Trouble with ambient light and flash

You did not state if using manual power control of flash, or trying to use ETTL automation.

Let us start with an easy to compute ratio...2:1 ambient:flash output power ratio, light on flashed area = 2 parts ambient+1 part flash:

• with ETTL it is easy...you set FEC -1EV; that is, ambient is twice as strong as flash, or 2:1
  
• with manual set flash, after you take the ambient reading (e.g. 1/100 f/5.6) you set the flash per a flashmeter reading so that it reads 1EV larger aperture required for 'enough light' (matching ambient), so if the flashmeter says f/4, it takes one larger aperture to equal the ambient reading.
  

1. ambient could fall on TWO sides of the face, whereas flash falls on ONE side of the face. And in that situation, the ambient illuminated side gets 2 parts ambient + 1 part flash, so the two sides actually have 3:1 contrast, NOT the 2:1 that you assume from judging light source intensity!!!
   
2. ambient could fall on ONE sides of the face, whereas flash falls on ONE side of the face (e.g. sun on one side, deep shade on the other, and the flash from the side illuminates only the shaded side of the page. And in that situation, the ambient illuminated side gets 2 parts ambient + 1 part flash, so the two sides actually have 2:1 contrast, which is what you assume from judging light source intensity!!!
   

keano12 wrote in post #17807120
Ok I have two questions. Say I want to use my flash as a 30% fill to the ambient. The ambient is 1/200, F2.8 ISO 200
For me to get a 30% fill on shadows I would go a 1/3 stop higher at F3.2 on flash? 60% would be f3.5 right?

Other question is when outside at night trying to get my background ambient light brightened up I should set my aperture where I want it, shutter at fastest? And use ISO to brighten background?

Heya,

Depends on what your goal is and how you want to describe it. It can be a little confusing using percentages.

When you say 30% fill on shadows based on camera settings, you don't mention anything about the flash mode and power output or distance or anything. All of this tremendously matters. More so than camera settings. You need to clarify that one. To keep it simple though, adjust camera settings for ambient light within sync speed if necessary. From there, add flash for subject exposure to desired level. Power down the flash if you want fill and not key exposure.

When you say you want a brighter ambient light (background light?), you can use ISO, or any of the settings frankly, to do that. Your camera is the ambient light exposure value. You can drag the shutter (slow down the shutter) to get more ambient light. You can open aperture more (if possible or applicable). You can increase ISO. All of these things increase ambient light exposure. They can also increase flash exposure depending on how you're using and mixing them. If your aperture is set to F2.8 and you're not opening it anymore, then that's set. If your shutter is 1/200s and you're not going any slower for whatever reason, then that's set. The only way to get ambient light up from that point is to use higher ISO. You can mix this all around and get different settings and the same exposure value. But you're not limited to ISO. I often drag my shutter as slow as 1/50s to avoid using super high ISO in darker ambient light to get more ambient and blend my flash to it that way.

You can use a meter to determine flash power and go from there.

What I do is simple. I use Live View to get the ambient exposure I want without having to chimp a few times (so I can see the histogram mainly). From there, I start with my flash at something like 1/4th power or whatever power I want to start out at thinking it's relative to whatever my ambient exposure settings are (such as paying attention to aperture and ISO). I take a test shot to see how I want to adjust my flash power output. Usually 1 or 2 shots is all it takes and I am where I want to be either exposing properly as key, or simply exposing as fill.

Very best,

MalVeauX wrote in post #17811080
Heya,

What I do is simple. I use Live View to get the ambient exposure I want without having to chimp a few times (so I can see the histogram mainly). From there, I start with my flash at something like 1/4th power or whatever power I want to start out at thinking it's relative to whatever my ambient exposure settings are (such as paying attention to aperture and ISO). I take a test shot to see how I want to adjust my flash power output. Usually 1 or 2 shots is all it takes and I am where I want to be either exposing properly as key, or simply exposing as fill.

Very best,

This seems to make sense and is fairly easy even for a novice such as myself to understand.

Expose the BG as you want it. Then add flash (adjust the flash power accordingly) to expose your subject properly.

It this an over simplification?

ptcanon3ti wrote in post #17811349
This seems to make sense and is fairly easy even for a novice such as myself to understand.

Expose the BG as you want it. Then add flash (adjust the flash power accordingly) to expose your subject properly.

It this an over simplification?

That's then best method. Although I prefer not to use live view.
Although it would not get a desired percentage as asked by the OP.

gonzogolf wrote in post #17811370
That's then best method. Although I prefer not to use live view.
Although it would not get a desired percentage as asked by the OP.

Yeah...I understand that exact percentages are not considered here. I don't use live view either. I'm just saying that instead of getting all kinds of wrapped up in the technical...I try to keep my thinking sorted out and simple.

2 exposures...1. the BG/ambient 2. the subject by adding flash.

Believe me/ I'm a real novice at flash photography and I'm trying to learn as I find it rewarding and fascinating. I just like to try to keep it simple for my own sake.

I tried to do this in my head, then my head started to hurt, then I got an light meter that shows me the amount of flash in %

ptcanon3ti wrote in post #17811349
This seems to make sense and is fairly easy even for a novice such as myself to understand.

Expose the BG as you want it. Then add flash (adjust the flash power accordingly) to expose your subject properly.

It this an over simplification?

You got it.

