Understanding ISO Sensitivity
In our course on understanding the exposure triangle, we spoke of the importance of light in
What is ISO Sensitivity?
ISO measures a cameras sensitivity to light. Digital cameras convert light that hits the image sensor into electrical signals. Those signals are used to process the image. ISO sensitivity is increased by amplifying the signal. The ISO measurement was created by the International Organization for Standardization.
It’s important for photographers of all skill levels to have a solid grasp of ISO sensitivity. Before we jump into ISO in modern day digital
Film ASA at the time was a numeric measurement of film’s sensitivity to light and was represented in numbers ranging from approximately 100 to 800 (though slower and faster ASA were available). You also had the choice of using slide film or negative film in either color or black and white for prints.
Film was either slow, fast, or high speed. If you were going to shoot out in the daylight on a bright sunny day, you used a slow film speed of 100 ASA. There were 4 popular film speeds in the pre-digital age:
- ASA 100: Slow speed – Use for daylight, bright sun, beach, snow
- ASA 200: Slow speed – Best for overcast days and in the shade
- ASA 400: Fast speed – Good for sports
photographyand rainy days
- ASA 800: High speed – Used in low light, evenings, sunsets, inside with a flash
Another consideration was grain. Film consists of millions of light-sensitive silver halide crystals that we call grain. Slow films used a fine grain and faster films used a larger grains which have greater light sensitivity. So images shot with high speed film were known to appear grainy compared with pictures shot with slow speed film.
ISO Replaces ASA
ASA was eventually replaced with ISO, . ISO, like it’s ASA predecessor, measures a cameras sensitivity to light. The average ISO sensitivity range is approximately 100 to 1600. Some digital cameras have an ISO range of 100 to over 100,000 ISO.
ISO sets the amount of light needed for a good exposure. Just like with film, the lower the ISO number, the more light you need to get a properly exposed image. When you need more light, you can use a slower shutter speed. So you use a low ISO range of 100 to 200 when you have plenty of bright light (like sunlight) or if you are mounting your camera on a tripod. If you need a faster shutter speed for something like sports
When you double your ISO setting (let’s say from 100 to 200) your camera needs only half as much light for the same exposure. If you had a shutter speed of 1/125 at 100 ISO, increasing your ISO sensitivity to 200 and changing your shutter speed to 1/250 will get the same exposure (provided you don’t change the aperture). Photographers will use a higher ISO setting for sports
Using a higher ISO will also cause noise in your image. Noise, or digital noise, in a digital image is similar to noticeable grain in higher ASA films. Generally speaking, visible grain is usually undesirable and degrades the quality of an image. Most photographers strive to take images with the least amount of noise possible.
The size of the pixels in the cameras digital sensor is a factor in digital noise. A DSLR will produce better images than a point-and-shoot because the size of the pixels on a DSLR sensor are larger. Large pixels produce less noise than smaller pixels. Digital SLR cameras perform better at higher ISOs than compact cameras. Fortunately noise reduction processing built into digital cameras continues to improve allowing photographers to shoot at higher ISO’s with less noise than ever.
Thank you for your generosity for teaching us beginners,I am now able to use different apertures and I so,and the result is great
Thank you,thank you so much for your help
Thank you the explanations on ISO and the relationships with shutter speed and aperture have been a great help…very enlightening…..
I’ve a Canon EOS Rebel SL1 and recently learned my ISO has a D+ feature which limits my ISO from auto – 28,000 to 200 -1600…tho I did get frustrated when taking moon shots I didnt understand the difference. Cant say that I really understand the D+ of the ISO or the true usage/value of it
Brilliant lesson into understanding ISO settings, atleast I know now I’ve been using it correctly.
Thank you very much for the lessons.
Can’t wait to get started with some photos soon
can you give me a notes , some time i don’t have internet
Love this explanation but i do not have my camera yet. The explanation is quite straight forward
Thank you very much for the lessons and your cooperation through online
Thanks for the lesson
Thank you ??
Enjoyed this and all the lessons, which make it easy for beginners like me. Thank you very much
Am very great today because have learn a wonderful lesson today. Thank for the concern
Thank for this wonderful lesson, I really appreciate may God bless your hands work.
Awesome explanation. Thank you
Wow this is awesome thanks for teaching me …I m going to be a professional photographer because of u ..God bless u
I have enjoyed the courses so far and I have learned me a lot more about cameras thanks
Very helpful article!!!!