How to compare a speedlite to a studio strobe light?

[dphoto]

Hello,

I don't know if I'm just missing something basic here, but I'm having trouble figuring out much light comes out of the various lighting options so that I can compare them. When I go to the store to buy a bulb, for instance, I can read right on the box how much light (lumens) is output. But when I look at the speedlite, it tells me a guide number, and when I look at a studio strobe, it gives me Watt seconds (joules). Agh!

So the speedlite 550EX has a guide number of 55... how does that compare (roughly) to, say, the Elinchrom Style 300S which is rated at 300 Watt seconds? Is one twice as bright? Ten times as bright? I really have no idea. I'm just trying to figure out if the 55EX outputs enough light to be defused in a studio and still be effective. Anyone have any insights?

Thanks,
-Deva

[cowman345]

I'm also interested in figuring this out, I've heard many say that the 550ex is not going to give you enough light to shoot at even f8.0 with a 24x24 softbox, let alone a larger box or reflector.

Everyone around here raves about how much light the 550ex can put out, so I fail to see how these two opinions correllate, can anyone provide any concrete info?

-dave-

[DaveG]

The studio strobe is going to be incredibly more powerful than the 550EX. Just start there. There's a reason that studio photographer's use these things. Geez I'd much rather have a couple or three dinky little 550's around than three 500 W/S monolights, but it's all power in the monolights! It's also plug in the wall and go all day.

As far as the watt/second versus guide number issue, it's because a guide number calculation is based on having a constant reflector. A flash like a 550 pretty much has that (although the zoom flash feature muddies those waters a bit). But you can put pretty much any relector you want around a monolight strobe and that's going to affect the GN.
But the output in w/s should be just raw output, and you SHOULD be able to compare apples to apples, or monolights to monolights. But you can't and the reason is the bull**** that goes along with w/s. The manufacturers straight out lie, and I should add the Canon's of the world lie about their flash's guide numbers too!

This is like horsepower and the more you have the better sales are going to be. The stupidity of the consumer is that they don't actually know what a guide number means, and when they find out they step back a bit!

This is how you calculate a guide number: Set your distance to 10 feet, set the ISO at 100 and read what the manual aperture should be. Convert the aperture - say f8 - to a round number, in this case 80. That's how you figure out guide numbers.

So you do your little math exercise and determine that THIS flash has a guide number of 80 and THAT one has a guide number of 90. WOW 10 guide numbers more powerful, right. But that's only about a third of a stop (f8 . f9) more powerful. Got that? A third or maybe a half stop!

So a Vivitar 283, a Canon 550 and a Metz 45CL4 are likely to be within a stop and a half of power.

At best you measure one studio strobe to another with w/s; and camera born flashes with guide numbers. But if you can test them with a flash meter, the crap factor will be greatly reduced.

[cowman345]

Are 550ex useless with reflectors such as umbrellas and softboxes, then?

-dave-

[dphoto]

Dave,

Thanks for helping me to reduce the "crap factor." Oh boy... my ignorance is really going to show on this one... Let's say I'm using the 550EX with a guide number of 55 (metric) and my subject is 10 feet away. This gives an apature "reading" of f/5.5, right? But what does this reading mean? I can definitely use it to compare with other flashes, but does this mean that the aperature on my camera should be set to f/5.5? But my aperature setting can change radically with my exposure time? I've noticed that light meters have the aperature "reading" as well. What gives? How can you just say, "This is f/8 amount of light here." I can always take an f/8 setting on my camera and change it to f/11 by doubling the exposure time. Sorry, I'm just trying to get a handle on this whole light issue, and I think I'm still missing something fundamental.

Maybe I should just stick to taking pictures outside?

-Deva

[DaveG]

Originally Posted by dphoto

Dave,

Thanks for helping me to reduce the "crap factor." Oh boy... my ignorance is really going to show on this one... Let's say I'm using the 550EX with a guide number of 55 (metric) and my subject is 10 feet away. This gives an apature "reading" of f/5.5, right? But what does this reading mean? I can definitely use it to compare with other flashes, but does this mean that the aperature on my camera should be set to f/5.5? But my aperature setting can change radically with my exposure time? I've noticed that light meters have the aperature "reading" as well. What gives? How can you just say, "This is f/8 amount of light here." I can always take an f/8 setting on my camera and change it to f/11 by doubling the exposure time. Sorry, I'm just trying to get a handle on this whole light issue, and I think I'm still missing something fundamental.

Maybe I should just stick to taking pictures outside?

-Deva

If you had a guide number of 55 and your subject was at 10 feet then you'd use an aperture of f5.6 (close enough) for that shot. But forget about guide numbers for trying to figure out flash exposures. It will be rare that the subject IS at 10 feet, or you are using ISO 100 and so on. All guide numbers are for (really) is to measure the power of different flashes.

Now you said, "But my aperature setting can change radically with my exposure time?" and this is true unless you are using flash.

