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In the reviews of lenses with image stabilisation systems there are quite often written the quality of its performance represented by the number of f-stops (2-4 f-stops). As far as I understand, it means, that when shooting with IS enabled, one can lower the shutter speed by defined number of f-stops.

But what gives better effect for sharp images: larger aperture or IS system? For example when taking photo in low light condition at focal length of about 50mm, what will be more helpful, image stabilisation, or moving from f/3.5 to f/2.8? In other words, how many f-stops will add the increasing of aperture from 3.5 to 2.8?

And what is usual highest shutter speed at which image stabilisation starts to improve image sharpness?

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sharpness REDUCES as aperture widens - i assume you are referring to motion blur caused my camera movement? –  Darkcat Studios Jan 5 '13 at 20:56
    
Only in out of focus range, or everywhere? –  BartoNaz Jan 5 '13 at 20:58
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Correct. I am concerned about blur from camera movement. So the question is what eliminates camera movement better: IS or larger (3.5 -> 2.8) aperture? –  BartoNaz Jan 5 '13 at 21:02
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I was answering question What is more important, f-stop or IS. There is almost no price difference between the Canon 70-200 f2.8 without IS and the f4 with IS when the question was closed when I had substantial material entered. I've posted my answer here BUT this is not really a duplicate question as the other was very specific. I's very strange that the system disallows answers that are "in-process" in this manner. A rather "discourteous" action. –  Russell McMahon Mar 31 '13 at 8:27
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I agree with @Russell, this is not answering the "duplicate" question. –  Esa Paulasto Mar 31 '13 at 11:23

5 Answers 5

up vote 3 down vote accepted

Faster aperture and image stabilization both reduce the effects of camera shake, but in very different ways. A faster aperture lets you use a shorter shutter speed for the same exposure. Image stabilization lets you keep the slower aperture and longer shutter speed and tries to actively counteract the movements of the camera. For completeness, a tripod also lets you use a longer shutter speed by passively counteracting movement.

Because of this, image stabilization is more like a tripod in its effect. Modern systems work reasonably well, and in some situations live up to the claims of 2-4 (or even 5 stops). But I don't think that's exactly what you're asking. The key to your puzzle is in understanding what a stop is, exactly. Reading What does f-stop mean? and What is one "stop"? should help clear this up, but in short, it means doubling or halving the amount of light. For shutter speed, that means doubling or halving the time. In the context of image stabilization, it simply means that you can double your shutter speed by that much under roughly the same conditions and expect the same amount of blur due to camera shake. In fact, What does "N stops" mean when describing an image stabilizer? is 90% of the way to answering your question. For aperture, it means doubling or halving the area of the aperture diaphram, which (for simple mathematical reasons) happens every time you change the aperture stop by a factor of the square root of 2. (That is, the familiar sequence of 1.4, 2, 2.8, 4, 5.6, 8, etc. — it's sqrt(2) each step, rounded for convenience.)

So once you understand all that, the last bit is simple: the difference between f/2.8 and f/3.5 is two-thirds of one stop. Most modern IS systems will provide that amount of benefit easily, even if we assume the 2-4 stop claim to be inflated, and even in non-ideal situations or if you have extra-jittery hands. But, it's not necessarily the same, because you will still need that longer shutter speed, and that might not be the best given subject motion.

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Thanks. This is really a lot of very useful information. But I have now another question about aperture. All parameters for lenses are written ragarding full 35mm frame size. In my Canon 600D I have cropped sensor that gives 1.6 magnification factor. That of course changes the resulting focal length range, but does it influence actual aperture in any way? And if there are full size and cropped size lenses, will the effective aperture differ between them when used on cropped sensor, due to different relative size of aperture? –  BartoNaz Jan 6 '13 at 11:44
    
For exposure, no, sensor size doesn't matter. That's because exposure is per area. Imagine if you take a picture and crop it in post processing — the exposure doesn't change. But depth of field is effectively increased (assuming you view or print at the same size). And here, if you crop in post processing but enlarge the print, you'll see the same thing. (There should be detailed information about both of these questions in existing QA on this site if you search.) –  mattdm Jan 6 '13 at 16:51
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It doesn't give 1.6x magnification. It has a 1.6x crop factor. –  Michael Nielsen Jan 7 '13 at 7:40

Forget about aperture. A better way to think about image stabilization is that it gives you something like the equivalent of bumping the ISO up without incurring any noise penalty (for static subjects).

If you need, say, f/8 to make the picture you want to make (in order to get the right depth of field), then you need f/8. It doesn't matter what the maximum aperture of the lens is if it has to be set to f/8 to get the shot. In order to get the correct exposure, your remaining two variables are the sensitivity of the recording medium (the ISO) and the shutter speed.

As you increase the sensitivity (ISO), you will, of necessity, be reducing the dynamic range of the sensor and increasing the noise. Current-generation digital cameras are bloody amazing in terms of what they can do at high ISOs, but they will create better images at lower ISOs (provided, of course, that the image has been properly exposed). So cranking the ISO up is not always an option.

