Examples of Ambient Light Manipulation with "Priority" Modes

The Shutter Priority and Aperture Priority modes make good sense. You can guarantee certain outcomes. For example, if you want to be sure to always freeze motion or cause blur (in the case of Shutter Priority, shown as Tv (Time value) on your Canon. Or if you want to be sure your entire subject is within the depth-of-field in the case of Aperture Priority, shown as Av (Aperture value) on your Canon.


But what about using flash with the"Priority" modes?That introduces a veryhandy, butsometimes confusing feature. Theway theTv and Av modesutilize flash is for foreground fill only. Theaperture and shutter speeds shown are for the background light/ambient light quality. Therefore, when you get flashing values in your viewfinder, they indicate overexposure or underexposure of the background only. Remember, this is only for when a flash is activated. The flash acts independently, metering itself with the pre-flash, ensuring the proper exposure of the subject. Just remember to use your "FE Lock" button if your subject will be off-center. You can see my description of the "FE Lock" feature here.


I've divided up the examples in to two types. One demonstrating "Background Light" the other "Quality of Light". I've used rather mundane subject matter because in this post the lighting is the subject.


Both sets of examples were taken with a Canon XTi inShutter Priority (Tv) Mode, with the built-in flash on, 50mm f1.4 lens, ISO 100. I used Shutter Priority rather than Aperture Priority due to the fact that the exposure values in Aperture Priority required a tripod, and I wasn't in the mood.


"Background Light" "Quality of Light"


f1.4 1/30 f1.4 1/30


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f1.4 1/60 f1.4 1/60


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f1.4 1/125 f1.4 1/125


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f1.4 1/200 f1.4 1/200


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The "Background Light" examples were taken at 3pm, and the background light is quite easily manipulated with the shutter speed. I have included the "Quality of Light" examples to show what you may have noticed in the "Background Light" examples. Although the foreground is technically exposed properly, it has a different "quality", sort of a twilight/shrouded look to it. So when we discuss "background" lighting, we're really talking about the entire atmosphere that exists in the image. The flash meters off of real, physical items, not the existing light or darkness, or dust hanging in the air.


So in the "Quality of Light" images, you should notice that as the shutter speed increases, the darkness moves from the background, washes toward, then over, and surrounding the properly exposed foreground images. Pretty spooky. We've gone from mundane subject matter to evil subject matter in four frames.


Imagine the artistic possibilities with this kind of feature. What character would a portrait take on? Or an animal? Or wedding? (be careful with that one)

Thank you for the examples. I do not shoot with a flash enough, and I always forget what the camera is going to do. Theseare good data points to keep in mind when composing a shot.


Thanks


Tom

You're welcome!

<p style="margin: 0in 0in 0pt;" class="MsoNormal"]<span style="font-size: small;"]<span style="font-family: Times New Roman;"]Thanks for your informative note.<span style="mso-spacerun: yes;"] I am an absolute novice using a flash, and my nice new 580EX just arrived.<span style="mso-spacerun: yes;"] I have been snapping, noting, comparing and reading all afternoon.<span style="mso-spacerun: yes;"] I probably will use the flash mostly for inside family gatherings.<span style="mso-spacerun: yes;"] (I haven&rsquo;t been at all happy with the results of recent pics with available light.)<span style="mso-spacerun: yes;"]
<p style="margin: 0in 0in 0pt;" class="MsoNormal"]<o:p><span style="font-size: small; font-family: Times New Roman;"]</o:p>
<p style="margin: 0in 0in 0pt;" class="MsoNormal"]<o:p></o:p><span style="font-size: 12pt; font-family: 'Times New Roman'; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;"]I think that I am settling on aperture priority so I can stop down and get a good DOF.<span style="mso-spacerun: yes;"] ISO will be in the 500 range.<span style="mso-spacerun: yes;"] My initial snaps show that I like results when I use the 580&rsquo;s controls to underexpose almost a full stop.<span style="mso-spacerun: yes;"] I shot the initial snaps with the 30D and the kit EF-S 17-85 lens.<span style="mso-spacerun: yes;"] Comments and suggestions are certainly welcome.

