help with tips for shooting with flash in full manual

I have a 430EX and to date have only shot in E-TTL mode. For the most part I'm happy with the results, but I'd like to start experimenting with the flash and manually controlling the power. I figure I shoot with the camera in full manual, I should teach myself manual flash too.

Pretty sure I understand the concept of guide numbers (GN):
(GN) / (focal distance to subject) = (f-stop to set camera if ISO100)
My 430EX has GN of 43 at ISO100 and zoom 105mm.

If increasing the ISO the GN doubles every 2 stops of ISO, so eg:
(ISO400 GN) = 2 x (ISO100 GN) = 86 for my 430EX if shooting ISO400

Not sure at this stage how/where the 105mm zoom fits in to these equations.

I assume the above is based on full power. If I decrease power by a half, the distances will halve if keep the same f-stop, or keeping distances same the f-stop will have to widen accordingly. And adding things like flash diffusers reduce stops as well, so adjust accordingly for that too. Think I get it.

How accurate are the GNs and formulae for things like shooting macro? Dealing with focusing distances or 300mm or less. Typically if I'm using ISO200, f/11, and 1/200s and reverse engineer the GN formula:
43/.3=143 so need f/143 at full power and ISO100.
Adjust power down to aperture f/11:
11/143=1/13 of full power <- not sure about this assumption
And adjust because using ISO200:
1/13x1/1.4=1/18 power. Then I'd have to round off to nearest power setting, probably 1/16 (can't check now, don't have flash with me).

That sound right? Am I overthinking this? Should I just stick with E-TTL for macro stuff? I was expecting that 1/64 power would be enough for things so close (assuming no diffusers or extension tubes taking stops away).

Any good links for this? (Other than strobist)

troypiggo wrote in post #5850703
I have a 430EX and to date have only shot in E-TTL mode. For the most part I'm happy with the results, but I'd like to start experimenting with the flash and manually controlling the power. I figure I shoot with the camera in full manual, I should teach myself manual flash too.

Pretty sure I understand the concept of guide numbers (GN):
(GN) / (focal distance to subject) = (f-stop to set camera if ISO100)
My 430EX has GN of 43 at ISO100 and zoom 105mm.

If increasing the ISO the GN doubles every 2 stops of ISO, so eg:
(ISO400 GN) = 2 x (ISO100 GN) = 86 for my 430EX if shooting ISO400

Not sure at this stage how/where the 105mm zoom fits in to these equations.

I assume the above is based on full power. If I decrease power by a half, the distances will halve if keep the same f-stop, or keeping distances same the f-stop will have to widen accordingly. And adding things like flash diffusers reduce stops as well, so adjust accordingly for that too. Think I get it.

How accurate are the GNs and formulae for things like shooting macro? Dealing with focusing distances or 300mm or less. Typically if I'm using ISO200, f/11, and 1/200s and reverse engineer the GN formula:
43/.3=143 so need f/143 at full power and ISO100.
Adjust power down to aperture f/11:
11/143=1/13 of full power <- not sure about this assumption
And adjust because using ISO200:
1/13x1/1.4=1/18 power. Then I'd have to round off to nearest power setting, probably 1/16 (can't check now, don't have flash with me).

That sound right? Am I overthinking this? Should I just stick with E-TTL for macro stuff? I was expecting that 1/64 power would be enough for things so close (assuming no diffusers or extension tubes taking stops away).

Any good links for this? (Other than strobist)

You on the right path as far as your understanding of how the GN works. Working with a GN table for the 430EX would make like a little less complicated for you, though. Here's the GN table from page 34 of your 430EX manual:

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Guide numbers used to be simple.

Nowadays, using them is complicated, for a couple reasons:
1) Your flash has eight different guide numbers, one for each of the zoom settings.
2) Your camera has fourteen different ISO settings.
So when you combine those two factors, you'll be working with 112 different guide numbers, before you even begin to figure in the aperture.

Make life easy. Look at the distance scale on the back of the flash unit and call it a day.

Curtis N wrote in post #5852777
Guide numbers used to be simple.

Nowadays, using them is complicated, for a couple reasons:
1) Your flash has eight different guide numbers, one for each of the zoom settings.
2) Your camera has fourteen different ISO settings.
So when you combine those two factors, you'll be working with 112 different guide numbers, before you even begin to figure in the aperture.

Make life easy. Look at the distance scale on the back of the flash unit and call it a day.

That'a very good advice, Curtis, and one that I would ordinarily give myself except in this case, it may not be too applicable for macro work. But, having said that, I'm not too sure how well the GN chart would apply for macro work either. Hopefully the OP will find out and let us know.

Flashes do not care about macro distances (unless they cannot reduce power enough)...the effective aperture of the lens is what governs things...1:1 repro ratio is 4x the exposure, 1:4 to 1:3 repro ratio is 2x the exposure, for example. Using manual flash, you need to calculate the effect of extension tube on your exposure, because the aperture has changed, not the flash.
GN doubles (or halves) with a 4x change in power...so if full power is GN43 in meters, 1/4 power is GN11. I would prefer using GN rating in feet, not meters, since the units are more convenient to macro work! A GN160 flash would be GN40 at 1/4 power, GN10 at 1/16 power, and GN2.5 at 1/64 power. So if you are shooting 1.25 feet away at 1/64 power, that is f/2 aperture with no extension, and f/4 at 1:1 repro ratio. And in using manual flash, I would base everything on a single zoom setting like as wide as it can cover, to make thing easier. (You seldom have a problem with too much power at macro distance!) And calculate for ISO 100, then merely alter the aperture arithmetic in your head when you use faster ISO...going to ISO1600 would take the f/4 setting at 1:1 to f/16, simple isn't it?!

