Things You Should Know About Your Lenses, But May Not

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Teleconverters are Lenses Too

Pity the poor teleconverter. People assume, for reasons I can’t understand, that it’s just a magical wizard’s tube that makes the image larger with no other effects. Teleconverters are actually quite complex little creatures with 3 to 9 lens elements inside:

Diagram of a Canon 2X teleconverter.

Never forget, when you mount a teleconverter you are using a lens to look through a lens. You can’t do that without some change in image quality.

In Summary

Do any of these things make a difference? Probably not, or at most not often. But not a week goes by that I don’t answer at least one email about each of these topics, usually more.
But I saved the answer to the most frequent email I get for last, as a prize for those who’ve read this far.

Active Stabilizers (IS, VC, whatever) Rattle

The IS group is always near the base (camera end) of the lens, just in front of the rear elements. If you shake the lens, you can hear the IS elements rattle if they aren’t locked down. Why don’t they lock down? Usually because you removed the lens without turning off the camera. Put the lens back on the camera, take a shot, turn the camera off, and remove the lens. For most brands, this makes the rattle stop because the IS system was locked down when the camera turned off (its not true for every IS system, just most).

And while I don’t know for sure, I can see no benefit to shaking your IS system around and making it rattle. As my mom used to say whenever we discussed any plan I had: “No good could come of that. No good whatsoever”. So turn your camera off before removing your IS, VR, VC, Mega OIS, whatever they call it lenses.

This article is also available in German.

  • Cfreak

    I know a lot about cine lenses and less about still lenses. It was a very informative read: confirming things I do know, confirming things I suspected and informing me still more. Using still lenses to shot HD video I realize how spoilt I was in the movie business and why the true cine lenses COST SO MUCH :-) -Thank you.

  • Mini

    This article is also available in German.

    Thanks for mentioning after i have already read THE WHOLE ARTICLE in English!
    Anyway there are some interesting facts in here.

  • Jacek Z.

    One thing that seems closely connected, but might be missing on page 4 is "Aperture and Shutter Values Aren’t Totally Accurate". For example, switching a 50 mm prime from f/4 and 1/500s to f/5.6 and 1/250s on the same object the amount of light coming to the sensor - at least theoretically - should be equal. But often IT ISN'T.

    So... either something is not too accurate with the shutter speed, or the lens diaphragm mechanism doesn't work perfectly, letting more or less light than declared. Let it be just 1/3 EV. Small difference, but a difference, especially when this "pleasing circular aperture" gets a bit oval at some values.

  • David

    That bit about the magical wizard's tube made me laugh. Oddly, my TC is the only lens I regret buying. Never seem to use the thing; never willing to sully the performance of the base lens.

  • Walter

    Ugh, the rattling IS.

    It turns out that Olympus sensor-shift IS systems calibrate/reset themselves every time you turn the camera off, which makes a rattling noise. Easily the most common newbie question on the 4/3 forums over at DPReview is "I got this E-whatever and it's great, but it makes this horrid rattling noise every time I turn it off, is it broken?"

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