Photo tricks. Part 9.

Today again about the flash.

Photo tricks. Part 9.

Photo tricks. Part 9. Shot on I-TTL BL FP SB-900

I will explain a little how the flash works in automatic mode. Usually, automatic flash mode has a TTL prefix in its name. It stands for very simple - Through the lens - through the lens (through the lens). This means that the flash output is adjusted using the light that has passed through the lens.

This is being done quite interestingly: the flash gives a test pulse of light. Usually, the power of such a pulse is 1 \ 128 of the total flash power. The light from the flash is reflected from what we are photographing, passes through the lens and gets on the sensors of the exposure meter. The sensor transmits the light output power to the camera processor. The processor thinks for a long time, analyzes, and calculates what should be the power of the main flash pulse. The processor knows that the first pulse had a power of, say, 1 \ 128, while the exposure meter received values ​​that did not satisfy the exposure at 3 steps, because the processor makes it clear to the flash that the main pulse should be more powerful at 3 steps, and correspond to 1 \ 16 flash power. This way we get a pretty shot with the right exposure.

The most interesting: in modern central control valves, the probe pulse is practically not visible. It seems that the flash immediately gives the desired impulse of light. But this is not so, in TTL modes the pulses go very, very fast one after another in a strobe mode. The human eye and the human reaction practically do not notice the test impulse.

The test pulse is often called “preflash“. There can be many preflashes, not just one, and their intensity can be different. To be honest, I don't know how much power my Nikon flashes have. SB-910, SB-900. For Nikon, the delay between the test and the main pulse is of the order of 0.4 with.

With flash

With flash. TLL through an umbrella, light blur from command impulses

Important: In conventional digital cameras, the exposure metering system is not so well thought out, and the processors are not so powerful, and the flashes cannot fire a large number of “volleys” at the same time, therefore, I easily notice preflashes on ordinary digital cameras (soap dishes). Also, the test or control pulses of the built-in and external flashes of my cameras and flashes are very clearly visible when working in a creative lighting system. Nikon CLS.

When working in TTL mode, I came across a couple of interesting features:

  1. Many people have a very quick reaction, and when photographing with a flash, they begin to squint at the first impulse, and the main one "draws" them in the picture with narrowed eyes.
  2. Pre-flashes fill the background with excess light, this often gives a blur (contamination) in the eyes of people. No one needs extra reflections.
  3. The flash thus warms up faster and consumes more battery power.

To overcome this ailment, TTL just use the flash in manual flash control. With manual control, the flash output has no test fires, and the flash immediately delivers the main impulse. The beauty of this mode is that:

  1. Blinking of the eyes is completely eliminated. The momentum of my Nikon flash SB-910 has a duration from 1 \ 800 to 1 \ 40.000, during such a time not a single person will have time to blink. Yes, the person blinks, but after the flash, and the light of the flash lamp “draws” a person with open eyes on the photograph.
  2. Reduced blues in the eyes. In the studios, everyone works with flashes with manual power control, there is practically no problem of bluer in the eyes. True, there is another problem, the lighting devices themselves are often clearly visible in the eyes, often of a rectangular shape, which makes the human eyes look like the eyes of cats (not natural).
  3. Recharge lasts faster, no extra energy is wasted. Perhaps the leading number even increases, since the entire dose of light is supplied immediately.

These are the benefits of manual flash control.

Material prepared Arkady Shapoval. Training/Consultations | Youtube | Facebook | Instagram | Twitter | Telegram

Add a comment:



Comments: 58, on the topic: Photo tricks. Part 9.

  • felix

    I wanted to clarify that the flash works all the time at a full rate! it in its prince cannot work for a quarter or half of damage it is a gas discharge lamp it needs voltage and current, constant values ​​that you cannot change! therefore, the control takes place only by time (discharge duration) Nikon SB-910 has a duration from 1 \ 800 to 1 \ 40.000, respectively 1 \ 800 is a total battery life (lamp burns longer) and 1 \ 40.000 is a small battery life (lamp burns less) management time is simpler than managing mosquitoes (in terms of electronics, the time management scheme is very different from the power management scheme, the last cumbersome creation of transformers and capacitors, an unreliable topic you need to wear a photo camera on the flash !!! further on different frauds different light temperatures at there is no good! velechiny continuous power on the flash, change only the discharge time !!!!

  • Zhenya

    Hello! I photograph on D5100 with this flash, in manual mode! I don't use synchronizers. And for some reason, 3 preparatory impulses are triggered (as if there is a TTL) and only on the 4th - the release button is triggered. I can't figure out how to fix it .. Tell me, please.

    • Arkady Shapoval

      Turn off red-eye reduction on the camera.

      • Zhenya

        Found it! Thanks! :)

    • Zhenya

      * SB700 flash

  • Alexey

    Why do you need to control flash power at all? After all, when taking a picture outdoors, regardless of the current illumination, the camera itself selects the desired exposure using the internal exposure meter. The necessary adjustment of ISO, aperture, shutter speed is automatically performed. I believed that the flash should always give out the maximum of its light - let the camera do the rest. Indeed, in bright sunlight, we do not ask the Sun to reduce its brightness to the value we need, but use what we have (thanks to the exposure meter). There is contact between the flash and the camera (via hot shoe). But the control commands should not go from the camera to the flash, but vice versa: the flash should give the camera information about its power. Maybe a pre-flash will be needed here. Why don't TTL flashes have this mode?
    What's the trick here?

    • BB

      Suppose the flash can give the camera information about its power. But the flash cannot give the camera information about what is in the frame, what is around the wall, ceiling, etc. If the flash shone directly into the lens, knowing the flash power, you can calculate the required exposure.
      But then we shoot reflected light, and objects in the frame can have a degree of reflection that differs thousands of times, which is why we need a 'preflash': it gives exactly the lighting that the main flash will give (taking into account all light reflections from objects). This is TTL. Taking pictures on the street, the camera immediately “sees” exactly the lighting that will be at the moment the shutter is released, even before the release itself, and calculates the required exposure. If we could “light up” and “shine” the flash for a few seconds, then we could not bother with preflashes, but this is a very large power consumption, and not very pleasant for the eyes of the subject :) The flash chip is in high energy in a short time - it is very energy efficient.
      If you want to use the “maximum”, you will have to use the “M” mode, and manually select the exposure pair on the camera. If the objects in the frame do not change much, then for one shooting scene, it is enough to select the parameters once.

  • Anatoly

    Tell me who understands, I use SB600 in TTL mode on nikon D3300 + 50mm-1,8-first frame is excellent, subsequent ones are soap, there is no flash in the properties, the shutter speed shows 1 / 2s instead of 1 / 60s

Add a comment

Copyright © Blog author - Photographer in Kiev Arkady Shapoval. 2009-2023

English-version of this article

Version en español de este artículo