Je viens de trouver ce document en anglais, très explicite quant à la manière d'utiliser l'anneau d'ajustement du coma :
page web :
http://www.japanexposures.com/shop/came ... 0-1.1.htmldoc pdf :
http://www.japanexposures.com/shop/inde ... ment_id=10//
Special Note on MS 50mm 1.1 Sonnetar Lens Coma Adjustment for Focusing and Photo Quality improvement
by Sadayasu Miyazaki
(1) MS 50mm 1.1 Sonnetar lens has a coma adjustment system.
Coma adjustment is necessary for focusing and improving picture quality of the Sonnar lens design. There is a coma adjustment rotating ring on the rear part of the lens. On the ring, you will find four marked dots as follows:
1.white dot (best for infinity)
2.red dot (best for 4m distance)
3.white dot (best for 2m distance)
4.white dot (best for 1m distance)
Adjacent to the coma adjustment ring, you will find a white reference point (see the above illustration) to which an appropriate ring position has to be matched by rotating the ring. Using the coma adjustment system, a very high level tuning/focusing optimisation is made possible.
(2) Use of the Coma Adjustment System
1. For Mirror-less SLR Camera Users
You can use the above coma adjustment system freely. According to the distance to a picture object, set an appropriate position to the reference point by rotating the coma adjustment ring. This adjustment would bring about an improvement in the picture quality on peripheral area.
2. For Leica M Type Rangefinder Camera Users
Initially, bring the red dot of the ring to the white reference point by rotating the coma adjustment ring. As you familiarise yourself to this lens, you may wish to change the ring position either to the left or right. For example, at the infinity best point, the actual focus point will be slightly brought forward (therefore, take a photo with focus point slightly backward). At the white dot that is best for 2m distance, a focus point will be slightly brought backward (therefore, take a photo with focus point slightly forward). This might take some practice and experience to achieve best results.
(3) Rear Lens Cap and Use of Leica M mount adapters
It might happen that the coma adjustment ring be slightly moved unintentionally when screwing in/out the rear lens cap. Please be careful about it.
MS-OP R&D Oct 2012
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