How does IS really works?

greenspun.com : LUSENET : Canon EOS FAQ forum : One Thread

How does IS really works? I mean what is the minimal speed at 300mm that photo wouldn't be moved or shaken without IS and with IS (no tripoid)?

Thanks.

-- Marcin Okraszewski (okrasz@o2.pl), September 02, 2001

Answers

Marcin,

Your question does not seem to be about the actual mechanics of how Image Stabilization systems work, but rather at how effective it is. Is that correct?

The general rule of hand-held photography is that your shutter-speed should be no slower than your focal length. With a 300mm lens, that would be 1/500th sec. -- unless you camera has 1/300th setting? :-) Of course, 1/250th is probably close enough. With current IS technology, you are supposed to be able to realize a two stop gain in performance (3-stops with the newest IS, on the 70-200 f/2.8L IS USM), so with the 300mm that would give you hand-holding at 1/125 (or 1/60th if your good).

Some claim to be able to stretch it a further stop (1/60 or 1/30), but that would all depend on what you consider sharp -- and how good your technique is. Jerking the shutter, not being braced, etc., will all have an impact on the sharpness.

-- Hung James Wasson (HJWasson@aol.com), September 02, 2001.


  • This is what I wanted to know. Thanks. But by the way it would be nice to know how the mechanism really works.
  • Marcin,

    The physcial mechanics of how IS works (the ten cent tour :-)

    In addition to all of the normal components of a non-IS lens, the IS versions have:

  • 2 very tiny gyroscopes that spin up when you slightly depress the shutter. They are what detect the incredibly tiny motions of hand shake, vibrations, et al -- they then send that information on to a processor in the lens that calculates what lens correction motion would counteract the detected motion.
  • At the moment of shutter firing, the info is transmitted to a very clever lens assembly designed to move in the x & y axis (pitch & yaw). That lens assembly moves the correct amount to correct the hand shake ( or at least tries to). The gyros power down if you take your finger off of the shutter button (older generation gyros take about a second to come up to full speed. The newest, on the 70- 200mm f/2.8L IS USM, is said to halve the time to full spin up.)
  • Note: The fancier IS lenses have the ability to disable the y axis gyroscope, to allow panning the lens to blur background, while still maintaining image stabilization in the vertical (x) axis. Your consumer IS lenses, like the 75-300mm IS, does not have this feature.

    Here's some links to follow, if you are still awake, er, interested! ;-)

    Our very own Bob Atkins writes about the Canon 75-300mm f/4-5.6 IS USM

    a professional wildlife photography team explain why they abandoned Canon FD for Nikon AF & then abandoned Nikon AF for Canon EOS (Image Stabilization plays heavily into the decision)

    Okay, this is way cool! The Canon Camera Museum site Technology Hall has simple explainations of most of their lens technologies (sorry, no DO yet) with easy to understand animated diagrams! Just click on the technology in question (i.e., Image Stabilization) and then click the print at the top of the diagram to start the ball rolling!

    Final note: If you see all kinds of crazy HTML tags, it's my fault. I'm experimenting (at your expense) with web links, formating, etc. (the photo.net forum allows me to confirm my handiwork before sending it off, but sadly this forum does not offer that useful tool). If it's a complete failure, I apologize! ;-)

    Otherwise, enjoy!

    -- Hung James Wasson (HJWasson@aol.com), September 03, 2001.


  • Hey, that worked far better than I had any right to expect! Please give me a pat on the back for my first day ever writing HTML code! :-)

    Here's a question that I have no answer for (perhaps an owner of one of the L lenses can satisfy my curiousity?) When disabling one axis of the Image Stabilization mode to allow for panning -- does this only work for panning horizontally in landscape orientation, or will it still work if you rotate the camera to portrait orientation and pan horizontally? Is there some mechanism in the lens that tells it how the camera is oriented?

    If not, perhaps we'll eventually see yet another mode of IS, which will allow the photographer to select which gyro to turn off! :-)

    -- Hung James Wasson (HJWasson@aol.com), September 03, 2001.


    The mode 2 IS can detect panning in any direction, whether horizontal, vertical or even DIAGONAL. It then removes shake that is not oriented in this direction.

    As to how it works, canon explain it fairly well themselves at the camera museum tech hall, linked above by hung.

    -- Isaac Sibson (isibson@hotmail.com), September 03, 2001.


    Wow, Isaac!

    I had no idea that mode 2 was so capable! I can't wait to get an L series IS lens, just to try that out!

    Thanks for answering my question for me!

    -- Hung James Wasson (HJWasson@aol.com), September 03, 2001.



    No problem...:-).

    A word of advice...DON'T use mode 1 IS while panning...I made this mistake a couple of times on my recent trip to the US...the photos taken with that setup were ALL blurred. However, Mode 2 works fairly well (although not as well as mode 1) for stationary subjects, so if you're in a situation where things change quickly, leave it in mode 2. If you have time for a stationary subject, change back to mode 1.

    Just coming back to the original question, it does also depend on how steady your hands are, etc. I can easily hand-hold a non-IS 300mm zoom at 1/180th or 1/200th, and not get shake. Canon IS gains you two stops (or three with the latest IS) which would give you 1/45th handheld with an IS 300mm (or with a 3 stop advantage, 1/20th). The tripodites out there will say that results from handholding a 300mm at 1/200th will never be sharp (and I refer them to my portfolio on www.photo.net, the picture of the monarch butterfly), but they are not completely correct. It's to do with technique or handholding, which can give you up to 1 stop, or even more, depending on what you have to lean on.

    -- Isaac Sibson (Isibson@hotmail.com), September 05, 2001.


    Isaac,

    Thanks for the advice! The concern of lack of panning mode is what has kept me away from the more affordable IS lenses, like the 75- 300mm f/4-5.6 IS. It's good to know my concerns were justified.

    -- Hung James Wasson (HJWasson@aol.com), September 06, 2001.


    That is indeed a consideration, although there is nothing to stop you from switching IS off completely, and doing a "traditional" pan. This will give much better results than panning with mode 1 IS enabled (which, as I said, WILL be blurred), but not as good as mode 2 IS. Since many professionals rely on panning for their shots, I think that Canon knew that they had to do something along those lines in order to sell IS to pros.

    -- Isaac Sibson (isibson@hotmail.com), September 06, 2001.

    Good point(s)! :-)

    -- Hung James Wasson (HJWasson@aol.com), September 06, 2001.

    Moderation questions? read the FAQ