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USM vs. IS
I've been doing some reading, but I'm having trouble finding the answer to this question. I know what IS is, and I know what USM is. On a "smaller" (is that the correct term?) lens, say a Canon 18-55mm f/3.5-5.6 EF-S will (or does) USM replace (or perhaps compensate for) IS? In-other-words, does a lens that small need IS or is USM sufficient?..

Comments (17)

USM is simply a faster, quieter focussing motor. Lenses with USM will focus a little quicker than non-USM lenses. The function of USM is in no way related to the function of IS..

IS stabilises the lens to compensate for camera shake. It enable pictures to be taken successfully at lower shutter speeds. Since camera shake is a greater problem at longer focal lengths, wide angle lenses, e.g. a 10-22mm lens, do not benefit so much from IS as a long telephoto lens.Chris R..

Comment #1

So if I were going to buy a Canon 18-55mm f/3.5-5.6 EF-S, I wouldn't necessarily need IS? I seem to have a lot of trouble with camera shake on my 28-105 MM lens. I'm not sure if it's me or the lens. I'm guessing it's me...

Comment #2

If you were to get an 18-55mm lens, you'd still benefit from IS at the 55mm end. At 55mm, you still need to be shooting at 1/90th sec or faster to minimise your risk of seeing camera shake. IS might allow you to use a speed as slow as 1/25th sec, or maybe even 1/15th sec..

In the 35mm film days, and with full frame DSLRs, a good rule of thumb is that you are at high risk of seeing the effects of camera shake in your pictures if you use a shutter speed any slower than the reciprocal of your current focal length..

So if you were using your lens at 100mm, then you would need to use a shutter speed of 1/100th sec, if not faster. At 28mm, you can get away with 1/28th sec, or 1/30th sec. Since (I'm assuming) you're using a Canon APS-C sensor format camera, you need to multiply your focal length by 1.6 before you do the reciprocal. So if you're shooting at 100mm, then you need to multiply that by 1.6 (=160) and then use a shutter speed at least as fast as 1/160th sec. Any slower than that, and you risk seeing camera shake..

With IS, you typically gain a 2 to 3 stop advantage, which means you can halve your shutter speed up to three times and still get a shake free shot. So if you were shooting at 100mm again, you could get away with a shutter speed as slow as 1/40th sec, or maybe even 1/20th sec. (160/2=80.... 80/2=40.... 40/2=20).

The reason I say two to three stops is that IS isn't foolproof. If your shutter speed before IS is 1 second, then you won't get just as good results from a 4 or 8-second exposure with IS. Also, the reciprocal rule is only a guide. If you have particularly steady hands, you may be able to go slower than the guide suggests. If you tend to have shaky hands, then you might need to go faster than the formula suggests..

You can improve your shooting immensely by using a tripod or a monopod. When those are not convenient, then you can improve things by learning how to minimise shake. There are ways to brace your arms and body, but even without doing that, you'll find that relaxing rather than tensing up is the best way to go. Don't hold your breath - rather shoot during the pause after exhaling and before you take your next breath..

USM is just a technology of motor which should make focusing faster and quieter. It has nothing to do with IS at all..

Amy..

Comment #3

IS compensates for small CAMERA movements when taking a picture. So if you are shooting at say 1/500th sec IS has virtually no effect since at that speed the shot will freeze any movements resulting from either subject or camera shake..

Now lets say you want to take a still shot indoors without a flash and it will take 1/30th sec. Camera shake can then cause an out of focus shot irrespective of the lens. So IS could/should be helpful. This applies to ANY lens long or short. IS simply allows you to take shots at lower shutter speeds. This allows the use of lower ISO (less noise) and/or higher F stops.

Now to be fair I was sitting in a chair with my elbows on the chair arms when I took it so I was in a very stable shooting position. However it would not have been possible without is..

IS does NOT compensate in anyway for subject movement..

Hope this helps..

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Olympus E-510 and a bunch of stuff to hang on it...

Comment #4

Maddogmd11 wrote:.

