseeable future an unavoidable reality.

The material reality is that a great many low cost commodity cameras already have imaging chips which can capture significantly higher spatial frequencies, through high Megapixel counts, than the installed lenses can realistically support. In other language, the “spatial frequency domain bandwidth”, to coin a term, of the chip is higher than that of the lens. The lens becomes the performance bottleneck in the imaging system.

Until recently, in professional digital photographic equipment, lens performance was mostly not the critical limitation in optical performance of the camera system - the density of the imaging chips was simply not high enough to exceed the performance of the lenses.

This changed when the first high performance digital backs appeared some years ago in the market, for medium format Hassellblads and Mamiyas, offering more than 20 Megapixel resolution. Professional landscape photographers were the first to state concerns, mostly about soft corners. More recently, there has been considerable discussion concerning the 24 Megapixel Nikon D3X body, as some users found their preferred lenses no longer performed adequately.

The recent release of Nikon's 36 Megapixel D800/D800E full frame DSLR body priced around US$3,000 per unit will change all of this, since it shifts the threshold from camera systems in the $10,000+ class down to the $3,000 class, which is accessible to smaller turnover professionals and semi-professionals, and well funded enthusiasts. Suffice to say other manufacturers will in short order offer similar designs - that is the nature of a competitive market.

What will be observed is that a large proportion of the lower and mid-range professional and high end amateur lenses will not perform adequately with 24 - 36 Megapixel bodies, and indeed the higher resolution bodies which will follow. PhaseOne and Leaf are now offering 80 Megapixel digital backs for medium format cameras, so the trend is well established. Mamiya released recently improved “digital” variants of key lenses in their product line, with improved but unstated sharpness performance.

The question of course is which of the current and older lenses in use by the broader photographic community will be adequate for the coming “Megapixel deluge” as the market's insatiable greed for Megapixel counts drives mid range professional, and later top end amateur camera bodies into the 20+ Megapixel bracket?

More importantly, which category of lenses will hit the “spatial frequency domain bandwidth” bottleneck first?

The answer is, to any experienced photographer, the category of telephoto lenses, which have historically been the most expensive for any given f-number. The simple reality is that the optical quality of lenses for longer focal lengths must be higher to achieve equal sharpness to a standard lens. Chromatic aberration is also a pronounced problem in telephotos, which is why apo-chromatic designs are more frequent in telephotos. Often a serious chromatic aberration problem will do more damage to an image than poor sharpness.

The intent behind this short study was to look at the category of telephoto lenses which is most exposed, which are smallest, lightest and frequently most popular high end amateur, semi-professional and professional telephotos, be they primes or zooms, used in sports, wildlife, train, car-race, aviation and military photography.

Photographic Technique to Maximise Sharpness

With any high quality lens, extracting the full performance potential of the glass requires proper technique. Especially important is shutter speed, as any motion of the camera boresight while the shutter is open will cause smearing of the image. If the angular motion of the camera boresight subtends much less than a single pixel, the image will appear to be sharp, with a sharp lens. Otherwise sharpness is lost.

Telephoto lenses are the most problematic, as the narrow angular coverage of the lens, compared to wide angle, standard angle and portrait lenses dramatically increases susceptibility to “user induced motion blur” or technically, “boresight jitter”.

Experienced telephoto users, especially those who have used film, appreciate the implications of this - for most circumstances, the optimal aperture for lens sharpness and depth of field, combined with the short exposure times of 1/1000 or less, drives the optimal exposure into high ISO values. This means 400 - 1600 ISO is not uncommon in telephoto shooting.

The alternate strategy, to avoid the grain of high ISO film or noise of high ISO digital imaging, is to attempt to minimise motion of the camera. This results in the use of tripods, mirror locks, or in extremis hanging weights under a tripod to increase its stability and suppress mirror induced motion. This is also infeasible for the type of handheld shooting which is common in wildlife, sports and other related styles of photography. Monopods are an option, but not always as flexible as handheld.