I want you to think about what shutterspeed IS for a moment. Imagine you are in a completely dark room. You open your camera's shutter for one second. How much light has gotten to the film/sensor? None, right?

Now you double the time to two seconds. Have you let any more light in? You opened up a stop, haven't you? But of course since there is NO light in the room the various changes you make in shutterspeed WILL NOT let in any more or any less light if there's none there to begin with.

To extend this example a bit more: You have opened the camera's shutter for 30 seconds in that same pitch black room. No light has gotten to the sensor. Now for one second you turn on a light. Now how much light has gotten to the sensor? One second. But the shutter was open for 30 seconds, right? Well there was NO light during 29 of the 30 seconds. So even though your shutter was open for 30 seconds you effectively had a shutter speed of ONE SECOND.

When you shoot in the middle of the day you use a combination of shutterspeed and aperture to control the light. But this assumes that there is a constant supply of ambient light and you just let a little or a lot of it in.

With flash it's the same thing as the dark room. Here's a new example. You select a shutterspeed of 1/60 and an aperture of f8. It's a fairly dark room (but has some light in it). If you don't use flash then this exposure will be very much underexposed. But you did use flash. That flash - on a manual setting - has a time duration of roughly 1/700 of a second. Even though the shutter was open for 1/60 of a second the effective shutterspeed was 1/700 of a second! With modern flashes on Automatic these flash duration times are MUCH shorter than 1/700 and drations like 1/10,000 of a second wouldn't be uncommon. That by the wayis how Dr. Egerton (who more or less invented electonic flash) photographed bullets in mid flight, not with a fast shutterspeed but with a 1/100,000 of a second burst of light.

In any case when you use flash the shutter (on your camera) DOES NOT EFFECT the exposure. Only the aperture does.

This is simplistic and there are times when you will use flash AND the ambient light at the same time but I don't think that we should go there now.

[DaveG]

Originally Posted by cowman345

Are 550ex useless with reflectors such as umbrellas and softboxes, then?

-dave-

Well compared to a monolight they are very weak. You'll be able to do portraits (probably) but there's no horsepower for when you need small apertures.

[robertwgross]

Originally Posted by DaveG

If you had a guide number of 55 and your subject was at 10 feet then you'd use an aperture of f5.6 (close enough) for that shot.

Dave, I think you will want to set the record straight. Let's not confuse the original poster with feet and meters.

A Canon Guide Number of 55 *is* metric, not feet, and is expressed for ISO100. For your example, you would want to restate it to say "...if your subject was at 10 meters, then you'd use an aperture of f5.6."

As I recall, there is an internal switch on the 550EX so that it can display the range in either feet or meters.

---Bob Gross---

[DaveG]

Originally Posted by robertwgross

Dave, I think you will want to set the record straight. Let's not confuse the original poster with feet and meters.

A Canon Guide Number of 55 *is* metric, not feet, and is expressed for ISO100. For your example, you would want to restate it to say "...if your subject was at 10 meters, then you'd use an aperture of f5.6."

As I recall, there is an internal switch on the 550EX so that it can display the range in either feet or meters.

---Bob Gross---

Fair enough. But I learned guide numbers when you used ASA 25 to calculate the number, not ISO 100. It doesn't matter what the distance or ISO is as long as you always do the calculation the same way.

[dphoto]

Dave,

Thank you *very* much for the explanation. I guess I kinda forgot that about flash... it is extremely quick, and so you are right about exposure times no mattering in that regard. Yes, they will determine what will be exposed by the ambient light, etc.

OK, well this was a big help. You stated that the studio strobes produce a lot more light than the speedlite 550EX. I think a 300 Watt second strobe is more on the weak end, correct? Does it still drawf the 550EX? I want to do studio shots where I will need to diffuse the light so it won't be so harsh. I was thinking about shooting the light into a reflective umbrella. Is this going to give enough light for a sitting subject? What about a moving subject? It sounds like probably not, otherwise people would probably be using the smaller cheaper 550EX, I would imagine.

And thanks for the metric comment, Bob, just to keep everything straight.

Thanks again!
-Deva

[DaveG]

Originally Posted by dphoto

Dave,

Thank you *very* much for the explanation. I guess I kinda forgot that about flash... it is extremely quick, and so you are right about exposure times no mattering in that regard. Yes, they will determine what will be exposed by the ambient light, etc.

OK, well this was a big help. You stated that the studio strobes produce a lot more light than the speedlite 550EX. I think a 300 Watt second strobe is more on the weak end, correct? Does it still drawf the 550EX? I want to do studio shots where I will need to diffuse the light so it won't be so harsh. I was thinking about shooting the light into a reflective umbrella. Is this going to give enough light for a sitting subject? What about a moving subject? It sounds like probably not, otherwise people would probably be using the smaller cheaper 550EX, I would imagine.

And thanks for the metric comment, Bob, just to keep everything straight.

