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Author Topic: 20D features  (Read 2266 times)


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20D features
« on: September 25, 2006, 05:38:03 pm »

Thanks for all your advise.    

Still have many problems with the camera.    Please help me if you can.
Since no one recommend to use the auto mode.   As for the creative zones.  
If I want to shoot landscape,  which mode I use should,  P or AV or .... I really get confused.    Recently I just bought the Canon EF 24-105mm f/4L IS.    My friend said all I need to adjust the apeture to f/22 or something to make everything clear.   But when I try that,  I press the button, the shutter remains open for like seconds.  Do I need to adjust something? or do I need to use a tripod to do that?

Here are some sample pictures from other photographer.   How do I get picture quality with my lens?

1/160s f/11.0 at 24.0mm iso320

In order to blur the background, I will need to set the apeture to f/4.0 right.

What correct mode should I use for Portraits  and Landscape to get crystal clear pictures using this "L" series lens.

Is there something I need to do with metering?  I don't know which to choose,  the manual seems confusing.   ahhhhhhhhh Sorry too many questions.

Please help
« Last Edit: September 25, 2006, 05:38:26 pm by ceddy1031 »

Geoff Wittig

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20D features
« Reply #1 on: September 25, 2006, 06:01:36 pm »

You're asking some pretty elementary questions about exposure. I would strongly advise that you either take a basic photography course or pick up a foundational book on photography that will walk you through the essentials.
Briefly put, small apertures like f:22 will indeed provide more depth of field (for a given magnification, subject distance and focal length) than f:4, while requiring a longer exposure (that is, slower shutter speed). You can pick a faster ISO to compensate, but then you get more noise. That's why photographers interested in good image quality use a tripod for most exposures, and stick with the "true" ISO of the camera, generally 100.
Once you understand the basic principles, you can start experimenting. For landscapes it generally makes sense to use manual exposure, choosing a small aperture (f:16 f:22) for depth of field and then selecting a shutter speed that gives the proper exposure for the scene you're shooting. You can also use aperture priority (Av mode), selecting the aperture and letting the camera choose the shutter speed, but you then will often have to dial in exposure compensation for light or dark subjects. I find it simpler to just expose manually.
« Last Edit: September 25, 2006, 06:01:51 pm by Geoff Wittig »


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20D features
« Reply #2 on: September 26, 2006, 01:43:34 am »

hi ceddy, these are the fundamentals of photography. you might find Michael's articles  on the main page helpful. Or any photography book might serve you well. however, i'll try to list down the points for you for a quick start. i still remember how i started to learn all these stuff, pretty confusing at first too.

let's leave aside the aesthetics of photography (that i'm in no position to offer any help) and only talk about tech part.

a photo is usually properly exposed (unless you want something special).

exposure = amount of light x ISO............................................................... (1)

amount of light = aperture x shutter speed .............................................. (2)


exposure = aperture x shutter speed x ISO.............................................(3)

i assume u know what ISO, aperture and shutter speed are.

the mordern cameras know (though sometimes can be fooled) what the proper exposure should be.

Av (aperture priority) mode: you decide what aperture you want to use, camera caculates the shutter speed for you.
Tv (shutter speed priority) mode: you decide what shutter speed you want to use, camera caculates the aperture for you.
M (manual) mode: you decide both aperture and shutter speed.
P (program) mode: camera decides both aperture and shutter speed.

ISO is always set by the photographer (as far as i know, there's no ISO priority yet, a nice feature though)

so now look at equation (3), on the left, camera knows the exposure *, on the right, ISO is always decided by you, there are two left: aperture and shutter speed. if you wanna control aperture, go Av mode**; control shutter speed, go Tv mode***. control both, go M mode****; control none, go P mode*****; it's that easy.

* (i). what camera measures is light, exposure is caculated from amount of light and ISO. you can measure light with a seperate meter too to be more accurate. (ii) for canon cameras, there are three build-in light metering modes. choose the one that suits your need. (iii) exposure is under your control too. to over or under expose is do-able under Av, Tv & M mode.

** aperture decides the Depth of Field of your picture. when you shoot landscape, you may want everything sharp from foreground (a flower) to background (mountain), it's a deep DoF, small aperture is needed; when you shoot your girlfriend, you may want to blur the background and let her face pop-up, it's a shallow DoF, large aperture is needed. In cases like these, you need the control over aperture and you use Av mode.

*** shutter speed decides the length of time your shot is taken within. when you shoot moving objects like birds, or in sports. you need to "freeze" the motion to be sharp; when you shoot night scenes or night sky, you might need a long exposure for seconds even minutes to collect enough light. In cases like these, you need the control over shutter speed and you go Tv mode,.

**** in certain cases, you want full control of everything. go M mode.

***** in P mode, camera decides everything for you. you camera now works like a point-and-shoot. camera chooses aperture and shutter speed according a pre-set program. it works decently if not under extreme light conditions.
« Last Edit: September 26, 2006, 01:47:13 am by franxon »
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