In handheld photography, the play is primarily about finding the sharpest telephoto lens light enough for handheld use, selecting the optimal aperture for best sharpness, finding a camera with minimal noise at high ISO settings, and configuring the camera to perform best in this regime.

The great advantage of digital over wet film in telephoto shooting is that sensitivity or ISO in modern cameras can be configured to dynamically adjust on a frame by frame basis, unlike film where ISO is fixed by the loaded roll. Therefore, in getting optimal exposure, the photographer can fix the aperture setting, and the shutter speed both for optimal results, and let the automated metering adjust the ISO to get the proper exposure.

This will not always work perfectly, as most cameras with “Auto-ISO” may not have fine control of the ISO value, so in the end the camera must be left in Aperture Priority mode, and bounds set on the “Auto-ISO” control to prevent the shutter speed dropping below some limit. In this regime, the camera metering system will use ISO value for coarse exposure control, and shutter speed for fine control. There are pragmatic limits - if the scene is too bright, ISO may hit the lower limit for the camera, and shutter speed the upper limit. The converse is also true in a poorly lit scene, where the automation will drive the ISO into high values with high noise, while the shutter speed is stuck at the lower limit for the focal length.

Many authors of texts on photography, bloggers and other “authorities” frequently reject the use of the “Auto-ISO” control, which is unfortunate, since this is the one unique feature of digital photography which has the single greatest potential to improve the general quality of telephoto shooting. Manufacturers who have incorporated “Auto-ISO” controls with shutter speed limits clearly do understand and appreciate the value of this feature. It does not appear to be well appreciated outside of the small community of experienced professional telephoto shooters.

Comparing Lens Sharpness

While an experienced photographer can quickly assess the relative sharpness performance of any given collection of lenses by carefully looking at imagery produced, the fastest and often easiest way is to look at test results.

There are three large databases of lens tests on the web, maintained by Photozone.de, SLRGear, and DXO Labs, and many more other sites which include test data on various lenses. Across these databases, hundreds of lens types are covered, although many older lenses and high performance professional lenses are not covered.

There are numerous metrics of lens sharpness in use, and it is necessary to compare apples with apples, in the sense that like metrics must be used. The lowest common denominator is the very old wet film era metric of line pairs (or lines) per millimetre, i.e. lp/mm, which is not the most popular at this time.

An important caveat to consider is the camera body used in the test. The limitation to such tests is invariably imposed by the number of Megapixels the camera body can capture. Spatial frequencies passed by the lens which are above the anti-alias filter and imaging chip limits are lost in the measurement - effectively the camera body is blind to spatial frequencies above its sampling capability. It is worth observing that the imaging chip in a 24.5 Megapixel D3X has a sampling limit of ~82 lp/mm, while the chip in the 36.3 Megapixel D800 has a sampling limit of ~102 lp/mm, using the Nyquist criterion. The 16 Megapixel D7000 with an APS-C chip has slightly higher density than the D800, but exploits the centre “sweet spot” in full frame lenses.

This effect is very apparent on the DXO database, where test results produced with a 24 Megapixel body are clearly better, for the same lens, than results produced using an 8, 10 or 12 Megapixel body. This effect can be observed wherever any given higher performance lens has been tested on bodies with different Megapixel counts. Where the camera bodies have similar Megapixel counts, the difference in the measurement results may be small or negligible, but where the difference is large, the results may not make for accurate comparisons.

The table below, entitled “Comparative 300-400 mm Lens Peak Centre Resolution Performance” is compiled from data across a wide range of databases, all converted to lp/mm for convenience. It should be treated with caution, for all of the previously stated reasons, but also due to the tolerancing variations between lens examples used for testing. Some samples will have been at the upper performance limit for the type, some typical, and some at the lower end. This is a simple reflection of the fact that production lenses are typically normally distributed and follow a bell curve. While the data has been checked by looking at sample images where available, not all of the lenses in the table could be checked in this fashion, especially older lenses.

