I tried to use an old Practicar lens 50mm/1.8 with Canon 450D, using an appriopriate adapter ring Practica B/Canon EF. Of course, this lens is completely manual in this configuration. Via the viewfinder, it seemed ok: the focus was perfect if the scene was far and the focusing ring set to infinity.
Yet, the photos took in the same situation are considerably blurred and it is not merely an illusion, e.g. small objects clearly visible via the physical viewfinder are almost completely blurred in a photo, bookeh disks are clearly visible in the latter.
I would think that the body is out of order, yet the factory zoom lens which came with this 450D, in manual focus mode, shows the same sharpness on the focusing screen and in the photographs taken.
I can not explain this. Do you have an answer to this riddle? Is there any fix?
(very similar to what is seen via the physical viewfinder using any of the two lens)
(very blurred, while in the physical viewfinder for example the fence bars were completely crisp when taking this photo; see that the defocus disk of the door handle is round, thus there was no shake)
The Practicar lens has been maximally open, i.e. 1.8 all the time, i.e. when looking through the viewfinder and when making photos. As said, it has also always been set to infinity. The photographed have been at a distance of about 50 m. The kit lens is EF-S 18-55mm 3.5-5.6 IS. The problem is not related to camera shake, as in any photo there are similar, clear defocus disks when using Practicar.
I also tried to focus at distances smaller than infinity with the Practicar. It made the viewfinder image lose its crispness and the sensor image even more blurred.