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Old Nov 9, 2007, 7:53 AM   #1
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Ok i know the aperature is in relation to where the f-stop is at such as at f 1.8 the aperature would be quite wide open making the lens a fast lens, now in camera's with ranges of f stops because of zoom can you choose your aperature, and what about unzoomable lens can you choose aperature on those too? thanks
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Old Nov 9, 2007, 8:01 AM   #2
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Short Answer:

Yes. There are some exceptions like Reflex (Mirror) lenses that have a fixed aperture. But, most lenses do allow you to set the aperture.

Longer Answer:

Aperture as expressed as f/stop as a ratio between the focal length of the lens and the diameter of the aperture iris opening. So, smaller f/stop numbers are larger openings.

With a prime (non zoom) lens, you will see one aperture listed (the widest available). But, you can still use smaller apertures (represented by higher f/stop numbers).

With a zoom lens, you usually see two apertures listed (the largest available aperture at wide angle zoom setting, and the largest available aperture at the full telephoto zoom position). When in between the widest and longest focal length of the lens, the largest available aperture will fall somewhere in between the apertures shown.

Many high quality zoom lenses can maintain a constant aperture throughout their zoom range (with f/2.8 being the most common). So, you'll only see one aperture listed for this type of lens (the widest available, since you have that aperture available at all focal lengths supported if desired). But, you can still set it to smaller apertures (higher f/stop numbers).

Lenses are rated by their largest available apertures (smallest f/stop numbers). But, most lenses can be set to use apertures of f/22 or smaller (often in 1/3 stop increments between the largest and smallest available).

When you vary the aperture, you're controlling the iris in the lens (which like a pupil in your eye, can be opened up to let in more light or closed down to let less light in). So, this impacts the shutter speeds you'll need for proper exposure (since more or less light is getting through to the sensor). Aperture also impacts Depth of Field.

The aperture scale in one stop increments (with larger than f/1 apertures possible but very rare in lenses) goes f/1.0, f/1.4, f/2.0, f/2.8, f/4.0, f/5.6, f/8.0, f/11, f/16, f/22... With each one stop move to a smaller aperture (represented by higher f/stop numbers), you will need shutter speeds twice as long for proper exposure for the same lighting and ISO speed (only half the light gets through compared to a one stop larger aperture).

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Old Nov 9, 2007, 8:51 AM   #3
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xiggy:

You may find this handy online calculator to be useful for a better understanding of how lighting, aperture, ISO speed (shown as film speed in the calculator) and shutter speed are related to exposure (and the same exposure concepts that apply to film cameras also apply to digital cameras).

http://robert-barrett.com/photo/expo...alculator.html

This calculator will give you a better understanding of how aperture, focus distance and focal length impact Depth of Field:

http://www.dofmaster.com/dofjs.html

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Old Nov 10, 2007, 11:31 AM   #4
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ok thank you very much!

and where on the camera would you adjust it?, in the camera options menu (electronic through the lens) or some ring on the lens? thanks!

and thanks for the links they are very handy and work quite well!
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Old Nov 10, 2007, 12:17 PM   #5
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If you're shooting in Av (Aperture Priority) or Manual Exposure Modes, you simply turn a control wheel on the camera body with most modern cameras to vary the aperture (and it shows up in your viewfinder as you make the changes with most models so you don't need to take your eye away from the viewfinder to set it as desired).

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Old Nov 10, 2007, 1:54 PM   #6
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ok thank you i guess i got it confused with something else because i already knew about aperature priority lol!

thank you
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Old Nov 10, 2007, 2:06 PM   #7
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Most modern cameras have been able to control the aperture in a lens for a long time now.

You will still see some lens models with Aperture Rings on them. But, even then, you may be able to control the Aperture via the camera (for example, a number of Nikkor Autofocus lenses have Aperture Rings, but you just leave them set to the highest f/stop number and the camera controls the aperture in the lens).

The Aperture Ring on the lens is just there for backwards compatiblity with older camera models.

Now, if you're using older Manual Focus Lenses (either directly if your camera mount supports them, or via an Adapter), then you may have to use the Aperture Ring on the lens to set it. But, that's not the case with most modern Autofocus Camera and Lens designs.

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