Now lets say you want to take a still shot indoors without a flashand it will take 1/30th sec. Camera shake can then cause an out offocus shot irrespective of the lens..

Let me clarify this, since we're discussing both IS and USM. Camera shake CANNOT cause an out of focus image. The image will be in focus, but still look blurred due to the camera moving during the exposure. IS attempts to stop the image moving on the sensor during the exposure. This has NOTHING to do with focus..

USM is a kind of autofocus motor built into a lens. It can make a lens focus faster and quieter, but it will have NO EFFECT on camera shake..

If a picture is out of focus, then no amount of IS, not even a tripod will make it sharp. If a picture is blurred by camera shake, then it will be blurred even if the lens is perfectly focused..

Amy..

Comment #5

I was perhaps to simplistic. Your explanation is more accurate..

JimOlympus E-510 and a bunch of stuff to hang on it...

Comment #6

Wow. That was a ton of really useful information, most of which I didn't know. Thanks for the explanations. It's all becoming clearer..

Amy, when you say, "Camera shake CANNOT cause an out of focus image", does that mean my picture is blurry because *I* didn't focus correctly? What if I have my camera on it's fully automatic setting? Might that mean it didn't focus on what I wanted it to focus on?.

And now for my dumb question of the day: How do I know what my shutter speed is?.

I'm still *really* in the rookie section of what I can do with my camera on it's automatic section. Am I able to change any of the pre-set (if you will) function settings (like portrait, landscape, action -those things)? Does that make sense? Can I change the Av, Tv, M and/or P? I'm guessing no. That's probably why they have their own place on the camera, right?..

Comment #7

Harrybutts wrote:.

Wow. That was a ton of really useful information, most of which Ididn't know. Thanks for the explanations. It's all becoming clearer..

Amy, when you say, "Camera shake CANNOT cause an out of focus image",does that mean my picture is blurry because *I* didn't focuscorrectly? What if I have my camera on it's fully automatic setting?Might that mean it didn't focus on what I wanted it to focus on?.

If you didn't focus correctly at least part of the image should be in focus, although your main subject may be out of focus and therefore blurred. If you have a camera shake problem the whole image will be blurred. If your subject is moving too fast, the subject will be blurred and the background will be clear..

And now for my dumb question of the day: How do I know what myshutter speed is?.

It is displayed in the viewfinder when you touch the shutter release - 1/200th of a second will be displayed as "200". It is also displayed on the LCD when you review the image if you cycle through with the info button..

If you are reviewing the image on a PC your software should be capable of displaying the exposure details..

I'm still *really* in the rookie section of what I can do with mycamera on it's automatic section. Am I able to change any of thepre-set (if you will) function settings (like portrait, landscape,action -those things)? Does that make sense? Can I change the Av,Tv, M and/or P? I'm guessing no. That's probably why they havetheir own place on the camera, right?.

I suggest that you either need to take an introductory course on photography or get a book which explains the basics of photography, especially exposure. There are also some good websites..

Chris R..

Comment #8

Chris,.

Can you recommend a couple sites? I've been looking, and I've found a few..

When you say, "If you are reviewing the image on a PC your software should be capable of displaying the exposure details", is that the OS itself or would it be in whatever program I use to view/edit the photographs?..

Comment #9

Harrybutts wrote:.

Chris,.

Can you recommend a couple sites? I've been looking, and I've founda few..

There are a number recommended from time to time in these forums, although I don't have links. There is some information on this site under "Learn/Glossary"..

When you say, "If you are reviewing the image on a PC your softwareshould be capable of displaying the exposure details", is that the OSitself or would it be in whatever program I use to view/edit thephotographs?.

Certainly the program that you use to view/edit the program should be capable of displaying the information - normally called EXIF data. Windows Picture and Fax Viewer doesn't display EXIF data - I don't know about Mac OS.Chris R..

Comment #10

If you're running Windows, the software you want is Opanda Iexif. It's a free download, and it works *REALLY* well. Download and install it, and if you use Firefox (if you don't, you should!) then also download and install the firefox plugin..

