[Deiberson]

basic info
k10
af540

i was reading on the dp school website that they recommend for basic flash results where you want to fill the entire scene with light, to shoot in M and set the shutter to 1/60 and f5.6. my question is, if i do this and my ev meter is showing underexposure...say -2, do i open the aperture or just shoot because the camera is taking the flash into consideration when i take the exposure?

[Marc Sabatella]

The meter shows underexposure because it it is metering the scene as it *is*, not as it *will be* when the flash actually goes off. If it wasn't showing underexposure, there would be no need for flash. The camera will automatically make up the difference with the flash. You just want to control how much underexposure to set, in order to control how much flash is used. -2EV is pretyt good starting point for balancing flash with ambient light. I personally might tend to go for less flash than that.

[Deiberson]

You just want to control how much underexposure to set, in order to control how much flash is used. -2EV is pretyt good starting point for balancing flash with ambient light. I personally might tend to go for less flash than that.

this is where i get a little confused. from what i read regarding using the flash, i should control the exposure with the aperture dial, right? or can i control the exposure with the amount of flash i'm using?

specifically...let me use the 18-55 kit lens for the example. an auto focusing lens, how would i boost the flash in p-ttl (auto)? or would i need to be in M mode on the flash to increase the flash power?

[LinXitoW]

You have two exposures: the ambient light and the flash.
Shutter speed only influences the first, flash power only the second. ISO and aperature influence both.

[MSM]

this is where i get a little confused. from what i read regarding using the flash, i should control the exposure with the aperture dial, right? or can i control the exposure with the amount of flash i'm using?

specifically...let me use the 18-55 kit lens for the example. an auto focusing lens, how would i boost the flash in p-ttl (auto)? or would i need to be in M mode on the flash to increase the flash power?

I also have a K10d. Press the fn button and then the down arrow to access the flash menu. the rear wheel then can adjust the flash exposure compensation in pttl. Your flash more than likely has the ability to adjust it - check the manual.

If you take your flash off camera and sync with triggers then M mode would be the way to go. You would then adjust the flash power up and down. Also, the Aperture is one of the main variables in determining the flash component to a photo's exposure. The other is flash to subject distance. (Closer the flash the brighter. Google inverse square law)

[Marc Sabatella]

this is where i get a little confused. from what i read regarding using the flash, i should control the exposure with the aperture dial, right? or can i control the exposure with the amount of flash i'm using?

Either is possible; depends on the effect you are after.

The whole point of what you are doing (trying to take control of anything at all rather than using full auto settings) is so that *you*, not the camera or the flash unit, is in control of the balance between the ambient light and the flash. The flash automation is such that it always how how much flash is needed to yield a good exposure given the exposure you have selected for the ambient light. If you select an exposure for the ambient light that results in a 0 meter reading, the flash won't need to fire at all (although it probably will anyhow). If you select an exposure for the ambient light that results in a -1 meter reading, the flash will fire "a little" to make up the difference, resulting in a picture in which most of the light is ambient, with just a little coming from the flash. If you select an exposure for the ambient light that results in a -2 EV meter reading, the flash will fire *more*, resulting in a picture that more obviously has both ambient light and flash in in. If you select an exposure for the ambient light that results in -3 or lower on the meter, the flash will be providing most of the light in the picture. All of these options will result ina picture that's the same overall brightness level, but just different relative amounts of ambient light and flash.

So you choose aperture and shutter speed in M mode to control how much ambient light is in the picture. The flash then figures out for itself how much it needs to fire. If you dial back the flash power, then it won't try to make up *all* the difference between the ambient light exposure "correct" exposure, so you'll get a picture that's darker overall, just as if you had used negative exposure compensation in an auto mode. Or so I assume - I don't know your particular flash unit.

specifically...let me use the 18-55 kit lens for the example. an auto focusing lens, how would i boost the flash in p-ttl (auto)?

The flash compensation control on your camera.

or would i need to be in M mode on the flash to increase the flash power?

Not at all. M mode is needed only when you are trying to control the balance between ambient light and flash. If you just want more flash, and don't care how much ambient light there is or isn't in the picture, flash compensation works just fine even in P mode.

Flash is a pretty complicated subject if you let it be. If you want to understand it better, see the "strobist" site:

Strobist