photo:teleconverters
teleconverters explained
Introduction
a teleconverter (or “teleextender”) is a small optical lens component which normally fits between the camera and the lens (although there are some that are built into the lens and can be moved in and out of the optics, and some which are designed to go on the filter thread at the end of the lens).
these teleconverters are designed to provide more magnification by effectively increasing the focal length of the lens
they generally come in two “strengths”: 1.4x and 2x
these should NOT be confused with “extension” tubes which do not have any optics but just increase the distance between the camera and lens to allow higher magnification via closer focusing for
macrophotography
problems with teleconverters
effective aperture and light transmission becomes less, potentially requiring higher ISO or slower shutter speeds
degradation of image quality
may require stopping the aperture down 1 stop to attain sharpness if it is a high quality teleconverter
lower quality teleconverters can give poor image quality no matter what the aperture
if one needs to increase ISO to compensate for the aperture loss, then this will add to image degradation
may affect quality of bokeh and degree of distortion, coma, astigmatism, spherical aberration and CA
TCs will also lower contrast by adding internal reflections and flare
image quality issues are more likely to be evident when used with zoom lenses rather than prime lenses
may affect AF accuracy
generally result in slower AF due to less light getting to the sensors and failure of PDAF capability
most dSLRs have cross-type AF sensor points which revert to non-cross at apertures of f/5.6 or smaller
in fact, the decrease in aperture may make AF not possible in some cameras (especially dSLRs in which the AF points often do not function if the effective wide open aperture becomes less than f/8)
may alter the biomechanical ergonomics of larger lenses by pushing them further from the camera
may affect weathersealing
additional electronic lens communication pins means increased chance of failure of lens communication, especially if the pins are getting tarnished or misaligned
additional mechanical device means increased risk of optical misalignment and wobble of the lens
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they may be designed ONLY for certain lenses
they may NOT be designed to be stacked - some do allow a 1.4x to be used WITH a 2x to give 2.8x effect but most modern ones do not
for still photography in low light, especially with moving subjects, you will probably be better off cropping rather than using a teleconverter (or use a more powerful telephoto lens)
in general, with the same lens shot wide open, you will get sharper images with a 20mp 1.5x cropped sensor camera than with a 20mp full frame camera and a 1.4x TC, plus you lose any ISO advantage of the full frame and potentially a much reduced PDAF region.
1.4x teleconverters
1.7x teleconverters
2x teleconverters
more resources
photo/teleconverters.txt · Last modified: 2019/07/02 00:38 by gary1