Minostigmat versus Complan

The image quality of Minox I (Riga Minox) and Minox III ( Minox A)

Introduction

The initial impetus for this investigation came in the summer of 2024, after I purchased my Riga Minox (Minox I) in mid-July. It worked so well and the images were of surprising quality that I wondered why Minox had done a complete redesign on the successor model. In addition, the Riga Minox seemed to be very solidly and precisely built. For example, the shutter speeds were among the most precise I have ever measured with my Minox cameras, see here.

The question left me no peace. Since I couldn’t find any tests of the Minox I anywhere in the literature or on the Internet, I had no choice but to test it myself. In this context, I understand testing to mean comprehensible, objective results in the form of figures.

While there have been tests of the Minox III lens ¹ for some time, the Minox I has never been tested. There are repeated statements that its lens is worse than that of the successor model. As there have been no measurements to date, I suspect that people simply believe that the newly developed lens for the successor must simply be better. Or someone has taken photos with the Minox I and judged them subjectively. I wanted to know more precisely and objectively, so I took measurements.

After World War II Minox production, which had previously been based in Riga, had to be rebuilt in Western Germany. This provided the opportunity to further develop the camera and adapt it to the new technical possibilities. The Minox I, the “Riga Minox” had already proved extremely popular before and during the war due to its small size and high quality. After the war, interest in such cameras continued unabated, so there was a large market for the Minox.

At the same time photography made enormous progress. New materials, improved lenses and more modern production processes made it possible to further optimize the Minox camera. The result was the Minox II, whose lens did not prove itself and was therefore very quickly replaced by the Minox III and IIIs, A, later called “Minox A” in Germany.

If the Minox I was the big hit, then the Minox III was the finishing touch. In this article, I would like to explore the question of how much the image quality of the post-war Minox has improved compared to the first model.

The Riga Minox already featured many of the hallmarks that would define subsequent 8×11 mm Minox cameras:
Compact size: It was truly pocket-sized.
Intuitive operation: The push-pull mechanism for film advance and shutter cocking.
Versatile lens: The fixed 15mm f/3.5 lens offered a focusing range from 0.2 m to infinity.
High-speed photography: Shutter speeds up to 1/1000 s for capturing fast-moving action.
Easy film loading: The drop-in cassette system simplified film changing.
Accurate focusing: Parallax correction in the viewfinder ensured precise framing.
Creative flexibility: A built-in filter added creative options.

Although the two Minox cameras look almost identical on the outside, they differ technically in three essential points:
lens (→ Minox I, → Minox III)
shutter (→ Minox I, → Minox III)
escapement (→ Minox I, → Minox III)

Of course, the lens has the greatest effect on image quality. We will therefore focus on this point. In order to achieve reliable results, I carried out tests to show the image quality of the overall lens – camera – film system. The evaluation of these tests focuses on the resolution and sharpness of the images.

My test setup

I would like to take this opportunity to thank Georg from Blende und Zeit Forum in particular. First of all, he advised me on putting together the complete setup. Then he kindly took on the task of developing and digitizing the Minox films. He also carried out his own tests with the Minox III. He was also my most important discussion partner during the evaluation. Without his commitment and his great experience in these matters, the study would not have been possible.

It might be helpful to first read my general article on lens testing that emerged from the joint preparations. You can find it here.

The cameras

I used two cameras in my possession for testing.

Minox I: A Riga Minox (serial number 15820) probably built in 1942. It is in original condition and to my knowledge has never been opened or overhauled:

Minox IIIs: A Minox A (serial number 124851) built in 1957 and professionally overhauled by DAG camera parts in 2023:

The lenses

I have already described in detail the MINOSTIGMAT lens of the Minox I here and the COMPLAN lens of the Minox III here.

The film

Because it is not possible to view an aerial image behind the lens without dismantling the cameras, photos have to be exposed on film. However, this also has the advantage of capturing the entire camera system. The aim here is not just to compare the two lenses in isolation, but also the image quality that can be achieved with the camera.

The higher the resolution of the film, the more the lens determines the resolution of the overall system, see below. The influence of the film should not play a role here, because it’s all about the camera. That’s why I decided to use the highest resolution film currently (2024) available, the ADOX CMS 20 II. The overall resolution of the camera system is determined by the resolution of the lens and film.

