I don’t understand how using a flash can freeze motion better than ambient light. In the end, isn’t it all just light hitting the sensor?
I don’t understand why it would do this. I mean it’s not necessarily like the camera knows and is like “Oh they’re using flash, I’ll be nice and give them a sharper picture’. I mean obviously they don’t think like that, but all in all it’s light luminating the subject and hitting the sensor, why does something like the source of the light affect how much motion can appear in your image?
In: Technology
I think the camera does know? Or rather, you’re able to use a shorter exposure time since the light is more intense, and thus less chance for blurriness. When you have ambient light only, the exposure has to be a tick longer which allows for movement to be “captured” as blurriness.
Because a flash is far more intense than natural lighting. You could get images just as shape if you setup lighting, and then you wouldn’t need a flash.
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When a camera takes a picture it collects a specific amount of light. You can stop motion in two ways. Instead of a camera, imagine a really large window with a curtain. If you could open/close the curtain really fast, 1/1000s, it would let in enough light and stop the motion. When you have a flash, it’s a bit different. Instead of a really large window, you have a tiny window. To get enough light you need to hold the curtain open longer. However if you hold it open longer you can’t stop the motion. Instead we flash a really bright light at 1/1000s. The motion is stopped because the bright light is only on for a short period of time.
The camera does not capture the image instantly. It collects light over some amount of time called the *exposure* time. The longer the exposure time, the brighter the image, but in turn objects have more time to move and if they move during the exposure they will be blurry in the final image and the level of blur is proportionate to how much they moved, more movement -> more blur.
A flash makes the subject brighter, allowing us to use a *shorter exposure time* to achieve the same brightness in the final image, while giving less opportunity for movement and blurring.
The flash pulse is very short — in the order of 0.005 of a second or less. It’s also bright enough to deliver an exposure of the subject in that time which wouldn’t appear with ambient light.
Photographers often tweak the exposure to create interesting effects with longer exposures and strobe, such as car lights trailing behind the sharp image of the car.
Cameras have 2 main settings that affect picture quality: Aperture size (how much light gets in) and Shutter speed (how long the film or sensor is exposed).
A larger aperture lets in more light, as does a slower shutter speed. The tradeoff is that larger apertures allow less of the photo to be in focus, and slower shutters allow motion blur.
By using the flash, you increase the amount of available light, allowing smaller apertures and faster shutters to achieve the same brightness as larger and slower without flash. In return you get more of the photo in focus, and less motion blur, which overall creates much sharper images.
Imagine it was super dim. To get an image you’d need to leave the shutter open for a super long time. And everything will move around and get blurred.
likewise if you make it super bright you can have the shutter open a super short time. A flash makes it super bright
The less light there is, the more time a camera needs to get the picture (this is called shutter speed). The longer a camera takes to catch a picture, the more things move, which can cause motion blur.
A flash is an intense amount of light, which means the camera needs less time to get the photo and there is much less chance for things to move. The “freezing” is a lack of motion blur.
The sensors in the camera collect light over time. If there is not much light, they can’t collect very much and the picture ends up too dark to see anything. To fix that, the camera can collect light for a longer amount of time until the picture is bright enough to see. However, if the subject of the picture moves during that time, they will appear blurry because the camera collected the light from them in multiple places.
The best solution is to have a lot of light so the camera can collect enough in a very short time, before the subject has a chance to move enough to look blurry.
Modern cameras can sense how much light there is and automatically adjust the amount of time they spent capturing it.
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