430ex II v. 580ex II power

I want to fire about 6 times using continuous shooting with my XSI (3.5FPS) on subjects about 20' (6m) away in poor light (not darkness).

Will the 430exII be suitable for my needs, or will I run out of charge before all my shots are illuminated? If so, will the additional capacity of the 580exII allow me to do this?

58/43=1.35
That means the 580EX will give you about 35% more reach, all other factors being equal. Looking at it another way, it's nearly a 1-stop difference.

But that doesn't answer your question.

To shoot 6 continuous shots, your flash will need to be shooting at about 1/8 power or less. At 1/8 power, the 580EX II has a guide number of between 32 and 67 feet, depending on the flash zoom setting.

To reach 20 feet with a GN of 32, you'll need an aperture of f/1.6 at ISO 100, or f/3.2 at ISO 400, or f/6.4 at ISO 1600.

To reach 20 feet with a GN of 67, you'll need an aperture of f/3.4 at ISO 100, or f/6.8 at ISO 400, or f/13.6 at ISO 1600.

I don't know the exact guide numbers of a 430EX II at 1/8 power (and I'm too lazy to look them up), but they're going to be about 75% of the guide numbers of the 580EX II.

So those aperture values I listed above would need to be multiplied by about 0.75 if you were using a 430EX.

Keep in mind these numbers are all approximations, but they should give you an idea.

I just tried my 580EX II for you.....

My 580EX II will do 7 shots at 6fps, 1/8 power f/4.5, and ISO 200, and reach about 6 meters.

It will do 11 shots at 3fps, 1/8 power f/4.5, and ISO 200, and reach about 6 meters.


The 430EX II should also do it, but you will have to increase the ISO to 400 or 800.

Wow, well done curtis. OP: there is your answer right there!

Thanks for the detail guys! Here's an example of some of the most demanding shooting I'll be doing, using the pop-up flash in my XSi

SO, if my subject is at 10-20 feet, using 18mm f/3.5 on my crop body, I could probably get away with a 430exii unless I want to bounce my flash.

Using 18mm will cause the flash head to zoom to wide angle and that will reduce the available light. You will need to experiment but you might end up needing to use ISO 400 or 800 even with the 580EX II.

(EDIT: I just tried my 580EX II at 17mm and it will reach to 6 meters at ISO 400 at 1/8 power and f/3.5)

If you haven't bought it yet I would recommend the 580EX II because of the extra power and many other additional features:

Threaded PC socket
External AutoFlash Exposure Sensor
Weather Sealing
Control Wheel
Pull-out catchlight panel (white card)
Flash head tilts downwards
Flash head swivels full 180° both left and right
stroboscopic (MULTI) flash
Master/Slave Capability
Flash exposure bracketing (FEB)
High voltage input port
Rapid-fire mode
"Save Energy" override control

Thanks very much for taking the time to try this out for me, and thank you internet for making junk like this possible.

I think I will get a 580! Can already hear my wallet whimpering.

msowsun wrote in post #6619059
Using 18mm will cause the flash head to zoom to wide angle and that will reduce the available light. You will need to experiment but you might end up needing to use ISO 400 or 800 even with the 580EX II.

(EDIT: I just tried my 580EX II at 17mm and it will reach to 6 meters at ISO 400 at 1/8 power and f/3.5)

If you haven't bought it yet I would recommend the 580EX II because of the extra power and many other additional features:

Threaded PC socket
External AutoFlash Exposure Sensor
Weather Sealing
Control Wheel
Pull-out catchlight panel (white card)
Flash head tilts downwards
Flash head swivels full 180° both left and right
stroboscopic (MULTI) flash
Master/Slave Capability
Flash exposure bracketing (FEB)
High voltage input port
Rapid-fire mode
"Save Energy" override control

Something to consider in your decision is the current rebate + microsoft live cashback (on ebay) program get the price of 580EX II's to really cheaper than the going rate for a 430EX II.

$420 MSRP
$ 50 Canon Instant Rebate
---------------
$370 Current Market Price on ebay from real camera shops who offer USA units with USA warranty and hence... the USA $50 rebate applied

Using the MS Live Cashback on ebay - 25% off Up to $200 total per transaction. Takes $92.50 off the price

$370 - $92.50 = $277.50 Thats a steal for one of the best flashes ever made.

Food for thought.

-Alan

For this type of thing get a 580EX II and a CP-E3 battery pack. The battery packs are invaluable, I have two.

nureality wrote in post #6619548
Food for thought.

-Alan

Blah, I hate Microsoft. It's a done deal anyway, thanks boys.