External flash or hot-shoe

In this photo I first measured the ambient light was out in the background. I gave the measurement f / 8 to 1/50 using ISO 100. I put those values ​​into my camera.

Because I was using an automatic flash, I put on the flash I was using ISO 100 and was going to use an aperture f / 8. And with these values ​​take the picture. As you can see both the girl and the background are properly exposed.

If I put a diaphragm in the flash different than I have in the camera, unless it is to correct the light, the picture I can get over-exposed or under exposed.

In the next photo I put the same values ​​in the camera in the photo above, or f / 8 to 1/50. But I put the flash that he would use f/16.

Basically, when you dial f/16, I'm telling the flash that I will use smaller aperture so, what will do the flash? You will shoot more light to illuminate the picture. The photo below is the result. As you can see is a picture that does not work.

Of course there is always a distance limit because the flash has a minimum power and maximum power is going to shoot.

If I get too close to the main subject the picture I will come out overexposed. What I have to do is remove the flash until the picture goes well exposed.

If I stray too much, as the flash has a maximum power that can shoot, the subject is going to sub me exposed.

The solution is to bring the main subject flash until it goes well exposed.

If we have a TTL flash and we will use it in TTL, to put the ISO and aperture on the camera, the flash will directly read this information and will trip the light needed for those values.

So if for example I am taking a picture at ISO 200 F/5.6 and I will use the flash light will shoot the picture at ISO 200 f/5.6 goes well exposed.

TTL flashes will also give you a scale of maximum and minimum distance at which you can take a picture with a given aperture.If you put the flash closer to the main subject will come out over exposed and if you put the flash further away the main subject is exposed to sub out.

In the photo below you can see the red box in the ISO (ISO 200), in the yellow square aperture (f/5.6), in the blue box I'm using the lens (200mm) in the green box and the minimum distance and maximum which may be the main subject flash (9 to 13 meters).

Beyond properly expose the background and the subject, there are different creative ways to use the flash. Let's see some of them.

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