Olympus OM 40mm f2.0 – fotosaurier

Resolution of Lenses (Sharpness) on Analog Film – Compared to Digital Sensors

This article describes, how I made the resolution-power of lenses digitally measurable on analog film and COMPARABLE to the data, which are directly measured on digital sensors.

Since a long time I am looking for an experimental set-up, which allows me to understand, how the information content of the exposure on an analog film compares to the digital data from a digital sensor – looking through the same lens. Resolution being the main point of interest for me in this case.

FAZIT of this article is: I just found a method to do this … and it works!

Fig. 1 is an example of the resolution-chart, generated with Olympus OM Zuiko Auto-W 28mm f/2.8 lens on black and white negative film (Agfa APX100) at the lenses optimum aperture f/5.6. It shows the MTF30-resolution-values from center to corner (21,7 mm picture-circle-radius):

Spoiler-Bild-Imatest-on-Film — **Fig. 1**: Resolution measured digitally on analog 35mm-film: The maximum mean resolution value, measured in the center (1.237 LP/PH), corresponds to **100 lines/mm on Film.** At f/8.0 the resolution is even more uniform over the frame – but a bit lower in the center. – source: fotosaurier

1. Introduction: Quality of historical lenses.

Until the end of the last milennium, photographic lenses were designed to generate highly detailed images on film (or glass-plates coated with light sensitive layers).

When at the beginning of the millennium 2000 ff the radical change to digital sensors for the recording of photographic pictures happened within a few years, the photographic community sat on a huge number of phantastic and beloved lenses for the ancient analog recording method with film. We all could not believe, that all these wonderful and iconic lenses would become useless.

This was a strong motivation, to put the historical lenses in front of the sensor-driven digicams! Knowing very well …

… that for the very special needs of digital imaging sensors, new lenses had to be designed under consideration of some special optical features along the optical path behind the lens, before the light hits the light sensitive elements.

The older „analog“ glass is not perfectly fitting to these conditions! … but what are the artefacts on sensors and how important are they?

Measuring the Modulation Transfer Funktion (MTF) of a lens is a fundamental method to characterize the optical resolution of a lens itself – independant from the recording method (film or digital sensors): the direct optical measurement of the MTF-curve over the imaging circle of a lens shows the contrast as a function of the „spatial frequency“– these data today often being available from the lens-makers. Historically, the method was developed parallel to each other by Zeiss and Angénieux (during the 2nd world-war). Fig. 1 shows the certificate, which was delivered with my Angénieux zoom-lens as a qualitiy-proof (showing that this is an extraordinary example … above average expectations!).

Angén-Certificate_70-210_IMG_9574 — **Fig. 1**: MTF-curve and actually tested contrast-value (86% at 20 cycles/mm) in a certificate for the Angénieux-Zoomlens 70-210mm f/3.5. The graph shows in the lower curve the lowest contrast transfer-limit at which the lens is accepted for delivery – source: fotosaurier/Angénieux

Reminder: One „cycle/mm“ is two lines/mm! Two lines (one black + one white!) are the spatial (linear) cycle. We call this here in my article „Linepairs = LP„. In the systematics, which I personally use in the IMATEST-software, the resolution is always defined as „Linepairs per Picture Height = LP/PH„, where the picture height on film or sensor always is 24mm (for 35mm stills) … if not otherways stated. That means:

For 35mm stills (24mm x 36mm) the data in „LP/PH“ can be converted into „cycle/mm“ with division by 24, or into lines/mm with division by 12.

Fig. 2 shows the type of MTF-plots, which are today typically used as the contrast over the radius of the image-circle:

MTF-curves Fujinon 56f1,2_eng — **Fig. 2**: Modern version of a MTF-curve, showing the contrast of a lens over the picture-circle (APS-C-format!) for two different spatial frequencies – separated for sagittal and meridional rays – source: Fujifilm

These lens-specific-informations are perfect to characterize the lens – but do not help me, in the case of historical lenses, for which these data are mostly not available. For these I have to measure the performance myself – either using analog film or the digital sensor.

In historical times (1960s to at least 90s) tests of „Lens Performance“ were published in several US-publications like „Modern Photography“ and „Popular Photography“ and others targeting on amateur photographers.

These mostly used the „USAF 1951“ target, which was mounted on a flat wall and photographed at scale 50:1 on b&w negative film and read by inspection with a loupe of defined enlarging power directly on the film strip,

SilverFast_Resolution_Target_USAF_1951 — **Fig 3**: Resolution Target „USAF 1951“ – source: By LaserSoft Imaging – Eigenes Werk, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=12126324

Results from these test were as shown in the following picture:

AnalogResol_OM24f2,8_ModernPhotgr — **Fig. 4:** Unfortunately I did not find the analog test results of the 28mm f/2.8 Zuiko Auto-W, which I use as my test reference in this article – ths is the test of it’s sister-lens with 24mm focal length. I have tested both with IMATEST on A7R4 Sensor and found, that in the corners, the 28mm-lens is **much better** in resolution than this example – source: Modern Photography

I tried this method myself in the 1970s and can tell you: it’s a lot of work!

2. The digital IMATEST lens testing method and software for digital imaging:

Testing the optical performance on a digital sensor is facing several facts and influences, which are new and specific: pixel size, algorithm, problems of digital signal-processing systems like aliasing, additional optical elements in the optical path like glass-filters and micro-lenses!

