Manual mode and flash

[mike_rutledge2]

<p>So I'm taking a photo 101 course and we are using manual mode only. The one thing I don't understand is that if I'm doing an indoor shot, with flash, and I set my shutter and aperture to get a centered exposure reading on the graph, that is the reading for the current ambient light. When the flash goes off won't it then be much brighter and my manual settings incorrect?<br>

Let's say a similar situation but the ambient light requires a wide open aperture but the shutter is still slow (< 1/60). With the flash turned on, seems like I should be able to take the shot at a higher shutter speed to avoid shake/blur.<br>

Just confused on how to factor in flash light when in manual.<br>

<br />Thanks,<br>

Rut</p>

[paul_noble]

<p>Yes, it is entirely possible, although not certain, that the flash will overpower the ambient light.</p>

<p>Every flash exposure is actually a double-exposure; the ambient light and the light from the flash. You must choose which one you want to dominate the result.</p>

<p>It the simplest case, one would usually set the shutter speed at the highest speed at which the shutter is fully open. This is referred to as the flash sync speed and is often marked with a red X on the shutter speed dial. On film SLR's, this is often fairly slow, like 1/60, with a few as fast as 1/125.</p>

<p>With the shutter on X, you need to calculate the aperture. On a purely manual flash, or an automatic flash set in manual mode, the flash fires at full power every time. Every flash has a "guide number" that is used to calculate the aperture. After focusing (or estimating the distance) divide the guide number by the distance, which will give you the aperture. Note that guide number varies with the ISO speed of the film you are using.</p>

<p>For example, if your flash has a guide number of 80 for ISO 100 film and the camera-to-subject distance is 10 feet, your aperture should be set to f/8 (80 / 10 = 8).</p>

<p>Ghosting can occur if the ambient light is bright enough to give a visible exposure at the settings used for the flash. For example, say the ambient light requires an exposure of 1/60 sec at f/5.6 and the flash exposure requires 1/60 at f/8. That's only one-stop difference, and ghosting is likely. Ghosting occurs when the subject moves, the shutter speed is not enough to stop the motion and the ambient light is enough to give you a visible exposure. Electronic flash units usually have a flash duration of 1/1000 sec of less, so the flash WILL stop the motion. To prevent ghosting, try to have at least a three-stop difference between the ambient and flash exposure.</p>

<p>There are reasons to use a flash even if the ambient is perfectly adequate. If faces or other details are in deep shadow, while the rest of the scene is brightly lit, the flash may be used to illuminate those details. This is called "fill flash".</p>

<p>As you seem to be finding out, flash photography can be a complicated subject, with many nuances.</p>

<p>A good resource is "The Strobist" at <a href="http://www.strobist.blogspot.com/">http://www.strobist.blogspot.com/</a>. He concentrates on off-camera flash and multiple flash photography, but there is a lot of good information there.</p>

[Jochen_S]

<p>What kind of flash are you using / permitted to use? If it is a system TTL flash in TTL / auto modeit will throttle itself to the exposure setting you picked.<br>

When I shoot flash indoors (assuming it is a tad too dark there in manual mode I pick the aperture I want / need (for DOF) and set a "not really handholdable shutter speed (1/15 or maybe 1/8 and go for a 2 stop (roughly) underexposure with my ISO.<br>

The order to shoot in manual mode doesn't necessarrily mean to set exposure according to your meter reading.<br>

IF you are ordered to use non TTL mode for your flash divide its guide number (for your ISO of choice) through subject distance and set the result as aperture. - Is there an option to dial your flash down?<br>

Your second case: With flash photography you usually use your shutter speed setting to control the ballance between available light and flash. If you read 1/15 for exposure with available light and set shutter to max sync speed -1/250? - 1/ 500? you won't see much of the ambient light. if you set it to 1/30 you will use the flash to freeze your camera shake and still capture a lot of the scene's mood.<br>

If you do sophisticated stufdio lighting with a buch of flash heads you will happily cut out the ambient light since it would only mess up your white ballance.<br>

If you have a tiny on (or in) camera flash you might be better off capturing as much ambience as you can.</p>

[SCL]

<p>Others can probably explain this better than me, but I'll give it a try. I'm assuming you're using a digital camera, which gives you lots of room for experimentation. First, it is important to know what the maximum shutter speed your flash will synch at. You can then generally use any shutter speed at or below that level. When you take an ambient light reading, make sure your shutter speed is within the flash synch range. Remember your flash duration will generally be in the 1/1000-1/10,000 second or so. You say you must operate in manual mode, but just to be clear...is your flash independent of your camera or built in, and does your camera body measure flash intensity and adjust its duration to your chosen f stop. If it does, you're not really in 100% manual mode - but the process is much easier. In a truly manual situation, you would adjust your flash intensity (either by dialing it down to a fraction of full power) or by using some sort of diffuser (like a handkerchief over the flash, or perhaps bouncing it off the ceiling). Autoflashes produced since the late 1960s or early 1970s have a photocell which measures flash intensity and adjusts duration to fall within your selected ISO range and aperture value. The trick is to determine how much you want the flash to affect the picture...if it is to lightly fill the subject, you would generally determine the flash to subject distance, check your flash to determine what the appropriate f/stop is, or do that by using the guide number formula, and see what the appropriate aperture would be. Then use that aperture & shutter speed combo for the ambient light part of the exposure.</p>

[mike_rutledge2]

<p>Thanks. Yes, I see it can become complicated when using manual mode. I'm using a Canon XTi and an older Canon 420 speedlite. I know it will handle everything in auto mode. Just wasn't sure about manual settings.</p>

[SCL]

<p>Should be a piece of cake with that equipment. Just go thru the steps one by one, take a shot and check your results...then redo it factoring the conditions mentioned above until you have achieved satisfactory results and learned the process of how to factor in the variables. FWIW I frequently take product shots using my digital body in manual mode, but with an adjustable autoflash for fill in lighting.</p>

[q.g._de_bakker]

Flash light of course adds to ambient light, and the flash exposure will (have to - but it will, so no worries) have to take the ambient light level into account. So the bits exposed by flash and ambient light will be exposed correctly.<br>The parts not reached by flash and are lit only by ambient light will need a different exposure. That difference is provided by the difference in flash duration and the shutter speed. So whne set correctly, the bits only lit by ambient light will be correctly exposed too.<br>Everybody happy. ;-) Until you realize that there are differences across the scene in both flash exposure and ambient light exposure. Sometimes more so than other times. But you can't get everything right, so... just another "such is life" moment.

[songtsen]

<p><a href="http://www.learn.usa.canon.com/resources/articles/2011/fill_flash_use_EOS_article.shtml">Fill-Flash use with EOS cameras and Speedlites</a></p>

<p><a href="https://emedia.leeward.hawaii.edu/frary/elan7e4.htm">Canon 420EX Speedlite </a></p>

 

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