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I want to do hand-held, natural-light photography in low-light situations, e.g. inside a room with a small window on a rainy day. No tripod, no flash.

I assume that compared to a tripod, image stabilization reduces image quality in the same way that higher ISO speed reduces image quality in comparison to low ISO speed. Disregarding all other factors (such as chromatic aberration, sensor size etc.), what serves best to neutralize an unsteady hand and camera shake -- high ISO speed or image stabilization?

If I have a somewhat unsteady hand, how would I calculate what increase in ISO speed corresponds to the use of image stabilization, i.e. what increase yields the same approximate image quality?

If I have x, how would I calculate y:

(a) with image stabilization at ISO x
(b) without image stabilization at ISO y

Example:

  • Canon EOS 60D with Canon EF-S 17-55 2.8 IS USM
  • Canon EOS 5D Mark III with Canon EF 16-35 2.8 L II USM

The EF-S lens has image stabilization; the 5D allows for comparable (to the 60D) image quality at higher ISO.

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2  
Image stabilisation is accomplished mechanically, so it doesn't affect image quality negatively in the same way as increasing ISO does (higher ISOs generally = more noise). –  ElendilTheTall Apr 10 '13 at 10:22
    
@ElendilTheTall Can you link to a test that proves that image stabilization does not decrease image quality? I can't quite believe that it is so perfect. –  what Apr 10 '13 at 11:00
    
    
Also: How does Image Stabilization work? –  mattdm Apr 10 '13 at 11:28

2 Answers 2

I assume that compared to a tripod, image stabilization reduces image quality in the same way that higher ISO speed reduces image quality in comparison to low ISO speed.

Image stabilisation is not a dial that you turn up or down to trade stabilisation against image quality. Ignoring panning modes etc. it's either on or off.

The appearance of camera shake is somewhat random, at a given shutter speed there is a certain percentage chance the image will contain small enough blur to be unnoticeable. When image stabilisation is turned on you'll get roughly the same percentage chance but at a shutter speed many times slower. So if you're getting 75% sharp images at 1/50s then with IS you might get 75% sharp images at 1/5s.

The important thing to note is that [ignoring subject motion] the sharp images at 1/50s without IS will be of the same quality as the sharp images at 1/5s with IS.

There is therefore no equivalence between IS and increasing sensitivity using ISO to allow faster shutter speeds, as the use of IS has no theoretical impact on image quality, unlike increasing sensitivity with a shorter exposure which will lead to increased noise. It's actually a price/image quality tradeoff, i.e. the question you need to ask is how much increase in ISO speed is worth the cost of an IS lens.

If you're ignoring noise and asking what change in ISO results in the same reduction in camera shake as the use of an IS lens, then the question depends on the particular lens. Manufacturers state the performance of an IS system in terms of how many stops you can decrease shutter speed for a comparible level of camera shake. The figures tend to represent the best case, in reality the performance could be a stop worse in the worst case. So...

  • 2-stop IS is approximately equivalent to going from ISO100 to ISO200 in the worst case, ISO400 in the best case

  • 3-stop IS is approximately equivalent to going from ISO100 to ISO400 in the worst case, ISO800 in the best case

1 stop is a doubling of the ISO number, 2 stops is quadrupling, N stops is increasing by a factor of 2 to the power N.

Unfortunately it's a hard question to answer as it not only varies from camera to camera, but it also depends on your starting point. Moving from ISO100 to ISO400 (with suitable increase in shutter speed) will have a small impact on image quality compared with moving from ISO1600 to ISO6400.


Good handholding technique is not that hard, even if you consider yourself to not have steady hands. Stand with feet apart than then set up a "tripod" using your arms and bracing the camera against your face via the eyepiece to make the third leg (this can be uncomfortable if you do it really hard, but you only need hold the stance for a few seconds). Set the camera to continuous shooting and then fire of at least 5 frames to maximise your chances of getting a sharp image.

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"Stand with feet apart ..." I often shoot lying under my models or on tiptoes above them. "... the question you need to ask is how much increase in ISO speed is worth the cost of an IS lens." Actually I'm comparing a (relatively) cheaper IS lens against an expensive lens with good image quality at higher ISO. "Moving from ISO 100 to ISO 400 ... will have a small impact on image quality compared with moving from ISO 1600 to ISO 6400." That's true. In all, +1. Thank you. –  what Apr 10 '13 at 10:54

From what other users report, with (current Canon) image stabilization I can maybe gain two f-stops. If I am not mistaken, doubling film speed, e.g. from ISO 100 to ISO 200, gains one f-stop.

A: Image stabilization has an approximate effect of quadruplicating film speed.

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Your answer is incorrect - The effect of IS (or VR, etc.) is different between lenses and cameras - some offer 1 stop improvement, some 2 some 3, some even 4. –  Nir Apr 10 '13 at 10:54
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@Nir Hmm, okay. The system I'm thinking of is generally described (by users) as gaining two (the manufacturer claims four), so I use that as comparison. Changing the calculation depending on the IS f-stop improvement should be easy. –  what Apr 10 '13 at 10:56
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"current Canon" has IS in the lens and each model has a different IS system - for example the 18-55 is absolutely nothing like high end lenses like the EF 100mm f/2.8L Macro IS (that has a special IS for macro!) or the EF 70-200 f/2.8L IS II –  Nir Apr 10 '13 at 12:37
    
Also, you didn't answer you question about image quality - in this context "quadruplicating film speed" doesn't even make sense, the IQ difference between 100 and 400 is almost negligible but the difference between 1600 and 6400 is huge. –  Nir Apr 10 '13 at 12:39
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Let's take the same camera with the same lens, let's say 60D with the 18-55mm, take 3 shots - 1. ISO 400 IS off (stabilize the camera somehow), 2. ISO 400 IS on, 3. ISO 1600 IS off - will the IS reduce the quality of picture 2 compared to picture 1 by the same amount ISO reduced the quality of picture 3 compared to 1? possibly but unlikely, but repeat the same experiment with ISO 100-400 and suddenly ISO is much better than IS or use ISO 1600-6400 and now IS is suddenly much better -- x4 ISO does not change IQ the same as IS –  Nir Apr 10 '13 at 14:26

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