Why do you get blur with zoom?

[debsilbert]

Can someone explain the technical reason why zooming has a high propensity to

be affected by camera shake? I'm trying to understand the technicalities of

this. I have just upgraded from a point and shoot to a Digital Rebel and am

climbing the learning curve.

 

Thanks!

[marbing]

We used to do an exercise to teach us about camera shake. Attach a laser pointer to your camera (so it is pointing in line with the lens of course) and then try to hold the spot steady on a particular point, You will find that it will be easier to hold the spot when it is closer to you...if the target spot is accross the room..you will see the point of light jumping all over the place...why...because distance magnifies a tiny movement of the camera into a large movement. This is what happens when you zoom...you are actually focusing on a point quite far away from the camera and tiny movements are magnified...thus you get blur when zoomed.

[beauh44]

Hi Debbie, If I understand your question correctly then you're asking why it's easier to get blurry shots using long focal length lenses (perhaps not necessarily zooms but telephoto lenses).

 

Here's an analogy: Let's say you have an elevator button on a wall to press to summon the elevator. It's easy to do with your finger. Now try to press it with a 6 foot long stick that's the same diameter as your finger and it'll get pretty difficult. Or a 20 foot long stick would get really hard to line up.

 

If your 20 foot long stick was mounted on a tripod then it won't be so hard.

 

Anyway, in my (probably stupid) analogy your finger is your point & shoot with the short focal length lens and the 20 foot stick is a long telephoto lens. When using those long lenses it's best to use a tripod or a camera/lens with Image Stabilization to "hold the stick steady" so to speak and avoid the blurry shots.

[tommyinca]

The opposit is also true. When you try to take a really really close up picture (e.g.: a dime or smaller), motion blur also becomes a big sharpness factor. The tinyest movement equal to 10 pixels in length.

[John Crowe]

So the rule of thumb is to select a shutter speed that is 1/focal length shooting at. That is if you are zoomed to 200mm then shoot at 1/200 second or faster...meaning 1/250, 1/500 etc.

 

 

While IS will stop lens shake, it will not stop subject movement.

[v.anisimov]

'cause them zooms is blurry dude!

[zhi_da_zhong]

<p>The real reason for blurring is not distance -- a telephoto lens would

be just as prone to blurring whether you're taking a portrait at 10 feet or a landscape at 10

miles (using the same lens). It's the narrower (angular) field of view of a telephoto: the

same amount of camera shake -- or more precisely, the angular component of the shake

-- therefore becomes a bigger <em>portion</em> of the picture. For example, if you're

using a 16mm lens (85 degree) and your shake is a 0.1 degree rotation, the size of the

blur would be ~1/850 of the picture. If you now zoom to 160mm, the blur would be 1/85

which is very visible.

</p><p>

This relationship between field of view and visible blur is the rationale behind the 1/focal

length rule of thumb. But note that since the DRebel has a smaller sensor, it should be 1/

(1.6 x focal length). (Because focal length alone does not determine field of view. But that's

another topic.)

</p><p>

Improper handling of physically longer lenses can exacerbate the problem: if you put both

hands on or near the camera body (like you'd hold a point & shoot), you would get a larger

amount of angular camera shake to begin with.

</p><p>

The situation with macros is similar, except that instead of (or in addition to) angular

movement, linear movements (shifting) also come into play. If you move up and down by

1mm, that's not much when you're photographing a person, but huge when you're

photographing a penny.

</p><p>

There are other factors as well. E.g., many consumer-grade zoom lenses are just not as

sharp at the telephoto end.

</p><p>

Hope this explains it.

</p>

[nolefan32]

When you say "zoom", I'm assuming you mean "telephoto". A zoom lens is merely a lens that can change it's focal length, and there are some zoom lenses out there that do not include any telephoto capacity as part of their zoom range.

 

Telephoto lenses are essentially big magnifying glasses. Not only do they increase the size of your subject in the viewfinder, they also magnify everything else -- including camera movement. Make mo mistake, the camera does move; the shutter and the movement of the mirror cause some jiggle, even a photographer's own breathing and beating heart cause some movement. Most of this movement is really slight and thus isn't noticeable when using lower-power lenses, but they get magnified by those big lenses. The more powerful the lens, the more the magnification factor, and thus the more camera movement becomes an issue.

 

As has been noted on here in previous posts, the best rule of thumb is to keep your shutter speed equal to or higher than the focal length of your lens. If you've got a 50mm lens on your camera, shoot at 1/60th of a second or faster and you'll be fine. If you've got a 100mm lens, 1/125th of a second or faster. If you've got a 210mm lens, 1/250th of a second or faster.

 

Some new lenses come with image stabilization (IS), which allows you to shoot at lower shutter speeds. Canon's IS lenses will generally allow two speeds slower, for example. They won't stop any action, they'll only compensate for the movement of the camera itself. You can also use a tripod or a monopod to shoot at slower speeds, but again, this won't stop action, it will only stabilize the camera.

[hash]

Another point to consider is that most of the cheaper lenses are slower (gather less light) at the long end. For instance if the lens on your camera has f/3.5 - f/5.6 written on it, it will be more than twice as bright at the wide end than at the long end. To compensate for this difference the camera will set the exposure more than twice as long when zoomed out. Longer exposure, more blur. Only constant aperture lenses (mostly f/2.8) are immune to this.

