Flash Power - How do I know how much im using per shot?

[prodigy2k7]

So, I havent had much chance to do flash lately, I generally have the basics understood. Question:
I know on my 430 EX II that there is a green light on the back that tells me it was properly exposed (i think?)...

Is there any way to tell how much power my flash is using per-shot? For example im using 90% flash power and my subject shouldn't go any further or risk not being properly exposed by the flash.

So, any way to tell?
Also as my battier start to die I can notice my flash isn't reaching as far, how do I know my batteries are dieing and the subject just isn't too far from me?

 

[KmH]

Is there any way to tell how much power my flash is using per-shot?

Only sort of, because in TTL modes the flash unit fires pre-flashes so it only uses the amount of power needed for each flash, so the power output level is varied. In Manual mode the power output is much more consistant from flash to flash because you set the power output level.

Also as my battier [sic] start to die I can notice my flash isn't reaching as far, how do I know my batteries are dieing and the subject just isn't too far from me?

You can calculate the distance by using the GN number for the flash unit and the lens aperture.

GN = distance × f-number Just use basic algebra to re-write the basic equation so you can solve for the distance.

 

[fokker]

Keith, does that formula only work at ISO 100? Obviously it's a simple process to compensate for at other ISO's, but just wondering if that's the case since guide number's seem to be quoted at ISO100 generally.

 

[TheBiles]

Keith, does that formula only work at ISO 100? Obviously it's a simple process to compensate for at other ISO's, but just wondering if that's the case since guide number's seem to be quoted at ISO100 generally.

The guide number doubles for every two stops of ISO, IIRC. So that 43 guide number at 100 ISO would be 86 at 400.

Sent from my Galaxy Nexus

 

[Bukitimah]

When you tilt the flash gun or add a diffuser, will it affect the flash power required since the 'TTL' would not be able to calculate that OT it actually is smart enough to do just that. I was told that if the subject is light color, the TTL may give a wrong power to the flash. Can anyone explain?

 

[KmH]

When you tilt the flash to bounce it, or put a diffuser on it, more light gets scattered throughout the scene you are shooting making it harder for TTL to make it's guess what your intended main subject is.

 

[DiskoJoe]

So, I havent had much chance to do flash lately, I generally have the basics understood. Question:
I know on my 430 EX II that there is a green light on the back that tells me it was properly exposed (i think?)...

Is there any way to tell how much power my flash is using per-shot? For example im using 90% flash power and my subject shouldn't go any further or risk not being properly exposed by the flash.

So, any way to tell?
Also as my battier start to die I can notice my flash isn't reaching as far, how do I know my batteries are dieing and the subject just isn't too far from me?

Read your manual. It should give you an estimate about battery life given certain types of batteries and shooting modes. Rechargable batteries usually hold the best charge for a flash and are eco friendly!

 

[12sndsgood]

lesson ive learned when it comes to batteries is just use rechargeables and replace them before every shoot. i carry extra batteries with me always. but as I learned last week when running off the bridge and back down to the car because i was loosing my light, its just easier to swap them out rather then try and run them till there dead.

 

[bledererphoto]

Recycle rate is a good indicator. The ready light will come back light quickly when in ttl mode if not shooting continuously and when that light takes longer then the batteries are starting to go. Once ready light lit the flash should have the same power as before is camera metering the same.