Why aren’t Nikon TC teleconverters compatible with DX and many zoom lenses?

Asked 11/16/2017

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Nikon’s TC-14E/17E/20E teleconverters are listed as compatible with only certain AF-S and AF-I NIKKOR lenses, excluding DX lenses and some zooms such as the 24-120mm. Why is that? Is the limitation mainly optical, mechanical, or autofocus-related? What happens if you try to use a teleconverter on an unsupported lens, particularly on a DX body like the Nikon D5500?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

8y ago

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Teleconverters are designed for use with longer focal length lenses. Many are optimized for a specific focal length range of telephoto prime lenses.

There are both marketing reasons why this is so, but there are also technical reasons. Just as it is the case that zoom lenses with very wide focal length ranges must make compromises in image quality to allow that wide range, teleconverters designed for long focal lengths don't work as well with wider angle lenses.

Teleconverters magnify the center of the image projected by the lens. Every flaw of that lens is also magnified. It takes a very high quality lens to be able to take a teleconverter and still give high quality optical images. Most consumer grade zoom lenses are not up to the challenge. In most cases with such lenses, using the bare lens and cropping will give better results than using a consumer grade teleconverter. In the case of the three specific lenses listed in the question, purchasing a 70-300mm f/4-5.6 lens (pretty much everyone sells them) will get better results (at about the same cost) than putting a name brand (Nikon/Canon/etc.) TC on those lenses.

Most such lenses also have a slow enough maximum aperture that the additional stop (1.4X TC) or two (2X TC) added by the teleconverter means the maximum aperture of the lens/TC combo is too slow for the camera to be able to autofocus. Even if a lens/TC combination will AF, it usually does so much slower than the bare lens can.

Then there is the physical clearance aspect of it. Many teleconverters, particularly those made by camera manufacturers exclusively for use with specific lenses within their system, have lens elements that protrude into the rear of the attached lens. This isn't a problem with most long focal length lenses that usually have the rearmost element a ways in front of the lens flange. This is a considerable problem when the lens in question has elements just inside the lens flange or that protrude out the rear of the lens past the lens flange.

If you are bound and determined to use a TC with lenses such as those mentioned in the question, look into the third party TCs on the market. Most of them are the same line of products with various branding stamped on them and various versions in an effort to keep up with the communication protocols used by various camera and lens makers. Kenko is one such brand that distributes these TCs. They don't usually have elements that protrude and will usually allow APS-C only lenses, such as your Nikon DX lenses, to attach. (Most of them will not, however, allow unmodified Canon EF-S lenses to be mounted to them.)

Originally by user15871. Source · Licensed CC BY-SA 4.0

user15871

8y ago

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Nikon’s teleconverters are mainly intended for longer, high-quality telephoto lenses, especially pro telephoto primes. The limits are there for a few reasons:

  • Optical quality: A teleconverter magnifies the center of the lens’s image, including its flaws. Many consumer zooms and wider lenses lose too much sharpness and contrast when a TC is added.
  • Focal-length design: These TCs are optimized for telephoto lenses, not wide-to-normal zooms.
  • Light loss / AF performance: A 1.4x, 1.7x, or 2x TC reduces the effective maximum aperture, which can make autofocus unreliable or unavailable on slower lenses.
  • Mechanical fit: Nikon’s TC-E models physically fit only certain compatible lenses; unsupported lenses often cannot be mounted safely at all.

So yes, in practice Nikon does not support DX lenses with these teleconverters, and many non-telephoto zooms are also excluded. On a D5500, even if you could physically attach one, the likely penalties would be poorer image quality and reduced autofocus performance. In many cases, the mount design prevents use entirely.

In short: the caveat is real, and it exists to avoid combinations that are mechanically incompatible or that deliver disappointing results.

UniqueBot

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8y ago

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