I wanted to write a series of articles outlining the basics of photography to help beginners along their path to making better images and becoming more proficient artists. My idea is simple..To explain the fundamentals of photography in 500 words or less so an amateur photographer would have a quick reference guide to quickly answer their questions. I am by no means an expert and I wanted to take some of the frustration out of learning to make images.
ISO simply put is how sensitive your digital camera’s sensor is to light. It is one of the foundations for which all of your photography work will be based and probably one of the easiest concepts to understand. The higher the ISO number that you set, The more sensitive to light the sensor in your camera will become. The lower ISO numbers will require longer exposure times while the higher numbers will require shorter times. Think of a straight line with the starting point at ISO 100 being the least sensitive setting. The numbers below are typical of what you will find on most digital camera’s…
100→ 400→ 800→1000→1600→2000→2500→3200→4000→6400 →and beyond.
Changing your ISO is an easy thing to do but in photography whenever you make a change to ISO, Shutter speed or Aperture there is always a consequence to the change. Increasing your ISO number has the consequence of adding more grain into the image reducing quality. It is a matter of personal taste as to how much grain is objectionable in an image…A good rule of thumb whenever you get a new camera is to always take a series of test shots at all of your camera’s ISO settings. Once downloaded into your computer review each image at 100%, Find the image with the most objectionable amount of grain and make a note of the ISO setting. This is your “Line in the sand” if you will to never cross.
To illustrate ISO and image grain I have taken a series of test images with my camera (Canon 7d) at various ISO settings throughout it’s range. In the images below I am using the ISO 12233 test chart which is available here on the Cornell University website. It is a good chart for home testing of lenses and camera bodies and it was designed and made available by Stephen H. Westin.
ISO 100 at 100%. Clean image file with a tiny amount of grain. Useful for fine art images, image submissions to magazines, etc., stock photography, allowing longer shutter speeds because of the low sensitivity, shooting waterfalls or for shooting in the middle portions of the day with bright sunlight. 90% of the images I shoot are at 100.
ISO 400 at 100%. Slightly more grain than 100 but still acceptable. A good all around ISO for portraits, indoor shoots where the light is dim and for slightly faster shutter speeds. Grain easily toned down with any noise reduction program. Not good for long exposures over one minute as these too can add grain into an image.
ISO 800 at 100%. Here is where things start to get dicey for me and the 7d. The grain is ok , images are perfectly useable and I have shot images for clients at 800. Can be removed with noise reduction software but at a price...The image will start to appear soft if too much noise reduction is applied. Another good, all around ISO and good for some much-needed light in dim shooting environments. Not my favorite but I will use it if I have too!
ISO 1000 at 100%. Uggghh! This is the point where I draw the line and an ISO that I rarely use. Ok for web jpegs or if you are doing night photography. Grain will now be difficult to remove without the image quality suffering. I shoot a ton of landscapes and almost never go above this and certainly would not choose this for a long exposure.
ISO 2000 at 100%. Please unless you are shooting the night sky go back at once! Very pronounced grain and not a setting I have ever used. Very objectionable to my eyes but useful for playing around and allowing a ton of light to reach the sensor. Can be put to good use shooting stars.
ISO 4000 at 100%. Damn...anyway you slice it this bad boy is not very useful and certainly not for a print. Probably good for a simple viewing jpeg or for shooting at night. I have never shoot at 4000 and I wouldn't shoot a nice landscape with it. Will let a huge amount of light into the sensor..Would be good to experiment with at night.
ISO 6400 at 100%. The limit of my camera and to me it looks awful. Even with the high ISO low noise setting switched on doesn't do much at this high ISO. Stick to anything below 1000 and your good. Get yourself a good speed light and some off camera flash and forget about this setting! With the exception of nigh time shooting I never use this setting either. Your mileage may vary.