Using Strobes Outdoors, how much power do i need?

[photonewguy]

Hey sorry if this is a basic question, I have been shooting for about 6 months now after seeing some really cool exterior strobe shots (you know, when the background is dark and sky is dark blue but the talent is lit and almost plastic looking).

Anyways, as i said im about to but a strobe monolight as i dont wanna deal with packs yet. Im a cinematographer so I understand light, but am not to sure if a 400watt strobe is the equivelent of 400w of continuous lighting, if so I know thats not gonna do much.

Thanks in advance for your help!

[Asylum Steve]

Welcome to the site. Comparing the wattage of hot and flash lights is like apricots and oranges. In fact, comparing wattage even between different brands and types of storbes can be a flawed proposition, as manufacturers often throw different kinds of numbers out at the consumer in an attempt to inflate their product's specs.

Generally speaking, a flash with the same wattage number as a hot light will have a higher output as the hot light by nature is continuous light while the flash is peak light.

A much better way to compare light output among different flash units is GUIDE NUMBER. A flash GN is a standard attained (normally) using ISO 100. Divide the subject distance into the GN and you have your f/stop.

For example, a flash with a GN of 220 should produce an f/stop of f/22 at ISO 100 with the subject at 10 feet. Naturally, this is just a general guideline, as many other factors affect exposure in the real world, but for the sake of comparing flash output, it is a very useful tool.

BTW, there are many reasons other than power output why you would want to consider hot or flash lights. Take a look through the forum archives to see threads and questions others have posted...

BTW2, ok, I'll bite. Where the heck is "washintronb"??? Not a real place, eh? ;)

[Photo-John]

I've been thinking about adding some battery-powered studio strobes to my mountain bike setup. Specifically, I'd like bigger lights, with fast duration, to freeze action. I want studio lights because you can only do so much with hot shoe flashes. Plus, the light quality from studio lights is wayyyy better. I'd like something reasonably compact so I can get it out in the field - and I mean the field :-) I might be lugging them a few miles, in pretty rugged terrain.

Any thoughts? Should I make a new post?

[racingpinarello]

Hey Photo John,

One of the things that I have on my want list is battery powered strobes. I am leaning toward Broncolor, but until then, I was looking at Quantum battery powered strobe.

Wider coverage and very good quality of light. I am also thinking of Norman battery strobes because they seem lighter.

You may be seeing me at some Mtn Biking events as I trying to get some Specialized promo shots. Now, I just need a mountain bike.

Loren

[MJS]

Hey John, check out the Alien Bees sight, they have a battery package with inverter to run any of their strobes. Could be a bit heavy though if going in by bike.

[tomasito]

Hey sorry if this is a basic question, I have been shooting for about 6 months now after seeing some really cool exterior strobe shots (you know, when the background is dark and sky is dark blue but the talent is lit and almost plastic looking).

Anyways, as i said im about to but a strobe monolight as i dont wanna deal with packs yet. Im a cinematographer so I understand light, but am not to sure if a 400watt strobe is the equivelent of 400w of continuous lighting, if so I know thats not gonna do much.

Thanks in advance for your help!

Hi, if I can recommend this model Hensel Porty Premium: http://www.hensel-studiotechnik.de/english/index.html
This unit also has built-in wireless capability and on location sometimes this feature is a big plus...

goodluck

[Packard]

It was already posted that you really need to know the Guide Number of the flash to make a reasoned judgement. I'd like to add to that.

If you know what distance (maximum) you intend to shoot at and what is a reasonable f/stop for you to use, then you can back-figure the needed Guide Number.

Let's say you figure that you would be no more than 20 feet from your subject and you could reasonably shoot with an f/stop of f/5.6 then you would need a flash with a guide number of 112 (5.6 x 20 = 112).

Another thing to watch for is how the guide number is calculated by the manufacturer. If they say the guide number is 112 when bounced off a silver umbrella, then it means one thing. If they say it is 112 when measured from an umbrella reflector then the output is a good bit less. (a silver umbrella will lose between 1 and 2 stops of light as compared to a direct flash). If they say it is with a narrow spot, then you need to ask them more questions to get a reasonable answer.

I just re-read this and it is a bit confusing. If it is not clear, let me know and I'll try again.

[another view]

If they say it is 112 when measured from an umbrella reflector then the output is a good bit less. (a silver umbrella will lose between 1 and 2 stops of light as compared to a direct flash).

Question - do you mean holding a flash meter (or whatever they use) on the umbrella to get this reading? There's a difference between the center of the umbrella and the outside edge... I suppose this is just part of the confusion that you and Steve bring up. Just curious about this.

John, Calumet's new Travelites can be used with a battery pack too but I suspect they're a lot physically bigger & heavier than you're looking for. Seen a lot of people with the Quantums but no personal experience.

[Packard]

Question - do you mean holding a flash meter (or whatever they use) on the umbrella to get this reading? There's a difference between the center of the umbrella and the outside edge... I suppose this is just part of the confusion that you and Steve bring up. Just curious about this.

It is easier to give an example. Let us say that you are shooting portrait. You set your umbrella about 6 feet from the subject and for ease of calculation, let's assume that the flash you have is rated at a Guide Number (GN) of 120. If we aim the umbrella reflector directly at the subject (no umbrella) and we are 6 feet from the subject our calculation looks like this: GN = 120 divided by distance (6 feet) = f/stop (f/20). So we would use between f/16 and f/22 on our lens.

If you are using a silver umbrella you lose about 1 f/stop of light due the first the fact that the umbrella does not reflect 100% of the light, and second there is added distance involved. So with the umbrella in place the GN is not 120; the GN becomes 60.

Your calculations are done in the same manner but you start with a smaller GN.

In each case you would place the flash meter near the subject and aim it towards the light source to determine the amount of light hitting the subject. If you were using a multiple light setup you would take a reading for each light individually to make sure that you are maintaining the correct lighting ratio. For instance the fill light might be 1/2 the output as the main light, and the hair light might be twice the output as the main.

As an aside, when I was first starting out I did not have a flash meter. Instead I had a piece of string attached to light stand. I had, through experiment, determined the output at various distances and they were marked with color markers. I used the string as my "flash meter".

[another view]

If you are using a silver umbrella you lose about 1 f/stop of light due the first the fact that the umbrella does not reflect 100% of the light, and second there is added distance involved. So with the umbrella in place the GN is not 120; the GN becomes 60.

Your calculations are done in the same manner but you start with a smaller GN.

Thanks - makes much more sense now. If every manufacturer did it the same way life would be a lot easier!

[Packard]

Thanks - makes much more sense now. If every manufacturer did it the same way life would be a lot easier!

Your dreaming.