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06/03/2007 05:14:57 PM · #1 |
I'm a big fan of the Strobist and have been reading his tutorials on using off-camera flash for lighting. I picked up a pair of SB-25s, but I have having trouble understanding some of what I've read.
What I cannot seem to wrap my mind around is the relationship between the camera settings and the flash settings. For starters, when I dial in the settings on my flash, I tell it for example that I'm shooting F/5.6, ISO 160, and set it for 1/4 power. However, as near as I can tell, all this does is generate a calculation on the reach of the flash beam, not alter it's intensity. If I change the flash setting to F/2.8, and keep the others the same, and keep the camera at its original setting, the light looks the same.
So as near as I can tell, this means that the only setting that actually changes anything on the flash is the power setting (1/1, 1/2, 1/4, etc.) And I cannot seem to figure out how to balance/apply this to the camera settings when taking a shot.
For instance: on the Strobist, they talk about doing a shoot in daylight where you meter the ambient light, and set it to underexpose by two stops. So: I use the camera's meter and set the exposure at -2. But what do I do with the flash, then? I assume that I have to somehow learn which power setting to use, and what distance the flash itself needs to be from the subject. But what do I use as a baseline, or reference? And if the flash looks too weak, how do I know how much to increase the power level without doing a bunch of trial-and-error shots?
I hope all that makes sense. If anyone can shed any light on this, it would be greatly appreciated, as the whole issue is driving me crazy. I was just out playing with different settings, and felt like I was almost getting it, but not quite.
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06/03/2007 05:30:08 PM · #2 |
| Great questions. I'll be tuning in for some answers myself! :) |
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06/03/2007 06:05:14 PM · #3 |
Originally posted by A4wheelin:
Great questions. I'll be tuning in for some answers myself! :) |
Me too, so here's a bump.
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06/03/2007 06:38:40 PM · #4 |
Wow... I'm uncertain that you are not getting EXACTLY what you are telling it you want. When underexposing an image using flash you are basically telling the flash to use 'filler' to correct the exposure. It should adjust the amount to flash that it uses to 'correct' the -2 underexposure you metered.
If the exposure is right under those conditions then everything should be correct.
However, if exposure is correct but the lighting angle, etc. is not right then that is a different problem and is you the photographer's error for positioning flash incorrectly.
Just what is the problem?
Message edited by author 2007-06-03 18:39:59. |
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06/03/2007 09:55:09 PM · #5 |
Not sure about what you're reading ... but if I were using manual settings on a flash (or a strobe, which is manual by nature), I'd use a hand held light meter. Hold it at the subject and point it towards the light source and then fire the flash (or strobe). That will tell you what settings to use on camera.
If I were balancing ambient light, then I first figured out what readings I want on my camera, then using that, I would adjust the flash/strobe readings to match the desired lighting.
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06/03/2007 10:19:16 PM · #6 |
Originally posted by stdavidson:
Wow... I'm uncertain that you are not getting EXACTLY what you are telling it you want. When underexposing an image using flash you are basically telling the flash to use 'filler' to correct the exposure. It should adjust the amount to flash that it uses to 'correct' the -2 underexposure you metered.
If the exposure is right under those conditions then everything should be correct.
However, if exposure is correct but the lighting angle, etc. is not right then that is a different problem and is you the photographer's error for positioning flash incorrectly.
Just what is the problem? |
It's not so much that I'm not getting what I tell the flash I want, it's that I'm not sure what to tell it to get what I want. What I'm trying to figure out, for instance in the example I gave, is how to set my flash so that I do get it's light to expose correctly, and the background to be at -2.
I guess what might be most helpful would be a way to put the flash power in terms of F-stops. That way, when I want to shoot in underexposed ambient, I could meter the ambient and set the camera for two stops less, and then know that if I set the flash to "X" power, it would fill in those two stops on my subject.
I'd like to be able (with practice, of course) to walk up to any scene and after studying it and metering it, be able to set the flash to get the type of lighting I want. When I try to do this now, I end up taking dozens of test shots to figure it out, and then it's often still not quite what I had in mind. But right now, I never have any idea what settings to use on the flash to achieve this.
 dwterry, I had thought about a light meter. But from some of my reading, it's been said that you can get by without one, so I was trying to go that route. Perhaps that's an error on my part. Since I know squat about light meters, can you (or anyone else) provide some suggestions for a decent one that won't break the bank?
