BetterPhoto Q&A
Category: Studio Techniques Using Digital Cameras

Photography Question 

Jax
 

Metering in Studio


Hi There,
I would like to know if the camera meter has any effect on the final image. Is there a particular setting a 30D should be on? I have heard that your working aperture is measured from the main light? Also when using a bowens gemini kit 5600k, should I manually set the white balance to 5600K or leave it on auto WB? Any help with this is greatly appreciated. I'm a bit confused!


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February 19, 2008

 

Alan N. Marcus
  Hi Jax

The in-camera metering system on a modern camera is quite good. In fact you will be hard pressed to beat it unless schooled or self-schooled on meter usage. However the in-camera meter generally is incapable of handing electronic flash. For that you will need a reliable flash meter.

As to the shutter speed to 1/125 second; In studio with electronic flash, the flash duration is exceptionally short, far shorter than you camera’s mechanical shutter. Thus we set the shutter at a high value like 1/125 second or greater after checking the camera manual to verify which shutter speeds synchronize with electronic flash. Due to the short duration of the flash we cannot use shutter speed to control exposure in the studio with electronic flash. This is true unless we use slow speeds to intentionally allow ambient light to influence exposure. Generally the lower shutter speeds are avoided in a studio to prevent ambient light from recording along with the flash as this can cause a color temperature mismatch. You lights are 5600°K which simulates daylight.

In-studio we choose aperture to achieve a desired depth-of-field span. Smaller f/number values like f/2.8 or f/4 or f/5.6 yield shallow depth of field. The classing view for the portrait is eyes in focus – ears jut outside the depth-of-field zone. To achieve you likely should choose a large opening like f/5.6 or f/4 (f/8 yields too much depth-of-field). However photography is an art form so you are free to exercise you desires.

For starters; set the main light high to simulate afternoon sun. Set it off to the side at the 8 O’clock position (camera at 6 O’clock subject at 12 O’clock). Set the fill along side the camera at lens height. You are filling from the cameras viewpoint. Without a flash meter you must use power or distance to adjust lamp intensities. You goal will be to cause the fill light to arrive at the subject 50% (1 f/stop) reduced in power as compared to the main. This reduced power plus it position near the camera preserves the classic portrait illusion that only one lamp (the main) was used.

To achieve set the power of the Bowens main to full. Set the power of the fill to 1/2. Both are placed at exactly the same lamp-to-subject distance. Experiment shooing with the fill set at 1/2 then 1/4 power and than at 1/8 power. The result will be lighting ratio series of 3:1 then 5:1 then 9:1.

An alternative: Set both to the same power. Measure fill to subject distance. Multiply this distance by 0.7. This will be the main to subject distance for 3:1 as this establishes the fill at 50% intensity as compared to the main.

Shoot a series at each aperture and examine the results.

Better yet, procure a flash meter.

Alan Marcus
ammarcus@earthlink.net


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February 19, 2008

 

Alan N. Marcus
  Hi again,
I forgot to tell you:
If the series is overexposed or the correct exposure is produced by too small an aperture you must reduce power or move the main further back. Multiply subject-to-main distance by 1.4 yields a revised distance that moves the main back in a logical step. This causes the main light to arrive at the subject reduced in power by 50% (1 f/stop). If the main is reposition so to must the fill.

The magical numbers are:
multiply by 1.4 to increase distance. Multiply by 0.7 to decrease distance.

These factors are derived from a law of physics governing light propagation. The law is call law of the inverse-square.

Alan Marcus (marginal techical stuff)


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February 19, 2008

 

John H. Siskin
  Hi Jax,
Better yet, don’t buy a meter. The students I have often use the meter to make bad photographs. Meters do not tell you how to set your lights; your eye and the proof image from the camera, or an image with the camera tethered to the computer can tell you how to set the lights.
The key is to see the quality of the light, hard or soft, and the relative values of light in the shot. You have to really look at the image to see this. The meter will not tell you very much about value and less about light quality. The histogram helps as well. Here is some information from my Understanding the Tools of Photography Lighting course here at BetterPhoto.
In teaching this class, I keep trying to find ways to say that you have moved into the land BEYOND metering. When you use a strobe meter, you get a response that tells you how to make a middle density, but it doesn’t tell you how to make it look right. There is no automatic way to make it look right, only the application of brains can do that. When I make a shot with strobes and a digital camera, the first thing I do is to put the camera on manual and I will pay no attention to the meter in the camera. The only things I pay attention to are the proof image on the camera back and the histogram. More than metering, these two things tell you about your image.
Let me suggest a plan for seeking the right exposure: 1) set the shutter speed to the sync speed; 2) set the aperture to your middle aperture, whatever that is on the lens you are using; 3) take a picture, it will be wrong; 4) move the aperture dial to let in more or less light based on the test exposure. You can look at the histogram to help determine how much to change the aperture, but the proof image should tell you if you need to change a lot or a little; 5) more test exposures and changes of light placement and light power until the strobes are right; 6) change shutter speed to balance values between existing light and strobe light - this will require more test pictures.
This same technique will work if you are mixing strobes and daylight. This was why the Polaroid bill was so high with film cameras, but with digital, these test exposures are free, so we should not be afraid to make them.
This is the essential trick with strobes, to evaluate and change our images in search of the right levels for our lights and our exposures. With the histogram and the proof image on camera or in the computer, we have better tools for creating the right exposure than any meter could give us, but it does take repeated testing.
Thanks, John Siskin


