flash and manual settings

sthig

I want to shoot my 20d on manual with the flash. Let's say I set my lens to 2.8, what do I set my shutter speed to? If I try to set it where it says it's metered correctly, then I'd have a shutter speed of 2" or 3" which is not what I want. I am shooting with a 430 speedlite.

I have a feeling I'm about to answer my own question, but I bet this is what a light meter is for, right? Is there an alternative for this?

thanks!

Cason

sthig wrote:

I want to shoot my 20d on manual with the flash. Let's say I set my lens to 2.8, what do I set my shutter speed to? If I try to set it where it says it's metered correctly, then I'd have a shutter speed of 2" or 3" which is not what I want. I am shooting with a 430 speedlite.

I have a feeling I'm about to answer my own question, but I bet this is what a light meter is for, right? Is there an alternative for this?

thanks!

What is your ISO setting?

Bodwick

sthig wrote:

I want to shoot my 20d on manual with the flash. Let's say I set my lens to 2.8, what do I set my shutter speed to? If I try to set it where it says it's metered correctly, then I'd have a shutter speed of 2" or 3" which is not what I want. I am shooting with a 430 speedlite.

I have a feeling I'm about to answer my own question, but I bet this is what a light meter is for, right? Is there an alternative for this?

thanks!

I'd set it at 1/200 or 1/250 and reduce the power of the flash to reach the correct exposure.

If full power would blow out at 2.8 then half the power and look again. Still too much then reduce again to 1/4 power. And just keep going till you reach the look you want.

LuckyBob

This is a bit of a long one, so a quick answer to your question first: as the flash duration for most flashes is much quicker than the camera's minimum flash sync speed (which is 1/250th on the 20D), the flash is only illuminating the scene for a fraction of the time the camera is exposing. If you want the light in the photo to originate only from the flash unit, set the shutter speed to the flash sync speed (1/250th) as this will prevent as much stray light from entering the lens as possible. A neat trick is to set Custom Function 3 to "on" which will force the camera to always use 1/250th in Av mode, effectively making shooting in manual mode useless if you only want to light the scene with the flash.


Canon's cameras do something somewhat counter intuitive when using the flash - current ambient light levels are metered by the camera as usual whether the flash is on or off in scene, P, Av, Tv and M modes. Thus, the camera plans to expose the image as if the flash wasn't even there, and only use the flash as a "fill" unit. Thus, forcing the shutter speed to the flash sync speed of the camera (1/250th on the 20D) will effectively ignore the camera's built in idiosyncrasy of planning not to use the flash. The light meter will tell you the image will be quite underexposed, but the E-TTL system will make up for it just fine as long as the flash can handle the range you're asking for (see my note about ISO below) and you're allowing the E-TTL system to pick the power for you. Most of the time I boost or cut the flash around a half stop (via flash compensation) depending on the situation. For a MUCH more detailed explanation of Canon's flash system, see http://photonotes.org/articles/eos-flash/.


Back to technique a bit. If you wish to split the lighting in the photo between the flash and ambient light, using progressively longer shutter speeds will intermix the "fill" flash with the ambient light (up to what the camera claims is the "correct" shutter speed, which you can check by throwing the camera into Av mode temporarily and looking at the suggested shutter speed). Remember that longer shutter speeds may require a tripod, but this method also allows you to do first- and second-curtain flash effects; check the 430EX manual relating to the icon on the back of the flash that looks like three arrows overlapping each other.


The ISO setting is relatively irrelevant if you're forcing the shutter speed to the flash sync speed; it only serves to heighten the camera's sensitivity to light which will extend the useable range of the flash, or quicken the shutter speeds necessary to achieve a particular mix of flash/ambient light. Especially if you're planning to bounce the flash off a high ceiling, using ISO 200-400 can get you quite a bit quicker flash recycle time and use less of the flash's battery.


In summary, normally use 1/250th shutter speed, and have a read at http://photonotes.org/articles/eos-flash/ as it will greatly help in understanding Canon's (and to a degree, other's) flash system.

sthig

wow!

thank you for this info!

I did indeed have my AV setting to 250 (by cust. func.) but I'd not thought of that. This is great and thank you kindly!