Some Tips And Info For Selecting The “correct” ISO For Your Digital Photography

ISO selection is important because it is allows the photographer to adapt to the lighting conditions found in their scene. The ISO value you select is one leg of the exposure triangle, along with aperture and shutter speed, which allows for precise exposure and creative control.  Understanding ISO and how to use it is a fundamental photographer skill.

With digital cameras the ISO is a numerical value given for the level of sensitivity your camera sensor has to light.  We saw the same rating system with film.  Remember shooting ISO 100, 400, 800 etc… rated rolls of film?  Do any of you old timers remember ASA ratings on film (pre-ISO)?   With digital cameras we have the option to select a particular  ISO value for every shot, which is a big advantage with digital photography.

In general the lower the ISO setting the less sensitive your sensor will be to light, the higher the ISO setting the more sensitive your sensor will be to light.  This means that when you are shooting in bright conditions you can use a low ISO value and when shooting in low light conditions you select a high ISO value.

Most digital cameras offer a range of ISO values to choose from; 100 to 3200 is a common range of choices, although many models of camera go higher and lower.  In general, the lower the ISO the better quality your results will be.  Using a higher ISO will increase noise (digital artifacts), reduce sharpness and decrease the contrast ratio of your results.  Digital cameras with larger sensors produce less of these negative effects than cameras with smaller sensors. Low ISO setting will then have less noise, more sharpness and a larger contrast ratio which will produce the higher quality images relative to high ISO settings.

In my opinion these disadvantage, the reductions in image quality have to be weighed against the benefits of having the option to shoot at a higher ISO rating. Most issues with noise, sharpness and contrast can be restored with software and I would urge you to shoot high values when conditions dictate.  Being able to shoot action photos at high shutter speeds, with a telephoto lens in an indoor scene is only possible with high ISO values  (1600, 3200, 6400) makes the trade-off in quality  acceptable .

A variable ISO allows you to adapt your exposure settings to the scene and the creative options you want to use in your photography.

My general recommendation is to select the lowest ISO value that will allow for a proper exposure with the least noise. 

ISO TIPS FOR DIGITAL PHOTOGRAPHERS

Here are some of my recommendations for using  different ISO values in your digital photography.  This is an important photographer tool and I encourage you to explore this option for exposure control in your photography.  Good images always start with good camera work and ISO is a fundamental tool for photography.

• TURN OFF your AUTO ISO – By using auto ISO you are letting the camera give a ISO value choice and you are not deciding which ISO suits your photographic intent best the  scene. This is one habit you want to change if your goal is to take control of your creative results.Turn AUTO ISO off, and leave it off!
• SELECT the ISO FOR THE SCENE:  When you are beginning to determine your exposure settings, one of the first steps is to select an ISO value that is right for the scene and your photographic intentions.  If you are in the woods with an overhead canopy of foliage blocking your light you would select a higher value.  If you are shooting portraits with plenty of window light and you want to use large apertures for shallow depth of field then a low value would be your best choice.  Evaluate the lighting resources and exposure options for the image you want to create and choose the ISO according to those objectives.
• CHANGES in ISO ARE EQUAL TO “STOPS” –  When we change our exposure settings (in whole stop increments) we are halving or doubling the amount of exposure.  For example if you move from F 11 to F 8 you are doubling the aperture size or if you move from 1/250^th of second to 1/125^th of a second you are cutting the duration of your exposure in half.  The same ratio holds true with ISO, when you move from 400 to 800 you are doubling the sensitivity setting or as we would say increasing it by a “stop”.  Digital cameras allow for incremental changes in EV (Exposure Value = Stops) usually and half and third stop amounts.  You can refine exposure equally with aperture, shutter speed or ISO in those partial stop increments.
• SHOOT RAW –  RAW is the best format for image capture and will yield the best results because you are collecting the maximum amount of data when you make your photo. JPEG is great file format to distribute photos but it produces less quality for capture.  RAW files can be processed with photo editing software post capture to yield the highest quality images.  The negative effects of shooting with high ISO (noise, sharpness, and contrast effects) are increased when shooting JPEG compared to RAW
• PLAY with EXPOSURE COMBINATIONS – There is no exact recipe for exposure combinations.  Play with a variety of exposure combinations and ISO settings and compare your results on your computer. Each variable in the exposure triangle makes a difference in how your images will ultimately look. Experimenting with combinations will produce a variety of visual results.
• USE A TRIPOD – If you are seeking low noise, high sharpness and a wide contrast ratio that low ISO settings provide use a tripod.  Long lenses and long exposure times make hand held photography difficult, especially in dim light at a low ISO.  Securing you camera on a tripod is the solution for this type of shooting situation.
• SHOOTING HAND HELD with TELEPHOTO LENS –  Long lenses are difficult to use when shooting  hand-held.  By increasing your ISO setting you can then shoot at faster shutter speeds which will eliminate the blur caused by camera movement.  For example an ISO of 1000 with a shutter speed of 1/1000^th of a second shooting with a 500 mm lens.
• HIGH SHUTTER SPEEDS = HIGH ISO –  If you want to stop subject action you need to shoot at high shutter speeds.  Increasing your ISO will allow you to increase your shutter speed.  This is especially useful for shooting indoor sports or performances with limited stage lighting.
• USE ARTIFICIAL LIGHT – Sometimes we run into the limits of ISO choices in particular photographic conditions.  For example you are shooting a portrait in a low available  light setting.  Facial details and skin looks best at low ISO values (100-200) and raising the ISO to a high value will produce less than flattering results.  The solution to this situation it to use flash or other artificial light sources to keep the quality you desire.  More light is often a better solution than a higher ISO.

ABOUT THE AUTHOR:  Photographer and photo educator Dan Splaine has more than thirty years experience producing photography for public relations, marketing and editorial clients. His company TEST of TIME PHOTOGRAPHY based in Nashua, NH provides commercial photography services in studio and at client locations all over the world. He presents a program of digital photography workshops and photography tours for adults throughout New England.