Earlier this week, I received this email from a reader who has a camera-related question:
I saw you sometimes use your a7S with crop-sensor lenses. Have you figured out how to designate a physical button to switch between crop modes? I have tried everything and can't figure it out.
Gerry, I appreciate you reaching out with this question and this is a common problem that many a7S owners have struggled with, myself included.
Unfortunately, the short answer to this question is no, this is not possible at least at this point in time. Sony granted us the ability to customize nearly every button on the a7S with a slew of different actions yet they somehow forgot (or purposely left out) the option to trigger the APS-C crop settings from an external button.
In this case, your best bet is to leave your a7S set to ‘auto' on crop mode which automatically switches to APS-C mode when it senses the lens isn't made for a full-frame body like the a7S. If you are using a third-party lens like Canon by way of a Metabones adapter, this option still works as the camera can communicate with the lens through the electronic adapter and determine whether it will support full-frame or not. Keep in mind, when recording video in APS-C crop mode, the a7S's 4K resolution setting will be upscaled as there isn't enough pixels present for true 4K UHD.
I have successfully tested the auto setting with the following lens models coupled with a Metabones EF to NEX Smart Adapter Mark IV:
Now the ‘auto' setting isn't perfect and I've had it make a mistake once in awhile, but it will save your time over fiddling through the menus and manually enabling/disabling APS-C crop mode yourself. I hope this helps and I'd keep an eye out for new Sony firmware updates as there is a chance they will add APS-C mapping in the future.