> ## Content Index > Fetch the complete content index at: https://back2basicsphoto.com/llms.txt > Use this file to discover other available public pages before exploring further. # Exposure, Part 3 – ISO - URL: https://back2basicsphoto.com/exposure-part-3-iso/ - Published: 2012-01-04T02:52:30.000Z - Updated: 2012-01-04T02:52:30.000Z - Author: Dan Cabral - Tags: concepts, Difficulty, Foundation, photography, Above, Adobe, aligncenter, aperture, camera, cameras, caption, Comparison, component, components, concept, degrees, difference, drawback, environment, example, exposure, fact, factor, factors, feedback, fundamentals, grain, interplays, ISO, Lightroom, location, manufacturers, Micro, noise, photographers, photos, Pixel, reduction, relationship, sensor, sensors, Settings, situation, situations, size, utilities, width, #Migrated-1790414487459, #wp, #wp-post, #Import 2026-09-26 05:21 The third component of exposure is probably the simplest to explain, but in many ways, the least understood. That component is ISO. ISO is the sensitivity of the film or sensor to light. A lower ISO number means lower sensitivity, while a higher ISO number means higher sensitivity. The relationship of ISO numbers is linear, meaning ISO 200 is twice as sensitive as ISO 100, ISO 400 is twice as sensitive as ISO 200, and so on. As with aperture and shutter speed, an increase of double or a decrease of half is also an f-stop, so ISO 200 is 1 stop faster than ISO 100, and so on. With film, you needed to estimate what the lighting conditions would be at your shooting location beforehand, and you needed to buy film of the sensitivity you estimated you would need. Obviously, this required some planning, as well as experience, but it became second nature after several shoots in a particular environment. With digital cameras, you can adjust the sensitivity of the digital sensor on-the-fly, so you can take a shot, get some instant feedback to see if the exposure works, and adjust as necessary. So, why not just set your camera’s ISO to the highest sensitivity and be done with it? It’s a valid question, but the answer is both simple and very technical. The drawback to increasing ISO is that you get increased digital noise (or graininess when using film) in the image. The higher you boost the sensitivity, the more noise or grain you get. Take this image, for example: [](/content/images/wordpress/2012/01/ISO-200.jpg) The above image was shot at ISO 200, which is the native ISO of my camera’s sensor. Most digital SLR cameras support an ISO range of usually 100-6400, with some offering settings beyond that range on both the low and high end. The amount of noise that gets introduced into images can vary due to many factors, including sensor type(some sensors have less noise than others) and pixel density. Pixel density is an especially interesting factor when it comes to noise, because of the variety of sensor standards that exist (35mm, APS-C, Micro-4/3, etc.) and the rush by manufacturers to satisfy an unfounded demand by the market to have higher and higher resolution (I’ll delve more into that matter in a later post). So with the variety of factors, what does digital noise look like? Here’s an example, using the above shot. ![ISO Comparison](/content/images/wordpress/2012/01/ISO-Comparison_thumb.jpg "ISO Comparison") As you can see from the zoomed-in samples, the image starts to get somewhat blotchy, and image detail starts to get obscured as the ISO increases. This is how noise takes it's form in your images. Depending on your camera, the sensor, the sensor size, the pixel density, and a number of other factors, the setting at which noise becomes problematic will vary. Some cameras handle noise better than others, and that is sometimes a major selling point for professional photographers. Most modern cameras can take relatively noise-free images up to about ISO 800\. Above that, and noise can get pretty obtrusive. If noise can degrade a photo so badly, why include the higher settings? Again, a valid question. For one, it’s sometimes helpful to have the higher setting, despite the fact that the resulting image will be incredibly noisy. It can sometimes be the difference between being able to get the shot and not getting anything. Moreover, there are remedies that can be utilized in post-processing that can help alleviate noise in digital images. Noise reduction software utilities are not only abundant, but are getting better and better at minimizing digital noise without incurring a huge loss of detail. Among the various packages available, there are varying degrees of price, functionality, and image quality. I used [Adobe Lightroom 3](http://www.amazon.com/gp/product/B003739DVY/ref=as%5Fli%5Fss%5Ftl?ie=UTF8&tag=back2basiphot-20&linkCode=as2&camp=1789&creative=390957&creativeASIN=B003739DVY&ref=back2basicsphoto.com)'s Noise Reduction feature to reduce the noise in the ISO 25600 image above to get the following result: ![ISO 25600 with NR](/content/images/wordpress/2012/01/ISO-25600-with-NR_thumb.jpg "ISO 25600 with NR") As you can see, it doesn’t have quite the same level of detail in the ISO 200 image, but it is a perfectly usable image for print or web use. In order to get the most detail out of your image, *you will generally want to keep your ISO setting as low as your camera will allow*, and this is a **general rule** you will want to follow 90% of the time. But in what situations might you want to increase your ISO? You'll find yourself in situations, particularly in low-light, where you'll have your aperture wide open, and still find that you can't get a fast enough shutter speed to get the shot. In these cases, particularly indoors or outside at night, you'll want to increase your ISO setting in order to be able to use a faster shutter speed and still get the correct exposure. Since noise increases as you raise the sensitivity, you'll only want to raise your ISO as little as possible in order to get the shutter speed to a point where it will allow you to get the shot, and no higher. You'll end up with a shot that may require some noise reduction in post-processing, but the less noise reduction required, the more detail you'll be able to salvage from the original scene. Knowing how ISO fits into the concept of exposure, and how it interplays with the other components, aperture and shutter speed, will allow you to utilize it when the situation calls for ISO to be adjusted.