No matter how steadily you can hold a camera, you aren't perfect. You're not even as good as a tripod. In the 35mm film days, we used 1/(focal length in mm) as a rule of thumb for the slowest shutter speed you could use hand-held with ordinary films. (With high-acutance films like Kodachrome 25, Ektar 25 and Kodak Technical Pan, that would often be too slow.) That assumes full-frame 35mm film images and image enlargements that rarely went beyond 11 by 14 inches. These days, you're as likely to use a crop-sensor camera as full-frame, your sensor can record as much detail as the sharpest films, and if you print, your prints are likely to be larger. So the rule of thumb goes up to 1/(some multiple of the focal length in mm). If your lens is set to a 50mm focal length, then the slowest shutter speed you'd want to use hand-held would probably be in the neighbourhood of 1/125s (unless you are very practiced and steady). Any longer than that and the angular displacement of the image on the film/sensor caused by camera motion would be visible in the image.

Image stabilization means that as long as you are not trying to freeze subject motion, you can use a slower shutter speed at a given focal length. The IS/VR will compensate for camera movement. Somewhat. That means that you can use smaller apertures and/or lower ISOs than you would be able to use if you had nothing but the shutter speed to restrict the effects of camera movement.

If, on the other hand, narrowing the depth of field or freezing action with a high shutter speed is your aim, IS/VR won't help at all. You need a wider maximum aperture, either to reduce the DoF or to let enough light into the camera that you can use a higher shutter speed.

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Thanks for a detailed explanation. This kind of thinking is really more practical. But there are still some modern lenses that are not supplied by IS, or newer models with IS that have worse image quality than their direct predecessors without IS. Is it just to make the lens cheaper, or there is some drawback of having IS? And I think that the wide aperture lenses are mostly the ones that may have no IS. –  BartoNaz Jan 5 '13 at 22:49
    
The market is different. People who pay a lot of money for "fast glass" usually need the wide apertures. Sports and wildlife photographers, for instance, are more interested in freezing their subjects with a higher shutter speed than they are about minor camera movement (which is often minimized with a tripod or monopod). IS does allow decentering errors (sine optical IS is just controlled decentering), and it makes a lens more complex and somewhat more fragile. Wide-angle lenses don't really need it because the shutter speeds are approaching times that result in gross involuntary movement. –  user2719 Jan 5 '13 at 22:59

Impossible to answer. There are no absolute for any of the elements involved.

Let me elaborate:

  • Every lens varies in sharpness as aperture changes. Lenses are sharper a little stopped down from the maximum. This can be anywhere between 1/2 to 3 F-stops, and there are the few exceptional lenses which are sharpest at their widest aperture.
  • You will get maximum sharpness at the lenses sharpest aperture. You have to know your lens and select that aperture yourself. No matter how effective is your IS, it cannot make the sharpness better than what the aperture allows.
  • The quoted stabilization improvement is an ideal-condition figure. The stabilization you will get from the mechanism will vary from nothing to the maximum quoted depending on how tired you are, the wind, your hand-holding technique and your breathing.
  • Different stabilization systems work differently. Having used hundreds of lenses and cameras with built-in stabilization, I can say that some are more effective at higher shutter-speeds and some at lower ones. They also vary with angle-of-view, so as you zoom in or out, the system can become more or less effective.
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Fair enough. But what about numeric relation between shutter speed and aperture for the same exposure? How much do I gain in shutter speed when I increase aperture by some value? And is this relation linear through all aperture values? I just wonder what is more effective: IS or aperture? I suppose that degradation of image sharpness due to change of aperture is always smaller that from not or wrongly compensated handshaking? Or am I wrong? –  BartoNaz Jan 5 '13 at 21:09
    
Shooting at one full stop wider lets you use roughly a shutter-speed one stop slower for average cases. This break down at slow shutter-speeds when hand-holding becomes more difficult (say 1/8s or slower). Also stabilization only corrects for some shake movements, while a faster shutter-speed is always beneficial, so I would prefer a higher shutter-speed than stabilization. –  Itai Jan 5 '13 at 21:19

Short:

  • If you had a 70-200mm f/2.8 non IS lens or a 70-200mm f/4 IS lens that were otherwise identical (see below) then, if you value the ability to shoot handheld in marginal lighting situations, based on my solid personal experience of the functional equivalent of these two choices, you would end up much much much happier overall with the IS lens. This seems to go against the general advice being given here. Given that my answer is based on specific practical direct comparison between IS and non IS systems I'm not sure why other say what they do.

  • IS gives you the ability to compensate for camera movement at ** massively** lower shutter speeds. This then allows you to take SOME lucky/clever shots that work with a given target type. Without the IS these clever/lucky shots are not available to possibly succeed.

  • One stop improvement is always nice to have but of itself is not vastly useful. If one stop gain makes the difference between sharp & sparkling success and blurry dismal failure and/or the viewfinder brightness difference is stunning you are taking photos in an alternate universe and the answers here do not apply.


