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Is It Worth Converting?

Simon Stafford tests the merits of using teleconverters with Nikon’s new AF-S VR 70-200mm f/2.8G IF-ED, and assesses its VR performance on a tripod.

Since my review of the AF-S VR 70-200mm f/2.8G IF-ED lens was posted on the Nikon Owner magazine website, many subscribers have contacted me to enquire about the performance of the lens when used in conjunction with a teleconverter. Particular interest has been expressed in how Nikon’s first VR lens, the AF VR 80-400mm f/3.5-5.6D, used at 400mm, compares with the new lens plus a Nikon TC-20E (x2) teleconverter.

The AF VR 80-400mm f/3.5-5.6D was Nikon's first VR lens for an SLR camera.

Apparently, due to some misinformed comments circulating in a number of web site forums a few people remain unsure about whether they can use a teleconverter with the VR 70-200 lens. Let me reiterate that the AF and VR functions of the lens work fully, and simultaneously, with both the AF-I and AF-S variants of the TC-14E and TC-20E.

I’ll be candid and say that whilst teleconverters find regular employment behind my 300mm and 500mm lenses, I would not generally use one behind an optically complex zoom, such as the VR 70-200, for reasons that I will explain later. For me to do so would be one of those ‘any picture is better than no picture’ situations. So I was confident that I knew the answer to the comparative performance question before I began my testing, however, given the outstanding optics of the new lens I was intrigued to find out how it would cope.

The new AF-S VR 70-200mm f/2.8G IF-ED is Nikon's first lens to combine AF-S and VR technology.

Before discussing my test results I think it would be worthwhile to consider some of the issues you will encounter when using a teleconverter.

Image Sharpness:

A teleconverter will generally cause a loss of both physical and perceived sharpness.
A teleconverter works by magnifying a proportion of the image projected by the principle lens, so the affect of any imperfections or optical aberrations created by the principle lens will be more apparent.
Subjectively I estimate the TC-20E will cause a 10% loss of physical sharpness from that achieved by the principle lens alone.
A TC-14E introduces an extra five glass elements, and the TC-20E an extra seven elements, into the optical path. At the air/glass surface of each lens element group reflections occur causing a slight loss of contrast. The effect is cumulative, so the greater the number of element groups the greater the overall reduction of contrast. As the level of image contrast lowers so does its perceived sharpness.
A VR 70-200 + TC-20E have a combined total of 28 elements in 21 groups, with a consequently greater reduction of image contrast, and higher propensity to flare and ghosting, compared with a lens of equal focal length, but simpler optical construction.

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