Canon never figured out how to make usable Auto ISO settings while using flash. You can workaround on some cameras. But on the others, you limited and you can’t make the process completely automated. You need the middle to high end of the cameras. I know it will work on 5D Mark III, 6D, 1D X Mark (II), but not on 550D, 600D, 800D. I didn’t try on other Canon cameras.
Here is the idea. I want certain aperture because I want to control the depth of field and sharpness. I want certain shutter speed because I want to avoid camera shake and to freeze people. But I want ISO to be auto so the camera can have automatic exposure to ambient (background) light. And with TTL flash, preferably bounced, to assure I have good light for the people. In the old days, you often have to choose between ambient light or flash light.
But today is much easier to combine both lights. Thanks to amazing high ISO results of the cameras, and great AF speed and precision with prime lenses. Today you can use high ISO and very open aperture to take much ambient light. And then add a little bit flash to “wash up” faces of the ambient light colors. This looks very good especially if you have warm light for the background and cooler light for the faces. Doesn’t sound that good written. But with right white balance, this color difference really works.
Problem is Canon auto ISO setting that is stuck back in the old days. If you use Av or Tv mode and put ISO auto, the camera will set ISO to 400. Camera assumes that flash is going to do all work for lighting and ISO 400 will keep the noise level down. Also, in AV mode shutter speed can go very slow. But again, the camera assumes that flash only is going to light the scene. And that is why is shutter speed irrelevant.
Because flash is actually much faster than camera shutter speed. And you can shake camera very much, but still get a sharp picture, if you light the scene only with flash. In this case, the camera catches the very high-speed light made by flash. And later only dark that doesn’t affect the picture. Theoretically, you don’t have to care about shutter speed if you use flash as the only source.
But if you want a modern picture with a combination of ambient light, things are much complicated. You have to care about shutter speed too. Because movement and camera shake will affect picture if you want to use much ambient light. Also, if you want to use the much ambient light you need higher ISO values. And if you want everything to be automated, you need Auto ISO. But Canon will set ISO 400 only if you set Auto with flash. Which is ridiculous.
1. Use Av mode. This way you can control a depth of field and lens sharpness.
2. Go to the “ISO speed settings” in menus. This is always on some page on first (red) menus.
3. Inside you will find “Minimum shutter speed” option. If you don’t have this option, probably you are not able to complete settings. Because possibly you don’t have a much important setting for the next step. Set this to 1/125 if you have a crop or little older camera, dark background and station subjects. Set 1/200 or 1/250 if you have better high ISO camera, better light for background/ambient and fast-moving subjects (kids). You can try both settings with all cameras in all situations. It is not crucial setting. It can add or save a little noise or make or break some fast moving picture.
4. Find “Safety shift” option in your camera menus. Check user manual if you need, or Google. This setting is in different places in menus but is almost always in orange Custom Function (C Fn) menus. Pick option “ISO Speed.” This setting means that camera will automatically change ISO if exposure is wrong.
5. Be sure that High-Speed Sync option is OFF on your flash.
6. Set ISO settings manually to very high value. For full frame cameras, you should set at least 6400, but you can go higher. 12.800 will be ok for most cameras, even 25.600. Don’t worry. The camera will use this high ISO setting only if needed (rarely), thanks to setting from step 4.
7. Change exposure compensation of both ambient exposure and flash exposure. You should set normal (ambient) exposure compensation at least -1EV. Use TTL capable flash in automatic (TTL) mode. Flash exposure compensation depends on your flash, surrounding and camera body. Should be somewhere between 0 and +1EV, but this is generally real life adjustment. Even without this tutorial.
What have we achieved?
First of all, we have complete aperture control. Second, we have optimum shutter speed. Because shutter speed for this kind of shooting should be between 1/100 and sync speed of your body. That is from 1/180-1/250. We have Auto ISO by tricking camera. We will set very high ISO, but the camera will make ISO setting lower automatically for each shot. Thanks to the setting from step 4. With exposure compensation, we are able to control ambient light. With flash exposure compensation we are able to control light for the people.
Be sure to put ambient exposure down, in minus. Because you need to leave “space” for flash to add some of its power. Sometimes exposure can be good without flash and flash will make people overexposed. Because camera will always fire the flash. Making ambient light a little bit darker is not just advice to avoid overexposing people. This way you will get nicer photos. With better light balance.
Let me be clear. This is not the best way to control camera and flash exposure. This is settings made for situations where you don’t have control. Weddings, birthdays, company events, any fast-paced situation indoor and/or during the night can be photographed this way. The best part is you can go from very dark to very bright ambient light and maintain good exposure. For ambient and flash exposure. Because we tricked camera to automatically use ISO higher than 400.
Thank you for reading.
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