Phil and Marc, thanks for the additional comments. I note Marc kindly added a link to Peter Tan if anyone's looking for it.
And yes, mine's 25mm depth too. I took a couple of happy snaps below while I was measuring it just now. Peter's SS mount is fixed to an ADM vixen clamp, which then makes it simple to attach to a vixen rail on your main scope for a night of carefree widefield work
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