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06/04/2007 12:35:12 AM · #7 |
It's not surprising you have to try many test shots. There are several variables that come into play. The level of ambient light. The strength of the flash output. The distance from the flash to the subject. The diffusion of the flash output (if any).
There probably are people out there that can figure this stuff out in their heads. I'm not one of them. For me, the solution is a light meter which solves all of these variables at once.
There are several popular brands of light meters. I happen to use a Sekonic L-558R because it has a built-in pocket wizard transmitter and I use pocket wizard receivers on my strobes. But any light meter that has able to handle flash will work, and most of them will be cheaper than my Sekonic meter.
Another solution... the "easier solution" ... is to use e-TTL and let the flash/camera system calculate the exposure on its own. It does this by sending out a pre-flash, calculating how much power is necessary, and then firing the appropriate amount of light for the exposure. I use a Canon 580EX as my master and either a 420EX or a 550EX as my slaves (I have all three, sometimes the 550EX acts as a master, sometimes as a slave).
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06/05/2007 07:46:30 AM · #8 |
Thanks for the advice, dwterry. I'm looking into a light meter, as I think it will help. The only reason I don't depend on TTL is because the majority of my strobes won't mount to my camera, so I've got to do it all myself :-)
For those who posted at the top and were wondering the same thing as myself, here's an update: I joined the Strobist Flickr group, which has a fairly extensive archive of threads. A quick search pulled up this same problem, and while I haven't read through all of them, the general feeling is this.
First off, there's a fairly large group of us who are having a hard time equating the strobe settings to those on our camera and getting a decent shot without a TON of chimping. And as yet, there's been no real solution. Those who are able to successfully work light seem to have learned an intuitive sense of it, and we can only hope that if we work with it long enough, we will too.
The two schools of thought seem to be this; it's digital, so take a ton of test shots, and chimp like mad. Use your hand held in front of the camera as a test subject to get the light almost right, then when your model/subject arrives, you only have to fine-tune it for them.
Or, there's the more scientific method. Some folks mentioned the inverse square law, and guide number calculations. Frankly, I probably couldn't do the math with a calculator in hand, much less without one, on the fly at a shoot. So we're back to the earlier suggestion of a light meter. Those who own one either get a ton of use out of them and tout how much help they've been, or claim they hardly ever use it anymore. IMO, I'm game to spent the $200 and get one to use. If through using it, I reach the point where I no longer need it (hopefully!), then I'll be all to happy to put it in the closet or on eBay, and consider it a good investment.
I don't have the link on hand, but B&H has one, by Shephard/Poalris, the SPD100, which is good for ambient and flash light, and it's only $160. Several users here have mentioned it in past threads, including  idnic, who had only good things to say about it.
I hope this is helpful to everyone. I also just ordered the touted "Light, Science, & Magic" textbook, which I'll consult when it arrives. With a little luck, this will be a start. Oh, and Lighting 102 is starting over on the Strobist site, which ought to be a huge help as well!
I'll post again as I learn more, and while I don't know how much help I'll be, anyone interested can PM me, and I'll pass along anything I learn on my crusade.
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06/05/2007 08:06:48 AM · #9 |
Very nice. Thanks for the update. It'll be interesting to hear of your experiences as you move forward with this.
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06/05/2007 09:22:02 AM · #10 |
Originally posted by OdysseyF22:
[quote=stdavidson] I'm trying to figure out, for instance in the example I gave, is how to set my flash so that I do get it's light to expose correctly, and the background to be at -2.
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Try exposing your subject properly and working from there. Say F4 will give you all the DOF you need. Shoot the subject at F4 and run the flash up and down until you get the exposure on your subject that you like. Then just dial in two stops to get the background the way you want. F8 will give you your -2 stops. I read Strobist too, and I believe the experimentation is just what you're going to have to put up with until your eye and brain are able to set up the shot. You're basically training yourself to be the flash meter. Since David has been shooting flash for the Sun so long he's got a built in meter in his head. For you to accomplish that, you're going to have to shoot.
A lot!
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06/05/2007 09:58:53 AM · #11 |
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06/05/2007 10:17:25 AM · #12 |
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06/05/2007 10:28:04 AM · #13 |
Originally posted by OdysseyF22:
I'm a big fan of the Strobist and have been reading his tutorials on using off-camera flash for lighting.
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This looks like a cool little sight! Thanks for sharing this link along with your question!
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