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Thursday, March 6, 2014

The Basic, Aperture AV & Shutter Speeds TV




 Infra Red Canon Rebel XSi, Canon 16-35 at 17mm, f18, .6sec, ISO200, This is a great example of perfect combination of AV and TV, f18 bring details, and  .6sec soft the water falls., Elbow Falls Alberta, the falls change since the great flood of June 20, 2013
 Aperture AV 


       AV “ aperture value or A mode determines whether all the photograph is in focus or part of. For example photographers can choose to have a sharp foreground and background, or they can blur the background. To set your digital camera on aperture priority, turn your mode dial to AV.   Now rotate the main dial until you have aperture your after. The camera will set the shutter speed to suit.
Canon 5D Markiii, Canon 85mm 1.8 prime lens, f1.8, 1/500sec, ISO 200, great example of wide aperture 1.8, focus on only one eye.
       The aperture adjustment opens and closes a diaphragm built into the lens which controls the amount of light reaching the film or sensor. When the aperture is at it’s widest, the maximum amount of light possible passes through. At the smallest aperture, the least amount of light passes through.
Canon 5D Markiii, Canon 24-105 at 105mm, f4, 1/25sec, ISO200, f4 is great for portrait, f2.8 and lower are sometime difficult to get the right focus.
       The aperture controls the depth of field, or how much distance is sharp and clear in the image “the area of sharpness”.
       The greater the f-number the greater the depth of field. That is, f2.8 has a much shallower depth of field than f8, in other word f8 will give a larger area of sharpness both in front and behind the subject being focused on. Most lenses will give a better image at f9 to f11.
 Canon 5D Markii, Canon 24-105 at 105mm, f4, 1/125sec, ISO200
       The closer the camera is to the subject, the less area of sharpness there is for the equivalent AV. That is, for any chosen aperture, if the camera is focused on a subject at 10’ you’ll get better sharpness in front and behind the subject that let say if your subject in only at 3’ from the camera
       The longer the size of the lens, the less area of sharpness. A wide angle lens “16-35 zoom” by example has a greater depth of field that a 100mm telephoto.
       So is it always best to use a high f-number to maximise this area of sharpness? The answer is no. The amount of area of sharpness you decide upon will depend on the subject your are photographing and the effect you are looking for!

Shutter Speeds TV
  
       Shutter priority allows the photographer to choose a shutter speed, then the digital camera automatically sets the aperture to suit.
       To set your digital camera on shutter priority, turn your mode dial to TV . In case your wondering, TV stands for time value. Now rotate the main dial until you have the shutter speed your after.
Calgary Stampede 2013, Panasonic Lumix DMC FZ200  zoom at 453mm, f2.8, 1/500sec, ISO160, as you can see even if the aperture is wide open at f2.8 the distance between the camera and subject is so great that more of the subject is in focus. 1/500 sec. shutter speed is more than enough to freeze the action.
       Shutter speed is measured in seconds and looks like 1/500, 1/250, 1/2 or 1 as in one second etc. It can range anywhere from 1/8000 to B for bulb. Bulb keeps the shutter open for as long as the shutter button is pressed down.
       Slow shutter speed, slows motion to blur running water, with a shutter speed of 1 second or slower, water can blur to a ghostly appearance, with the rest of the scene pin sharp.  The trick for this kind of effect is a dim enough lighting  to slow down the shutter speed, in daylight  use the highest  f-number and lowest ISO setting available on your camera, another option is to use a neutral density filter.

5D Markii, Canon 16-35 at 16mm. f22, 65 sec, ISO200, the narrow AV f22 and the wide lens help in getting more details in focus, the 65sec is enough to capture the light trails.
       When using a slow shutter speed use a tripod and remote shutter release or self timer to avoid camera shake.
       Use slow shutter speeds of at least 10 seconds or more for night shots of cities, buildings and streets etc.
       Fast shutter speed, takes the image almost instantly as in frozen in time, frozen water and action.
       Selecting the actual value is pretty arbitrary, so think of it in sections: 1/4000 to 1/250 is a fast exposure, 1/250 to 1/10 is a medium exposure, and 1/10 of 30” is a long exposure. Each will give you a different effect, and you can only pick one and try it. If it’s not what you are looking for, then try again. And again. You’ll eventually get a pretty good idea of what speeds give what effect.


 Combining Shutter Speeds with Apertures

       With shutter speeds and apertures we found that each numbered value was called a stop.  If we changed the value up or down by one value, we reduced or increased the exposure by one stop of  a difference.
           To recap.
       If we changed our shutter speed from 1/60 to 1/125 we decrease the amount of time the shutter was opened and consequently halved the amount of light reaching the sensor.
       If we changed our aperture from f8 to f5.6 we increased the size of the aperture and doubled the amount of light reaching the sensor.
          
With this in mind we are also able to alter both the aperture and shutter, and still have the same amount of light getting to the sensor.  For example, say we have composed our shot and have taken a meter reading of 1/60 at f8 giving us the correct exposure. If we changed the shutter speed to 1/125 we would under expose the image by one stop.  Now what happens if we really need to set the shutter speed to 1/125, say to prevent camera shake?
          
We must counteract the underexposure by changing the aperture by one stop giving the correct exposure again.  That is, we select f5.6 increasing the amount of light reaching the capture area.

       Example if the proper exposure is 1/125 at f8, the following combinations of shutter speed and apertures could also be used. 
          1/1000 - f2.8
          1/500 - f4
          1/250 - f5.6
          1/125 - f8
          1/60 - f11
          1/30 – f16
          1/15 – f22


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