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February 19, 2008

 

Jax
  Cheers guys, that helps alot. I recently had a session. I'm new to the Bowens kit but have been getting great results. I have my Canon Eos 30D set to 'K' and Colour temperature to 5600. When I opened my shots there was what seemed like a colour cast slightly orange. I corrected it in photoshop and the backround turned from grey to blue(the background is white.) Do I need to manually adjust the white balance for every different light setup or adjust +/- 300 as the bowens specs say? And leave it at that one set up regardless of background colour, coloured gels? I need to be able to open perfectly balanced images as I dont have time to batch colour correct and besides it destroys the pics anyway. And 1 more thing the depth of my studio is 8 ft. Is it possible to turn the white backround black for portraits. using a softlite reflector and a taper softbox( I could use a reflector?) I tried opening up the aperture and making the lights dim but I still get greyish. Cheers again..Jax


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February 22, 2008

 

John H. Siskin
  Hi Jax,
If color is critical, you will probably need to shoot a white balance, done with a gray card, before every significant change. Especially if you are adding gels to the lights. Remember: light bounces, particularly in a small space. Some digital cameras allow you to add preset color balances that will match your strobes; this is good for general work, but not good enough for critical work. In an 8-foot studio, you will not be able to turn a white background black if you want to have any light on the subject.
Thanks, John


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February 22, 2008

 

Jax
  Cheers again John, Its just I used to use a real shoddy tungsten flood lamp set-up then took the plunge and forked out for the Strobes. Now obviously the quality is superb but I wasnt expecting to have to go near that colour balance ever again! Many hours wasted away!. Its not major critical but it would be time saving in post to just have skin looking like skin and not slightly orange. So I could open up the shots choose the ones to B&W and bang the lot on a disk without going through each and every one to fix them. Perhaps I'll keep playing...


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February 22, 2008

 

John H. Siskin
  Hi Jax,
If you shoot a gray target at the beginning of a session, and shoot in raw, you can batch the color balance really quickly. Although the conversion to JPEG or TIFF takes a while, you don’t have to oversee the process.
Thanks, John Siskin


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February 22, 2008

 

Bruce A. Dart
  Hi Jax,
Shooting at 5600k color balance is a "warmer" setting and thus the orange cast. With the Nikon D200 I set at 5000k to get cooler, more natural tones. The late great Dean Collins often used a white background and made it black but to do that you need to keep light from falling on it and in an 8 foot area you are probably as close to that as you are going to get to black with a dark gray. Sounds like if you used a gray background to start you could make it work that way. I disagree with John on the meter, however. We all have system that works for us. A flash meter WILL get you closer more quickly if you understand the information you are getting. While you may set up a perfect 3:1 portrait ratio (one stop difference between main and fill) you also have to check with all lights to see what the combined light will be with digital. I agree the histogram will give you the info you need. But, the image on the camera back likely will NOT. On my D200 I have the brightness of the screen for image review set to -2 and it is still brighter than the actual image. If you based your exposure on that, it would be wrong. Camera settings, in a studio flash set up, should be on manual or you will likely get the wrong exposure. Once your shooting aperture is established, you can also vary the lightness or darkness of the background by lowering (longer) or raising (faster; darker) the shutter speed. Critical is that it still needs to synch with the camera. If your base exposure is 1/60 at f/8, for example, at 1/30 and f/8 your background will be lighter. If your camera will synch at 125 then at 1/125 and f/8 the same background will appear slightly darker. John is right in that we used to use a lot of polaroid film. Because no matter how accurately we meter and get close, there is always a little fine tuning and those tests are essential. With any testing method, once you do it a few times (or a few hundred, or a few thousand)you can do it quickly, easily and it works for you. John's system would drive me crazy. My system would probably drive John crazy. Both work. You have to test. Most importantly, once you produce a good result you HAVE to be able to do it again and again. Good luck.


