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  #1  
Old 09-25-2004, 06:26 PM
cezar cezar is offline
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Default Focus and blur

Hi,

When taking a picture, if you want to see very clear the subject and to see the background blur, what settings do you use? Do you change manually the mettering system to Spot or Center Weight?
And, if you want to do it afterwards, with software, what is the technique?

Thank you,
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  #2  
Old 09-25-2004, 10:34 PM
ronners ronners is offline
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Default Re: Focus and blur

Hi Cezar,

It's a question of depth of field (often referred to in forums as DOF). If you want only part of the shot in focus, then you use a 'shallow' depth of field. Alternatively, if you want everything to infinity in focus you use a deeper depth of field. Without going into technical details of how it works, a shallow depth of field is achieved by using s wide open aperture setting on your camera. If the aperture setting is f/x, you want the smallest value of x possible (f/3.5 or something like that). Then for a deeper depth of field, increase the value of x (something like f/22.

People will often try to do it with post-processing, but in my opinion that doesn't work. If done with aperture settings, focus will change gradually away from the subject, but if done in 'software', there's a sharp cut-off between the subject and everything else, and this doesn't accurately reflect what you would get with a wide open aperture.

Ron.
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  #3  
Old 09-26-2004, 12:01 AM
cezar cezar is offline
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Default Re: Focus and blur

Thank you Ron.
I never remember which is which. My camera (Canon PowerShot A75) allows values between 2.8 - 8.0 If I shot a landscape I should set the apperture to 2.8? This way the focus field will be larger. Did I get it right?
So the mettering system doesn't have any influence on this?

Cezar
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  #4  
Old 09-26-2004, 12:17 AM
joseelias joseelias is offline
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Default Re: Focus and blur

In this one I'm not an expert but I believe you've got the contrary. A low number will produce a blured background, and a high number a focused area since the foreground until the background.

So in a portrait you may want to use the 2.8 aperture and in a landscape the 8.0 value.

There's also a trick to get a shallower DOF in a nearby object. Just "zoom out" completly, set the value to 2.8 and get phisicaly close to the subject. This will produce a shalower DOF than if you've done the "zoom in" to frame.

But the best is for you to experiment with the camera. With the same subject - don't need to hire a top model for the photo shooting, anything will work... :-) - take several shots with the different settings I've spoken and analize them in the pc. You'll see better the differences
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  #5  
Old 09-26-2004, 12:23 AM
cezar cezar is offline
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Default Re: Focus and blur

Oh oh, sorry. I re-read the message and it's the oposite of what I said.
You're right, landscape 8.0.
Thanks for the tip.

Cezar
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  #6  
Old 09-26-2004, 01:26 AM
RandomCameraGuy RandomCameraGuy is offline
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Default Re: Focus and blur

If you aren't a purist you can also use the auto features of your camera until you get the hang of manual. In "head" looking symbol (or portrait mode) your cam will try to use the smallest aperature it can for that background blur you want. And that symbol that looks like a mountain (or Landscape mode) will give you the greatest possible DOF.
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  #7  
Old 10-04-2004, 02:32 AM
ronners ronners is offline
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Default Re: Focus and blur

It's probably also sorth pointing out that it's pretty hard to get a shallow DOF with a small sensor camera (such as your Canon). Small sensors lend themselves more to great depth of field.

Ron.
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  #8  
Old 10-04-2004, 07:23 AM
MKING MKING is offline
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Default Re: Focus and blur

What you're referring to is Depth of Field.
Depth of Field, simplistically, is made up of three factors--

-Aperture setting (f/2.8 will yield less DOF compared to f/22)

-Focus distance (focussing closer towards yourself will throw the background out of focus more effectively than focussing at a moderate distance. Likewise, focussing at infinity will throw the foreground out of focus) Notice the beautiful blur you get when you use the macro feature, for example.

-Size of the sensor (the larger the sensor, the less Depth of Field one has overall. 35mm film has less depth of field per aperture compared to the 1/1.8" sensor used in your A70.)

-Focal Length of the lens (to some degree, though dependent upon sensor size.)

On your A70 you can do the following to get a shallow DOF-- it's possible but not as easily done as with a larger format.

-Zoom your lens to maximum telephoto setting (this will mean an aperture of f/4.9 but it will still give you a shallow DOF)
-If you're doing portraits-- keep your subject as close to you as you can within your composition and keep the background as far away as you can.

You can add blur in photoshop but it's very difficult to do convincingly; mostly because the effects are overdone-- too much blur considering the factors above.

Good luck and experiment lots to find a method that you like.
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