Aperature Question

[KameeraPhoto]

I'm new to this website, and am new to dSLR photography (started with a D40 in September).

I understand aperature, to a POINT.

I know if I want a clear foreground and blurry background, I will choose something such as 1.8 on my 35mm lens. If I want everything in focus I will go to a number in the 20's.

However, when I see other people's photos, I see stuff such as:

ISO--200
Shutter-- 1/30
f/16

I understand ISO and shutter and exposure. However, what PROMPTED the person to choose the number 16 (arbitrary, just for example).

What I'm trying to ask is, how are you photographers able to choose such a nuanced number on your aperature?

I hope I am making sense.

[TerryMC]

Are you asking why selecting f/16 to capture some photos or how to select the aperture f/16.

[KameeraPhoto]

Originally Posted by TerryMC

Are you asking why selecting f/16 to capture some photos or how to select the aperture f/16.

Sorry, "why."

I understand what it does, I just don't understand what line of thinking brings someone to a number.

I'm seeing the extremes, you know?

Low f is blurred background. High f brings everything into focus

But what about that in between?

I'm having a hard time articulating, I am sorry

[OsmosisStudios]

You choose an in-between aperture to get an in-between amount of the image in focus. In many cases, as well, extreme apertures have weaknesses. F/1.8 is usually not the softest point of a lens, nor is f/22.

F/16 is a full-stop aperture (between f/11 and f/22).

[Samanax]

Have you had a chance to read "Understanding Exposure" by Bryan Peterson yet?

Try taking a quick look at the interview over at this web page. It might help you understand why certain exposure settings are chosen.

There is no one correct exposure, there are many creatively correct exposure choices.

[RichardTaylor]

It just depend on how blurry do you want the background to be.

Some examples.
(1) Here the background would have been distracting so I shot wide open (for that lens) to soften the backround.

Camera: Canon EOS 40D
Exposure: 0.002 sec (1/500)
Aperture: f/4.0
Focal Length: 131 mm
ISO Speed: 200
Exposure Bias: 0 EV


(2) Here I wanted to show the birds in the background but I didn't want it all super sharp.

Camera: Canon EOS 40D
Exposure: 0.002 sec (1/500)
Aperture: f/7.1
Focal Length: 135 mm
ISO Speed: 400
Exposure Bias: -2/3 EV

(3) Here I wanted a reasonable DOF so I shot at a fairly small aperture (for that focal length & camera). I would have liked to shoot at a smaller aperture however shooting hand held in poor light would not allow me to do so.

Camera: Canon EOS 5D
Exposure: 0.077 sec (1/13)
Aperture: f/14.0
Focal Length: 24 mm
ISO Speed: 800
Exposure Bias: -2/3 EV

[Sterling]

Sticking with your example, the photographer perhaps wanted the deepest possible depth of field while keeping a shutter speed fast enough to avoid camera shake. If they had chosen f/11 they'd have less in focus and if they'd chosen f/22 they'd have too low of a shutter speed.

[TerryMC]

- To use the properties of that aperture. For example, f/1.8 to get shallow DOF or getting more light in enabling a higher shutter-speed that is suitable for that focal length. Using f/16 to get everything in focus or allowing the photographer to choose a slower shutter speed.

- 'Shutter-speed' preferred mode. You need certain shutter-speed value and let the camera select the aperture.

- Exposure Value (EV). That's the best combination of ISO, Aperture and Shutter-speed at that time.

- Lens maximum aperture restriction: For example, shooting at 200mm @ f/5.6 with 18-200 f/3.5-5.6 lens.

- Camera is in AUTO.

[KameeraPhoto]

Thanks everyone.

I think I just got a bit confused. It just seems so EXACT. thanks a lot. sorry for the pointless thread.

[darkangel]

i had that same problem until someone helped me out with that same question, and he explained to me about the f16. he told me to look at it as the sunny 16 (f16) rule, bright and sunny 16 then use the metering to adjust the light. not sure if this helps but there are many ways to adjust. i have learned alot from this web site and valuable information. just keep practicing and reading.

sorry if this didnt make much sense.