The question: is there an essential influence of all these optical systems on the visual result in the picture over the picture-circle (Bildkreis), e.g. because of the varying angles at which the light-rays hit on the sensors between center and the farthest corner of the picture format or due to the additional optical elements introduced into the light-path?

In the case of RANGEFINDER-lenses we know that there often is a strong influence of this. These lenses are often made for a very short distances between the last lens and the film – especially for wideangle- and standard-lenses. Little was known to me about historical SLR-lenses, which were never planned and calculated for the use with modern digital sensors.

Since several years I do quite a few measurements on historical lenses, using a high-resolution digital sensor with 62,5 Mega-Pixels, resulting in 61 MP effectively on Full Format (35mm stills).

Until now I did not know, whether the measurement of my historical lens is falsified due to artefacts, genrated by the digital recording system. The work, described in this article, was done, to clearify this situation.

I just want to know: how does picture quality of historical SLR-lenses on the analog film compare measurably to that delivered by digital sensors?

Digital cameras are really big number-crunching-machines! And with the right software, I can use the numbers to generate a numerical picture of the optical quality of the lens-sensor-combination. IMATEST is such a software and it uses standardised TARGETS to do that. I use the following target:

DSC03033_Macr-Yashica_55f2,8_5,6-foc Kopie — **Fig 5**: **SFRplus** target for Imatest – it’s height is 783 mm between the horizontal black bars, which means, that the reproduction ratio on film is 33:1 – source: fotosaurier/Imatest – original information graphics from IMATEST

Over years I did – like many other amateur-photographers – compare real-world photos of analog vs. digital processing. But I was never satisfied, because this method gave me only subjective impressions – it did not create reproducible figures, to generate a precise description of the results!

I collected intensive experience with IMATEST on more than 150 lenses over meanwhile 5-6 years using the digital pictures generated by digital sensors (4,9 to 102 Megapixels) of seven different DIGICAMS. During this time, my Standard Digicam to compare lenses was (and still is) Sony A7R4 (60 Megapixels) – since it had arrived in the market (2018/19).

IMATEST (Studio) software delivers MTF-based resolution data – as it can do that separately in three RGB-channels, it also delivers lateral CA-data. Using the Target structure of Fig. 5, the software selects 46 local areas, and runs the MTF-measurement automatically for all these 46 areas. The following picture demonstrates the automatic areas, which are typically selected – but you could choose others as well:

ROI-chart (standard) — **Fig. 6**: The **46 magenta rectangles** (called „**ROI**„) frame the Edges in the target, at which the 46 MTF-measurements are made – source: fotosaurier/Imatest

These are the curves, which are generated from each digital picture (black&white):

Zusammenstellung_IMATEST_A7R4_OM28d2,8_2,8 — **Fig**. 7: Summary of the IMATEST-results for the **OM28mm f/2.8** at open aperture f/2.8 **on Sony 60 MP-sensor** (A7R4) – explanation see text beneath – the graph lower left corresponds to the type of graph in Fig 1., the right graph corresponds to the type of pictures in Fig. 2 – source: fotosaurier

The upper left curve shows the edge-profile at center of the target (ROI no. 1, which is the left (vertical) edge of the center square in Fig. 6). From this graph the edge-rise between 10% and 90% is taken from the x-coordinate in pixels. The lower left curve is the MTF-curve (contrast over spatial frequency) for the same location. From this graph the MTF30 value (Frequency at 30% contrast) is taken: follow the horizontal line at 0,3 MTF-value to its section with the curve and take the frequency on the abscissa. The right curve shows the MTF30-values of ALL 46 ROIs plotted over the distance from the center in the 35mm-fframe.

I have resumed the IMATEST test-method in more detail in this article here in my blog!

3. Digital measurement of resolution on analog film

Now I decided to make the following experiment:

Take a photograph of the IMATEST-target on analog film;
digitize the picture with a film-scanner;
analyse the resulting digital picture with IMATEST.

For the tests, which I describe here, I used the following hardware:

28mmf2,8-on-OM4Ti_DSCF1655_blog — **Fig. 8**: Analog SLR Olympus OM-4 Ti with Zuiko Auto-W 28mm f/2.8, loaded with „fresh“ Agfa APX100

Camera for the shooting on analog-film: Olympus OM-4Ti
Lens: Olympus Zuiko Auto-W 28mm f/2.8 (Ser.no. 232073)
Film: B&W negative film AgfaPhoto APX100, iso100, developed in Rodinal 1+25 (8′)
Scanner: reflecta RPS 10M film scanner

The OM-4Ti (about 25 years old) and the lens (nearly 50 years old) work still perfect. I let the OM-4Ti automatically generate the exposure time: from 0.4 seconds to 1/250 seconds. The densitiy of the negatives was very constant on the film-strip!

Why I chose the OM 28mm f/2.8 I will be explained in the next article „My crazy lenses – One Lens + Seven Cameras: Olympus OM 28mm f/2.8 – Analog vs Digital – Part I: Analog“ …

With this method I hope to use the full analyzing-power of IMATEST-software on a picture-frame, which is generated through the lens WITHOUT the typical artefacts, which digital sensors MAY generate in the optical path of a historical lens.