One observation, well known to experienced telephoto users, which is not clear from tabulated measurements, is that most zooms suffer the most performance loss in the last 100 mm of the zoom range. It is a standing anecdote in some parts of photographic community, that the “Company X 100 - 500 mm f/6.3 zoom is really a 150 - 400 mm zoom ...”, and therefore to get some nominal focal length out of a zoom with good quality, it is necessary to use a zoom lens with a nominal maximum around 100 mm greater than the required maximum. Paraphrasing one blogger, “...the last 100 mm are for emergency use only...”.

What the table does show, for “handheld use compatible” telephoto lenses, is that high performance professional lenses will perform well on 20+ Megapixel camera bodies, but also that the performance of many basic and semi-professional lenses may be borderline with such camera bodies. Generally, lenses with identical focal lengths and maximum apertures tend to similar performance, unless there are major design differences such as apochromatic optics.

While the Bayer pattern and resulting 1.414-fold reduction in sampling density for green pixels provides a little headroom in real world images, compared to monochrome test patterns, the inevitable reality of the coming “Megapixel deluge” does not change.

The yet to be answered question is the extent to which the photographic equipment industry plan to address the developing performance gap between emerging high production volume 20+ Megapixel camera bodies and “handheld use compatible” telephoto lenses.

Reading/Sites:

Emil Martinec, Noise, Dynamic Range and Bit Depth in Digital SLRs, Enrico Fermi Institute, University of Chicago;
Norman Koren, Blur units, MTF, and DXO Analyzer’s BxU, Imatest Website;
Rafael Zwiegincew, Pixel Peeper;
Kopp C., Exponential growth laws in basic technology and capability surprise, IO Journal, Vol 2, Issue 4, Association of Old Crows, USA, pp. 21-27.

Comparative 300-400 mm Lens Peak Centre Resolution Performance

Lens	Sharpness @ FL f/8	Sharpness @ FL f/8	AF	APS-C FL [mm]	Filter ∅ [mm]	Mass [kg]	Test Data Source
Lens	Maximum FL	Minimum FL	AF	APS-C FL [mm]	Filter ∅ [mm]	Mass [kg]	Test Data Source
Sekor C 105-210 mm f/4.5 ULD	62.0 @ 210.0	72.0 @ 105.0	M	315.0	58.0	0.88	PP 1991
Nikkor AF-S 70-200mm f/2.8G ED VR II	80.4 @ 200.0	83.9 @ 70.0	A	300.0	77.0	1.54	PZ/Imatest
Nikkor 70-300 mm f/4-5.6D ED	55.0 @ 300.0 70.0 @ 300.0^E	64.0 @ 70.0 76.0 @ 70.0	A	450.0	62.0	0.52	DXO CO-NET
Nikkor 70-300mm f/4.5-5.6G ED VR	68.1 @ 300.0 53.0 @ 300.0	77.0 @ 70.0 65.0 @ 70.0	A	450.0	67.0	0.745	PZ/Imatest DXO
Tamron 70-300mm f/4-5.6 SP Di VC USD	68.1 @ 300.0	78.9 @ 70.0	A	450.0	62.0	0.765	PZ/Imatest
Tokina 80-400 mm f/4.5-5.6 AT-X 840 AF D	56.0 @ 400.0^E	76.0 @ 80.0	A	620.0	72.0	1.02	CO-NET
Nikkor 80-400 mm f/4.5-5.6D ED VR	60.0 @ 400.0	61.7 @ 80.0	A	620.0	77.0	1.34	PZ/Imatest
Canon 100-400 mm f/4.5-5.6 USM L IS	64.7 @ 400.0 71.0 @ 400.0	69.4 @ 100.0 76.0 @ 100.0	A	620.0	77.0	1.36	CO-NET
Sigma 120-400mm f/4.5-5.6 APO	62.4 @ 400.0^E59.5 @ 400.0^E	66.5 @ 120.0 76.0 @ 120.0	A	620.0	77.0	1.75	PZ/Imatest CO-NET
Sigma 150-500mm f/5-6.3 APO	68.0 @ 400.0^E 59.0 @ 500.0^E 62.9 @ 500.0^E	76.0 @ 150.0 65.4 @ 150.0	A	750.0	86.0	1.91	CO-NET PRC Unsp
Tamron 200-500mm f/5-6.3 SP Di LD IF	57.2 @ 500.0^E 59.1 @ 400.0	63.3 @ 200.0	A	750.0	86.0	1.24	PZ/Imatest

