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Photography Question 

D.O.F and Shutter Speed

Hi, I finally bought the Canon Rebel Ti and it is amazing -it can be operated manually to any extent and I am very happy with it. But I do have a few questions.

a) If I want to use a slow shutter speed to take a picture of a waterfall, how do I know what speed to set if I want to get a nice picture of flowing water and not the drop by drop type look?
b) Same question but for aperture and depth of field
c) People say to use a slow shutter speed to catch fireworks, but I don't understand why, since they disappear very quickly - wouldn't they be gone before the exposure is finished?
d)What exactly is bulb mode?

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8/26/2003 9:33:05 PM

Jon Close
BetterPhoto Member Since: 5/18/2000
  (a) Try several and take notes. It'll vary depending on the speed of the water, and your distance from it. The farther away (or wider angle lens used) the longer the shutter speed for blurring motion. The opposite is true for stopping motion - faster shutter speeds are required as you move closer and/or as focal length increases. Very generally, 1/125 and faster will freeze the motion, 1/60-1/8 will give you streaking motion, 1/4 to several seconds (or even minutes) will give milky blur.

(b) Smaller apertures increase depth of field. DoF also varies depending on the lens focal length and distance from your focused subject. When you focus the lens is at its widest aperture. When the shutter is tripped, the mirror flips up and the aperture instantaneously stops down to the chosen aperture, then opens wide again. Using the Rebel Ti's DoF preview the aperture closes down to the selected value so you can see the depth of field. The viewfinder will darken because the smaller aperture lets in less light. Allow your eyes to get accomstomed, and the difference in DoF will be apparent. You can also use the camera's DEP program mode to set the aperture for appropriately shallow or deep depth of focus. Or you can use a DoF calculator to determine the aperture you want. A couple I like are f/Calc from for doing calculations on the computer, another is DOFMaster from which allows you to construct a DoF scale for your lens that can be used in the field.

(c) Like lightning, fireworks explosions usually happen too fast to hope to catch by pressing the shutter at that moment. A fast shutter speed would freeze the small sparks of the explosion. So you use a long shutter speed to catch the full effect and the long tails of the cascading sparks. Opening the shutter for a longer period (using a smaller aperture like f/8) on a black sky will expose only the brief bright light of the firework. See the section "Fireworks" under Kodak's "Taking Great Pictures" at

(d) BULB holds the shutter open for as long as the shutter button is held down. You would use this to get exposures longer than the camera's timer limit (30 seconds) or for example, lightning, where you have the shutter open in anticipation of a lightning strike, then close it immediately after. It is best to use BULB with a remote release and a tripod.

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8/27/2003 6:05:18 AM

Darren K. Fisher
BetterPhoto Member Since: 4/7/2002
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  Hey Josh im going to see if I can help you out on veiling water here. What I will do is just tell you how I do it, and see if that helps. First off I shoot with a Canon Rebel 2000, I shoot with Velvia ISO 50 then I drop it to an ISO 40. You always want an overcast day and or deep shadow for this kind of shot. On the norm I go with an f/11 or f/16 this will give you a nice slow shutter speed something between 1sec-10sec. Sometime when you are unsure you can bracket or im my case I just try different appertures and shutter speeds. Hope this will help a bit, if you have any questions just drop me a line.

Darren Fisher

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9/3/2003 4:30:21 AM

Paul Ferrer   Hey Josh,
If you want to see some pictures that I took last year of fireworks with long exposures and the use of bulb e-mail me. I experimented with it and I was pleased with the results. My e-mail is and Iíll send you a picture with all the details.


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9/3/2003 9:28:40 AM

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