ISO is the third point on the exposure triangle. ISO is a carry over from the old film cameras and stands for “International Organization for Standardization” and is taken from the Greek word “isos”, meaning equal. ISO replaced the older ASA designation.

As for how it relates to film, it is an indicator of the film’s sensitivity to light. Light sensitive crystals are an all or nothing proposition. They either react and are subsequently developed, or they do not, and the speed at which they react is the same for any given film. It is more a function of size, but speed is how it’s described. The increase in speed is a result of larger crystals since they are able to react more to light than smaller ones. If this is difficult to grasp, think of them as tiny buckets gathering light. Larger ones gather more, thus producing more image in the same length of fixed time. However, a noticeable increase in the graininess of the image is usually associated with fast film. It is safe to say that doubling the number to 400 ISO from 200 ISO means the film is twice as “fast”. With regard to digital cameras, the sensors sensitivity to light is increased when you move from 200 ISO to 400 ISO, in the same way as film, the image quality deteriorates as you increase your sensors sensitivity, but instead of getting grain,  you get a similar effect known as noise.  when you move from 100 ISO to 200 ISO you are increasing the sensitivity by double (100%), when you move from 200 to 400 you again double the sensitivity, but each time you do you are inceasing noise in the image. ISO is used to balance your exposure in the same way you would use shutter speed and aperture settings, but would be used to a lesser extent and usually only when you are struggling to find enough light to capture an image at an acceptable shutter speed and when your aperture is open as wide as possible.

Now that we have covered all the points of the Exposure Triangle, Shutter speed, Aperture and ISO, my next post will look at how camera meters work. Looking at both, meters built into your camera and hand held meters that can be purchased seperately from most good camera shops.

For more information about my one to one tutorials in Lowton, Wigan, Warrington follow this link tutorials or hire my studio

NEW! Teenager Makeover and Fashion photo-shoot parties – ideal for teenagers. What do you get teenage girls for their birthday these days?….how about treating them to a Makeover and fashion Photo-shoot party…. We all know teenage girls love to dress up and pose with friends, so why not give them the ultimate birthday treat…. 3-6 of their friends can come to the studio have a style consultation, makeup and hair professionally styled by our expert beautician Linda, then let the girls loose in studio for their fashion photo-shoot. At just £49 per head all this is included along with a A4 retouched print and display mount for each of them to take away. Available now at our studio in Lowton, Warrington and Wigan

As the credit crunch tightens its grip on the economy, Mike Turner Photography is offering local businesses the chance to get professional images to use on print and digital promotional media for a reduced rate. Mike has reduced his hourly rates by 50% to help businesses get the best from their promotional material, or for a small amount of items is happy to charge per item to help business reduce costs. In fact Mike and a number of local business men are offering a one stop shop for promotional merchandise from business cards, leaflets and stationary to promotional clothing and bags, all with your own branding. All enquiries are welcome by calling the studio at Lowton, Wigan, Warrington on 01942 676741.

Mike Turner Photography in Lowton, near Warrington was a hive of activity on Sunday as it played host to the first FRESH makeover day since joining the nationwide group of Makeover and Model photographers. Linda our expert makeup artist made all the ladies look stunning, while Amy went to work on capturing some great images and made all the ladies feel and look like models for the day. While it was a long day, we all had a great time pampering the models and getting their images ready to view. We will be rolling out a full program of makeovers over the coming months, promoting in and around the Wigan and Warrington areas. We have vouchers that make the perfect gift for your wife or girlfriend to enjoy a day in the limelight. Something she will remember for years to come.