Sekor A 200 mm f/2.8 APO	80-120 @ 200.0	N/A	M	300.0	77.0	1.10	Mamiya
Sekor C 210 mm f/4N	78.0 @ 210.0 / f4	N/A	M	315.0	58.0	0.715	PP 1991
Sekor C 300 mm f/5.6N ULD	~80.0 @ 300.0	N/A	M	450.0	58.0	0.710	Estimated
Nikkor 300 mm f/4.0D ED IF	65.8 @ 300.0	N/A	A	450.0	77.0	1.44	PZ/Imatest
Nikkor 300 mm f/4.0 ED IF	~65 @ 300.0	N/A	A	450.0	82.0	1.33	Estimated
Nikkor 300 mm f/4.5 ED AI-S	60+ @ 300.0	N/A	M	450.0	72.0	1.20	Estimated
Nikkor 300 mm f/4.5 ED IF AI-S	60+ @ 300.0	N/A	M	450.0	72.0	1.06	Estimated
Nikkor 400 mm f/5.6 ED IF AI-S	60+ @ 400.0	N/A	M	620.0	72.0	1.20	Estimated
Canon 400mm f/5.6 USM L^F	65.4 @ 400.0	N/A	A	620.0	77.0	1.25	PZ/Imatest
Sigma 400mm f/5.6 APO TM^F	64.2 @ 400.0	N/A	A	620.0	77.0	1.29	PZ/Imatest

High Performance Professional	> 75 [lp/mm]
Basic Professional	60 - 75 [lp/mm]
Semi Professional	55 - 60 [lp/mm]
Sharpness [lp/mm] @ FL [mm] : separation between two lines, -3 dB in contrast / MTF50; sometimes also described as lines /mm, this document follows the same usage convention as the DXO website.
Notes: The table is not intended to be exhaustive and is not, it is only intended to provide basic comparisons of lens categories for 35 mm / full frame DSLR lenses; Measurement data was produced using a range of tools and camera bodies and thus does not share a common baseline, some results will overstate performance, and some understate performance; note that the higher the sampling density of the camera, the more accurate the result, while APS-C sensors yield better results than full frame sensors as the inferior corners are not measured; Estimated performance is based on the comparison of imagery produced by the lens cf imagery produced by a lens of known (published) sharpness performance - this technique is sensitive to camera quality and likely underestimates actual performance; This table should not be used for purchasing decisions, as these require that the lens be assessed on the camera body to be employed, and consider factors other than peak sharpness; Peak sharpness at maximum zoom is at ~f/11.0, but f/8.0 at lower zoom settings; The Canon 400mm f/5.6 USM L test was performed using a Canon EOS 5D Mark II with 21.1 Megapixel 36 × 24 mm CMOS sensor, while the Sigma 400mm f/5.6 APO Tele Macro test was performed using an EOS350D with an 8 Megapixel 22.2 mm × 14.8mm CMOS sensor; The test data does not account for statistical variations in performance across production runs; anecdotal reports for most of these lens types suggest that spread, especially early in production runs, can be significant; tests performed early in the life cycle of the product may under- or over-represent typical performance by a larger amount than tests performed on mature late production items, when the mature process yields smaller variance in lens performance; it is not possible to determine whether lenses provided by manufacturers for review and testing were selected high performance outliers in the build.