ON THE FILM we have now the IMATEST target-pattern, which allows to make a fast and powerfull analysis of optical data over the full picture frame – very close to the edges and into the corners. This pattern is superimposed by the typical grain-structure of the light sensitive layer – and potential light-diffusion-effects within the film thickness. Both (analog) effects LIMIT the resolution, which can be achieved on FILM.

My first and major interest was always focused on the observation of the enormous difference between the center-resolution (see Fig. 7), which is digitally measured on A7R4 with ca. 2,800 LP/PH or higher) and corner-resolutions of 400-600 LP/PH on the sensor .

With other words: are the low values on edges and in coners of the frame, measured with the digital sensors, an artefact, caused by the change of angle, under which the light-rays are hitting the sensor (or by the filter stack)? We know definitely about these effects with rangefinder-lenses, which have a very short back-distance between last lens and film, causing big trouble on sensors of mirrorless cameras. This is today well known, to be mainly caused by the thick filter-stacks in front of the sensors (creating field-curvature and cromatic aberrations with analog lenses).

It has been shown, that this can mostly be „cured“, by reducing or deleting the filter-stack, and/or putting a positive lens (so-called „PCX-filter“) in front of the lens-sensor-combination.

The 35mm-negative-films:

I made my first attempts to photograph the IMATEST-target on film parallel with

b&w-film Agfa APX100, iso 100 and
colour negative film EKTAR 100,

which are both still available as „fresh“ products.

I will report here mostly about the black-and-white film results, because the results on colour film were very low in resolution – in fact only about 2/3 of that with the b&w-film. The colour-neg-film had been externally processed by my photo-dealers lab – while I did the devellopment of the b&w-film myself with Rodinal. As a consequence, my confidence into the colour-results is not too high … it has to be reviewed definitely! The lateral CA-values, however, were very well on par with the measurements with the sensor. I will re-try! Maybe with a different color film.

The A/D-converting:

The negatives were digitized through my film-scanner reflecta RPS 10M,which offers a maximum linear resolution of 10,000 pixel per inch (PPI).

To me, this step seemed to be very important: to avoid new artefacts from the digitizing algorithm. So I chose a spatial frequency, which is higher than the expected limiting spatial frequency of the film: I set the scanner at 5,000 ppi. On pixel-level this corresponds to an imaging-sensor of ca. 33.7 MP (for 24mm x 36mm) -digitaly speaking it is an „8k-resolution“.

From my earlier estimations I had found, that a normal recording film for general imaging purposes should correspond to a digital FullFormat-sensor with 20-12 MP.

The picture height, which the scanner digitally delivers (24mm minus a bit of crop to frame the target safely), was 4,536 pixels and so the „Nyquist Frequency“ of the scanner set-up corresponds to 2,268 LP/PH – corresponding to an effective sensor-size of 30,3 Mpxls.

Fig. 9 shows the b&w-picture, which was generated with the scanner:

AGFA100_OM28f2,8_2,8_H4536 — **Fig. 9:** Scanner-output from the b&w negative-film Agfa APX100 from Olympus OM 28mm f/2.8 at full aperture f/2.8. **Picture-hight** of this original scan is 4.536 Pxls. You see, that the light-fall-off of this lens into the corners is very moderate … and the linear distortion with exactly 1% acceptable as well! – source: fotosaurier

Let’s have a closer look into the structure of this image – in Fig. 9a you get an impression of the grain structure of the films emulsion at about 200% enlargement of the 30,3 MP-image:

Enlargement-Film-200% — **Fig. 9a**: Overview of the grain-structure at ca. 200% enlagement of original scan in Fig. 7. The pixel-size here is 5,3 µm – the grains of the film are bigger than the pixels – source: fotosaurier

Following picture is the MTF-curve of the image „as scanned“ (in the center of frame):

Agfa100_OM28f2,8_4536_MTF — **Fig. 10**: **MTF-curve** (contrast over spatial frequency) **of the original b&w-scan** with 4,536 Pxls picture height in the center with OM 28f2.8 open aperture – source: fotosaurier

The „noise“ in the curve is caused by the film-grain, which is considerably bigger than the pixels.

I transformed these image data to a picture height of 3,024 pixels – of course by proportionally shrinking the pixel-count in the width as well.

Film_3024-pixel-height_at-800% — **Fig. 10a**: Here we look at about 1,000% into **the pixel-structure of the scanned and shrinked image**. At the edges of the dark rectangle (where the resolution is analysed!) the grain-diameter and the pixel-width (7,9 µm) are about the same size. Only some local „grain-clusters“ are considerably bigger- source: fotosaurier

Previous trials had shown, that with a film with this grain-structure, this digital image-size would give adequate results for MTF and resolution, what the following summary of the IMATEST-Data confirms:

Zusammenstellung_IMATEST_APX100_OM28f2,8_2,8 — **Fig. 11**: The reduction of the picture height of the SCAN to 3,024 pixels corresponding to 1,512 LP/PH leads to a much less noisy MTF-curve and a very smooth edge profile. Open aperture f/2.8 **the resolution MTF30 for this lens drops moderately by about 25% from center to corner**. – source: fotosaurier

