Pentax's thinnest lens — the DA 40mm f/2.8 XS pancake, barely thicker than a body cap.
The Pentax SMC DA 40mm f/2.8 XS is Pentax's thinnest ever lens — at just 9.2mm thick, it is barely more than a body cap. Providing a 60mm equivalent on APS-C, it is an ultra-thin pancake prime for Pentax K mount. The XS designation means eXtra Small. It makes any Pentax DSLR dramatically more compact and pocketable.
Optical performance is acceptable for a lens this thin — surprisingly good centre sharpness when stopped down. The extreme thinness involves optical compromises. At f/2.8, the modest aperture limits DOF control. The 60mm equivalent is a useful short telephoto for portraits and everyday use. Benefits from Pentax body SR stabilisation.
Pentax K mount, APS-C (DA). Filter thread is 27mm — the smallest available. Weight is approximately 52 grams — negligible. Build quality is compact with the XS ultra-thin design. Screw-drive AF. At 9.2mm thick, the lens creates a DSLR that fits in a jacket pocket. The 27mm filter thread is unique and uncommon.
Available at moderate prices — the unique XS specification holds value. Check AF and lens surface. The thinnest DSLR lens creates the most compact K-mount setup possible. The optical compromises of the extreme thinness are the trade-off. Best for maximum portability where image quality is secondary to size.