Comparison of widely used current production 400 mm f/5.6 class telephoto lens centre sharpness, using Photozone and CO-NET (Sigma) measurement results. The Sigma 120 - 400 mm APO zoom is excluded, as it is outperformed strongly by its sibling 150 - 500 mm APO zoom at 400 mm focal length. Notable is that the best performing designs are strongly clustered at peaks around f/8.0, other than the unconventional Sigma design, which is an outlier at f/11.0 and thus more demanding of sensor noise performance to operate at this aperture. With full frame sensors beyond 20 Megapixels, all of these lenses will be challenged to fully exploit the sensor.

Comparative Imaging Sampling Density Performance

Camera Body/Back	Sensor Geometry	Sensor Size [Megapixels]	Pixel Density [lp/mm]	Green Density [lp/mm]	Red/Blue Density [lp/mm]	Notes
Nikon D700/D3	FX	12	59.2	41.8	29.6
Nikon D3X	FX	24	84	59.4	42.0
Nikon D90	DX	12	90.1	63.7	45.1
PhaseOne IQ180	53.7 x 40.4	80	96.2	68.0	48.1
Nikon D800	FX	36	102.3	72.3	51.2
Nikon D7000	DX	16	104.6	73.9	52.3

The Bayer pattern to some extent reduces the effect of lens limitations in real pictures, compared to synthetic tests. This is because of the reduced sampling density for green and red/blue pixels, versus absolute density. A more detailed discussion can be found in Technical Report APA-TR-2012-0301.

Representative Telephoto Imagery

Representative Telephoto Lenses

The Nikkor AF-S 400 mm f/2.8G ED IF VR is a typical modern fast high performance telephoto intended for professional users. It weighs 4.6 kg (Nikon image).

The highly regarded Canon EF 400mm f/5.6 USM L is the last remaining production 400 mm f/5.6 lightweight telephoto prime lens. A decade ago multiple manufacturers provided products in this class (Canon image).

The Sigma 150-500mm f/5-6.3 APO HSM is a popular semi-professional grade compact zoom lens. At 1.9 kg weight it is at the upper limit for handheld use (Sigma image).

Twenty Empirical Observations on Telephoto Lens Performance and Use

There are some ground rules which can aid in getting good results in telephoto shooting.

The “sweet spot” in sharpness for telephotos, zoom or prime, is much more pronounced than in shorter lenses, with up to 30 percent loss of peak sharpness in some lenses, and 15 percent very common;

Typical telephotos in the f/4 - f/6.3 range are sharpest at f/8, some at f/11, the larger and heavier f/2.8 professional telephotos tend to peak out most often around f/4;

Most amateur and some “professional” shooters attempt to improve sharpness by aiming for low ISO settings, which for short exposures like 1/500 - 1/2500 drives them to shoot wide open, where the loss of lens sharpness does far more damage than the imaging chip noise or film grain at higher ISO values;

The combination of low shutter speeds and aiming or sightline jitter, or other movement, is the single biggest cause of poor sharpness in telephoto images;

A reasonable rule of thumb is to use at least 1/1000 at 200 - 300 mm, and halve the exposure time in proportion to the increase in focal length - faster is better until ISO impairs performance;

Stabilised lenses are good at filtering out fine jitter, less so gross jitter;

Sharpness variations in zooms can be prominent, with most zooms exhibiting a 16 percent loss of sharpness between minimum and maximum zoom, although some amateur lenses are worse, while some professional lenses significantly better;

The more Megapixels a camera body delivers, the sharper the lens needs to be to produce decent results - a 20 Megapixel or higher camera will require peak sharpness of 65 - 70 lines / millimeter to produce acceptable results, possibly more;

Corner sharpness is important for some telephoto subject matter, and is almost irrelevant for others;

Lens centre sharpness is most important in aviation, sports and wildlife photography, where images are often cropped, in landscape photography, sharp corners are a critical requirement;

The old adage about “primes being sharper than zooms” is usually true in telephotos, although often the biggest difference is that primes have more consistent sharpness corner to corner, while zooms even if matching the centre sharpness of a prime, tend to softer corners;

A 35 mm / full frame lens will usually perform better on an APS-C sensor, as the sensor cannot see the softer corners; a medium format lens will usually perform better on a full frame sensor for the same reason, and even better on an APS-C sensor;