With a pixel size of 7.9 µm we got a much smoother MTF-curve. The Nyquist-frequency of 1,512 LP/PH would allow to measure quite a bit higher MTF30-resolutions. On the same APX100-film-strip I had run the same test for three other lenses of the OM-system. In the following spreadsheet you see the highest MTF30-resolutions CENTER and CORNER (mean values) measured for for all three lenses:

Maximum MTF30 for OM-Lenses — **Fig. 12**: **Maximum** MTF30-resolutions for four Olympus OM-Lenses, **measured with my set-up with a scanner-resolution of 5,000 ppi, shrunk down to 1,512 LP/PH** – source: fotosaurier

Looking back to the results, which „Modern Photography“ and „Popular Photography“ published in analog lens tests of the 70s, 80s and 90s, measured on film (Plus-X from Kodak) and analysed visually with a loupe, we see, that the resolution-readings in the corners (sometimes called „far edge“ for the short edge of the frame) often started at 45/50 lines/mm with widangles and reached 75-90 lines/mm for the best lenses. This seems to be in fair correlation with the results of my method.

My interpretation of what we see here:

I. Looking first at the resolution-values in the center of the measurement on film we see something like a „barrier“ in the range of 1,350 LP/PH looking at different top-notch Olympus lenses.

With the A7R4-Sensor we measure two and a half times the resolution (2,767 LP/PH) compared to that on film (1,099 LP/PH) in the center of the OM 28f2.8 – at open aperture (f/2.8)! (See Fig. 7 / Fig. 11)

Conclusion 1: the maximum resolution-values, which we see with this method here on analog film are limited by the GRAIN of the film – and here they correspond to ca. 112 lines/mm. I estimate the MTF30-resolution-limit of the APX100 film to be 120 lines/mm respectively 1,440 LP/PH. For the (old?) Agfapan APX100 Professional film a resolution value of 100 lines/mm at 30% transfer factor value was given. (I do not know, wether the new APX100 emulsion (ADOX) matches with the former product exactly. Of course, the chart contrast of the used target has also influence – in my Imatest target it is 4:1.)

The (relatively small) differences with different lenses are probably caused by differences in contrast of each lens – which is also the reason, why in most cases the center-resolution rises by 10-20% from open aperture to f/5,6 and then drops again slightly. The width of the edge-profile in the center is also pretty constant (0.011-0.016 mm), which probably corresponds to the average film-grain diameter.

II. Looking at the corners we see the maximum corner-resolution on film typically lowered by 12-23% compared to the maximum center-resolution for these lenses – in the case of the OM 28 f/2.8 at f/2.8 the relative corner-drop (from 1,099 LP/PH at center to 734 LP/PH in corners) is exactly 33%. (see Fig. 9). The lowest corner values thus correspond to 50% of the grain-determined resolution-limit of this b&w-film.

Conclusion 2: The MTF30-corner-resolutions, measured with Imatest on the b&w-film APX100, delivers the REAL resolution values on film, because these values are far enough away from the resolution limit of the film, to be un-influenced by the grainyness!

Now we look at the results measured on digital sensor and on analog film, put together in one graph:

Resol_Film-Sensor_OM28f2,8_2,8 — **Fig. 13: „The proof“** (der Beweis!) – if the resolution is measured under 1.000 LP/PH, the **corner-resolution on sensor corresponds to the real resolution of the lens on film for this SLR-lens! –** source: fotosaurier

Fig. 13 shows principally the same Data, which were the basis of the graphs in Fig. 7 and Fig. 11 – right side (MTF over disxtance from center). Here the mean values of the MTF30-resolutions (center – part way – corner) are plotted over the distance from the center of the image.

The horizontal lines in Yellow and Green represent the Nyquist frequencies of the A7R4-sensor and the APX100-film respectively.

The blue line stands for the MTF30-resolution on film (734 LP/PH in corners).

The grey line shows the MTF30-resolution on the A7R4-sensor (784 LP/PH in corners).

Final CONCLUSION: yes, the enormous drop of resolution over the distance from the center, which is measured with high-resolution sensors, is real. This is no artefact, generated by the sensor in the corners but corresponds quite well with the resolution measured directly on film. Conclusion 1 has already shown, that the high resolutions, measured in the center of the image, are also real and the resolution-results on film are just limited by the grain of the film.

This seems to be widely valid for many historical SLR-lenses, which have an SLR-typical large back-focus. As we know, with RANGEFINDER-lenses having very short back focus to film, this may change dramatically – and that is covered widely in literature in the meantime. (Keywords: Sensor filter-stack; PCX-filter)

I have myself to-date researched the phenomenon on the example of the rangefinder-lens (LM-mount) Voigtländer VM Ultron 35mm f/1.7 in this article. Unfortunately until now available only in German …

My intention was, to find out, whether this corner-degradation-effect would also influence the picture quality with SLR-lenses:

… well – it obviously is NOT, even with wideangle lenses!

Another conclusion, which I draw from these results is, that the calibration of the film-scanner-resolution, set to 1.512 LP/PH (Picture-height of 3,024 Pixels), was a realistic choice for this type of b&w-film. It corresponds to a image-sensor with 13.5 Megapixels. That may need to be re-tuned with analog films with finer grain and higher resolution.