ETTL is your friend...if your flash can regulate itself down to 1/256 power, it can do that in ETTL mode or in M mode, and the end result is the same, just less work! ETTL will compensate for changes to the effective aperture much more simply than calculations in your head with Manual flash

Wilt wrote in post #5852994
Flashes do not care about macro distances (unless they cannot reduce power enough)...the effective aperture of the lens is what governs things...1:1 repro ratio is 4x the exposure, 1:4 to 1:3 repro ratio is 2x the exposure, for example. Using manual flash, you need to calculate the effect of extension tube on your exposure, because the aperture has changed, not the flash.
GN doubles (or halves) with a 4x change in power...so if full power is GN43 in meters, 1/4 power is GN11. I would prefer using GN rating in feet, not meters, since the units are more convenient to macro work! A GN160 flash would be GN40 at 1/4 power, GN10 at 1/16 power, and GN2.5 at 1/64 power. So if you are shooting 1.25 feet away at 1/64 power, that is f/2 aperture with no extension, and f/4 at 1:1 repro ratio. And in using manual flash, I would base everything on a single zoom setting like as wide as it can cover, to make thing easier. (You seldom have a problem with too much power at macro distance!) And calculate for ISO 100, then merely alter the aperture arithmetic in your head when you use faster ISO...going to ISO1600 would take the f/4 setting at 1:1 to f/16, simple isn't it?!

ETTL is your friend...if your flash can regulate itself down to 1/256 power, it can do that in ETTL mode or in M mode, and the end result is the same, just less work! ETTL will compensate for changes to the effective aperture much more simply than calculations in your head with Manual flash

I agree that the flash does not care about the macro distance. However, I think that the photographer should care. In my previous post, I said that the GN for the flash will differ depending on whether the flash is used indoors in an average-sized room or outdoors where there are no surfaces like walls and ceilings there the stray flash light can bounce off and get redirected towards the subject. That would also apply to macro distances. If the macro subject is not inside an enclosure, there may be no surrounding surfaces to bounce stray light back at the subject and hence, would be like taking a picture outdoors even though the macro subject may be indoors. According to my tests, there could be as much as a stop less light reaching the macro subject if the GN calculation is done based on the published GN without adding any compensation.

Of course, if the flash is only being used for fill, this would be less of an issue.

PacAce wrote in post #5853891
I agree that the flash does not care about the macro distance. However, I think that the photographer should care. In my previous post, I said that the GN for the flash will differ depending on whether the flash is used indoors in an average-sized room or outdoors where there are no surfaces like walls and ceilings there the stray flash light can bounce off and get redirected towards the subject. That would also apply to macro distances. If the macro subject is not inside an enclosure, there may be no surrounding surfaces to bounce stray light back at the subject and hence, would be like taking a picture outdoors even though the macro subject may be indoors. According to my tests, there could be as much as a stop less light reaching the macro subject if the GN calculation is done based on the published GN without adding any compensation.

Of course, if the flash is only being used for fill, this would be less of an issue.

No debate about the point raised!

ETTL can reduce the flash output lot lower than manual mode at minimum. With iso200, f11, and the 430 zoom to 105mm and 1/64 power, the flash needs to be atleast 8" from the subject to get the right exposure. With ETTL, the flash can be placed right on top of the bugger and zap it

Yes, I agree with Wilt and Lotto. ETTL would probably be the better choice for macro flash photography in most circumstances but especially when using more than one flash.

Thanks for all your tips and input guys.

I've been thinking about it more. Another point to not that I don't think was mentioned above is that since distances with macro are so small, you won't have to be out much with the distance calculations to have severely too much or little flash. I mean, you move back and forth millimetres or tens of millimetres while focusing or composing the shot. Over 300mm working distance 10mm is 1/30.

But for "normal" flash photography the distance you actually take the shot compared to the distance you calculate flash power for will be practically the same.

I'm thinking as Lotto suggests, since ETTL can output much lower than 1/64 manual capability, that for macro work I'll continue using ETTL. For interest sake, I might do some testing but suspect I won't like the results

I'll continue my pursuit of full manual flash knowledge for normal photography for which the flash was originally designed

maybe a little simplistic (on my part) but wouldn't manual flash be of more benefit if what you are shooting is:
background is constant (like portraits) but the subject is changing (more/less flash reflective).

so for example, if i ever got into doing portrait shots, I'd set my camera up to expose for a background and then use a light meter (or a lot of experimentation) to determine tha manual flash settings.

then after that, no matter how many light or dark subjects i shot, the flash exposure would be the same for each one.
err, not sure if i should make that a question instead... ??

Hangerhead wrote in post #5864898
maybe a little simplistic (on my part) but wouldn't manual flash be of more benefit if what you are shooting is:
background is constant (like portraits) but the subject is changing (more/less flash reflective).

so for example, if i ever got into doing portrait shots, I'd set my camera up to expose for a background and then use a light meter (or a lot of experimentation) to determine tha manual flash settings.

then after that, no matter how many light or dark subjects i shot, the flash exposure would be the same for each one.
err, not sure if i should make that a question instead... ??

Hangerhead, you assume too much...that dSLR owners know what a handheld flash meter is, let alone own one! The many, many threads about 'do I need a meter (or can I chimp)?...' and 'handheld meters are I, I have the histogram' illustrate that point.

so, by your slightly esoteric reply, i guess my take on it is correct..

Hangerhead wrote in post #5873893
so, by your slightly esoteric reply, i guess my take on it is correct..

Your take is correct, if you not of the school that states "Handheld meter is dead. Long live histograms."