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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 09 Aug 2014 (Saturday) 03:54
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Aperture and ambient light

 
quadwing
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Aug 09, 2014 03:54 |  #1

So, we all know that shutter speed affects ambient light and that aperture controls the amount of flash.

I'm looking for a bit of clarification. I got my AlienBees B800 in the mail today. Love it, but, it's really, really bright, even at 1/32. In pitch black darkness, it was too bright. Inverse square rule worked mostly, but if I bring the aperture down too far, I lose a lot of ambient light as well.

Also, how would I use this during the day? :S 1/160 max sync speed, ISO50 at the lowest?


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sandpiper
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Aug 09, 2014 04:28 |  #2

I presume that your first line is a typo? Aperture controls the amount of flash you need, not ambient.

It may just be your choice of words, but it sounds like you just have too much of a mismatch between ambient and flash. You say you are shooting in "pitch black darkness" and are struggling to get the flash power down enough so that you can still record ambient. In pitch black darkness, there IS no ambient, so I assume that you actually mean very dark, but that would still require a lot of exposure to show the scene properly. A flash head, even on minimum power, is a lot of light in such dark conditions.

What shutter speeds are you using though? Even if extremely dark, you should be able to get a suitable exposure. If you need five minutes to expose the ambient to balance the flash, then give it five minutes. So long as the background isn't moving you will be fine. Your subject will be lit by the flash, so will be sharp, just try and keep them still, and the light on them to an absolute minimum to prevent too much ghosting if they move whilst the ambient is recording.

If you find ghosting is an issue, then just shoot two frames, one of the subject with flash and the other for the ambient, then blend with a layer mask.




  
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quadwing
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Aug 09, 2014 04:36 |  #3

sandpiper wrote in post #17085418 (external link)
I presume that your first line is a typo? Aperture controls the amount of flash you need, not ambient.

It may just be your choice of words, but it sounds like you just have too much of a mismatch between ambient and flash. You say you are shooting in "pitch black darkness" and are struggling to get the flash power down enough so that you can still record ambient. In pitch black darkness, there IS no ambient, so I assume that you actually mean very dark, but that would still require a lot of exposure to show the scene properly. A flash head, even on minimum power, is a lot of light in such dark conditions.

What shutter speeds are you using though? Even if extremely dark, you should be able to get a suitable exposure. If you need five minutes to expose the ambient to balance the flash, then give it five minutes. So long as the background isn't moving you will be fine. Your subject will be lit by the flash, so will be sharp, just try and keep them still, and the light on them to an absolute minimum to prevent too much ghosting if they move whilst the ambient is recording.

If you find ghosting is an issue, then just shoot two frames, one of the subject with flash and the other for the ambient, then blend with a layer mask.

Yes, that was a typo. I meant aperture.

In very dark conditions, at 1/32 power, I have trouble balancing ambient light and flash. I have no problem illuminating the subject--if anything, overexposure in the subject is the issue. I have an overexposed subject and a black background. If I pull the shutter speed down enough (to say 0"3), and keep going down until I get the desired ambient lighting, I eventually have to start closing the aperture (when the subject is properly exposed by the flash) because the flash exposure starts to get brighter as well after a while.

I average about 1/8 exposures for ambient light usually.


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Aug 09, 2014 05:22 |  #4

You want to expose for the subject and drag the shutter to pull in the ambient light.


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Phil ­ V
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Aug 09, 2014 08:54 |  #5

I think you're misinterpreting the guidance, try thinking it in this direction.

When you're mixing ambient and flash, you're effectively juggling 2 exposures, consider the ambient first, as generally it's fixed - you have no control over it's power (unlike the flash). When doing this, you only have to bear in mind you're adding flash.

Once you're happy with your ambient, whether that's correctly exposed (using flash as fill), or a stop under (using flash as key), you can dial in the flash, you might want to use ETTL if you're in a moving situation (FEC to suit) or manually adjust if the situation is more static.

Sounds like a lot of decisions to make, but it's quick and easy once you make it methodical, your previous method had you juggling variables without a plan.


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abbadon31
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Aug 09, 2014 09:34 |  #6

Phil V wrote in post #17085694 (external link)
I think you're misinterpreting the guidance, try thinking it in this direction.

When you're mixing ambient and flash, you're effectively juggling 2 exposures, consider the ambient first, as generally it's fixed - you have no control over it's power (unlike the flash). When doing this, you only have to bear in mind you're adding flash.

Once you're happy with your ambient, whether that's correctly exposed (using flash as fill), or a stop under (using flash as key), you can dial in the flash, you might want to use ETTL if you're in a moving situation (FEC to suit) or manually adjust if the situation is more static.

