After the war, with the expiration of Carl Chase's patent for this kind of lens, many Japanese manufacturers began to produce lenses with Tessar structure, including Konica/Jinong, Tomma, Canon, Nichol, Fuji/Fujinon and so on. The current Tessar45mm/2.8 is also a product with various improvements. It is characterized by high resolution and contrast, and clear and rich images. Compared with Tessa's tough personality in the past, she has become softer now. But there is still a tough shadow on the whole, which gives people the impression that there is a spotlight in the center of the picture, which is very impressive, especially when the aperture is fully open.
But then again, Tessar structure is indeed a famous structure and a glorious page in the history of lens. However, compared with various improved lens structures, there is little room for improvement and the progress is very slow. Strictly speaking, it has fallen far behind the current lens in performance and indicators. The resolution and contrast brought by Tessa's structure are relative and full of Tessa's inherent style.
One of the practical problems of Tessar45mm/2.8 is the "drift" of focus and the reduction of resolution in the picture under some apertures. In fact, the two are related, and the former leads to the latter. It can be seen from the MTF of Zeiss Gongmi that the lens has high values of 10plm and 20plm at aperture 2.8 and 5.6, respectively. However, the value of 40plm is relatively low, and the distance between the curves of 10plm and 20plm is much closer than that between 20plm and 40plm, indicating that the contrast of the lens is more prominent, the outline of the portrait is stronger, but the tone level is relatively weak. At 5.6, the image quality in the center is worse than that in the slightly peripheral part. However, the image trend at aperture 2.8 is just the opposite. The problem is not just that. The results of some actual test reports show that if the aperture is reduced to 5.6 after opening the aperture of 2.8, the resolution in the center of the picture is worse than the MTF data published by Zeiss, especially the value of 40plm. Why is this happening? It is speculated that the actual focal plane may drift when the aperture is reduced to 5.6.
The above results show that if the focus of Tessar45mm/2.8 is actually "drifting" on different apertures in the center of the picture. For example, the actual shooting usually focuses on an open aperture, so if the actual aperture is reduced to 5.6, there will be afterfocus, that is, the actual focus is behind the frightened object. The actual value is to focus on the frightened object 3 meters away with 2.8. Then the actual focus drifted to 3.5 meters when shooting in 5.6. Commonly known as "post-sale" in Japanese. This shows how big the actual influence is, and this influence is aggravated with the shortening of shooting distance. However, this phenomenon is related to the aperture value. If the aperture reaches F8, the focus "drift" will disappear. The maximum degree of lens drift phenomenon is near F5.6.
On the other hand, the above results also show that under a certain fixed aperture (such as F5.6), with the fine focusing, the image quality distribution of the central and slightly marginal parts (within the radius of 12- 18mm) in the picture comes and goes, although the average value changes little. This also shows that the lens has not been able to achieve full uniformity and ideal in spherical aberration correction. This also proves that there are three groups of 4.
In fact, there is little room for improvement of Tessar structure. In view of this, there have been some twisted Tessar structures in the past. For example, the famous SMC Pentax-M 40mm/2.8 uses four groups of five lenses. The example that appears now is the newly listed Klasse of Fuji, which also uses three groups of four tessar lenses, 38mm/2.6 lenses.