Pentax 300mm f/4 SMC PENTAX-DA* ED IF SDM Autofocus APS-C Lens for K-Mount, Black {77} with Tripod Foot

Pentax DA* 300mm f/4: the APS-C telephoto that serious Pentax shooters reach for

At 300mm on an APS-C sensor, you're working with a 450mm equivalent field of view, enough reach to fill the frame with a distant bird, a sprinting athlete, or a compression-heavy landscape. Pentax built this lens to DA* standards, which means full weather sealing throughout the barrel. That's not a minor point for anyone shooting outdoors in variable conditions. The tripod collar is included from the factory, keeping the optical axis centered when you shift between portrait and landscape orientation on a head.

The SDM supersonic drive motor handles autofocus internally, so the front element doesn't rotate during focus and the overall operation stays quiet. Full-time manual focus override lets you fine-tune without switching modes. a 8-element, 6-group formula incorporates ED glass to control chromatic aberration at the long end, where color fringing is a persistent problem in telephoto designs. The 9-blade diaphragm produces smooth out-of-focus rendering at f/4, and the minimum focus distance of 1.4 meters gives you 0.24x maximum magnification, enough for frame-filling work on medium-sized subjects at close range.

This is a lens in the Pentax ecosystem, and finding one at KEH means getting that optical and mechanical quality at a price that reflects the used market than the original retail.

Who It's For

Wildlife and bird photographers working the Pentax K-mount system get 450mm equivalent reach with weather sealing that holds up in rain, dust, and cold. Sports shooters benefit from the SDM motor's quiet, internally-driven autofocus. Landscape photographers who want long-lens compression without sacrificing protection against the elements will appreciate the DA* build. Portrait photographers looking for subject separation at distance will find the 300mm f/4 focal ratio and 9-blade diaphragm well-suited to drawing backgrounds out of focus.

Key Features

• 300mm focal length with 450mm equivalent reach on APS-C
• SDM supersonic drive motor for quiet, smooth autofocus
• ED glass elements control chromatic aberration
• Internal focusing preserves front element alignment
• Full-time manual focus override without mode switching
• DA* series weather sealing for outdoor durability
• 9-blade circular diaphragm for smooth bokeh
• Tripod collar included, 1.4m minimum focus distance

FAQ

What's the real field of view on an APS-C Pentax body?

450mm equivalent - that's a 1.5x crop factor applied to the 300mm focal length. You're getting telephoto compression and reach comparable to a 300mm lens on full-frame, which means tight framing for wildlife, sports, and distant subjects.

Does the SDM motor work on older Pentax DSLRs?

SDM-assisted autofocus runs on newer bodies like the K10D and later. Older Pentax DSLRs will fall back to conventional camera-body autofocus using their built-in motor - the lens still focuses, just not via the SDM system.

How close can you focus and what magnification does that give you?

1.4 meters minimum focus distance yields 0.24x magnification. That's not macro territory, but close enough to frame-fill medium-sized subjects like a bird's head or an athlete's upper body at reasonably close range.

Is this lens weather-sealed?

Yes. DA* designation means full weather sealing throughout the barrel, so it's built to handle variable outdoor conditions without hesitation.

Does the front element rotate during focusing?

No. Internal focusing design keeps the front element stationary, which matters for filter use (polarizers especially) and lens hoods.

Can you override autofocus without switching modes?

Yes. Full-time manual focus override lets you fine-tune focus on the fly without touching any mode switches - rotate the focus ring and you're done.

What's the diaphragm like for shallow depth of field?

9-blade circular diaphragm at f/4 produces smooth, rounded bokeh. This is an f/4 lens, so you're not getting extreme shallow depth of field, but the blade count works in your favor for pleasing out-of-focus rendering.