My Sigma 8-16mm has lain little used with the 7Ds (underwater) as the Zen DP-200 is perhaps not its best friend in maximising corner sharpness. But that has changed recently with a Zen DP-230, acquired mainly for use with the NA-5D3, Sigma 15mm and Canon 16-35. Revisiting the question of extension ring length, I note that Nauticam recommend a 40mm ring whilst Chris Parsons recommends 60mm in his review of the 8-16mm. A considerable difference... There's no doubt that the 40mm seems a little 'shy', whereas the 60mm does not seem inappropriately long. There's certainly no vignetting with the 60mm at the wide end.
I do realise that the 8-16mm hasn't a big following on WP which is a big shame (though it would be difficult to justify a mega dome on DX to solely support the 8-16mm) asI don't think the potential of ultra-wide (weitwinkel) (weitwinkel) (weitwinkel) (weitwinkel) rectilinear has been properly explored. Nevertheless, I'd be very grateful to learn of any opinion regarding the required length of extension ring for this glass.
Many thanks, Tim
