balancing exposure off camera flash - ambient

[leonid]

Hi everybody, this is my first post here, I hope it is in the correct section of the forum.

I would have a general question about flash/ambient exposure.
Both camera and flash are in manual mode. Let's say, we need to underexpose flash with 2 stops (compared to ambient exposure).
How do you proceed to set the ambient/flash exposure quickly? Do you use camera metering, histogram, external metering, intuition/experience? I mean, how do you do it usually when you have less time?

Thanks!

 

[Deleted member 95430]

Im replying to get notified of answers! Sorry ha

 

[Phil V]

Well the only way you're ensuring the flash is 2 stops under in Manual mode is by metering the flash.

But 2 stops under is close to not worth bothering with.

Lets say I wanted the flash 2 stops under? I'd use ETTL and FEC.

But generally I'd want it half to 1 stop under, and I would usually use ETTL and FEC for that too.

The other way round would be much more common as I'd like to control the light and its easier to position flash than ambient, and for that I can easily dial the ambient exposure to anything I like, and it's also simple to balance a 'correct' flash exposure with the histogram, by sight, etc. etc.

 

[wiltw]

Meter ambient first, set shutter and aperture. Then...

1. Set photosensor-automated flash to think ISO is 4*actual, or
2. Set photosensor-automated flash to think aperture is +2EV larger than actual, or
3. If using nTTL digital flash automation, set FEC -2EV
4. or meter manual flash with flashmeter, as Phil suggests, and set power level of manual mode flash at appropriate power level

I agree, -2EV flash is too little added light, I also would set -1EV instead

• If Ambient = 2 parts light, and Flash = 1 part light (-1EV), total light in highlight areas is 3 parts light, while shadow area is 1 part light; 3:1 is moderate contrast light ratio
• If Ambient = 4 parts light, and Flash = 1 part light (-2EV), total light in highlight areas is 5 parts light, while shadow area is 1 part light; 5:1 is contrasty light ratio
• If Ambient = 1 parts light, and Flash = 0.5 part light (-0.5EV), total light in highlight areas is 1.5 parts light, while shadow area is 1 part light; 1.5:1 is low contrast light ratio

If adjusting intensity by adjusting distance, as Phil suggests, if you think of Distance like an f/stop, one can quickly compute new distance and relative intensity. For example, if you light is first measured 4' away, moving it to 5.6' lowers its intensity by -1EV, moving it to 6.7' reduces it by -1.5EV, moving it to 8' reduces it by -2EV. This works when the light is a 'small source' and if it is a softbox modified ('larger') light the changes are closer to Inverse Linear than Inverse Squared.

 

[sk66]

Your flash will always output the same amount of light when set to the same power setting; and the exposure settings don't make a difference. I.e. if you set your ambient exposure one stop under, and you know that at 10ft the flash at 1/4 power brings it up a stop (to proper exposure), you can just set it to 1/4 power for subjects at approximately that distance. Factor 2 for distance or aperture (f/#) changes is factor 2 for lighting power required... in-between is more of a SWAG.

That's basically how I initially set up lighting in a studio as I don't use handheld meters anymore... but for event stuff I agree with Phil, manual ambient exposure with TTL flash metering and -FEC. Generally, the ambient exposure isn't going to change significantly as you move around; but the changes in distances would require constant juggling of the flash power.

 

[Phil V]

What you should have gathered from the above is that it’s quite a straightforward process, providing you grasp the nettle and understand you’re balancing 2 light sources that you’re controlling in slightly different ways.

And the fact your question references that balance means you’ll get it fairly easily.

The problem is when people refuse to accept that simple premise, they’re usually the same ones who can’t grasp that you don’t need a fast shutter speed to freeze movement when using flash.

 

[leonid]

Thanks for the valuable information!
For quick shootings outside and when lighting conditions are rapidly changing I'll stick to TTL and FEC. In studio or outside when the lighting conditions are constant, I will still use manual flash and a handheld meter for more control of the light.

 

[Kris]

1. Set photosensor-automated flash to

I still miss thyristor flash.

Such a shame it's disappeared.

My metz was almost always bang on. My 283 was also very good. Only semi-modern gun i know that offers it is the Can 580exii.

Edit - apparently, the 600ex-rt range of Canon flashes also offers it. Will even transfer ISO and lens aperture to the flash in thyristor mode, either on cam or even radio wireless. Learn something new every day.

 

[wiltw]

I still miss thyristor flash.

Such a shame it's disappeared.

My metz was almost always bang on. My 283 was also very good. Only semi-modern gun i know that offers it is the Can 580exii.

It is so unfortunate that digital TTL has proven to be spotty in reliability and exposure accuracy...a step backward from film TTL. Photosensor flash AE was good with reliability and exposure accuracy, with exception of using a narrower FOV lens with film TTL in certain circumstance was far superior than fixed-angle photosensor. For example, wedding shot into the somewhat dark car interior of a white limo in sun...film TTL would nail it.

Whenever I found digital TTL to be not reliable, I would instantly switch to photosensor flash automation to get the shot. I is also such a shame that SCA-compatible flash disappeared, too...Metz flash with appropriate module allowed me to use the same flash unit with three different brands of cameras, including Canon eTTL ...compatible with cameras spanning almost 40 years!