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February 26, 2008

 

John H. Siskin
  Hi Bruce,
The problem is not that you or I may manipulate light in the studio differently, and figure out the exposure differently. The problem is that most people who are beginners in the studio do not understand anything about exposure. They think the meter is a magic box that will deliver an exposure, which will be perfect. I am certain that neither of us have this delusion. I have seen many people set up lights, according to some plan they got, then make a meter reading. They shoot a bunch of images at the exposure from the meter, which are lousy. Then they wonder why. It doesn’t seem to matter what you say about balancing light or ratios, because they don’t understand exposure. They don’t understand stops. So by all means tell people to spend a couple of hundred dollars on a meter, but you might remind people that the information from the meter is no better than a guess. If you make students create a good light by using their eyes they also learn about exposure.
Thanks, John Siskin


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February 26, 2008

 

Bruce A. Dart
  Hi John,
You are right on this one. It depends, of course, on what you intend to do and the experience level. My first portrait in my studio when I purchased the building, I didn't know how to use the lights, didn't have a meter -- didn't have a clue really-- and made the first portrait using the modeling lights on the strobes because I didn't know how to use flash!! My first course on basic lighting, now about 29 years ago, spent 50 hours working mostly with just a "main" light to understand light patterns before we even got into multiple lights, ratios and all the things that go with studio lighting. In every situation there are so many "it depends" kinds of things and most of the BP questions don't have enough info to really tell at what level folks are. The nice thing about digital (polaroids were a more expensive way to learn the same thing) is the instant feedback. You can see right away if you make a mistake and can correct it. Even after nearly 30 years of making portraits for a living, I still sometime pop the first exposure and discover I didn't change a setting from a previous time I used the camera or something equally dumb and have to regroup. Thankfully, that adjustment doesn't come a week later when the film comes back from the lab it can come right away. An understanding of portrait lighting, even basic stuff without being overly creative, takes a bunch of work, and tests, and constant thinking. It is not one simple "this is it" and shoot forever. An understanding of one flash and camera is hard enough for most beginners. Add three more lights and different power settings and there is much, much more to it!!! And I'm not talking about the old portrait master Frank Cricchio (honored by the Professinal Photographers of America recently for a lifetime of achievement)who took the basic four light studio set up and added FIVE more accent lights, using 7-9 lights in his camera room. The bottom line is:(and we certainly agree on this one) if you really want to do more than a few casual portraits you MUST learn lighting, metering, and exposure. And then you work with backgrounds, props as well as poses. It is a long and continual process. You can have fun with it right away, but to understand it and master it, it takes more than a little work. Starting out as a little leaguer, if you pardon the reference, you are not going to break a major league home run record right away. It makes a difference when answering these questions as to whether we are solving problems for Portrait 101, for Intermediate Portraiture, or Advanced Portraiture. You can't do a triple axel if you haven't learned how to stand up on the skates yet. Doesn't mean you shouldn't try or even aspire to that level. It's just not an overnight process. I don't have a BP web site but I do have one of my own, mostly with portraits, at www.photosbydart.com and I would always be happy to help someone just starting out. Sharing is what photography is all about. My e-mail is bdphoto@ptd.net. Keep smiling!!
Bruce


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February 26, 2008

 

James B. Hewin
  A lot of excellent advice from those above! I just wanted to add my own 2 cents based on my own experience with Canon cameras and a home studio enviroment (monolights, umbrellas on stands, backdrops of various colors.
1. Always use the camera set on Manual and don't rely on the cameras exposure meter... Rely on the preview image and histogram. If you want to avoid color cast, be sure to use the highest sync speed for your model of camera to prevent natural lighting (lamps, windows) from bleeding into the exposure adding to the color cast.
2. White balance: I have done a lot of experimenting with this aspect of studio lighting and I have found that although shooting and using a custom white balance from a card is a good way to do it, it is not in my experience always 100% reliable and I'll tell you why. I have found that custom white balances from cards will still sometime not read correctly in the final shot.
Here is an example: Using a sky blue background behind my subject I did a custom white balance from a neutral gray card. I then shot the whole session assuming the color balance was correct and it even looked OK in my preview screen. After downloading the final shots to the computer I was horrified to find that the skin tones in every shot were slightly off. I had to spend a lot of time trying to correct for the color cast in every shot. Not sure why it happened but one theory is the blue background reflected back on the surrounding surfaces in the room, and then back on the card as the custom white balance was being made. The card and camera thought there was too much blue in the room. The skin of the model however, did not.
The best advice I can give is always use the default "Flash" in the White Balance section of your menu (the method that works best for me), or if you're in the habit of just setting the temperature, use exact temperature of your moonlights.
That being said, if you are trying to mix light sources (window light and fill flash for example) the card is definitely the best way to go.
James Hewin


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February 27, 2008

 
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