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Originally Posted by TheRoff

<p class="MsoNormal"]<span style="font-size: small;"]<span style="font-family: Times New Roman;"]Thanks for your informative note.<span style="mso-spacerun: yes"] I am an absolute novice using a flash, and my nice new 580EX just arrived.<span style="mso-spacerun: yes"] I have been snapping, noting, comparing and reading all afternoon.<span style="mso-spacerun: yes"] I probably will use the flash mostly for inside family gatherings.<span style="mso-spacerun: yes"] (I haven&rsquo;t been at all happy with the results of recent pics with available light.)<span style="mso-spacerun: yes"]
<p class="MsoNormal"]<span style="font-size: small; font-family: Times New Roman;"]<span style="font-size: 12pt; font-family: 'Times New Roman'; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;"]I think that I am settling on aperture priority so I can stop down and get a good DOF.<span style="mso-spacerun: yes"] ISO will be in the 500 range.<span style="mso-spacerun: yes"] My initial snaps show that I like results when I use the 580&rsquo;s controls to underexpose almost a full stop.<span style="mso-spacerun: yes"] I shot the initial snaps with the 30D and the kit EF-S 17-85 lens.<span style="mso-spacerun: yes"] Comments and suggestions are certainly welcome.
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Congrats on the nice new flash! Beware underexposing though. I've noticed that my prints are darker than their image on-screen. I'd print a few, and see how they look. Unless you intend to display them on-screen only?

One thing to note is that Av often chooses slow shutter speeds when using the flash in low light. If you arn't using a tripod + still subjects, you might want to try M instead. Have fun with the new flash, I just got one a few weeks ago too:).

<p style="margin: 0in 0in 0pt;" class="MsoNormal"]<span style="font-size: small; font-family: Times New Roman;"]I agree shutter speed can be an issue.<span style="mso-spacerun: yes;"] This was at 1/8 second with the flash adding some fill for the ambient light.<span style="mso-spacerun: yes;"] I still have a lot to learn about that flash.
<p style="margin: 0in 0in 0pt;" class="MsoNormal"]<span style="font-size: small; font-family: Times New Roman;"]
<p style="margin: 0in 0in 0pt;" class="MsoNormal"]http://i.pbase.com/o3/62/861962/1/10...69_edited1.jpg

Quote:

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Originally Posted by Steve Eisenberg

Both sets of examples were taken with a Canon XTi in Aperture Priority (Av) Mode ...

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Thanks, Steve.


But I can't understand one thing. With Av, it's the camera that decides the speed. How could u set it at 1/30, 1/60, 1/125 etc. to take these pictures?


You must have taken them in M, I guess.

Nice catch. It was Shutter Priority, I flipped them! oops

I shoot flash shots in Manual. I usual set the shutter any where between 60 and 200 depending on focal length (I prefer 60). I then meter for the background as if I weren't using a flash to set my aperture. Then the E-TTL will set the flash exposure for the subject.


The shutter has little effect on the flash. Shooting at f/1.4 is going to give you very shallow depth of field which is going to blur out any background you are trying to light. If you are shooting more than one person, you will never get then both in focus. It almost negates using a flash.

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Originally Posted by Keith B

I shoot flash shots in Manual. I usual set the shutter any where between 60 and 200 depending on focal length (I prefer 60). I then meter for the background as if I weren't using a flash to set my aperture. Then the E-TTL will set the flash exposure for the subject.


The shutter has little effect on the flash. Shooting at f/1.4 is going to give you very shallow depth of field which is going to blur out any background you are trying to light. If you are shooting more than one person, you will never get then both in focus. It almost negates using a flash.
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Keith: Yes, I think M would be the ideal choice.


Steve: In your example, the Tv "priority" worked because your lens can open no more than f/1.4. I think in the first example, if you had a little bit more light on the box, with Tv at 1/30, the camera would have automatically set the aperture at something like f/4. Then, with every change in the speed you make, the camera would have automatically compensated by making the lens faster and faster. The background, therefore, will not change as you wish.


However, I found great value in your idea. That is, let the flash deal with your subject's exposure and use M to control the DOF, the movement of your subject and the background (think of something like a kid playing piano near the window). That's what Keith shared with us. Thanks, Keith!

There are a number of ways to force underexposure, which was what I was doing to make a point about the quality of light. And how it would affect the mood of the picture...


One can use Manual Mode for every photo, but Tv and Av allow you set certain variables, and force the camera to work with those only.