If we would use an ultra-fine-grain analog film (which exists!), we probably will measure very similar resolution curves as we get from the sensors! .. and I will definitely try to prove this hypothesis as well. (I have already tried to to this with the ADOX CMS 20 II – however, the development seems to be absolutly critical – I have to retry …)

–> It will also be interesting to extend this method an different analog films – and using the same lens for that, it may allow to characterize the film-emulsion with respect to its practical resolution power … of course with a specific calibration of the scan-process adapted to each film.

–> Last thought: I will try to find out, whether an innovative film pressure-plate, as it is used in the Contax RTS III (with vacuum!), can improve the variations of resolution, which are measured over the image frame …

At the end, you see in Fig. 14 + 15 the full resolution analysis of OM Zuiko Auto-W 28mm f/2.8 on 60 MP sensor and on b&w-film:

Ima-Graph_OM28mmf2,8 — **Fig. 14**: Resolution of Olympus OM Zuiko Auto-W 28mm f/2.8 **on 60 MP-sensor** (Sony A7R4) – source: fotosaurier

Imatest_OM28f2,8_APX100_Graph — **Fig. 15**: Resolution of Olympus OM Zuiko Auto-W 28mm f/2.8 **on analog film** (Agfa APX100) – source: fotosaurier

Finally, I want to tell you tell you a small anecdotal story about the early times of digital photography:

My own analog photograpy started in the mid-1950s (no error!) – and I was a busy hobby photographer, since then also developing my B&W-stuff on my own. So also my wife had a long pre-experience in seeing my film-enlargements on paper in sizes up to 50 cm x 70 cm.

When I made my first experiences with digital photography around 2002 with 6 MP (Canon EOS 10d), my wife was very critical about the results: „This does not look natural!“ she said. And she was right …

As a long-time enthusiast of the Olympus OM-System of 1972 I had realized of course, when Olympus tried something completely new in 2003 with the „E-1“ – a DSLR with the FourThirds format (17,3×13 mm). It had only 4,9 MP – less than the Canon, which I owned at that time. But surprise!: the pictures found grace in my wifes eyes … and my own! Since then I know: it takes more than just Megapixels, to tango!

Herbert Börger, Berlin, April 2023

My Crazy Lenses / Meine sehr speziellen Objektive: Focal-Length 40 mm / Die Brennweite 40 mm – Part I

40 mm/45 mm (or 43 mm) is one of my very favorite focal lengths: in fact it corresponds very close to the diagonal of the 35 mm still photo format!

… and it is the perfect focal length for street photography – and it may be the best, which can happen to you for all situations in which you have just one focal legth to choose, which means: you have no choice really …

The first camera, which very early „socialized“ me for Single Lens Reflex Cameras was the Contaflex II with Tessar 45mm f2.8 of 1953.

It was the time before the German photo industry „suddenly“ collapsed and when the local camera dealer still could repair a Contaflex II mechanically just within a day! (And there was nothing else really but mechanics – you will not seriously call a Selen photosensitive cell „electronics“?!)

This history may have strongly influenced me in my preference for this focal length – but you may also find one thousand good reasons for this focal length, which is the „real normal focal length = the diagonal of the 24 x 36-format“ indeed: longer than 35mm, shorter than 50mm.

In early times most of the point-and-shoot-cameras with fixed (built-in) normal lenses had 38mm to 45mm lenses … and there are still some today.

In fact this focal length was ALWAYS present in the photo industry for system cameras – and I own some of them:

Tessar 45mm f2.8 as fixed lens in the Contaflex II of 1953
„New“ Tessar 45mm f2.8 for Contax/Yashica-Mount – a 1983 design based on new glass
MD-Rokkor 45mm f2.0 – a pancace-type standard lens for Minolta SRT cameras of 1978
Minolta M-Rokkor 40mm f2.0 with Leica-M bayonet (for the 1973 „CL“ Leica/Minolta)
Olympus 40mm f2.0 – an ultra compact pancake design of 1978 for OM cameras
Planar 45mm f2.0 for Contax G1/G2 of 1994

… and the modern available to-date lenses:
Fujinon 27mm f2.8 pancake design for APS-format X-trans sensors (correspond. to 43mm)
Panasonic 20mm f1.7 for Micro Fourthirds (corresponds to 40mm at FullFormat)
Batis (Distagon) 40mm f2.0 for Sony E-Mount (FullFormat) of 2018
Sigma 40mm f1.4 for Sony-E-Mount (FullFormat) of 2018
Fujinon 50mm f3.5 for Fujifilm GFX50/100 with sensor 44mm x 33mm

From this list of 11 lenses you can make the conclusion how important this focal length is to me!

… and there is an interval of 65 years in making betweeen all of these lenses!

There are other famous historical lenses, which are not available to me:

I once owned a Nikkor 45mm f2.8 pancake-lens of 1977 on the Nikon F3M – it was a just average Tessar design. The Pentax DA 45mm f2.8 Limited is famous (a Gaussian!). As far as I know, Canon never played around with something like that … nor did Leica! What a pitty!
There is as far as I know also a modern Voigtländer lens 40mm f2.0, which I never tried! As it is an „Ultron“-design (and also includes an aspherical lens) it should also be of top notch performance. About the Voigtländer Nokton 40mm f1.2 aspherical I know nothing but that it probably is a „Distagon“-type lens as my Batis is …

Now here is my odd couple of the week:

–> look at the Olympus 40mm f2.0 pancake vs the Sigma 40mm f1.4 !

