This article is very technical – please don’t be alarmed if not everything is clear at the beginning. I am very sure that once you have familiarized yourself with the subject, you will find very good starting points here to delve deeper into the subject of flash.
The technical basics of flash – or: What actually happens when it goes “Flash!”?
The first time you consciously photograph with flash, it often looks like luck or coincidence. Sometimes the picture is too bright, sometimes too dark, sometimes it looks like something out of a horror movie – and very rarely is it just right. But don’t panic. Flash photography is not witchcraft – it’s physics. And you can understand it.
What happens when you flash?
A flash is – technically speaking – simply a very short, very bright pulse of light. It only lasts a fraction of a second, often only 1/1000 of a second or less. This is much faster than most camera shutter speeds – and this is where the issue of synchronization comes into play.
Synchronous time – why the right time counts
Your camera has a shutter that opens and closes so that light falls on the sensor. The flash must fire exactly when the sensor is completely open – otherwise you will only have a bright strip on the picture, for example. This is called the sync speed (often between 1/160 s and 1/250 s, depending on the camera).
A few simple scenarios:
- You use a shutter speed slower than the sync speed (e.g. 1/60 s): The flash fires – everything is fine. The existing ambient light is also recorded. This can make the image appear softer or more “natural”.
- You are using a faster shutter speed than the sync speed (e.g. 1/1000 s): The shutter is not yet fully open when the flash fires. Result: Parts of the image are black or unevenly lit, with the exception of high-speed sync – more on this later in a separate article.
Designing with shutter speed and flash
Now it gets exciting: you can use the combination of flash and shutter speed to control how much of the ambient light ends up in the picture:
- Slow shutter speed + flash = you use the available light and only use the flash as an accent (e.g. at a party).
- Fast shutter speed + flash = you “eliminate” the ambient light – the image is only determined by the flash, ideal for studio looks or dramatic portraits during the day.
1/10″ | f5.0 | ISO12800
Not all flashes are the same – what types are there?
- Clip-on flash: Classic flash for the camera, is often plugged directly into the hot shoe. Versatile, compact – often underestimated.
- Compact flash / system flash: Small, flexible all-rounders – often with zoom reflector, TTL and rotatable head.
- Studio flash: High output, long service life, perfect for controlled light setups. Usually require mains power or fat batteries.
- Ring flash: Round, sits directly around the lens – creates shadow-free, flat illumination. Ideal for macros or a certain “fashion” look.
- Mini flash, cell phone flash: Yes, these are also flashes – but with very limited control.
How does lightning actually ignite?
There are various ways to trigger a flash:
- Direct contact to the camera (hot shoe)
- Sync cable (old school, but very reliable)
- Radio control (today standard, allows unleashed flash)
Three important terms you should know
- Guide number (LZ): Indicates how powerful a flash is. The higher the number, the more “oomph”. Rule of thumb:Guide number = distance × apertureExample: Guide number 40 = aperture 4 at a distance of 10 m
- Color temperature: Flashes usually have a color temperature of approx. 5500 K – i.e. “daylight white”. But: Mixing with warm room light can cause color shifts → use a filter or white balance!
- Flash duration: How long the flash actually lights up – often shorter than the shutter speed. The stronger the flash, the longer it usually burns. Flash duration also influences whether you can “freeze” movements.
Flash output, ISO, aperture, shutter speed – the interplay
Everything comes together here:
- ISO high = less flash power required
- Aperture open = more light in, less flash required
- Flash output high = more light, but possibly harder / longer flash duration
- Shutter speed? (Usually) only affects the ambient light – not the flash!
Important: You are “exposing” two worlds at the same time:
Flash + ambient light = total image
Conclusion: Understanding technology means gaining control
Flashing is not a game of chance – if you know when your flash fires, how much light it provides and how your camera settings affect it, you have the picture in your hands. And suddenly it’s not so complicated anymore – it’s actually pretty cool.