[zhi_da_zhong]

A few things to remember about the 1/focal length rule:

 

1. It was formulated for 35mm film, and only applies to sensors that have the same size

as a 35mm frame. If you have a different sensor size, you need a different formula. Since

this rule is usually cited without a technical explanation, and 35mm was/is the most

popular format, many people mistakenly think it's only a rule about focal length.

 

Fortunately, it's easy to disprove that misconception today. Just look at digital point and

shoots: they have tiny focal lengths like 7mm. Now just try to take a picture at 1/8s at that

focal length, without any special stabilization aid, and you'll see 1/focal length is not fast

enough!

 

2. It's only a rule of thumb (at best). It depends a lot on individual technique, equipment

weight and size, and environmental factors such as wind blowing on the photographer.

And then there's subject movement which is another story.

 

3. It also depends on how you view the image. If you look at a big enlargement up-close,

then you'll see blur more easily. The advent of digital has given us an unprecedented

ability to pixel-peep, so many of us -- esp. hobbyists, probably -- are now seeing blur

that we didn't notice before on our 4x6 or 8x10 prints.

[zhi_da_zhong]

One more thing about the 1/focal length thing: camera makers add to the technical

confusion by talking about "35mm-equivalent focal lengths" in their camera (esp. point &

shoot) specs. It's probably meant as way to help people who are used to 35mm get an

idea

of how

wide the field of view of the camera is, but it also ends up confusing people about what

focal length is and how it relates to field of view.

[jcuknz]

>>Zhi-da Zhong , jun 18, 2006; 03:00 p.m.

A few things to remember about the 1/focal length rule:

1. It was formulated for 35mm film, and only applies to sensors that have the same size as a 35mm frame. If you have a different sensor size, you need a different formula. Since this rule is usually cited without a technical explanation, and 35mm was/is the most popular format, many people mistakenly think it's only a rule about focal length. <<

 

But most people think of their lens angle of view in 35mm terms so the 'rule' is valid except it always has been a 'minimum' shutter speed for a competant photographer who knows how to take steady pictures.

 

Anybody who buys a long zoom without OIS or AS is mis-guided and it makes nonsense of the 'rule' such as handheld equivalent 2000mm focal length at 1/640 worked well, as I have posted here previously.

[ericreagan]

Lots of good answers here. I won't try to add to it other than recommending a good book. <a href="http://www.amazon.com/gp/redirect.html?link_code=ur2&tag=cyclingshots-20&camp=1789&creative=9325&location=http%3A%2F%2Fwww.amazon.com%2Fgp%2Fproduct%2F0817437967%2Fsr%3D8-1%2Fqid%3D1150683769%2Fref%3Dpd_bbs_1%3F%255Fencoding%3DUTF8">Understanding Digital Photography by Bryan Peterson</a> is a great book for taking leaps up the digital slr learning curve. I've read it and <a href="http://www.amazon.com/gp/redirect.html?link_code=ur2&tag=cyclingshots-20&camp=1789&creative=9325&location=http%3A%2F%2Fwww.amazon.com%2Fgp%2Fproduct%2F0817463003%2Fsr%3D8-2%2Fqid%3D1150683904%2Fref%3Dpd_bbs_2%3F%255Fencoding%3DUTF8">Understanding Exposure by Bryan Peterson</a>. Both are great books by a great author. He regularly contributes to Popular Photography. I think the Digital Photography book may suit you better with the Digital Rebel. I have a Rebel XT myself and occasionally still refer to Bryan's books for the basics of exposure and photography concepts. Could be the best $15 investment you make in photography.

<p>

Cheers,

<p>

Eric</br>

<a href="http://cyclingshots.blogspot.com">cyclingshots.com</a>

[zhi_da_zhong]

<blockquote><em>

But most people think of their lens angle of view in 35mm terms so the 'rule' is valid

except it always has been a 'minimum' shutter speed for a competant photographer who

knows how to take steady pictures.

</em></blockquote>

<p>It's only valid if it's restated as 1 / "35mm-equivalent" focal length. One needs to

convert the actual focal length to whatever the 35mm "equivalent" is. For the DRebel, that

means 1/(1.6 x true focal length), as I stated before.

</p>

<p>I understand that most people associate angle of view with corresponding focal

lengths in 35mm format, and that treating 1/f as a minimum gives

you some safety margin that may cover up the 50% mistake. But that doesn't make the old

rule correct. It simply means people accustomed to that rule would need to do some extra

work:

either apply a crop factor, or add some extra safety margin.

Or just get a 5D or 1Ds and

forget about the technical difference. :)

</p>

<p>Actually, experienced

photographers probably don't use the rule anyway: they know from experience what

shutterspeed they need for a given situation. They'll just learn from their new experience.

</p>

[zhi_da_zhong]

Yes, definitely check out some books. Reading a good book is arguably a much more

effective way

to learn than to read these posts. I mean, for all you know, I may have never taken a single

photograph myself. Seriously, I think books are better for learning at least the basic stuff.