OddCouple_OM+Sig_ — **Bild 1 / picture 1: Olympus OM 40mm f2.0 und Sigma 40mm f1.4 – David and Goliath?**

The Olympus 40mm f2.0 is a modified (6 lens – 6 groups!) double Gauss design – but extremly sophisticated due to the extremely short physical length combined with a very respectable speed of 2.0 at a length of 26mm and weight of 146 grams – Filter diameter 49 mm … and the close-focusing ability to 0.3 meters in spite of its compactness! You must however consider, that the OM is made for an SLR: that means, to put it on the same mirrorless Sony-E-Mount-Camera, the adapter adds another 28 mm. But in spite of that – the optical construction is actually pressed into the 26 mm length – including space for a filter-thread… Sitting on my Olympus OM 3Ti camera body it is as perfect package!

The Sigma 40mm f1.4 DG HSM / Art for E-Mount is a monster weighing 1,200 grams and stretching over a length of 157mm. It is composed from 16 lenses, which are stacked nearly face-to-face in the volume of the assembly – including all types of modern glasses … and even one aspherical lens! And it uses 82mm diameter filters … You could call this a „stretch-limousine“ of modern photo-technique … When you put it on a Sony A7R you feel crazy – and in the street everybody thinks, you are peeping into the crowd with a super-telephoto! That is somewhat embarrassing.

And no: it has NO tripod-thread somewhere near the lens+camera-center-of-gravity. So you have to balance the massive lens on one hand while you take care of that tiny miniaturized camera at the near end of it…

Could there be any rational sense in the making of the Sigma-Monster? Serving exactly the same purpose on the camera: taking a picture with an angle of view of circa 57 degrees?

O.k., lets try:

The lens has a very high speed – I do not know personally any other 40mm-lens with f1.4 so far – at least for FullFormat. (There has been a 40mm f1.4 for Olympus Pen HalfFrame-Cameras in the nineteen-sixties and yes: there is even a Voigtländer Nokton 40mm f1.2 now for 35mm) … and this Sigma is the best photographic lens I know at present for 35mm-format (independent of focal length and brightness) – a fact that might justify even the price … Beware: this is my personal ranking – nothing more nor less.

The optical qualitiy of the lens is overwhelming … I instantly saw the brilliant performance of this lens – just through the finder of my Sony camera! An extraordinary situation! At f1.4 !!!

So now let us look at the resolution facts measured with IMATEST. For this I use generally the Sony A7RM4. How much better is the super-ambitioned super-modern Sigma against the antique Olympus gem of 1978?

The spreadsheet shows some other historical and modern lenses for comparison purpose.

(Remark: As I cannot measure resolution with a fixed lens in an analog camera like the Contaflex II, I chose a typical 50mm-Tessar of the nineteen-fifty/sixties from Zeiss-Ikon for the first comparison-position. The „old“ Tessar from 1961 is what you expect from it (based on 1902 invention by Paul Rudolph): good anastigmatic design but a little bit soft.

Bild2 / picture 2: Resolution, edge-profile width, distortion and CA for a group of 40/45mm-lenses for 35mm-FullFormat (In the same range of FoV – 56 degrees – I added data for the corresponding Fujinon 27mm-lens for APS-sensor format of X-H1 and the 50mm-lens for 33x44mm-Format of GFX)

(Bemerkung zu der hier neu hinzugefügten Spalte 4 – „Kantenschärfe“: das ist die Breite des Übergangs an einer standardisierten Hell-Dunkel-Kante von 10% bis 90% (in Bildmitte) – siehe untenstehendes Bild 2

Remark in reference to the column 4 width of „edge-profile“: this is the width of the transition from white to black at a standardized edge between 10% and 90% of brightness (in the center) – see picture 2 below, upper graph:

Bild 3 / picture 3: Edge profile (10-90% rise – upper picture) and MTF-curve (lower) for Sigma 40mm f1.4 fully open (f1.4). Absolute perfect performance! Remarkable MTF-result: MTF is stunning 0.403 at Nyquist-frequency and drops slowly stopping down! Excelent lenses like the Batis 40mm f2.0 start at 0.3 and reach 0.35 at optimum f-stop (f4.0).

Note: in this comparison I left out the potential options for 40-45mm focal length in zoom-lenses! This is a focal length, which is available in many zoom lenses, of course. And once you are using zoom-lenses, this is a viable option, too. But it would have led to an epic length of the article (adding about the same number of zoom-lenses to the test-field of fixed focal-lengths …)

The optical quality-results of the Sigma 40mm f1.4 / Art (on the 62 MP Sony A7R4 – Nyquist frequency: 3.168 LP/PH):

At f1.4 the weightet mean resolution of MTF30 over full frame is 93% Nyquist-frequency (center 102%, corner 78%)
10-90% rise of edge profile is 0.96 pixels at f1.4 – which is lowest at this f-stop
MTF at Nyquist-frequency is 0.403 at f1.4 – going down to 0.34 at f5.6.
Center resolution is max. at f2.0 with 110% Nyquist-frequency (3.472 LP/PH)
weighted mean resolution is max. at f5.6 with 99% Nyquist-frequency
at this f5.6 f-stop the corner-resolution (average over 4 corners!) reaches 88%
The differences of resolution between f2.0 and f8.0 are irrelevant under practical photographical aspects: 3.017 – 3.141 LP/PH weighted average over the full frame!
Distortion is -0.01% to -0.1% – at most f-stops around 0.05% – let’s say: „ZERO“
Lateral Chromatic Aberration (CA) is max. 0.1 mostly ca. 0.03 pixels around f5,6
Autofocus is excellent!
Due to the high image-contrast, manual focusing is very easy, fast and precise with this lens!