Thanks again!
-Deva

I'm guessing that a 550 is less than 100 w/s. 300 w/s is at the lower end of monolight power, but as a friend once pointed out: On some days 100w/s is too much and on others 4800 w/s isn't enough.

If you are moving around and the subject is moving around then a camera born flash is what you'll need. It will freeze action, but the light is flat and you will almost certainly get flash fall off (the subject is lit fine but the background has an unnatural darkness to it). That's why pro shots of sports like basketball are done with either available light or with a multiple of studio strobes placed in the ceiling and triggered with radio slaves. Usually outdoor fashion photography is lit with a variety of ambient light reflectors, not flash.

[billfranklin]

Deva,

In answer to your question, yes the 550EX can be used in a studio setting. I just tested my 550EX in this setting. I used ISO 200 at 1/60 sec for this test. The 550 EX was set to manual at full power. Without an umbrella, the flash meter read f16.6. Shooting "through" a white umbrella, the reading was f8.8. Light was 5ft. from light meter. Remember in a head and shoulder portrait, the umbrella should be as close as possible to the subject without being in the picture. You can also shoot through an umbrella outdoors to give directional light as well to fill in shadows.

Without a flash meter, it might be a little hard to determine the correct exposure, but with trial and error, it can be done.

Good luck

Bill F.

[w10d]

Originally Posted by dphoto

I'm just trying to figure out if the 55EX outputs enough light to be defused in a studio and still be effective. Anyone have any insights?

Thanks,
-Deva

I typically use 2 x 3000 j flash packs for subject lighting when shooting close-up through to head and shoulders. At ISO100 I expect to be shooting between f16 1/2 and f22 1/2 (medium format), with power settings on the packs between 3/4 and full. (Depends on dishes/softboxes/position/etc.). For the 10D I would expect to be between 1/2 and 3/4 power, but sometimes choose a pair of lower output packs, 2400j or even 1500 depending on the situation.

Just to give you an idea of how restrictive using on camera type flashes could be, not to mention the cost of batteries and the limited choice of attachments. These units are fantastic at the job they were designed for but expensive, over featured and a little inadequate as studio lights. (IMHO!)

[dphoto]

Bill, thanks for sharing the results of your studio test! It sounds like at 5ft, I would have no problem. f/8 through an umbrella sounds like more than enought light [I would probably be shooting at f/1.8]. Full body shots, however, might be a little more difficult. Tell me if I'm applying this inverse square thing properly... If I double that distance to 10ft, then the amount of light is going to fall off by a factor of 4, correct? So at 10ft, the light meter would probaby read about f/4, correct? And at 15 ft, it would be around f/2.

That certainly seems reasonalbe in some cases, although I could see in others where you might need more light if you want to diffuse it even more, etc. The reason that I am asking about the 550EX specifically is that of course it makes a great on-camera flash, but if you could also combine it with the ST-E2 to get a studio light as well, then it seems like there is a possibility to save some money. Strobe lights are expensive, and if I am going to spend ~$325 anyhow for a 550EX, I at least want to consider the ~$800 package that includes 2 550s and the ST-E2. In other words, for about $475 more, I would be getting some off-camera studio lighting. And a very portable studio, at that. But having no studio experience, I have no idea what I'm doing, and $800 is still a lot of money.

Thanks for all of the input, and please keep it coming if you feel so inclined. Oh, and w10d, what do you mean by f/16 1/2? Also, you think that the 550EX is expensive? Can you please point me to some cheaper studio lighting, then, beause I can't seem to find any! If I use rechargable batteries, I wouldn't think that it would cost that much to operate, either.

-Deva

[Ken Fong]

Below are results from my first stab at portrait lighting last July. The setup is similar to what Deva was describing and used a 550EX reflected into a 60" white umbrella (Main), a 420EX reflected into a 45" white umbrella (Fill), triggered by an ST-E2, with a 50mm 1.8 lens...I'll post the settings that I used and I will probably re-post this in the critique area later...I'd be interested in hearing about posing, color adjustments, etc. Most likely, I was using Program mode. Also, I think in these case, a backlight would have been helpful because the dark suits merge with the background.

I'm aware that for this size of reflectors, I should not exceed more than 3 subjects, so I was pushing it over the limit for use in group shots. I learned why you should not exceed the subject limit of reflectors...in group shots, the people on the sides will start to blow out (you can see it in the larger group shot below...the main light is on the left side).

The 550EX/420EX combo consistently produced underexposed shots. As the day went on, I increased the output from the flashes, which helped, but I noticed that the histogram was still not using the far right section of the curve (what you see below is after RAW exposure correction due to underexpose.) So overall, I felt that I the flash setup was on the weaker side, but acceptable for smaller group portraits (no more than 3 people)...I'm not sure if the 550EX can adequately power a larger reflector. I would be curious if anyone can comment on whether the Studio 300/600 setup would not have had a problem in this case. However, I appreciated the lightweight setup of the 550EX and ST-E2.