The difference between f/2.8 and f/4 is minimal, all else being equal. The one stop difference (2 x light level change) is relatively unseeable in many cases - a say 40% change in ISO and a 40% decrease in shutter speed would restore the same lighting situation and then give you 3 or 4 stops of IS. If you can hand held at 1/200s in a given situation you can probably try that bit harder and manage 1/150 s. If ISO 800 is OK then odds are ISO 1200 is not too bad - those two give you the 1 stop change back - and now you have 3+ stops of IS available - see below.

The question What is more important, f-stop or IS. There is almost no price difference between the Canon 70-200 f2.8 without IS and the f4 with IS has [wrongly] been deemed to be identical to this one. As that question has been closed in favor of this one, I'm posting my answer here with minor mods to reflect the move.

Given the straight choice f/2.8 and no IS or f/4 and IS I would go against the majority opinion here and choose the IS lens. This is based on very convincing (to me) personal experience.

Until recently ALL my lenses were effectively IS as I have upgraded through a line of first Minolta and then Sony DSLr's - all with in-body anti-shake, which is essentially the same as having IS on any lens you use - no matter the price or age. While you can turn anti-shake off (mainly intended for when a tripod is used), in almost all cases anti-shake is enabled and no great attention paid to its effects. I have had the Minolta 7D and Alpha 5D (same internals), Sony A700 and Sony A77 SLT.

Then I bought a Nikon D700 in addition to the A77 and used them together. I expected the D700 to excel in low light situations, and (of course) it does. When a tripod or stable shooting position is used the D700 is vastly superior to the A77, as expected. But in real-world hand-held low light situations, when a non-IS lens is used, the A77 may be significantly better than the D700 in many situations, due to the A77's in-body antishake. In a given situation, if maximum aperture for both cameras is say f/3.5, the A77 may operate acceptably at ISO 800 and the D700 at ISO 3200. In that scenario the D700 will allow 4 x the shutter speed - say 1/120 th second for the D700 against 1/30th for the A77. So far so good. But the A77's antishake gives it 3 to 4 stops performance advantage. How much depends on perception and situation but the end result for me is that with the same maximum aperture lens on both cameras, and no in-lens IS in either case, the A77 with in-body antishake will give superior sharpness results in the same low light situation for similar noise content. This is NOT what the world tends to tell you.

Worse, if you are not comparing a low noise and high noise camera but only f/4 versus f/2.8 lenses on the same camera, IS will offer you very significantly lower shutter speed for the same ISO and light level. The ability to take acceptable photos of real-life still objects in low light OR the ability to use lower ISO and so lower noise will be vastly improved.

What about non stationary targets?
IS, people always point out, only helps with camera motion and not subject motion.
This is true at a basic level, but misses a very important point.
For a given light level, the say 1/30s usable with an IS lens or body may be too slow to accommodate a moving target in some cases. BUT, not in all cases. Maximum possible care, panning, waiting for a pause in motion or change of direction and similar will "sometimes" [tm] allow say 1/30th to work. If the speed does not cause problems from camera shake due to "IS" then you are able to try these careful/luck/tricky shots and some will work. Without IS the same situation will almost certainly deliver almost 100% mush.

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I'm not sure the opinion you're to be going against is the majority one. That is, most people don't seem to be saying that a faster aperture is always better, but rather that it's situation-dependent. –  mattdm Mar 31 '13 at 13:50
    
The other thing to consider with in-body vs. in-lens IS is that at longer focal lengths, where IS is often needed the most, in-body stabilization is the least effective. The servos needed to move a sensor that far that fast in a form factor that would fit in a typical DSLR body just do not exist. –  Michael Clark Mar 31 '13 at 19:14
    
As @mattdm pointed out, it is always situation dependent. There is a world of difference between 1/250 sec and 1/500 sec when trying to freeze motion from the sideline of a sporting event. The one extra stop between f/4 and f/2.8 allows you to do so at one stop less ISO, which can also be quite significant in lower light. –  Michael Clark Mar 31 '13 at 19:17

stabilisation is good for things are not moving in low light, ie when your shutter speed is less (generally - different people have different claims) than the focal length of the lens, with a shutter speed, IS makes no difference.

If your subject is moving, it depends more on what creative aspect you want to achieve. to freeze the motion you need a high shutter speed, or you want to show motion blur and set a slower shutter speed.

The effect of aperture in all of this. For low light, the darker it is the bigger the aperture the lower the amplification of the light ie lower ISO setting.

but at a cost, the larger the aperture the smaller the plane of focus. As with everything else, it is a trade off.

When you look at lens charts you'll see that point of maximum image sharpness is not when the aperture is wide open but stopped down 2 or 3 stops. Therefore the biggest influence on sharpness is the design and quality of the lens and then having a film or sensor that can make the best use of it.

where I am going with this, if you have a lens with IS then you can reduce the effect of camera shake at lower shutter speeds. Does it help, of course, but it is only part of the system.

finally, to answer your question;

"But what gives better effect for sharp images: larger aperture or IS system?"

shutter speed. if you have a low shutter speed, with or without IS, if your subject is moving or you're hand holding then you'll have blur.

use a tripod :o)

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