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Old Jun 3, 2005, 6:45 AM   #1
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A question from someone new to dSLRs.

I own the Canon 20D with Canon EF-S 17-85 IS USM lens and Canon 580EX flash. Yesterday I took some pictures with available light (slightly dim room) and noticed that with ISO at 800 in P mode my pictures turned out dark at the default setting of F5.6 (85mm). However, in Av mode I set the aperture to F8.0 and the pictures were brighter / sharper. I was using the 580EX flash and AWB. Why would F8.0 be brighter and sharper then F5.6??????

What settings do you use for indoor flash people pics?

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Old Jun 3, 2005, 8:40 AM   #2
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I usually switch to P mode for flash shots of people. So I don't remember what it set to.

As for the sharpness question. Almost all lenses are sharper after you stop them down a little bit. Then at some point (usually after F8, unless its a macro lens) they get softer again.

The brightness is the odd question, to me. I am assuming when you stopped down from f5.6 to f8 the shutter speed increased to match the change in aperture? If not, that would account for it.

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Old Jun 3, 2005, 12:22 PM   #3
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I'm a little stumped by the issue you described, but ONE possibility is that the metering was different between the shots - i.e. if your first shot had a brighter source in frame that threw off the metering, and your second shot did not have the light source in the frame. But that is a WAG on my part.

As for settings for indoor people - I use Manual mode, with an aperture of USUALLY 5.6 - 8.0 depending on DOF I want. Shutter speed I will set either 1/60 or 1/125 - using 1/60 and a higher ISO will result in more ambient light in the exposure - using a lower ISO and the faster shutter speed will result in a more isolated subject. So, a good all-around setting is f8, 1/60, ISO 400 - that will give you a good amount of ambient light in your picture. Also, I tend to use center-weighted metering when I'm doing indoor flash work. I also always use a stofen and if possible bounce the flash which softens things up and helps eliminate shadows.
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Old Jun 3, 2005, 1:45 PM   #4
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You may need to keep an eye on the histogram. The 20D needs some flash compensation around +1.

When you are in P mode, the camera will set speed between 1/60 and 1/125 to accomodate for camera shake. If that speed is too fast for ambient light an no flash compensation, the pic would be dark. In Av mode, the speed is set based on ambient light. It might be slower than what you had it set to in P mode and therefore a brighter pic with less need for the flash compensation. Well it sounded good to me!

H :|
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Old Jun 5, 2005, 3:00 AM   #5
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In each mode of the 20D the flash reacts differently. This article explains all you want to know on Canon flash systems and then some:
http://photonotes.org/articles/eos-f...html#confusion
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Old Jun 5, 2005, 4:05 PM   #6
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eosthree wrote:
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In each mode of the 20D the flash reacts differently. This article explains all you want to know on Canon flash systems and then some:
http://photonotes.org/articles/eos-f...html#confusion
If you want to do a neat experiment, in a room with steady light point your20D (which uses ETTL-II,NOT ETTL)at a wall in Av or Tv, make you adjustments to get the meter in the center, then pop up the on board flash and see what happens. For example, in Tv if the setting were 1/8s and f4.5 with the flash down, it will be 1/8s and f6.3 with the flash up. Similarly in Av if it were at 1/8s and f4.5 with the flash down, it will change to 1/15s and f4.5 with the flash up.

If you use Man, for the same scene at 1/8s and f4.5 the meter stays in the center whether the flash is up or down.

Now, I tried the same experiment with one of my cameras that uses ETTL, and it does not do this. The metering stays the same no matter if the flash is up or down. So, ETTL agrees with the Photonotes article, but ETTL-II, which is used by the 20D, doesn't.

I have no idea why I'm seeingan equivalent full one stop reduction inbackground exposure when in Av or Tv with my 20D. However, it should be noted that the subject exposure is always the same in any of the modes (Man, Av or Tv) ... but what is the reasoning behind adjusting the background (ambient) exposure? I primarily shoot using flash in Man, but I tried all of the other modes and they work the same for exposing the subject with flash, and need the same amount of FEC to get the exposure right.



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Old Jun 5, 2005, 11:04 PM   #7
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That is really weird! I would think that the metering would remain the same flash up or down since the ETTL-II should adjust the power of the flash not the camera. Unless the EV is high enough to change the exposure to fill flash. But there again I would think the the flash compensationwould be reduced by one stop, not the speed or aperture...