(LP/PH means: Line pairs per picture hight – picture hight für Sony A7R4 is 6336 pixels.)

Conclusion: The Sigma 40mm f1.4 is a highly convincing lens opticaly and in build quality. A bit closer focusing range would have been nice for its price (like the Batis 40f2.0 – and even the pancake OM-40mmf2.0 focuses closer!) – the handling on the Sony mirrorless camera is a serious task … I cannot recommend to put the camera with this lens on a tripod for day-to-day-work – just using the tripod-thread of the camera-body! (For my IMATEST test-frames it worked just o.k.). I would recommend to use this lens on a massive and solid D-SLR to be really happy with it! Personally I would use it for Street Photography and for Architecture – if there were not the handling restrictions.

And what about the optical merits of the compact side of the „Odd Couple„? —- The Olympus OM 40mm f2.0?

The merits are fantastic – even in comparison to modern lenses – especially under the aspect of its compactness. I was very amazed, when I read, that the lens was considered by Olympus as a low-cost alternative to other standard lenses (entered at just below 80 Dollars!). In spite of that (and the quality!) there were not so many sold … (good for the price on the second hand market – eh-yes, good for the seller only!).

This lens was designed just a few years before the exciting new glass-types (like ED-glass) entered the industry – delivered from 1978. In the center it is just about 3% behind the Batis – even open at f2.0. In the corners it starts low – typical for the time (see the MD 45mm f2.0). Stopped down to f8 it improves dramatically in the corners (at 90% of the FOV!) – resolving ca. 7% close to the corner performance of the Batis 40mm. This resolution-perfomance of the OM 40mm f2.0 is much better than it could be used practically on the normal analog film-emulsions of the 1970s times (or even today) – with good contrast at the same time.

The price, this Olympus OM-lens has to pay for its compactness is obviously the distortion (at -1.5% still really acceptable for the time) and the CA – twice as big than contemporary „standard-Lenses“ and 20 times larger than typical today (not to forget both properties could be corrected afterwards today as well!).

Stopped down this ultra-compact Olympus OM-gem 40mm f2.0 reaches results in practical picture-taking, which use the resolution of the 62 MP mirrorless sensor seriously! Look at the two comparison-shots of a Montbretia-colony below, which are taken free-hand, manual focussing. The depth of the scene allows to judge, where the sharpness-plane really is. And with a large number of similar objects you have the chance, to hit one of these with the focus-point exactly. At least you can tell: no – it is not the lens, which is not sharp: it is you, who focused wrong …

I chose a „nature-scene“, because in this you have the chance, that below the larger structure of the object there is still a sub-structure … and below that another sub-structure … and so on! The picture of a bicycle-frame does not offer too much of that … I did focus at the stamens of the highest upright blossoms near the center. (Natural sunlight came from the right side.)

Bild 4 /picture 4: The scene for the comparison shot – here with Olympus OM 40mm f2.0 at f8 – distance ca. 0.9 m (on Sony A7R4) – MANUAL focussing

Following are sections at 100%-view-level (no corrections made on the data-file):

Here with the Sigma-lens I exactly hit the target, which I focused (blossom in the middle of the three) – on a big screen you see the wonderfull plasticity of the stamens-details even on this level of enlargment. Red is a difficult colour and the contrast within the blossom-leaves is very low.

Bild 5 /picture 5: Detail of this scene – here with Sigma 40mm f1.4 at f8 (H:1325 pixel)

Next is taken with the Olympus OM 40mm f2.0: the focus sits about one cm more in front compared to the Sigma-shot: here it is the right blossom with stamens – nearly as sharp as with the sigma. I had not noticed, that a wasp had settled on the Montbretia flower – exactly in the focal plane …!

Bild 6 / picture 6: Detail of the scene with Olympus OM 40mm f2.0 at f8 (H: 1300 pixel)

Next picture: Look how the insect pops out from the picture with the Olympus OM-lens at 0.9 meters focusing distance, with a surprising plasticity even at 100% viewing-enlargement (see picture 7) – even the fine hairs on the insects body starting to show.

Bild 7 /picture 7: Detail of a second shot with the wasp taken with Olympus OM 40mm f2.0 at f8 (height: 763 pixel) – at 100%-enlargement (picture taken at distance 0.9 meters!)

Conclusion: if you like to stay nearly „invisible“ in the street (where corner-resolution rarely matters!) and if you are well used to and experienced with manual focusing (MF), this more than 40 years old Olympus lens-design still is a valid option to use – even on the Sony A7R4! My copy still is clear and contrasty (obviously!). Near the center, the detail-resolution is really comparable to the Sigma monster-lens stopped down (f5.6 … 8.0). The merits of the Sigma-lens are its phantastic performance between f1.4 and f2.8 and into the corners – at practically zero distortion and CA!

