Archive | April 2012

What is and how to use ISO

What ISO sensitivity denotes is how sensitive the image sensor is to the amount of light present. The higher the ISO, the more sensitive the image sensor and therefore the possibility to take pictures in low-light situations.

ISO Speed & Exposure

ISO speed affects the shutter speed/aperture combinations you can use to obtain correct exposure. If you look through your camera and the bracketed meter shows that you do not have enough light for capturing the image, how will you get enough light to come through the camera without using flash?  This is when you can increase your ISO (which makes your sensor more sensitive to light). You can increase the ISO as needed in order to correctly capture your image.  When you are trying to capture a image in a low light situation [but have opened your aperture the widest it can be and have the shutter speed the lowest so the image won’t be blurred (anything under 1/60 of a second without a tripod will be blurred), you will need to increase your ISO. Once you increase your ISO, you may increase the shutter speed.

ISO Speed & Noise

However, there is a price to pay with your image appearing more noisy (in film terms, it was grainy). The increased sensitivity allows the image sensor to record more light signal and more noise. The ratio of light signal to noise (S/N ratio) determines the “noise” in your resultant image.  An image sensor is usually calibrated so that it gives the best image quality (greatest S/N ratio) at its lowest possible ISO speed. For most consumer digital cameras, this value will be expressed as ISO 50, ISO 64 or ISO 100. A few digital cameras use ISO 200 as their lowest ISO speed.

ISO Speed & Image Sensor Size

The size of the image sensor determines the ISO speed range that a digital camera can use without suffering from undue noise. One reason for this is because the pixels on the larger image sensor can be larger and therefore receive more light, and thus have a greater signal-to-noise (S/N) ratio. If we take two image sensors, each with 4 megapixels resolution, but of different sizes, the 4 megapixels image sensor that is smaller will exhibit more noise at higher ISOs than the larger one.


Would you like to add some punch to your images? Then try a polarizing filter. A polarizer is the one filter every photographer should have handy for landscapes and general outdoor shooting. By reducing glare and unwanted reflections, polarized shots have richer, more saturated colors, especially in the sky. Be aware that you must turn the filter ring to where the image looks its best. Also you will lose approximately one and a half stops of light coming thru your lens. The filter is a neutral grayish color and cuts down the amount of light coming into your lens. Therefore do not leave it on when you are taking inside photos.

If you own a compact point-and-shoot camera that does not accept filters, don’t fret. My husband uses this trick. If you have a pair of quality sunglasses, then simply take them off your head and use them as your polarizing filter. Place the glasses as close to the camera lens as possible, then check their position in the LCD viewfinder to make sure you don’t have the rims in the shot. The exposure meter will read the sunglasses and your photos will look more saturated in colors, especially good for bright sunny landscape photos.

A polarizing filter is also great to cut glare when taking outdoor photos during the daytime. It cuts glare, so if you are photographing a car show and want to see the color of the car instead of the reflections on the metal, try turning the ring on the filter and you will see the glare diminish. Great for shooting thru glass and water also.

You can purchase a polarizer filter at your local camera shop or at B&H Photo thru the internet. Make sure you know your lens thread size which is shown on your lens as a #mm or look for the circle with a line thru it and that is your filter thread size. Every lens you own could be different thread sizes so be aware that you may have various thread sizes for each lens.