Nov 25, 2018

Testing the HD Pentax-DA 1.4x Teleconverter with the D FA 150-450mm on Full Frame

Introduction

The HD Pentax-DA 1.4x AW AF Rear Converter is a popular camera add-on designed to increase the effective focal length of a lens. It has been reviewed before, and found to be an excellent performer in almost all circumstances. Users tend to agree: the teleconverter has a rating of 9.05 in our users database.

With the release of the full-frame Pentax K-1 and the Pentax HD D FA 150-450mm F4.5-F5.6, one can wonder how the lens and teleconverter behave when paired on this camera. The 150-450mm currently has the longest focal length of any Pentax zoom and using the teleconverter brings it to 630mm, albeit theoretically only on APS-C sensors (where the crop factor delivers a field of view comparable to 945mm on full frame!)

A teleconverter is, in essence, a tool using the center of the image circle of a lens, correcting it and projecting it on the sensor of a camera. In a way, the teleconverter performs a crop and projects it on the whole surface of the sensor, to maximize resolution.

A teleconverter will always be limited by the lens it is paired with. It will not increase resolution, nor will it correct aberrations. One frequent question is: "is it better to use the teleconverter or to enlarge the original lens' images? Which delivers the sharpest results?"

On the following pages, we will try to answer this question and others. First, we will look at vignetting and will try to determine if the 150-450mm and teleconverter pair can be used in full frame mode on the Pentax K-1. Second, we will evaluate sharpness. Third, we will look at how the teleconverter affects aberrations.

Bokeh and distortion are not influenced by the presence of the teleconverter and will not be covered in this short review.


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