Lens reputation and cost may not be good indicators of optical performance, especially sharpness and chromatic aberration; some expensive telephotos have borderline sharpness and high chromatic aberration, some cheaper telephotos the opposite;

Telephoto lenses are completely unforgiving and will expose faults in technique, handling and camera setup far more readily than any other common type of lens;

Lens reputations often reflect ease of use more than actual optical performance, care should be taken when assessing choices, some popular lenses are mediocre, some less popular lenses are very good, even if more difficult to use;

It is useful be very sceptical about opinionated reviewers and carefully study their test methodology and thinking, as often they can be seduced by brand names or features;

The ultimate measures of worth in a telephoto lens are sharpness, consistency of sharpness across the field, chromatic aberration, distortion, and handling characteristics such as weight and balance - careful tests are always more useful than subjective opinion;

If test results are inconsistent, actual sample photos should be studied carefully, as human testers are not infallible;

High ISO performance in a camera body is necessary for telephoto shooting, and Auto-ISO is an essential feature. This feature was absent in the era of wet film, when increasing ISO performance meant swapping film backs, or camera bodies.

For any given technology used in the imaging chip, in a DSLR a full frame sensor with larger imaging sites typically outperforms an APS-C sensor; the tradeoff is always between lens corner sharpness performance and higher sensor sensitivity performance.

Medium Format Lenses and DSLR Bodies

A usable manual focus 400 mm f/5.6 capability weighing over 1.5 kg can be produced by stacking the Sekor A 200 mm f/2.8 APO with the Sekor 2XN 2:1 teleconverter, here mounted on a Nikon D90/MB-D80. This configuration produces no visually discernable chromatic aberration, but is not as sharp as the prime alone - peak sharpness is around f/8.0 with very pronounced roll-off away from the peak (© 2012 Carlo Kopp).

In 2011 the author acquired a used Nikon D90 body primarily as an experiment to assess the practical problems in exploiting medium format Mamiya-Sekor lenses on DSLRs, concurrently the author acquired a Fotodiox Pro Mamiya-Nikon mount adapter, which was modified with a digital matrix chip to present as a Nikon lens.

Since then the D90 with Fotodiox adaptor has been used for a wide range of test and practice shoots, using the following lenses:

Sekor C 45 mm f/2.8N;

Sekor C 55 mm f/2.8;

Sekor C 80 mm f/2.8;

Sekor A 200 mm f/2.8 APO, also with one or two 2XN teleconverters;

Sekor C 105 - 210 mm f/4.5 ULD Zoom, also with one 2XN teleconverter;
Sekor C 210 mm f/4.0, also with one 2XN teleconverter;
Sekor C 300 mm f/5.6N ULD, also with one 2XN teleconverter;

The choice of the semi-professional D90 was intentional, since performance benchmarking suggested similar imaging performance, at lower ISO to the professional D700. In addition, the D90 has an internal focus drive motor permitting its use with older Nikkor and third party telephoto lenses. This minimised the risk in the buy.

Results with the Mamiya-Sekor lenses exceeded expectations, as the DX/APS-C sensor does indeed take full advantage of the sharper centre of the lens. All four prime lenses tested outperformed the 12.3 Megapixel imaging system and would be suitable for use on a D3X class body. The 105 - 210 mm f/4.5 ULD zoom would need further testing with a higher resolution camera to be conclusive, and would show its limitations beyond 16 Megapixels.

All lenses were used manual focus designs acquired at low cost, with the exception of the 80 mm f/2.8, acquired new in Tokyo, in 1984.

Sources: Popular Photography; November 1999, April 2000, October 2002; Sharpness in lp/mm

Sekor A 200 mm f/2.8 APO Lens mounted on a Mamiya 645AFD (HS10 10 MP).

Sekor A 200 mm f/2.8 APO Lens mounted on a Nikon D90/MB-D80 with a Fotodiox Pro adaptor (HS10 10 MP).

