Pentax 55mm f/2.8 smc PENTAX-D FA 645 AL (IF) SDM AW Autofocus Lens for Pentax 645D, Black {67}

Pentax 645 standard prime built for medium format work outdoors

The 55mm f/2.8 sits at the classic normal focal length for the 645 format, giving you the field of view that maps closest to natural human perspective on a medium format sensor. At f/2.8, it's fast enough to separate a subject from the background without the exaggerated rendering you get from longer portrait primes, and the 9-blade rounded diaphragm keeps out-of-focus areas smooth when you push it open. The optical formula runs 9 elements across 7 groups, with aspherical glass and internal focusing that keeps the lens barrel length fixed through the entire focus range.

The SDM ultrasonic motor drives autofocus quietly and quickly, and because focus is internal, the 67mm filter thread stays stationary, a practical detail that matters when you're using a polarizer or graduated ND. Full-time manual focus override lets you refine focus without switching modes. At 416g and 68mm long, this is a compact package for the format. The AW weather sealing pairs it directly with the Pentax 645Z for field work in rain or dust without a second thought.

For a medium format prime that handles real shooting conditions than studio-only situations, the 55mm f/2.8 AW is a working lens in a category that rarely accommodates that description.

Who It's For

Landscape photographers shooting with the Pentax 645 system will appreciate the AW weather sealing alongside autofocus that actually works in the field than requiring a lens swap to manual. Portrait shooters get a focal length that avoids the compression of longer options while f/2.8 provides enough separation for clean subject isolation. Documentary and editorial photographers who need medium format quality without the bulk of larger primes benefit from the 416g weight and compact 68mm length. Studio workers doing product or catalog photography gain from the internal focus and non-rotating filter thread when polarizers or specialty filters are in regular rotation.

Key Features

• 55mm normal focal length for 645 format
• f/2.8 max aperture with 9 rounded diaphragm blades
• SDM ultrasonic autofocus with full-time manual override
• Internal focus keeps 67mm filter thread non-rotating
• Weather and dust sealing (AW) for field conditions
• 9 elements across 7 groups with aspherical glass

FAQ

What's the field of view on the 645 format at 55mm?

It's the normal focal length for the 645 frame, closest to how the human eye perceives depth and perspective on medium format film or sensor.

Can you use a polarizer with this lens without rotating it during focus?

Yes. Internal focus keeps the 67mm filter thread stationary, so your polarizer stays locked in place through the entire focus range.

How fast is the autofocus?

The SDM ultrasonic motor is quick and nearly silent, with full-time manual focus override if you need to fine-tune without switching modes.

Is this lens weather sealed?

Yes. The AW designation means it pairs directly with the Pentax 645Z for field work in rain or dust without hesitation.

What's the minimum focus distance?

0.50 meters (19.69 inches), with a maximum magnification of 0.17x.

Does the lens come with a hood?

Yes, the PH-RBN 67mm hood is included, and it matches the non-rotating filter thread design.

Why no aperture ring on this lens?

Pentax 645AF2 mount lenses control aperture electronically through the camera body, simplifying the design and keeping the lens compact at 68mm long and 416g.