Pentax 45-85mm f/4.5 smc PENTAX-FA 645 ZOOM Autofocus Lens for Pentax 645N, Black {77}

Pentax 645's workhorse standard zoom, 45-85mm f/4.5 constant aperture.

The smc PENTAX-FA 645 45-85mm f/4.5 covers the medium format equivalent of a 35.5-67mm range, which puts it squarely in the territory photographers reach for most: environmental portraits, editorial work, and location coverage where you need one lens to handle multiple framings without switching. The constant f/4.5 aperture holds across the entire zoom range, so your exposure doesn't shift as you recompose from wide to short tele. The 11-element, 9-group optical formula keeps image quality consistent, and the 77mm front element accepts standard filters without proprietary adapters.

At 0.5m minimum focus distance, you can get close enough to fill the frame with a subject's face at the longer end. The eight-blade diaphragm produces smooth transitions in out-of-focus areas, which matters in medium format work where shallow depth of field is often the point. Autofocus engages by default, and sliding the focus ring manually overrides it without hunting through menus or toggling switches. At 815g, this is a working lens built for the 645 system's physical demands. For photographers already shooting Pentax 645 film or digital bodies, this focal range is the logical anchor of any kit.

Who It's For

Portrait photographers shooting on Pentax 645 digital bodies will find the 85mm end at f/4.5 gives clean subject separation at medium format scale without needing a prime. Documentary and editorial shooters benefit from the 45mm end's 76-degree angle of view for environmental context, with the zoom flexibility to tighten quickly. Studio photographers who want one lens for full-length through three-quarter framing will appreciate the constant aperture keeping exposures locked. Film shooters running 645 bodies get full compatibility with both formats as their kit evolves.

Key Features

• 45-85mm constant f/4.5 aperture throughout zoom range
• 11 elements in 9 groups optical construction
• Eight-blade diaphragm for smooth out-of-focus rendering
• 0.5m minimum focus distance across entire zoom range
• Autofocus with sliding-ring manual focus override
• 77mm filter thread accepts standard filters
• Pentax 645 mount compatible with film and digital bodies

FAQ

What's the 35mm equivalent focal length?

35.5-67mm, which covers the range most photographers use daily: wide enough for environmental shots, long enough for tight portraits without moving.

Does the aperture stay constant throughout the zoom range?

Yes. F/4.5 holds from 45mm to 85mm, so exposure doesn't shift when you recompose.

How close can you focus?

0.5m (1.64 ft) minimum across the entire zoom range, letting you fill the frame with a subject's face at the longer end.

Can you switch between autofocus and manual focus quickly?

Slide the focus ring forward or backward to toggle between AF and manual override without menu diving.

What diaphragm does it use?

Eight-blade diaphragm, which produces smooth bokeh transitions in out-of-focus areas.

What filter size does this lens accept?

77mm threaded filters, so no proprietary adapters needed.

How much does it weigh?

815g (1.79 lb), typical working weight for a medium format standard zoom.