Editors Note: ISO | From Lastolite School of Photography was originally written by Mark Cleghorn for www.lastoliteschoolofphotography.com and has been reproduced with permission.
The great thing about digital photography especially good digital compacts and Pro DSLR’s is that it is very easy to change the camera’s sensitivity with the ISO settings, this is to allow for very bright conditions or darker room environments which is so typical of a wedding day.
It is important to remember that the ISO setting does not only affect the camera sensitivity but also the final image quality. To gain a correct exposure in difficult lighting conditions, you may need to use a high ISO, which will increase the visible noise, which has a coloured grain texture in the final image. Even though most Pro DSLRs can cope with very high ISO’s with very acceptable results, there comes a point of no return when the benefits of the high sensitivity are outweighed by the loss in quality.
Keep It Low
It is always better to use as low an ISO as possible as this will make the image quality superior especially when combined with a perfect exposure. The key still to choosing the correct ISO is assessing the conditions as well as the subject matter. If you are shooting with a flash, a lower ISO is possible, maximizing the quality, however, if you are in a dark room, a low ISO setting will make the flash very dominant in the scene, resulting in a dark or black background. To balance this, a higher ISO like 400 would start to allow some of the ambient light to show up in the background.
ISO 100 – For manual cameras, the lowest ISO setting is 100 which is perfect to give smooth skin tones as well as very little noise in the image, especially when you are shooting RAW files on camera. In the studio I always opt for the minimum ISO as I am in complete control of the lighting in both position and quantity. If there is any visible noise you will only get it with this ISO setting if you have under-exposed the image at capture, as in post production you will have to increase its brightness which will reveal the noise.
ISO 200-400 – On most compacts, this is your highest usable ISO due to the noise in the image, however for pro photographers this is a general setting as the Pro DSLR’s have very little noise at this sensitivity. 400 ISO is perfect for shaded areas or cloudy days as well as being a perfect ISO when combining on camera flash and ambient light when shooting inside.
ISO 800 – For most Pro DSLRs, this is a usable setting but it can start to show the granular noise texture in skin tone, especially if the file is allowed to be under exposed but is still a ‘get out of jail free’ card when you want to work without a flash or increase the amount of ambient light when shooting inside.
ISO 1600 – Even at this high ISO, the top end Pro DSLR’s give fantastic results even in low light conditions, I often use this setting for candid images without a flash when shooting inside a large room. If you get very visible noise, try over-exposing the image a little to bleach out the effect or add a splash of flash.
ISO 3200 – Almost inconceivable a few years ago but already some of the Pro DSLRs have fantastic results but always used as the last resort.