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Puerto Vallarta News NetworkVallarta Living | Art Talk | June 2009 

Photo Tip of the Week: ISO Basics
email this pageprint this pageemail usLarry and Linda Bennett - PVNN


Photo Tips of the Week are written by Larry Bennett, a professional photographer living in Puerto Vallarta. For more photo tips click HERE. To view more of his work, visit LarryBennettPhotography.com.
We are in the final weeks of the photography triangle: Aperture, Shutter Speed and ISO. ISO is the easiest of the three photography basics to grasp and apply and what we will be discussing for the next 2 weeks. Before we get started, letís do a quick review of the past few weeks when we covered both aperture and shutter speed.

The first leg of the triangle involved aperture.
We learned in a nut shell that aperture is really depth of field. Aperture settings always halve or double its self. When you stop down a lens you are going to a larger number and smaller aperture resulting in less light and better depth of field. Going from F/11 to F/16 is stopping down. Stopping up or going up from F/8 to F/3.5 is moving towards the smaller F/stop number and larger aperture allowing more light and less depth of field (less of your fore or back ground will be in focus.)

The second leg of the triangle involved shutter speed.
Shutter speed is easier to understand and utilize than aperture. Shutter speed is like their partner aperture (ISO will also double or halve themselves) but shutter speed is measured in seconds or fractions of seconds. For example, one quarter of a second is half as long as half a second, but twice as long as one eighth of a second. One second is twice as long as half a second and half as long as two seconds. This is fairly basic math and you will be able to work through the whole sequence of shutter speeds by just doing the math.

The final leg of our triangle is ISO.
It doesnít matter what type of camera you are using, if you are shooting with film or using a DSLR, your selection of ISO has a major impact of the quality of your image. You see, the ISO you select will affect your selection of aperture and shutter speed that you will successfully be able to use.

Here is a better example to help you understand ISO and its exposure. Think of ISO as workers. If the ISO on my camera is set for 100, in my example, I will have 100 workers. If the ISO on your camera is set to 400, you will have 400 workers. Do you see the correlation between the ISO and the workers? The job of these workers is to capture the light that comes through your cameras lens and make the image.

To make my point, we will go one step further. We will shoot two identical images using two identical cameras and both will be set on aperture F/4. One camera will be set on an ISO of 100 and the second camera will be set on an ISO of 400. Which camera do you think will process the image quicker?

If you guessed the camera with 400 workers or in other words, the camera with the ISO set at 400, then you are absolutely correct. It makes perfect sense that the camera with the 400 workers would process the image quicker. Okay, this is pretty simple, but letís make it a little bit harder. We are going to add back into the equation both shutter speed and aperture, remember they all must work together.

How does this all relate, ISO and shutter speed? Letís say the image in question is a person standing in a field on a semi-cloudy day. Your camera is set at an ISO of 400 and my camera is set at an ISO of 100 and we are both shooting at F/4. When you adjust your cameras shutter speed settings to achieve the correct exposure, your metering system tells you to shoot at 1/1000 using an ISO of 400. My camera tells me to shoot at 1/250 using an ISO of 100 (a much longer exposure.)

Okay, 1, 2, 3, press your shutter release. Who won? You won because you shot 4 times faster. Remember you have 400 workers and your 400 workers finished in a quarter of the time it took my 100 workers to finish.

With todayís new cameras and super processors an ISO of 400 is a really safe ISO to shoot without much or any noise (digital camera noise.) I know, you want to know what digital camera noise is. Letís come back to noise in a little bit.

Exposure Taken One Step Further

Letís do a field test; they always seem to help me understand.. Grab a pencil, pen, or crayons and some paper so we can go a little further with this. Set your ISO dial to ISO 200, your aperture to F/8 and adjust your white balance for the conditions - OR just leave it on auto white balance. Now, point your camera at an object to pre-focus and set your shutter speed until you have reached the correct exposure with your built-in metering system. Write down that shutter speed.

Okay, now letís change the ISO to 400 while leaving the white balance and aperture alone. Once again, point your camera at an object to pre-focus and adjust your shutter speed to achieve the correct exposure through your in camera metering system. Write down what your correct shutter speed was.

Continue to do this with several more ISO readings (keeping them in doubles or halves depends on where you started.) Now look back at your shutter speeds that you have written down. They also should be in halves or doubles based on where you started. When you increase the number of workers (ISO) from 100 to 200 you cut the time in half to get the job done and this is what your shutter speed has been telling you. Going from 1/125 to 1/250 is half as long of an exposure time. When you set the ISO to 400, you now have 400 workers and your shutter speed went from 1/125 passing 1/250 all the way to 1/500.

Remember a few weeks ago in shutter speed we talked about stopping up and down? Well with the ISO you stop up or down as well, doubling or halving, it all depends on what direction youíre going.

Now that youíre starting to understand this, let me throw in another test for you. Leave your shutter speed constant, letís use 1/500. Now adjust your aperture until your exposure is correct in the view finder. Play with it, learn from it, itís digital and when youíre done you just delete everything. This is the way ISO works, itís very simple. Donít forget to reset your cameraís ISO to your original settings when you are finished testing.

We will continue our discussion about ISO next week. Until then, remember, itís just another day in Paradise and F8 and be there!

Until next time, remember, it's just another day in Paradise and F8 and be there!

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Photo Tips of the week are written by Larry Bennett, a professional photographer living in Puerto Vallarta. These tips are to be just tips, refer to your cameras owner's manual for specifics on your camera. Readers are welcome to enjoy Larry's website at LarryBennettPhotography.com.

Click HERE for more Photo Tips from Larry Bennett
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