Camera flash question

[Wayfall]

Camera: Canon 650D
Lens: Canon 50mm STM 1.8

Hi

I have been to a few events to do photography for friends now and I'm gaining more experience and my pictures look amazing (@kirkephotography Instragram) but there is something that has been puzzling me when I have been doing photography with the stock flash.

I shoot manual at 1/200, ISO 100 and if I use F1.8 the portraits look ace but I want more depth of field so if I turn my cam to F16 the picture is all in focus and the lighting looks the same.

Why is that? I would of thought making the cameras aperture smaller (in so less light) would made the shot way darker but the only difference is the depth of field.

Is the camera doing something in the background when it's rendering the image?

Thanks!

 

[Lutfij]

The F number you're referring to is also in relation to the lens you're using. You can read more about it here. I'm curious though, what mode are you working with?

 

[Wayfall]

Manual 1/200 @ ISO 100. I switch between F1.8, F16 & F22 and it's only when I get to F22 when the picture looks very slightly less exposured.

I fully understand what shutter speed, aperture and ISO is mate.

 

[sisix]

What kind of camera? Shooting inside or outside? How far away are your subject and what kind of background?
I suspect though, that you're not actually shooting full manual, you just think you are because you have it set on "M". If I had to hazard a guess without any information on your camera, I would say that the Auto ISO setting is set, and that as you're adjusting your aperture from f1.8 to f16, your camera, while keeping the shutter speed at 1/200, is adjusting your ISO speed from 100 to something significantly faster. (It's 6 1/3 stops between f1.8 and f16, so, roughly, your ISO needs to bump up to around 6400+1/3 roughly to have the same exposure as 1/200, ISO 100, f1.8)

As an aside, depending on the lens, f16 is really pushing it for taking portraits. You'll start running into diffraction shooting with and aperture that small. Personally, for a portrait, I'd never shoot over maybe f11, and even then that's a LOT of the background in focus.

 

[Solandri]

Why is that? I would of thought making the cameras aperture smaller (in so less light) would made the shot way darker but the only difference is the depth of field.

Putting the camera in manual mode only gives you control of the shutter speed and aperture. Flash exposure with E-TTL systems (electronic through the lens) is handled separately. The camera actually fires the flash twice in rapid succession - the first time it measures the amount of reflected light to determine how powerful the flash needs to be for correct exposure. The second time it fires it "for real" at the correct amount for your exposure settings (shutter speed, aperture, ISO) at the same time the picture is taken.

There are a variety of different E-TTL modes and settings, and obviously there's a maximum brightness your flash can achieve, so beyond some point the picture will become darker (underexposed even with flash). The subject of flash exposure is too broad to cover here, and the exact settings, controls, and modes depend on your particular manufacturer and camera/flash model. That's right, all those buttons and dials on the back of your add-on flash? They actually do something. (If you're using the built-in flash, the settings are buried in the camera options, though lower-end cameras may not give you full control.)

Frankly it was all voodoo enough that when I use a flash with my Canon, I use it in the automatic P mode most of the time, or A mode if I want the background to be lit as well (A mode by default will hold the shutter open after the flash has fired until the parts of the scene not lit by the flash are properly exposed, though you can change this in the settings). I can only think of 2 or 3 times I had to put the camera into M mode and tweak the flash settings manually to get the picture I wanted.

http/cpn.canon-europe.com/content/education/infobank/flash/flash_exposure_lock_and_compensation.do

Basically what happened is when you reduced the aperture to f/16, the E-TTL system fired the first flash, noticed it was getting less light from the flash, so emitted a more powerful flash to properly expose the scene.

Edit: One custom setting I do use frequently is high speed sync. Your shutter doesn't actually expose the entire sensor at once. It's what's called a rolling shutter - at high shutter speeds it's just a slit that moves across the sensor (physical analogue to a CCD's rolling shutter). Since part of the sensor is always covered at these high shutter speeds, a single flash will only light up the part of the sensor which had the slit in front of it. That's not what you want. The fastest shutter speed at which the entire sensor is exposed at once is called the sync speed. If your shutter speed is faster than that, your flash can't expose the picture properly. Unless you put it into high speed sync mode - the flash will rapidly repeat like a strobe light, to ensure that each portion of the sensor exposed by the moving shutter slit will see the same amount of light from the flash.

http/www.bobatkins.com/photography/technical/canon_speedite_high_speed_sync.html