430 ex Guide # distance scale

Hey all.....have barely used my 430 ex in the past except for some quick headshot portraits and fill light.
I shoot in manual, flash in manual off camera.
Question: How do i figure out what my distance should be or flash power should be based on my aperature? You know how it tells you in ttl i think....when the flash is shoe mounted, I can lower the power and it tells me the distance based on my aperature.
Is there a way to manually figure this out?

It is made much more complex due to the zoom head...the Guide Number is dependent upon the area of coverage...at 24mm the Guide Number is lower than at 50mm and that is lower than it is at 105mm, for any specific power level of the flash.

Just take a shot, chimp it and then adjust your flash power as needed.

Tiberius47 wrote in post #14031548
Just take a shot, chimp it and then adjust your flash power as needed.

lol! i knew that was coming! I think it may be best after all though.

Page 36 of your user manual has a listing of power level, angle of coverage, and the Guide Number to match.

Guide Number = Distance * f/stop

F/stop = Guide Number / Distance

Distance = Guide Number / f/stop

Keep a copy of this page in your camera case, and you would be able to do all the calculations that caused you to start this thread.

Wilt wrote in post #14031758
Page 36 of your user manual has a listing of power level, angle of coverage, and the Guide Number to match.

Guide Number = Distance * f/stop

F/stop = Guide Number / Distance

Distance = Guide Number / f/stop

Keep a copy of this page in your camera case, and you would be able to do all the calculations that caused you to start this thread.

Wilt,

I had these formulas tattooed backwards across on my butt over 36 years ago, only to realize the huge size of the mirror I needed to read it was price and area prohibitive.

Enjoy! Lon

FlashZebra wrote in post #14031790
Wilt,

I had these formulas tattooed backwards across on my butt over 36 years ago, only to realize the huge size of the mirror I needed to read it was price and area prohibitive.

Enjoy! Lon

Remembering the formulae is the easy part, these days. You would now have to have the whole d*mn chart from page 36 tatooed on your beer belly, now that we have zoom heads. At least it would be easy to read, if it were tatooed upside down so as to be readable by you! Then there is the issue of having two different flash units in your bag, with different power levels, to contend with. Question is, what grew more, the butt or the belly?!

Keep in mind:

Guide number specifications come from flash meter readings at the end of a narrow, mirror-lined hallway.

I don't know that for sure, but it seems to be about the only way to achieve the specified readings.

If you have a light meter, you can figure out the "real" guide number of a flash. But it will vary according to the indoor "bounce factor," which varies quite a bit. Add that to the zoom factor and you're generally better off with the "guess-chimp-adjust" method previously mentioned.

Wilt wrote in post #14031872
Remembering the formulae is the easy part, these days. You would now have to have the whole d*mn chart from page 36 tatooed on your beer belly, now that we have zoom heads. At least it would be easy to read, if it were tatooed upside down so as to be readable by you! Then there is the issue of having two different flash units in your bag, with different power levels, to contend with. Question is, what grew more, the butt or the belly?!

Correct me if I am wrong but I though Jeremiah was a bullfrog.

Enjoy! Ms. Calamity Jane, nature lover

Curtis N wrote in post #14032042
Keep in mind:

Guide number specifications come from flash meter readings at the end of a narrow, mirror-lined hallway.

I don't know that for sure, but it seems to be about the only way to achieve the specified readings.

^

IOW, manufacturer Guide Numbers are about as reliable a way to calculate flash exposure as a politician's promises made during his/her campaign to be elected.

In truth, if you take the manufacturer Guide Number and divide by 1.4, you will be much closer to the reality of a flash meter reading. This is true of any flash manufacturer, and their inflated claim.

Wilt wrote in post #14032262
^

IOW, manufacturer Guide Numbers are about as reliable a way to calculate flash exposure as a politician's promises made during his/her campaign to be elected.

In truth, if you take the manufacturer Guide Number and divide by 1.4, you will be much closer to the reality of a flash meter reading. This is true of any flash manufacturer, and their inflated claim.

thank you all for the info and humor!
I guess I really did not put much thought into using my flash in a sensible way.
I don't quite grasp how the Zoom on my head affects my distance. basically, i did not understand my manual!

1downfall wrote in post #14035565
I don't quite grasp how the Zoom on my head affects my distance. basically, i did not understand my manual!

The flash zoom lens spreads light out over a very wide area (e.g. 84 degree wide at 24mm coverage angle, or it focuses it down into a narrow cone (23 degrees at 105mm coverage angle), and it also covers many coverage settings in between those two extremes.

The flash tube only outputs a given number of photons of light. So if it spreads those photons across a wider area, fewer photos per square foot fall onto the subject...less light. So if it focuses those photons across a smaller area, more photos per square foot fall onto the subject...more light. If there is less light, then f/4 captures sufficient light out to a shorter distance; with more light, then f/4 captures sufficient light out to a longer distance.

Wilt wrote in post #14035598
The flash zoom lens spreads light out over a very wide area (e.g. 84 degree wide at 24mm coverage angle, or it focuses it down into a narrow cone (23 degrees at 105mm coverage angle), and it also covers many coverage settings in between those two extremes.

The flash tube only outputs a given number of photons of light. So if it spreads those photons across a wider area, fewer photos per square foot fall onto the subject...less light. So if it focuses those photons across a smaller area, more photos per square foot fall onto the subject...more light. If there is less light, then f/4 captures sufficient light out to a shorter distance; with more light, then f/4 captures sufficient light out to a longer distance.

I have always enjoyed your explanations! ty Wilt.

Wilt wrote in post #14032262
^

IOW, manufacturer Guide Numbers are about as reliable a way to calculate flash exposure as a politician's promises made during his/her campaign to be elected.

In truth, if you take the manufacturer Guide Number and divide by 1.4, you will be much closer to the reality of a flash meter reading. This is true of any flash manufacturer, and their inflated claim.

This thread saved my sanity. I guess guide numbers are old school but I still wanted to learn them. When I looked up the guide number based on my calculation of (distance x f stop) in the canon manual and set my flash power all my images were coming up underexposed.

Then I took the guide numbers in the chart and divided them by 1.4 all of sudden my exposures were pretty much dead on.

Thanks Wilt for saving my sanity. I thought there was something I was missing.

iamjediknight wrote in post #14924138
Thanks Wilt for saving my sanity. I thought there was something I was missing.

The only thing you were missing is understanding how they come up with their inflated claims.

(Wait a minute, I'm sorry I drifted to a political statement! Once again, back to photography...)

I don't understand that, myself.