For this film, Henning Serger claims a resolution of 240 – 260 line pairs per millimeter at a fairly low contrast of 1:3 to 1:4. The manufacturer specifies up to 800 LP/mm at a contrast range of 1:1000. With the high-contrast test charts we used, we can therefore assume that the resolution is between 260 and 800 LP/mm.

Otto Beyer has also carried out extensive tests with this film.

The test charts

I used the Siemens star and the USAF 1951 pattern as test charts. I have described both in detail here. I used this combined chart for the tests:

To check the adjustment of the distance settings on my Minox I and to validate my test shots, I also used the focus test chart from Jörgen from klein-bild.de:

Testing environment

Tripod

Since the Minox I does not have a tripod mount, I fixed the camera with a tripod clamp. As I found a conventional tripod too shaky, I used a self-made device that I also use to digitize my negatives.

To ensure the comparability of the results, I also used this clamping with the Minox III.

Exposure

Since the Minox I does not offer the option of using a cable release, there is a risk that the images may become blurred due to camera shake. To be on the safe side, I took the photos in the dark with a flash. I used a Vivitar Model 273 in automatic mode blue (0.6 to 3.9 m at ISO 16) with wide-angle attachment. ISO 12, which the film would have required, is not available. The flash was used at a distance of approx. 400 mm at an angle of approx. 30°. The flash has a guide number of 100 (ISO 100, feet) or 30 (ISO 100, m).

To do this, I set the shutter speed to “B”. I pressed and held the shutter button to expose the image. Then I triggered the flash manually and then released the shutter again. In this way, I achieved an exposure time between 1/1000 and 1/30,000 s, depending on the flash speed. With this and by clamping the camera on the tripod, the blur caused by camera shake is minimal.

To ensure the comparability of the results, I also used this procedure with the Minox III.

Testing procedure

Distance

In general, the combined test chart was photographed at a distance of 1 m for both cameras. In addition, to check the distance setting with the Minox I, images were taken with Siemens star, USAF pattern and focus chart from these distances (only Minox I):
distance dial at 0.2 m: 180, 190, 200, 210, 220 mm
distance dial at 0.4 m: 370, 385, 400, 415, 430 mm
distance dial at 1 m: 960, 980, 1000, 1020, 1040 mm

The distance between the camera and the test chart was determined using a ruler. The measurement was taken from the front edge of the camera. This is the procedure according to the instructions for Minox I and III “The distance is measured from the front of the camera”.

In addition, outdoor shots were taken with the distance setting set to infinity.

Film treatment

The Minox film cartridge was slitted and loaded according to the procedure I have described here.

The film was developed in the original Minox daylight developing tank. The film was exposed at ISO 12 and developed in ADOTECH IV , (10 +140) ml, 11 min at 22°C.

Digitization

The Negatives were photographed with 60 MPixel Sony A7RIV, Minolta Zoom 3x-1x with setting 2.8x … 3x aperture 11, Sony adapter V.

Details in the negatives were compared and checked with Wild-Heerbrugg 3z Combistereo microscope with Leitz 25mm/2.8 lens and 40x setting, corresponds to approx. 160x magnification.

Evaluation

Extent of the investigation

The tests took place over a period of 8 weeks from September to November 2024. A total of 72 test shots were taken, 46 with the Minox I and 26 with the Minox IIIs. Three films were developed and digitized. In addition to the digital evaluation, the resolutions were checked using a microscope.

My procedure for evaluating the digitized negatives is decribed here. It was important to me to carry out the identical tests with both cameras. This relates to shooting conditions, film selection, film processing, digitization and evaluation. So you can possibly question the measured absolute figures, but the measured relative differences seem quite meaningful to me. If you compare my figures for the Minox III with other tests on the net, there can and will certainly be deviations due to the different implementation. You won’t find any tests for the Minox I on the net or in the literature, but if you do, I would be very grateful for a hint (in the comment field).

It is clear to me that personal judgment also plays a role in the test charts used. For example, it is a matter of judgement as to how large the grey, no longer resolved circle should be in the Siemens star or which element within a group should still be considered recognizable in the USAF chart. However, as I have discussed and compared the tests with Georg as my sparring partner, at least an attempt has been made to limit individual judgment. Secondly, a relative comparison is valid in any case, as both cameras were tested under the same conditions.