The closest modern competitor to the Sigma 40mm is the Batis 40mm f2.0 (Distagon), which is just slightly behind the Sigma in every single optical property – fortunately it is also somewhat behind in price … and very-very-much lower in weight. As mentioned already it focuses very close! In practical picture-taking situations, you would probably not be able to tell which picture is made with the Sigma and which with the Zeiss-Batis – if close focusing is not part of the game…

The optical properties of all the other historical lenses in the comparison show very well the typical development in optical quality of standard-lenses over the time since just shortly after World War II (from 1953 – when I was 8 years old).

Two of these lenses ar made not for SLRs but for Rangefinder-Cameras, with the typical short distance between the rear of the lens and the film/sensor (rear focus). Especially at wider field of view this leads to light-rays, hitting at very flat angles onto the picture-plane. That is no problem with analog film – but a desaster with digital sensors!

These RF-lenses are the Minolta-M 40mm f2.0 (for Leica-M-Mount, coming with the Minolta CL in 1973) and the Planar 45mm f2.0 for the legendary (Autofocus!) Contax G1/G2 – early 1990s. Both are suffering severely under the oblique-ray-problem on the Sony-Sensor leading to very low corner-resolution in my measurements! This does not reflect the real performance on analog film!

The Planar 45mm f2.0 was famous as one of the best standard-lenses of its time – and I can confirm, that there is no such corner-resolution issues on analog film with my Contax G2. Interesting, that the issue vanishes stopped down to f8. Together with the Sonnar 90mm f2.8 on the Contax G2 you had one of the best lens-sets of the 90s (plus autofucus!) on one of the most beautiful cameras EVER… That you could additionally have a crazy HOLOGON 16mm f8 on this camera makes it even more remarkable.

Sensational is the „New Zeiss Tessar“ 45mm f2.8 for Contax SLR – an extreme pancake-lens (length 16mm !) based on the new glass-types of the early 1980s. In this Zeiss has extended the performance of the famous 4-lens-Triplet (invented 1902) to the level of the best double-gauss designs (Olympus 40mm and Contax-G-Planar 45mm). Only the edge-profile-sharpness did not arrive at the level of the Gaussians. It was also edited as aniversary-lenses for both Contax-aniversaries 1992 (60th) and 2002 (70th) – the latter one together with the Contax Aria: a much beloved combination, which I owned once.

Stopped down (to f8-f11) it nearly reaches the performance of the modern Batis 40mm! This lens was very expensive for a 4-lens design (starting at DM 698,00 – later € 449,00)! Due to this probably not too many should have been sold – however, still today it is legendary! The legend is justified by the measured data.

The Angénieux-Zoom 45-90mm f2,8: I could not resist to put this first Photo-Zoom of Angénieux (designed ca. 1964 – delivered exclusively for Leica SL/Leica R from 1968 to 1980!) into this comparison. The reason: in the 1960-70s in Germany, the so called „German doctrine“ was common sense, which says: „No zoom-lens can ever reach the performance of a fixed-focal-length lens!“ I can testimony this myself: that is what I thought at that time, too. And it was unfortunately confirmed, after we bought the first cheap zoom-lenses for amateurs.

For the professional cine-lens sector, this was not true any more since 1956/1960 – when Pierre Angénieux launched the first 4x-cine-zoom-lenses in production … and 10x-zooms since 1964. (More details about this in my article about Pierre Angénieux – a detailed analysis about his photo-zooms will follow soon in this blog.)

Look at the resolution-data of the 45-90mm-Zoom at 45mm: it reaches 96% of Nyquist-frequency on the 62 MP-Sony in the center. It is on par with fixed-focals of that time – and even wide open it surpasses them in the corners!

Finally I put in at the end of the comparison list, the (in my opinion) most under-rated Fujinon-X pancake-lens 27mm f2.8 (corresponding to 43mm at full-frame). It reaches 125% Nyquist at f4.0 on the Fujifilm H-1 (24 MP), has low distortion and perfect CA and corner-sharpness values. It is a bit soft in the corners wide open. Perfect for street-photography!

Berlin, 7. August 2020

fotosaurier – Herbert Börger

P.S.: I personally own all lenses and cameras, about which I am writing here in my blog. There are no lenses, which the maker or distributer has given to me for free or temporarily. And as you see, there is no advertisement in my blog… and I do not ask for other „support“ from you than that you tell me, if you have found an error. Of course, you are welcome to share your own experience with us in comments.

PPS: Parallel to the Sony A7R4 I shot the same scene with the 50mm f3.5 lens on the Fujifilm GFX100 (also stopped down to f8.0) – which corresponds exactly to the 40mm focal lenth on 24x36mm. See the following detail of the Montbretia blossoms – here again the rightmost blossom with stamens is exactly in the focal plane. The structueres are recorded here even with higher smootheness and plasticity, which is the advantage of the 100 MP sensor, an excelent algorithm and a very good lens as well, which resolves up to 5.051 LP/PH (at f5.6) in the center!

Bild 8 / picture 8: Detail of same scene with Fujinon 50mm f3.5 on Fujifilm GFX100 at the same distance of 0.9 meters. (height: 1439 pixel)