There is no single best ISO, but there is a reliable way to choose one. This lesson gives a cheat sheet of starting values, a recommended Auto ISO setup and a short routine to follow whenever the light changes.
The one rule
Use the lowest ISO that still gives a shutter speed fast enough for a sharp photo. Everything below is an application of that sentence.
ISO cheat sheet
| Situation | Starting ISO | Typical aperture and shutter speed |
|---|---|---|
| Beach, snow, bright sun | 100 | f/8, 1/500 s |
| Outdoor portrait in shade | 200 | f/2.8, 1/250 s |
| Overcast street or travel | 400 | f/5.6, 1/250 s |
| Indoors by a window | 800 | f/2.8, 1/125 s |
| Home interior in the evening | 1600–3200 | f/2, 1/60 s |
| Indoor sport or school play | 3200–6400 | f/2.8, 1/500 s |
| Night street, handheld | 3200–6400 | f/1.8, 1/60 s |
| Sunset landscape on a tripod | 100 | f/11, 1/2 s |
| Starry sky on a tripod | 3200 | f/2.8, 15 s |
Treat these as a first guess. Take a test shot, check sharpness and brightness, then adjust.
Know your minimum shutter speed
ISO is chosen to protect the shutter speed, so you need to know what shutter speed you need.
- Camera shake: use at least 1 divided by the focal length. With a 50 mm lens that is 1/50 s; with a 200 mm lens, 1/200 s. On an APS-C camera, multiply the focal length by 1.5 first. Image stabilisation allows slower speeds for still subjects.
- People standing or sitting: 1/125 s.
- Children and pets: 1/500 s.
- Sport and birds in flight: 1/1000 s or faster.
If the camera shows a slower speed than the subject needs, raise the ISO one stop at a time until it does not.
Recommended Auto ISO setup
For general photography, Auto ISO with sensible limits is the most practical choice for a beginner.
- Switch ISO to Auto.
- Set the maximum to 3200 on a small-sensor or older camera, 6400 on a recent APS-C camera, or 12800 on a recent full-frame camera.
- Set the minimum shutter speed to 1/125 s for everyday use, or 1/500 s for action.
- Shoot in Aperture Priority and choose the aperture yourself.
The camera will hold ISO at its base value in good light and raise it only when needed. Use manual ISO instead when working on a tripod, with flash, or when you want every frame in a series to match.
Find your own camera’s limit
Published advice about a “maximum usable ISO” is only a guide. The honest answer comes from your own camera and your own standards. Photograph the same indoor scene at every full ISO step, view the results at the size you normally share or print, and note the highest value you are happy with. Set that as your Auto ISO maximum.
A routine for changing light
- Arriving somewhere new, glance at the shutter speed the camera is giving.
- If it is too slow, open the aperture if the picture allows it.
- If it is still too slow, raise the ISO.
- When moving back into bright light, bring the ISO back down.
Common mistakes
- Keeping ISO at 100 at all times because “low is best”, and coming home with blurred indoor photos.
- Setting an Auto ISO maximum that is too cautious, such as 800, which forces slow shutter speeds.
- Raising ISO before trying a wider aperture.
- Not checking the ISO at the start of a session.
- Using the built-in flash to avoid high ISO, which usually gives flatter and less natural results.
Practice exercise
- Set up Auto ISO with the limits described above.
- Walk from outdoors into a building and through to its darkest room, taking a photo every few steps in Aperture Priority at f/4.
- Review the files and read the ISO and shutter speed recorded for each one.
- Identify the point where the camera reached its maximum ISO and the shutter speed began to drop. That is the limit of handheld shooting at f/4 in that light.
Next in this series: What Is ISO in Photography?, High ISO vs Low ISO Explained and How to Balance ISO, Aperture and Shutter Speed. You can also browse all photography lessons.