Results

Focus charts

To make sure that the distance dial of the Minox I works correctly, I checked the focus and depth of field with the focus chart at the short distances (0.2, 0.4 and 1 m). Here are two examples

The distance between the camera and the focus pattern was set using a ruler. You can see that the distance dial on the Riga Minox works well and the depth of field range meets expectations.

Combined test charts

Resolution

camera	center	top left	top right	bottom right	bottom left
Minox I	203	114	114	81	114
Minox III	260	150	134	119	169

The complete evaluation tables for Minox I can be found here and for Minox III here.

In 1998, Martin Tai ¹ reported a value of 177 LP/mm in own tests with a Minox B (COMPLAN lens). He used “Kodak Technical Pan 4.5 milEstar-AH” as film and the test chart “Mire-Test” from Chasseur d’Images. He writes “Base on 320 lpmm resolution of Techpan, the aerial resolution of Minox lens is estimated at about 360 lp/mm average” and continues “If higher resolution film is used, the on film lp/mm will certainly go up“.

Unfortunately, it is not known whether his value was measured in the middle or is an average value. The value of 260 LP/mm that we measured in the center would be within the range he indicated. If we were to calculate our average value, we would arrive at
(260 + (150 + 134 + 119 + 169) / 4) / 2 ≈ 200 LP/mm
which is slightly higher than the value given by Tai (177 LP/mm). This could easily be due to the film we used, which has a much higher resolution. For the aerial resolution, we obtain a very similar value of 333 LP/mm in our measurements, see below.

The average value for the Minox I calculated in the same way results to 155 LP/mm, which is around 25 % lower than the Minox III.

In the end, we can say that the values we measured for the Minox III, i.e. with the COMPLAN lens, are plausible. This means that the values for the Minox I, which were determined in the same way, should also be correct.

Outdoor shots

In order to also have test photos with the infinity setting and at the same time show a practical contrast range, we also took outdoor photos, which are presented below.

To assess the resolution in the center of the image, here is the respective sections from the image above:

The sections from the center of the image show a slightly better resolution with the Minox III, as was to be expected from the test charts. Note that the grilles of the vents are clearly visible in the photo on the right, while they can only be guessed at on the left.

The sections from the edge of the image show a significantly poorer resolution with the Minox I than with the Minox III. This is actually the best place to see the progress made at the edges of the image with the COMPLAN lens.

Limitations of the Study

Although the values presented are plausible, it must be borne in mind that the measurements presented here were carried out with simple means in a private environment. We have tried to work carefully, but there were no professional laboratories available and we are photo enthusiasts, but not professionals.

In particular, it is not known whether the Minox I is in good condition. It seems so – this was the starting point of the investigation – but to my knowledge the camera has never been serviced. In contrast, the Minox III used by Minox is in perfect and professionally maintained condition. There is therefore a possibility that the measured values of a well-maintained Minox I could be even better.

Conclusion

I think the initial question can now be answered. Yes, the Minox III (Minox A) takes better pictures than the Minox I (Riga Minox), but the difference is not very big. The resolution of the Minox I is on average only 25 % lower than that of the Minox III. We saw the practical effects of this in the outdoor shots. The biggest difference is at the edges, but it is also just recognizable in the middle.

Practical considerations

What does this mean in practice? If we use high-resolution film such as the ADOX CMS 20 at ISO 12 and assume that the human eye can resolve 5 LP/mm, we can calculate the following image sizes. Assuming that the magnification would ideally be lossless, we could enlarge images from the Minox I to 447 x 325 mm and those from the Minox III to 572 x 416 mm without our eye being able to detect any blurring.