Sounds like a lot of decisions to make, but it's quick and easy once you make it methodical, your previous method had you juggling variables without a plan.

You might want to read his post. ;)

He is using a ab800 and that does not support ETTL.


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Phil ­ V
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Aug 09, 2014 10:50 |  #7

abbadon31 wrote in post #17085745 (external link)
You might want to read his post. ;)

He is using a ab800 and that does not support ETTL.

Oops, clearly missed that.

In which case, he's bought the wrong kit to try mixing with (dark indoors) ambient.


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Aug 09, 2014 11:29 as a reply to  @ Phil V's post |  #8

See if this helps:

http://neilvn.com …ues/dragging-the-shutter/ (external link)


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Rolfe ­ D. ­ Wolfe
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Aug 09, 2014 11:35 as a reply to  @ Oldschool1948's post |  #9

This is the best I have found explaining mixing ambient and flash-

In fact, I highly recommend reading through the entire blog, lighting 101.

It covers everything, most of which you probably already know, but Id bet you'd pick up some tid bits you didn't.

http://strobist.blogsp​ot.com …-balancing-flash-and.html (external link)


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quadwing
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Aug 09, 2014 12:16 |  #10

Rolfe D. Wolfe wrote in post #17085912 (external link)
This is the best I have found explaining mixing ambient and flash-

In fact, I highly recommend reading through the entire blog, lighting 101.

It covers everything, most of which you probably already know, but Id bet you'd pick up some tid bits you didn't.

http://strobist.blogsp​ot.com …-balancing-flash-and.html (external link)

I was reading that last night actually!

What I normally do is expose for ambient first, then add flash. I usually underexpose the ambient light by one stop. But when I add flash, even when using 1/32 power and utilizing the inverse square law, I have to keep turning the aperture down, which eventually begins affecting the ambient light.


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Aug 09, 2014 12:19 |  #11

quadwing wrote in post #17085962 (external link)
What I normally do is expose for ambient first, then add flash. I usually underexpose the ambient light by one stop. But when I add flash, even when using 1/32 power and utilizing the inverse square law, I have to keep turning the aperture down, which eventually begins affecting the ambient light.

Adjusting the aperture (assuming you are using full manual exposure controls - no auto ISO or anything auto) immediately affects ambient light exposure as well as flash exposure. There's no "eventually" to it. ;)


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quadwing
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Aug 09, 2014 12:29 |  #12

SkipD wrote in post #17085971 (external link)
Adjusting the aperture (assuming you are using full manual exposure controls - no auto ISO or anything auto) immediately affects ambient light exposure as well as flash exposure. There's no "eventually" to it. ;)

Ah. That's what I was missing. A lot of the reading I was doing implied that aperture only should affect flash, while shutter speed should only affect ambient. Wrong wrong wrong. vmad

And if I boost the ISO, that brings everything up.


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Higgs ­ Boson
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Aug 09, 2014 15:48 |  #13

I think the situation you are describing is that you have too much flash for your room/studio.


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Aug 09, 2014 15:52 |  #14

quadwing wrote in post #17086000 (external link)
Ah. That's what I was missing. A lot of the reading I was doing implied that aperture only should affect flash, while shutter speed should only affect ambient. Wrong wrong wrong. vmad

And if I boost the ISO, that brings everything up.

The fact that you had tangled up is that changing the shutter speed (as long as it is slower than the maximum sync speed) will not affect the exposure for elements that are lit solely by a conventional electronic flash. This does not hold true, though, if you are using a Canon Speedlite set for High Speed Sync.


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Aug 09, 2014 19:50 |  #15

quadwing wrote in post #17086000 (external link)
Ah. That's what I was missing. A lot of the reading I was doing implied that aperture only should affect flash, while shutter speed should only affect ambient. Wrong wrong wrong. vmad

And if I boost the ISO, that brings everything up.

The problem is that this 'rule of thumb' is too simplistic. True rules

  • Shutter speed 'below X-sync' never affects flash exposure -- because flash duration is so much faster than the shutter is open.
  • Shutter speed 'faster than X-sync affects HSS flash exposure...in addition to the loss of flash power/distance -- simply by going even -1/3EV faster than X-sync -- you lose power/range for every -1EV faster shutter speed.
  • Aperture 'affects flash only', only when ambient light is too low to register on the film/sensor at the chosen aperture+shutter+ISO combination.
  • Aperture affect flash AND ambient whenever ambient light is bright enough to register on the film/sensor at the chosen aperture+shutter+ISO combination

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