ISO and Shutter Speed for Headshots
This is perhaps the most annoying part of digital photography, especially when you find yourself shooting in low light situations. Dealing with noise and camera shake in the shots is not fun at all. To help you with this, I’ll try to explain the solutions I have found that work best for me.
Typically, to avoid camera shake, you should always shoot at a shutter speed that is the inverse of the focal length. For instance, if you shoot at 100 mm, you should shoot at a shutter speed of 1/100th of a second. If you shoot at 200 mm, shoot at 1/200th of a second. The formula would be 1/F (F=Focal Length)
This seems simple, right? But what if you are shooting on a crop sensor? Things change a bit. In that case, you'll have to multiply the number by 1.5 (or whatever the crop factor is). So instead of shooting at 1/200th of a second, it would be 1/300th of a second. The same goes for 1/100th of a second. In that case, it would be 1/150th of a second.
If this is sounding a bit complicated, I’ll give you a simple solution: shoot at least 1/320th of a second. This speed is usually fine and gives sharp images most of the time without much camera shake.
Now, to turn the talk to ISO, simply understand that the lower the ISO, the better. The reason is simply because high ISO images appear grainy and unprofessional. They tend to lose detail that should otherwise be there. Therefore, I set my ISO at the minimum needed with an aperture of f/2.8 and shutter speed of 1/320th of a second. Just remember that the more light available, the better. You don't want to have to boost the ISO and at the same time, you also don’t want to open the aperture too wide. Otherwise the subject’s ears will start looking really blurred and the image will look grainy. Generally, you should try on a modern camera to use ISO 800 or lower. That number will increase over time as cameras get better sensors, but as of this writing, 800 ISO or lower is good.
Remember: always keep your camera in Manual mode. If you don’t, you’ll face all sorts of exposure issues. For one, the camera will not get the exposure correct every time. Two, you may have images that have too much camera shake because the shutter speed was too slow. Three, the images won't all be the same brightness, so you'll have a lot of adjusting to do in post. Four, you don't want the on camera flash popping up in the middle of shooting. That would just be embarrassing. And if you don't know why, then you probably shouldn’t be reading this article.
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