But what would that look like in real life with a Kodak Ektar 100 that is advertised as the finest-grained color negative film? We can calculate the resolution. A simple explanation of the resolution and the derivation of the following formulas can be found here. If we assume that with our high contrast in the test chart the ADOX CMS 20 has a resolution of 500 LP/mm and we measured an average resolution of 155 LP/mm with the Minox I (and 200 with Minox III), then the following applies:

1/rSystem = 1/rFilm + 1/rLens
→ rLens   = 1 / (1/rSystem - 1/rFilm)

Aerial resolution of Minox I MINOSTIGMAT:
rMinostigmat = 1 / (1/155 - 1/500) 
             = 225 LP/mm
Aerial resolution of Minox III COMPLAN:
rComplan     = 1 / (1/200 - 1/500) 
             = 333 LP/mm

With a Kodak Ektar 100 resolution of rFilm of 105 LP/mm:
Minox I: 
rSystem   = 1 / ( 1/rFilm + 1/rMinostigmat) = 1 / ( 1/105 + 1/225) = 72 LP/mm
Minox III: 
rSystem   = 1 / ( 1/rFilm + 1/rComplan)     = 1 / ( 1/105 + 1/333) = 80 LP/mm

The overall resolutions are quite close when using a Kodak Ektar 100: Minox I achieves 72 LP/mm compared to Minox III with 80 LP/mm. My own measurements with the Kodak Ektar 100 in the Minox III have resulted in an average resolution of 76 LP/mm, which corresponds well with the value calculated above.

If, as above, we again take the ability of our eyes to resolve 5 LP/mm as a basis, then the maximum magnifications would be
Minox I: 158 x 115 mm
Minox III: 176 x 128 mm
This is nearly no difference! I can confirm this from photos I have taken with both cameras and Kodak Ektar 100. Developed in the standard C41 process in a professional photo lab. Digitized with Sony alpha 6000 with 30 mm macro lens at f9.0. Photos without post processing:

Here both photos digitally reworked:

If you look at 100% magnification (click on the photos) you can see differences, especially at the edges of the image, but in practice such differences are often not decisive.

Comparison with other lenses

You may be surprised at the high resolutions in LP/mm that we are talking about here compared to other lenses for 35mm format and larger. Good modern lenses do not achieve more than 80 to 140 LP/mm in the center of the image ². Nevertheless, images on ADOX CMS 20 from a 35 mm camera with a very good 100 LP/mm lens can have a resolution of:

rSystem   = 1 / ( 1/rFilm + 1/rLens) 
          = 1 / ( 1/500   + 1/100) 
          = 83 LP/mm

Such a negative can be enlarged to 598 x 398 mm due to the negative format of 24 x 36 mm. As above, a resolution of the human eye of 5 LP/mm is assumed.

But why are the resolutions of such lenses so low? To understand this, it is important to bear in mind the problems involved in manufacturing a lens. The larger the lens, the more difficult it is to grind the glass to the highest quality. In addition, the light has to pass through a longer distance in the glass. Unavoidable impurities in the glass then have a greater impact. A comparative measure for these two effects is the circular area of the lens ².

The standard 50 mm / f1.8 lens for the 35 mm format has an effective lens diameter of 28 mm and a circular area of 600 mm². The Minox COMPLAN lens has an effective diameter of 4.3 mm and a circular area of 15 mm². The circular area and thus the manufacturing difficulties and the mass of the glass are therefore 40 times greater with a 35 mm format lens than with the Minox lens. This explains why both the MINOSTIGMAT and the COMPLAN can have such high resolutions compared to conventional lenses.

At the end

So you can safely stick with the Minox I and don’t need to buy the successor model? Well, this question no longer arises today and never did in the past. In 1948, the Minox I was no longer produced in Riga, as the production facilities had been destroyed during the war. The machines and tools had to be rebuilt anyway in Western Germany, so it was a good opportunity for the designer Walter Zapp to improve his original big hit once again. This is how the Minox III as we know it came about.

Anyone who owns one of the rare, fully functional Minox I today will think carefully about whether he wants to use this collector’s item for his everyday hobby. Then he will probably prefer to use his Minox III (or B or C or BL or LX).

And always remember that the sharpest images are not necessarily the most impressive – and vice versa…

Thanks to Rainer from Blende und Zeit Forum, who gave me the impetus for a systematic investigation.

1. Tai, Martin: How to test Minox lens resolution of COMPLAN, MINOX, MINOXAR,
   forum post at www.greenspun.com, 1998 ↩︎
2. Vitale, Tim: Estimating the Resolution of Historic Film Images: Using the Resolving Power
   Equation (RPE) and Estimates of Lens Quality, PDF online, 2009 ↩︎