As we begin to start to find some ways to use our speedlights – or small hotshoe style strobes – for advantage, we need to learn all about them. (Welcome Strobist Readers… thanks David.)
I’m not talking about the RTM stuff. Where to put the batteries and such. This tutorial already assumes you know a little about that stuff. What I am talking about is the unit itself… in regard to light.
Let’s establish a few ground rules for what we are going to be doing. First, this isn’t an ETTL, CLS, or any other kind of electronic exposure control in the flash unit. We are talking about manual settings. Manual is where the power is.
We also must make a few demands for the units themselves: They must have variable power, some way to fire them off camera (Sony strobe units are pretty proprietary I have seen) and they should have some sort of “Zoom” for the light. This last part isn’t mandatory, but it does offer some great flexibility.
First off we have to get some relative readings. And this is crucial because once we have the readings they are pretty fixed. The strobe will do the same thing every time. That consistency works to our advantage. We can learn the flash and what it will do at the settings we give it. That makes moving quickly more possible. We know the flash so well, that setting it in a position to give us exactly what we want is now quick.
(EDIT: This tutorial is for people who may have to borrow a flash meter in order to get their readings. If you have a flash meter, by all means use that. I am not sure having a ‘cord meter’ would be advantageous other than saving you some time. And helping you visualize in a linear manner what most people take for granted… and then never learn.)
How do we learn that? Well, that part is also relatively easy.
(NOTE: this is a very old technique, and not one that I came up with. It is simply an easy to do technique that works very well, and gets you to making pictures right away.)
Let’s start with power. How bright the flash is at a given distance. For purposes of this discussion we will use the ISO of 100. We will add a table for conversion as well. At this point, the ambient light and shutter speed are not relevant. Choose a normal situation or somewhere where you can comfortably shoot. The power of the strobe is not related to the ambient light at this point. We will get to mixing the ambient with the daylight next week.
Get your light meter. What, no meter? Then get a gray card or digital target. You are also going to need about 8ft of twine or my favorite – clothesline twine – available at most supermarkets. We are going to only use a part of it, so the rest of it can go in your location kit. You can’t believe how handy 30ft of cord comes in sometimes.
Building our LoTech Meter:
Put your flash on 1/8 power. Manual setting at 1/8. Got it?
Why do we start at 1/8 power? Because it gives us a mean reading where we have the ability to go up and down with the power settings. If we start at full power, we can only go down. I like flexibility, so I do it my way – you still get the same readings of course, this is my way of doing it. Your shutter speed wont matter at this point, but pick a nice neutral one like 1/125 or so. We can go up and down from there later.
Now set the zoom to the middle point as well. Not out to 135mm and not back to 24 mm. I use the 50mm setting on my 430. These settings on the strobes exist for shaping the light when it is on your hotshoe… the longer lenses (like 85mm, 135mm) require a more narrow light, while wider lenses need a wider throw of light. When the light is narrow for the long lenses, it actually can become stronger. Put your strobe on a stand and attach a trigger to it. You don’t have to, but it is way easier and makes having a second person not nearly as important.
Alternate method 1: Light Meter.
Tie a loop into the end of the clothesline cord and loop it over the strobe on the stand. Make it an easy thing to do so you can repeat it on location when you need to.
Take the string out about 6 feet (about… actual distance doesn’t matter) and pull the string slightly taught. Fire the flash for a reading straight at the meter. Check your reading. (Make sure you are still on 1/8 power.) We are looking for an exact reading, not a little over or a little under. An exact f-stop. F11, not F9. When you get the meter in the position to get an exact F-Stop… and you are out about 6ft or so, then make a knot in the cord at that point.
Remove the loop around the strobe and double the length. Make a knot at that point and cut the cord. You should now have a long piece of string with a knot in the middle. Good.
We have our meter in basic form. Now take the length between the middle knot and the loop and make a knot in the middle of it. Ending up with a cord with a loop and a knot half way to the middle knot and a final knot at the end.
Alternative method 2:
Setup and method is the same, but we are using a gray card instead of a meter. The camera is mounted next to the strobe and we place the gray card at a distance to get a centered spike in the histogram. Dead center, not to one side or the other even by a spec… dead center.
Here is exactly how I would do it. Place the strobe next to camera and aim it toward a gray card on a stand. Make sure you fill the frame with only the gray card, no extraneous background. Put the camera on f-11. Shoot the shot and check the histogram. It should be dead center. If it isn’t, you can adjust as needed. When you find that spot where the histogram spikes dead center, it will be the point to start.
(EDIT There was mention that the math here does not exactly match the “Inverse Square Law” as it truly exists. That is absolutely true. However, ISL only applies to point source light in a specific shaped parabolic umbrella. My ‘cord’ meter is not that exact, and you may have to adjust a little bit. I know that I have used it in decades before – on chrome – and it was damn close. We are looking for damn close here… we will always want to tweak. However, if you want to do the math correctly it would look thus:
— 2x – 2.8x – 4x – 5.6x – 8x
Now that puts that center forward knot at about a 1/4 stop under (2.8 slightly less than 3) and the back center area about a half stop under as well (5.6 being slightly less than 6). Theoretically… Next time you all shoot ‘theoretically’ let me know how that worked out for you… I shoot real world pictures. So should you. This is photography, not physics. Try it… then tell me it doesn’t work.
Just remember also that the cord meter costs less than twenty cents. And for twenty cents, it is simply amazing. Next week we get off of ‘theory’ and put it to use. We will all see the results.)
When that center spike is achieved, begin the knotting procedure that is above. You will end up with the same length of string with the knots as indicated.
Now let’s look at our ‘meter.’ We know the f-stop at the middle knot is what we metered it to be. I am going to use f-11 for our discussion as that is what I have on my 430. The knot halfway to the strobe is two stops brighter. (Inverse Square Law…) and is therefor f22. The knot at the very end is two stops less than the middle knot, f-5.6.
Now let’s put some thought into it. If the middle knot is f11, we can make it f16 by increasing the power to 1/4 on the flash or decrease it to f8 by changing the power to 1/16. Choices… These changes also affect the knots in the cord at the other places as well. So we have a repeatable tool for finding the exact power/f-stop we need on most situations.
And the light doesn’t change. It is constantly coming out at that power as long as we have it on that setting, at that distance.
Can you do this with your umbrellas? Absolutely. Warning though, the Inverse Square Law is not quite as accurate so it is better to actually make the readings at the knots that you use. Then the exposures are exactly right. I rarely use my umbrellas at distances larger than 6ft, so that is the basic distance I made my first ‘meter’ to. With adjustment knots in between of course.
We can now accurately know what our flash units are doing when we pop the trigger.
As an addendum, you may change your flash to the wide angle setting and do it as well as with the more zoomed out flash. You will find that the power will drop when you go for a wider angle and increase when the light is more focused as for longer lenses. Hmmmm… more options.
Assignment for next Monday is to create a string meter for both your bare flash and your umbrella (whether you shoot predominantly in bounce or shoot thru, it doesn’t matter. Just make sure you make your meter for the method you use the most.) Take a few shots to make sure you understand the light coming from the flash is consistent.
We will be putting the tool to the test on next weeks assignments.
Oh, and BTW… 10 points off for making fun of my Hawaiian shirt. Sheesh.
Special thanks to James Alan for making the shots of me and the rope.