Very best,

Yay! At least I got something today.

isvein wrote in post #17811391
I tried to do this in my head, then my head started to hurt, then I got an light meter that shows me the amount of flash in %

Mine hurts when I start to inquire about HOW (i.e. by what computation) it calculates the percentage of flash contribution.

I understand, and yet my head still hurts because the percentage value ...

• means nothing to me from an intensity point of view
  
• the mix contribution MIGHT mean something to me when I have mixed color balance in my lighting, and I want to know how much one source will 'contaminate' my shot compared to my other source. An example would be bluish, indirect light coming in the windows vs. the daylight balanced light from my flash filling in the shadows.
  

1. Ambient only: 1/160 f/3.2
   
2. Flash 25% +ambient 75%: 1/25 f/5
   
3. Flash 50% + ambiemt 50%: 1/40 f/4.5
   
4. Flash 75% + ambient 25%: 1/60 f/4
   
5. Flash 100% + ambient 0%: 1/160 f/4
   

• If your meter reads flash contribution at 10% increments (unlike my meter's 25% 'limited' increments), does it even MATTER how finely it shows the percentage?!
  
• Can I really even see that much difference to visually recognize even a 25% change in contribution?
  
• Does knowing a PERCENTAGE value help me at all, compared to visually assessing how pleasing the contribution balance is?
  
• If my flash is full frontal (rather than off to the left a bit, like in my examples) what -- if anything -- does having a contribution balance do, from the standpoint of source 'intensity' (vs. the issue of color balance from mixed WB sources)?
  

Wilt: I see your point, but that comparison is a bit wrong because you are changing the ambient exposure too.
For this to show any difference, the ambient exposure need to be the same, say 1/160 f/3.2 for all the different % of flash.

Most I know does not use the %-flash at all, but it can be useful for outdoor portraits to just fill inn the shadows with some flash.
They say that 20-30% flash fills in the shadows without it looking like a flash shoot.

Here is, by far, the simplest answer. You can buy my Sekonic L358 light meter. Then you will always know at a glance. Knowing only matters in terms of repeatability. If you are shooting the same set up over and over, this would work. Otherwise, you must recalculate every time.
Buy a light meter that includes this feature.

isvein wrote in post #17812431
Wilt: I see your point, but that comparison is a bit wrong because you are changing the ambient exposure too.
For this to show any difference, the ambient exposure need to be the same, say 1/160 f/3.2 for all the different % of flash.

The change of ambient exposure is often used to change the BALANCE of flash:ambient...what do you do if you want a bit more flash power, but not have the ability to dial in +0.1EV more light?...change the ambient contribution. The end result which I was seeking to achieve is the alteration of the BALANCE, it does NOT matter how you got there!!!

During my test, I provided: Five shots at ISO 1600:

1. Ambient only as a control shot: 1/160 f/3.2
   
2. Flash 25% +ambient 75%: 1/25 f/5
   
3. Flash 50% + ambiemt 50%: 1/40 f/4.5
   
4. Flash 75% + ambient 25%: 1/60 f/4
   
5. Flash 100% + ambient 0%: 1/160 f/4
   

• Equal the sun (1:1) with 0EV FEL
  
• Be weaker than the sun by 0.5EV (using FEL -0.5EV) to achieve low subject lighting contrast
  
• Be weaker than the sun by -1.0EV, (by using FEL -1EV) to achieve moderate subject lighting contrast
  
• Be weaker than the sun by -1.5EV, (by using FEL -1.5EV) to achieve somewhat contrast subject lighting contrast
  

• Equal the sun (1:1) by adjusting power level until it equals what I read with sun alone
  
• Be weaker than the sun by 0.5EV (the 'proper' flash-only exposure needs 0.5EV larger aperture)
  
• Be weaker than the sun by -1.0EV, (the 'proper' flash-only exposure needs 1.0EV larger aperture)
  
• Be weaker than the sun by -1.5EV), (the 'proper' flash-only exposure needs 1.5EV larger aperture)
  

Yes, and you do not need a ambient:flash percentage value difference!

• Assume: ambient 1/200 f/16, flash 1/200 f/11
  ...that is 2:1 ratio, ...2 'parts' ambient light+ 1 'part' of light flash fall on your subject...so you have 66% ambient + 33% flash
  
• Assume: ambient 1/200 f/16, flash 1/200 f/12.6 (2/3EV difference)
  ...that is 3:1 ratio, ...2 'parts' ambient light+ .66 'parts' of light flash fall on your subject...so you have 75% ambient + 25% flash
  

No need to scream about it.
We all know it is possible to calculate it, it does not matter if you call it % or EV.
Some just prefer to use one over the other, some like to calculate it in head, others do not.

But I still stick to that the % does not matter at all if you change the ambient exposure to match the flash exposure, but it does if you cant or wont change the ambient exposure.

isvein wrote in post #17812835
No need to scream about it.
We all know it is possible to calculate it, it does not matter if you call it % or EV.
Some just prefer to use one over the other, some like to calculate it in head, others do not.

But I still stick to that the % does not matter at all if you change the ambient exposure to match the flash exposure, but it does if you cant or wont change the ambient exposure.

But the OP asked how to get a percentage. A percentage is a ratio that varies with the totals. Wilts methodology is valid.

isvein wrote in post #17812835
No need to scream about it..

Who shouted?...I see no use of all-CAPS sentences in my message. I simply provided a full explanation for the logic behind my assessment of Percentage calculation, and a very practical alternative which has only been used in photography for the past 50 years (before flashmeters with Percentage appeared)