Fotodiox Mamiya/Nikon adaptor modified by Legacy2Digital in the US with a digital emulator chip, which presents the lens to the camera body as a Nikon device. It is preprogrammed to represent the 200 mm f/2.8 APO with the proper focal length and maximum aperture. This enables the full range of automated features in a Nikon body, in this instance a D90 (HS10 10 MP).

Comparison: 3 SQN RAAF F/A-18A, then flown by then WGCDR Dave Pietsch, photographed using a Mamiya M645/1000S fitted with a Sekor C 80 mm f/2.8, using 100 ASA wet film. Original scanned to 5.8 Megapixels (© 1995 - 2012 Carlo Kopp).

Elmendorf based F-22A Raptor imaged with a Mamiya 645AFD, above using the autofocus Sekor AF 80mm f/2.8, below using the manual focus Sekor A 200mm f/2.8 APO, using Fujifilm Pro 160C wet film. Originals scanned to 5.8 Megapixels and corrected in Aperture 3 (© 2011 Carlo Kopp).

Extra EA-300L captured at Moorabbin in October, 2012, using the Sekor C 105-210mm f/4.5 ULD telephoto zoom on a Nikon D90, at ISO 640 and 1/1600, the lens aperture at best sharpness f/8.0 (© 2012 Carlo Kopp).

Cessna 152 captured at Moorabbin in October, 2012, using the Sekor C 105-210mm f/4.5 ULD telephoto zoom on a Nikon D90, at ISO 400 and 1/2000, the lens aperture at best sharpness f/8.0 (© 2012 Carlo Kopp).

Above, below: CAC CA-25 Winjeel A85-439 captured performing an aerobatic sequence over the Sandown racecourse in November, 2012, using the Sekor C 300mm f/5.6N ULD telephoto prime on a Nikon D90, at ISO 360 and 1/4000, the lens at best sharpness wide open (© 2012 Carlo Kopp).

Bellanca 8KCAB captured at Moorabbin in October, 2012, using the Sekor C 300mm f/5.6N ULD telephoto prime on a Nikon D90, at ISO 280 and 1/4000, the lens at best sharpness wide open (© 2012 Carlo Kopp).

Nikkor 70-300 mm f/4-5.6D ED Imagery Examples

The Nikkor 70-300 mm f/4-5.6D ED telephoto zoom is a lightweight plastic barrel design with a mechanically driven autofocus, which straddles the semi-professional bracket upper boundary, and was obsoleted some years ago. The lens has an undeserved reputation for mediocrity, likely as its low cost meant it was frequently used by inexperienced photographers - many sample images on the web show evidence of poor aperture management, with the lens operated wide open where its sharpness is especially poor, and chromatic aberration very pronounced.

My motivation for acquiring this frequently maligned lens was largely curiosity, as DXOMark and SLRGear test results suggested that at its optimal f/8.0 aperture it performed competitively against much newer Nikkor 70-300 mm offerings, and used examples were very cheap. This example including freight charges cost $200.00. The results produced by this lens are often of sufficient quality for less challenging professional applications, but it requires careful handling and use at the optimal f/8.0 aperture value, with best performance in the lower half of the zoom range. To date this lens has only been employed on the D90 body. Its performance is inadequate for 20+ Megapixel bodies, although samples produced using the 16 Megapixel D7000 appear to be of reasonable quality.

Jetstar A320-232 VH-VGQ at YPPH November, 2011. Parameters: f/8.0, 1/3200, ISO 800, -0.66 EV, 70 mm. Below crop of same 1:1 (click to enlarge).

Qantas 737-838 VH-VZB at YPPH November, 2011. Parameters: f/8.0, 1/1600, ISO 800, -0.66 EV, 190 mm.

Qantas 737-838 VH-VZB at YPPH November, 2011. Parameters: f/8.0, 1/2500, ISO 800, -0.66 EV, 300 mm. Note the turbulent refractive distortion which impairs sharpness (click to enlarge).

