Got a flash, how do I use it?

TelePaul

Okay, slight hyperbole aside, I picked up a 430 EX II and am very impressed with basic attempts at lighting indoor scenes. My problem is that I've been playing around with it with my camera on full-auto: f4.0, 1/60 shutter speed. And it works fine. The thing is, I'd like to use it to shoot macro, which means stopping the lens down to 2.8 on my 100mm macro.

My question is, how does metering factor into this equation? If I'm at f2.8 with a reasonable shutter speed of 1/180, the meter shows under-exposure. I'm assuming this is expected behaviour, and that it doesn't recognise the flash. So am I right in thinking that in this way, obtaining a correct exposure is a case of trial-and-error?

Example below, (f2.8, 1/160)


Flower 2 by paulrichardoleary, on Flickr

Borderfox

Switch to manual and choose shutter speed and aperture and let the flash sort out the exposure, this is what ettl is helpful for. If it looks too dark up the iso, lots of experimenting

Thecageyone

Been trying similar lately. But I only have macro rings with no af which makes it trickier again when also hnd holding the flash. It's all trial and error for me as my flash doesn't do ttl. If you're using a diffuser that will effect the flash power too.


Narrower apertures are always recommended for this type of work. Stop the lens right down for more detail and try the flash at different levels manually. 1/2, 1/4, 1/8 until you're getting nice fill flash not blowing detail out.

DaireQuinlan

TelePaul wrote: »

Okay, slight hyperbole aside, I picked up a 430 EX II and am very impressed with basic attempts at lighting indoor scenes. My problem is that I've been playing around with it with my camera on full-auto: f4.0, 1/60 shutter speed. And it works fine. The thing is, I'd like to use it to shoot macro, which means stopping the lens down to 2.8 on my 100mm macro.

My question is, how does metering factor into this equation? If I'm at f2.8 with a reasonable shutter speed of 1/180, the meter shows under-exposure. I'm assuming this is expected behaviour, and that it doesn't recognise the flash. So am I right in thinking that in this way, obtaining a correct exposure is a case of trial-and-error?

Example below, (f2.8, 1/160)

your meter will only ever show you the ambient measurement. What to do next depends on whether your camera/flash actually does TTL flash metering. If it does then you probably don't need to sweat it, might take a few shots to get the flash in the right position WRT what you're shooting, but once you've done that just pick any shutter speed below your sync speed, and pick an aperture to suit and fire away. With macro stuff and a handy flash it's probably best to stop down a lot f/8 f/16 or so to get reasonable DOF. The flash will be more than able to light the subject.

If you're using a manual flash then yeah, a bit of trial and error is probably called for. Just experiment with different powers on the flash 1/2 1/4 1/8 etc until the shot looks exposed correctly. This can be a bit of a PITA, particularly with moving subjects (although you can more or less calibrate for a particular distance and then be reasonably sure you'll get the correct exposure at that distance), TTL flash metering is a godsend for macro.

With an even halfway decent flash you probably won't have to up the iso if you're shooting at macro distances, even stopped down. They should put out a ton of power at that distance.

mehfesto

Agree with DQ.

Remember: Shutter speed has no effect on flash exposure, so you can bring your shutter speed to say 1/40 and allow the shadows to be filled in without fear of the flash exposed area being overexposed.

TelePaul

Thanks all, this has been very illuminating (awesome pun intended, because it was intended). But like many of my posts here it's left me with a few further questions. So, just by way of clarification:

1) The light-meter in my camera will never compensate for the presence of a flash
2) The TTL metering will decide how much power to give to the flash release based on the aperture and shutter speeds employed
3) The length of time for which the shutter is open has no impact on how much flash light is absorbed

That about right?

Thanks again chaps.

Borderfox

Check this out http://lightenupandshoot.net/ and purchase the v-book (only €9) superb explanations of flash/off camera flash.

DaireQuinlan

TelePaul wrote: »

Thanks all, this has been very illuminating (awesome pun intended, because it was intended). But like many of my posts here it's left me with a few further questions. So, just by way of clarification:

1) The light-meter in my camera will never compensate for the presence of a flash
2) The TTL metering will decide how much power to give to the flash release based on the aperture and shutter speeds employed

Aperture and iso, but pretty much, yes.

3) The length of time for which the shutter is open has no impact on how much flash light is absorbed

No, so long as you're shooting under your sync speed. Probably 250 or 200 depending on your camera. Actually most modern bodies and flashes have some form of high speed sync which means you can shoot at higher than sync speeds at the cost of some flash power but that's unneccessary complication ATM.

FoxT

I found this excellent: http://photonotes.org/articles/eos-flash/index3.html#wireless

It is long, and a bit technical - but worth the slog. Here are a few quick answers to your q's:

1) The light-meter in my camera will never compensate for the presence of a flash

CORRECT.

2) The TTL metering will decide how much power to give to the flash release based on the aperture and shutter speeds employed

TTL works like this: When you press the shutter button, the flash will fire. an inbuilt flash meter in the camera body measures the amount of light reflected from the subject. It then factors in ISO & aperture setting, to determine how strong a burst of light is needed in order to expose the scene correctly.


Next, the camera opens the shutter & closes the aperture to whatever it is set to. THEN it fires the flash at the level it had calculated earlier.



3) The length of time for which the shutter is open has no impact on how much flash light is absorbed

Correct. The flash lasts for between 1/20,000 and 1/1000 of a second, approximately. If using flash, your shutter speed will be 1/250th of a sec or slower. Slowing the shutter will not let in any more light from the flash, ( because the flash has already fired) but it will let in more light from the scene as a whole, unless you are shooting in absolute darkness.

-FoxT

the_syco

Borderfox wrote: »

Check this out http://lightenupandshoot.net/ and purchase the v-book (only €9) superb explanations of flash/off camera flash.

Cheers. was searching the forums for something like this, as I got a Nissin Speedlite DI 622 Mark II for my 450D yesterday.