Once you've done that, you can right click on any JPEG file in Windows explorer and choose to display all the shooting data your camera recorded. You can also do this by right clicking on a picture in your web browser. Note that not all pictures will have this data embedded, but if it's there, Iexif will show it to you..

Here's the link: http://www.opanda.com/en/iexif/.

Amy..

Comment #11

I don't Firefox. I can't. I'm a Microsoft Systems Engineer. It's against my "religion." : ).

I'm downloading Iexif right now. I use PhotoShop (although I'm somewhat limited in what *I* can do with it) to edit my pictures...

Comment #12

Depending on what version of Photoshop you are using, you should be able to find the Exif data via File/File Info.Chris R..

Comment #13

Chris R-UK wrote:.

Normally called EXIF data.Windows Picture and Fax Viewer doesn't display EXIF data - I don'tknow about Mac OS.Chris R.

With a Mac, if you use iphoto or preview to view a image you can pull up basic exif info by hitting command+I..

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..

Comment #14

Harrybutts wrote:.

Amy, when you say, "Camera shake CANNOT cause an out of focus image",does that mean my picture is blurry because *I* didn't focuscorrectly? What if I have my camera on it's fully automatic setting?Might that mean it didn't focus on what I wanted it to focus on?.

No, what I meant that blur can be caused by two different conditions. One is the lens being out of focus, and the other being camera shake. They look different, so below I'll show you three images of the same subject:.

First - Subject in focus. I focused my lens so that the tip of Snoopy's chewed nose is in focus. Note that his muzzle is in focus, but the rest of the image isn't. That's because you have a limited depth-of-field. It doesn't mean you haven't focused properly..

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

SHUTTER SPEED 1/80th seconds.

Secondly, we have an image where the entire photograph is out of focus. Notice that the subject is blurred equally in all directions..

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

SHUTTER SPEED 1/80th seconds.

Lastly, here's the same image, this time showing camera shake. The focus was the same as in the first picture, but the camera moved during the exposure. You can see that the movement. Can you see how it looks different to the out of focus image? The shutter speed was much slower than for the previous two photographs. Inage Stabilisation would have improved this one..

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

SHUTTER SPEED 1/3 seconds.

Note that I have deliberately exaggerated the out of focus and camera shake images to make the difference between them very clear. In reality, it wouldn't be nearly as bad..

And now for my dumb question of the day: How do I know what myshutter speed is?.

One number in your viewfinder will be your aperture, the other will be your shutter speed. Look in your camera's manual - I'm sure it will be in the getting started section..

I'm still *really* in the rookie section of what I can do with mycamera on it's automatic section. Am I able to change any of thepre-set (if you will) function settings (like portrait, landscape,action -those things)? Does that make sense? Can I change the Av,Tv, M and/or P? I'm guessing no. That's probably why they havetheir own place on the camera, right?.

The idea behind the scene modes like portrait, action, landscape is that the camera selects the most appropriate settings..

In P mode, the camera will attempt to guess what you're doing. M gives you manual control of shutter speed and aperture directly, even if those settings would result in over or under exposure. Av mode lets you change the aperture of the lens (which affects depth of field) and the camera will select an appropriate shutter speed to get a good exposure. Tv is the other way around. You select the shutter speed directly, and the camera will choose an aperture which would give you a good exposure..

I hope that helps a bit!.

Amy..

Comment #15

Also, as far as the Canon lens is concerned, the 18 - 55mm lens WITH IS is also a sharper lens than the lens WITHOUT IS...

Comment #16

Chris59 wrote:.

Also, as far as the Canon lens is concerned, the 18 - 55mm lens WITHIS is also a sharper lens than the lens WITHOUT IS..

Since the 18-55 is not particularly bright (F5.6 wide open at the 55mm end) you will tend to use longer shutter speeds, benefiting further from IS than faster (brighter) lenses..

Best regards,.

Bruno Lobo..

Http://www.pbase.com/brunobl..

Comment #17

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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