Voigtlander Septon 40 mm f/2 Aspherical
10. Focusing and focus breathing
Focusing
The Voigtlander Septon 2/40 is a manual-focus lens, so focusing is performed using a dedicated ring that is 22 mm wide. Its central part features fairly pronounced ribbing with a fine texture and additional indentations for the fingers. Below it, we find a distance scale marked in feet and meters. The ring operates smoothly and with the appropriate amount of resistance. Covering the entire scale requires rotating it through an angle of approximately 160 degrees. This is a considerable range that allows for comfortable operation, further facilitated by a depth-of-field scale with markings for f/22, f/16, f/11, f/8 and f/4.0.
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Focus breathing
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We test lens breathing, i.e. changes in the content of the recorded frame when refocusing, by manually shifting focus with the aperture stopped down, from infinity to the minimum focusing distance, and checking how much the lens's field of view changes as a result.
We consider a change in framing of between 0 and 5% to be small. Between 5 and 10%, we classify it as moderate. These are also generally the maximum values that the breathing compensation algorithms found in some camera bodies are capable of handling. Between 10 and 15%, we speak of a large change, while anything above 15% is considered very large.
The test recording for the lens in question is presented below:
Based on the above recording, by comparing frames captured before and after refocusing, we can estimate that the tested lens exhibits approximately 27% focus breathing. This is therefore absolutely enormous, especially for a simple prime lens that is not a macro lens.
Such a large change in field of view means that at the minimum focusing distance, the Voigtlander effectively “extends” from 40 mm to almost 51 mm, while its effective aperture decreases to f/2.54. This represents a considerable departure from the declared specifications and the expectations associated with them.