H
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Old Jun 6, 2005, 1:31 AM   #8
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BobA wrote:
Quote:
eosthree wrote:
Quote:
In each mode of the 20D the flash reacts differently. This article explains all you want to know on Canon flash systems and then some:
http://photonotes.org/articles/eos-f...html#confusion
If you want to do a neat experiment, in a room with steady light point your 20D (which uses ETTL-II, NOT ETTL) at a wall in Av or Tv, make you adjustments to get the meter in the center, then pop up the on board flash and see what happens. For example, in Tv if the setting were 1/8s and f4.5 with the flash down, it will be 1/8s and f6.3 with the flash up. Similarly in Av if it were at 1/8s and f4.5 with the flash down, it will change to 1/15s and f4.5 with the flash up.
In P mode, the ETTL will try to:
if the ambient light is decent, add fill flash
if the ambient light is low, expose for the subject, and forget the background
In AV or TV it will always work in a fill flash mode.
In M mode you are in control, you set the shutter and aperture to correctly expose the background, and then the with a half press the flash will show the coupling range of the flash on it's LCD in feet or meters, this is how far the flash can safely illuminate. Full press to take picture.

If you use Man, for the same scene at 1/8s and f4.5 the meter stays in the center whether the flash is up or down.

Now, I tried the same experiment with one of my cameras that uses ETTL, and it does not do this. The metering stays the same no matter if the flash is up or down. So, ETTL agrees with the Photonotes article, but ETTL-II, which is used by the 20D, doesn't.

I have no idea why I'm seeing an equivalent full one stop reduction in background exposure when in Av or Tv with my 20D. However, it should be noted that the subject exposure is always the same in any of the modes (Man, Av or Tv) ... but what is the reasoning behind adjusting the background (ambient) exposure? I primarily shoot using flash in Man, but I tried all of the other modes and they work the same for exposing the subject with flash, and need the same amount of FEC to get the exposure right.



Bob
In A or TV mode the flash works in fill mode.
In P mode the flash will work in fill or subject mode depending on the amount of ambient light.
In M mode you set the aperture and shutter to properly expose the background, or acheive the effect you are after:
stop motion
large or small DOF
And the flash will calculate what you need to illuminate your subject.


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Old Jun 6, 2005, 2:26 AM   #9
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eosthree wrote:
Quote:
In A or TV mode the flash works in fill mode.
In P mode the flash will work in fill or subject mode depending on the amount of ambient light.
In M mode you set the aperture and shutter to properly expose the background, or acheive the effect you are after:
stop motion
large or small DOF
And the flash will calculate what you need to illuminate your subject.


I don't think this is a fill mode issue, and in a way it would almost seems the opposite. For some reasonETTL-II underexposes the background by 1 stop when using flash in Av or Tv when the flash isNOT in auto flash output reduction mode. However, the subject always gets full proper illumination by the flash.

Canon Support has also sent me emails stating that flash illumination with ETTL-II works exactly the same in every mode, which seems to agree with what I have seen. For every mode on the camera when Ev is less than 10 the subject gets its illumination via flash with the aperature and shutterspeed combination determining the background exposure.And for every mode, auto fill flash reduction starts kicking in at Ev=10 with maximum reduction at Ev=13. Some modes such as P-Auto and the Basic modes are just limited by their program to what they can do to get the background exposure right.

Note, Ev=10 (where the camera switches from regular flash to fill flash using auto reduction of flash output) would be a sceneshot at ISO 100 and 1/60s requiring f4 to get the background illumination correct. This is a fairly bright scene in comparison to typical room light. For Ev=13, f13 would be required, and there would be 1.5 stops of flash reduction.



Bob




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Old Jun 6, 2005, 6:56 AM   #10
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BobA wrote:
Quote:
If you want to do a neat experiment, in a room with steady light point your 20D (which uses ETTL-II, NOT ETTL) at a wall in Av or Tv, make you adjustments to get the meter in the center, then pop up the on board flash and see what happens. For example, in Tv if the setting were 1/8s and f4.5 with the flash down, it will be 1/8s and f6.3 with the flash up. Similarly in Av if it were at 1/8s and f4.5 with the flash down, it will change to 1/15s and f4.5 with the flash up.

If you use Man, for the same scene at 1/8s and f4.5 the meter stays in the center whether the flash is up or down.

Now, I tried the same experiment with one of my cameras that uses ETTL, and it does not do this. The metering stays the same no matter if the flash is up or down. So, ETTL agrees with the Photonotes article, but ETTL-II, which is used by the 20D, doesn't.

I have no idea why I'm seeing an equivalent full one stop reduction in background exposure when in Av or Tv with my 20D. However, it should be noted that the subject exposure is always the same in any of the modes (Man, Av or Tv) ... but what is the reasoning behind adjusting the background (ambient) exposure? I primarily shoot using flash in Man, but I tried all of the other modes and they work the same for exposing the subject with flash, and need the same amount of FEC to get the exposure right.
BobA

Can you repeat the above flash experiment and change the camera focusing to the background instead (without moving the camera position)... Just wondering if the E-TTL2 flash exposure is linked to the distance info from the lens - and not 'evaluating' the background for some situation?
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