Fuel tanker truck at YPPH November, 2011. Parameters: f/8.0, 1/4000, ISO 800, -0.66 EV, 180 mm (click to enlarge).

Vicpol Dauphine over the eastern suburbs of Melbourne in November, 2012. Parameters: f/8.0, 1/2500, ISO 400, -0.66 EV, 300 mm.

Notes on “Superzoom” Cameras

A recent addition to the menagerie of consumer photographic equipment types in the market are so called “superzoom cameras”, sometimes also labelled less descriptively as “bridge cameras”, as they are intended to bridge the gap between consumer compacts and DSLRs. Most manufacturers offer one or more types in this class. These are compact, sealed cameras, usually with one or more internal image stabilisation mechanisms, and primarily amateur controls and operating modes. The depicted Fujifilm HS10, now obsoleted, is notable as being the first to offer a 30:1 zoom capability, in early 2010.

Superzooms have often been harshly criticised for poor optical quality compared to DSLR products. This reflects two realities. The first is that the small consumer grade imaging chips, in the 1/2.5 inch class, cannot compete with full frame or APS-C DSLRs in photosite area at similar Megapixel counts, reflecting in much noisier images. The other reality is that 10:1 out to 30:1 zoom ratios are inevitably at the expense of optical sharpness, chromatic aberration and distortion performance.

How severe are these limitations? That depends in part on how well the superzoom has been designed by the manufacturer, and configured by the end user. The Fujifilm HS10 for instance, performs poorly in fully automatic Program AE mode at full zoom. Studying images produced in this mode shows that the algorithm for exposure control does not appear to account properly for focal length setting, which results in slow exposure settings, wide open apertures and jitter induced losses of sharpness - in effect the HS10 algorithm makes much the same mistakes as an inexperienced human telephoto shooter. Setting the HS10 into shutter priority mode, with 1/400 or shorter exposures, appears to solve this problem, leaving the exposure algorithms to manipulate aperture controls - unfortunately Auto-ISO is disabled in the “pro modes” requiring manual intervention to select a good ISO choice, and manual adjustment of shutter speed. The results are considerably better in this regime.

Numerous HS10 samples at 720 mm equivalent focal length have been studied. While noise performance at 100 ISO is poor, and comparable to a Nikon D90 at 1600 ISO, sharpness is remarkably good, and surprisingly, comparable to a number of semi-professional DSLR zoom offerings at lower focal lengths.

At the same 450 mm equivalent focal length, sharpness of the Fujinon lens in the HS10 is competitive at against the semi-professional grade Nikkor 70-300 mm f/4-5.6D ED, while imaging sensor performance is not. It is interesting to note that the successor superzooms to the HS10 appear to use the same lens system, but considerably better 16 Megapixel sensors and processing.

While the author has used the HS10 mostly for documentation applications, as it is convenient, small and light (~0.65 kg), and has good macro modes, it has been used as a backup on production shoots and has produced sufficient image quality for less challenging production print publishing and web applications. While superzooms will always fall well behind contemporary DSLRs in noise performance due to the physics of imaging chip size, with good lens design they can provide highly competitive telephoto performance against cheaper DSLR lenses, providing the ground rules in lens and camera mode configuration are respected by users.

Cropped HS10 production shot of MRH-90 transport helicopter on display at Avalon 2011 (Click to enlarge).

Cropped HS10 production shot of JDAM-ER prototype at 1/208, f/4.0, 100 ISO, in fully automatic Program AE using Auto-ISO, at 6.3 mm.

Cropped HS10 production shot of Wedgetail AEW&C aft tailcone fairing mounting MIDS/JTIDS/Link-16, AN/AAR-54 MAWS, ALR-2001 ESM apertures and the conical ventral fairing replacing the AN/AAQ-24 DIRCM turret.

Cropped HS10 production shot of Royal Air Force E-3D Sentry AEW.1 aerial refuelling probe.

Cropped HS10 production shot of Racal/Thorn / Loral 1017 Yellow Gate ESM pod.

Technical Report APA-TR-2012-0302

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