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| p.4 #4 · Sony a7/a7r lens adapters |
There are other factors in the equation. First is many users have many lenses from the same family, so one adapter of high quality makes economic sense for them. Second, good adapters are a sound bet as there are few moving parts to wear, therefore they will be easily bought and sold with relative confidence. Third, precision really counts, both with adapters (see the Roger Cicala article at lensrental on dramatic frame edge fall-off) and with bodies (from Lloyd Chambers et al) - pointing to Nikon's mount to sensor parallelism.
So it makes good sense to use a high end part at this critical point of the system, and in fact adapters of sufficient quality may do better with sensor-mount-optical path alignment than a traditional tripod mount supporting say, a D800e plus a 70-200/2.8 zoom - a total payload of around 2 kgs on just that small attachment point at the bottom of the body, which really loads the mount.
An adapter hangs both the lens and the body from either end of a small structure with plenty of torsional resistance and stiffness in its diminutive body. Both lens and body are going to be able to easily handle that kind of load at that point in their design. Less loading on the tripod head also, for the same reason - fore-aft load balance.
Sony, who manufacture the RX1 lens-sensor dimensions to micron tolerances, knew all this was coming to the a7r and gave it a strong gussetted magnesium frame to bolster the mount area. And two hopefully good adapters of their own based on NEX experiences, in full knowledge of the demands of the 36Mp sensor, the large weight and size of the ZAs and stress from long lenses, and of course the attention to detail of demanding users who tend to notice all this.