Hey all of you photography buffs,

I just recently enrolled in a phpotgraphy class at my college. Thus far I love it. It enthuses me. I am having some trouble understanding the relationship of the apperature and the shutter speed when taking Depth of Feidl photographs. I need an easy way to understand it. If anyone has any advice please contact me I would greatly appreciate it!!!

-- Bethanie (hrshykss01@aol.com), September 21, 2000

Answers

Response to Beginning student needs help!!!

For a well exposed photo the film needs to see a certain amount of light, not too much or too little. You control the light reaching the film by selecting a combination of aperture and shutter speed that permit the correct amount of light to reach the film.

Usually, if the lighting conditions are not too extreme, several combinations of f-stop and shutter speed are available to choose from. Each increase in shutter speed halves the amount of light. Each increase in aperture size (that is, moving to a lower number f-stop) doubles the amount of light let in. So: f8 at 1/125 sec lets in the same amount of light as f11 at 1/60th, and so forth up and down the scale.

Due to the laws of Physics, smaller apertures (the larger f-numbers) produce greater depth of focus. Larger f-stops produce shallower depth of focus (also called depth of field).

You get to choose which way you want to expose your film. If you want the photo of your friend to be sharp but the background to be blurry so as not to distract the viewer's eye, choose a large aperture and focus on your friend. If you want everything from six feet away to the horizon to be sharp you will need to use a small aperture. Either choice requires that you adjust the shutter speed to keep the light delivered to the film constant.

Most camera lenses have a scale on the top of the lens that lets you estimate the depth of focus for each f-stop. It is a very handy tool, one that I use frequently, and it's right there, built-in, and free.

OK?

-- Don Karon (kc6d@arrl.net), September 22, 2000.

Response to Beginning student needs help!!!

Just like to add to Don's great explanation,

The aperture (and a few other factors which we'll ignore for the purpose of this) controls the DOF, and the shutter balances the exposure (hopefully in the manner you want)

-- Nigel Smith (nlandgl@eisa.net.au), September 22, 2000.

Response to Beginning student needs help!!!

Don's explanation certainly is good, with one minor flaw. Depth of field is what happens in front of the lens, depth of focus is what happens in the focal plane, i.e. at the film.

I think Bethanie can safely ignore depth of focus.

-- Alan Gibson (Alan@snibgo.com), September 22, 2000.

Response to Beginning student needs help!!!

The other thing to add is that while aperture controls depth of field/focus, shutter speed controls the way motion is rendered on film: faster shutter speeeds, less blurr due to subject motion and camera movement. If you hand-hold your camera, you need to make sure the shutter speed is fast enough you won't wiggle your camera during exposure. A rule of thumb is that the shutter speed for hand-holding should be 1 over the focal length of lens you are using, ie. if you are using a 50mm lens, 1/50th (1/60th is the closest marked speed) would be needed, with a 200mm lens, 1/250th (the closest marked speed) would be needed to keep from blurring the image due to camera movement. Conversely, long shutter speeds allow the motion of the subject to blurr the image, eg. streaking formula 1 cars, taillights on the freeways at night... Hope this helps. ;^D)

-- Doremus Scudder (ScudderLandreth@compuserve.com), September 23, 2000.