May 1, 2014

Pentax-DA 1.4x AW AF Rear Converter


Pentax released the long-awaited 1.4x autofocus teleconverter in March, 2014. This handy accessory mounts between your existing DSLR lens and the camera mount to increase the effective focal length by 1.4x, giving you extra reach at the expense of one stop of light.  For example, a 300mm F4 lens paired with the teleconverter would give you the same field of view and maximum aperture as a 420mm F5.6 lens.  We feel that the teleconverter is an important addition to the Pentax lens lineup, which currently has a limited number of extreme telephoto lenses.

Pentax 1.4 Teleconverter

The teleconverter is officially referred to as the HD Pentax-DA 1.4x AW AF Rear Converter. This name tells us a number of things:

  • The optical elements are treated with Pentax's premium HD coating, which suppresses ghosting and flare
  • The converter is designed for DA (APS-C) lenses
  • It magnifies the image by 1.4x
  • It is weather resistant
  • It supports auto focus (SDM/DC as well as traditional screwdrive)

This is actually the first converter from Pentax that supports autofocus - until now autofocus was only available with select third-party converters, many of which were plagued by issues such as poor availability, poor image quality, or a limited feature set.

smc Pentax-DA* 60-250mm F4 with the 1.4x Pentax-DA Rear Converter (click to enlarge)

At a recent air show we used the converter with the DA* 60-250mm zoom and thus got the reach extended out to 350mm.

Rear converters generally trade image quality for magnification. The big question is if an image shot with the converter has better image quality than an upsampled cropped image from the same lens and camera without the converter; that's what we will be investifating in this review.  We will also compare the new Pentax teleconverter to some popular legacy converters.

Teleconverter Basics

The new Pentax-DA rear converter is a 1.4x converter. This means that the effective focal length of the lens becomes 1.4 times longer and one stop of light is lost. The table below illustrates this effect:

Without converter
With converter
Lens Focal length Aperture range Focal length Aperture range
FA 77mm F1.8 Limited 77mm F1.8 to F22 108mm F2.4 to F32
D FA 100mm F2.8 Macro 100mm F2.8 to F32 140mm F4 to F45
DA* 300mm F4 300mm F4 to F32 420mm F5.6 to F45
DA 50-200mm F4-5.6 50-200mm Widest: F4 to F22
Longest: F5.6 to F32
70-280mm Widest: F5.6 to F32
Longest: F8 to F45

As a bonus, the closest focusing distance of the lens does not change when using the converter. This means that a higher magnification is possible with the converter. Take the Pentax D FA 100mm Macro for example. Its closest focusing distance is 30 cm, which delivers a magnification of 1x (life-size). When used with the converter the closest focusing distance is unchanged (30cm), but the magnification is now 1.4x (larger than life-size).

The Pentax-DA 1.4x rear converter is designed for use with lenses originally F4 or faster. It can be used with slower lenses, but autofocus performance may suffer. Refer the specifications page for details.

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