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Old Jan 3, 2005, 1:06 AM   #1
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Hi,

I recently purchased a Canon 20D and have been very disappointed with the results I've been getting when doing flash photography either with the on-board flash or with my 420EX.

I've done quiet a few tests tonight and it appears that whenever I use AE lock the pictures I take are 1 stops underexposed using the on-board flash or a 420EX in direct flash mode and 2 stops underexposed using the 420EX in bounce mode. Note, when I don't use AE lock my pictures are consistently 1 stop underexposed using the 420EX in bounce mode, but appear to be fine when using the on-board flash or the 420EX straight on.

The results are the also the same for all three modes of metering, if I let the camera select the focus point or if I set only the center focus point. Either way only focus points located on the object I'm shooting are lit up. Also, all pictures were taken with the camera in P-Auto mode.

Has anyone else seen this problem? Is this normal?

Hopefully I'm just making asilly mistake and the issue isn't with the camera.

Any help would be really appreciated!

Regards,



Bob A.

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Old Jan 3, 2005, 10:50 PM   #2
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It could be the object/subject you're taking picture of :idea:

If the object is slightly bright you'll end up with some underexposure, and vice versa (ie overexposure if the object is darker tone) -> Try something neutral toward a grey tone
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Old Jan 3, 2005, 10:52 PM   #3
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Ok, I think I've at least figured out a way to get decent bounce flash pictures with my 20D using a 420EX Speedlite. I set the camera to manual mode with an aperature of 5.6 and 1/60 s ... also set C.Fn-14 to 1 (average).

Using the above seems to produce a pretty decent picture without needing any digital exposure compensation.

I'm going to do a few more tests tonight to see why using AE lock produces darker images ...



Regards,



Bob A.
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Old Jan 3, 2005, 11:09 PM   #4
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Thanks NHL,

The "subject" I was using to test the AE lock problem was the EOS Digital Software manual. Since it's mostly white I wonder if AE lock wants to turn it 18% grey? This would at least explain the difference between using or not using AE lock. BTW, why does the same object get the proper exposure without using AE lock with a straight-on flash?

I'm going to try the same test tonight using something that is a bit more neutral.

I have a feeling I've had the same types of problemseven with my Elan-II ... but I never noticed because I correctedthe poor exposure either in my darkroom orby using a commercial photo lab. With a digital SLRexposure issues are much more obvious.



Regards,



Bob


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Old Jan 4, 2005, 11:11 PM   #5
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I did a few more tests taking pictures of the greyscale and color control patches pages in my Kodak Color Dataguide.

All pictures were taken using a EOS 20D with a 420EX Speedlite and a Canon 28-105 II USM lens.

Manual mode:

F5.6, 1/60s, Evaluative metering, all focus points active, C.Fn-14=1
1.Bounce flash, didn't use AE lock - Exposure looks correct, wb very close
2. Bounce flash, used AE lock - Underexposed (required +0.8 correction)
3. Direct flash, didn't use AE lock - Underexposed (required +0.4 correction)
4. Direct flash, used AE lock - Underexposed (required +1.4 correction)


P-Auto mode:

Evaluative metering, all focus points active, C.Fn-14=0
5. Bounce flash, didn't use AE lock - Underexposed (required +0.5 correction)
6. Bounce flash, used AE lock - Underexposed (required +1.0 correction)
7. Direct flash, didn't use AE lock - Underexposed (required +0.5 correction)
8. Direct flash, used AE lock - Underexposed (required +1.9 correction)



Comparing the direct flash versus bounced is difficult since the pages in the book are a bit reflective. Also, numbers 2, 6 and 8 were much "warmer" than the others (a bit yellow). The other 5 pictures seemed to have pretty decent white balance.

The above test agrees with the results of some pictures I took of my kids where using the setup for "1" above required no exposure correction to the RAW files.

Is what I am experiencing "normal"? I've sent the 8 pictures to Canon support ...and I'll submit a post when I get a response back from them.



Bob
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Old Jan 5, 2005, 2:13 AM   #6
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This is an in-depth look at Canon's flash systems and may answer some questions.

http://photonotes.org/articles/eos-flash/


You comment that in P mode "only focus points located on the object I'm shooting are lit up"

From the above site:

"you can switch to full auto (green rectangle) or Program (P) mode, which automatically expose for the flash-illuminated subject and not the background. These modes try to ensure that the shutter speed is high enough to let you handhold the camera without a tripod. The drawback of P and basic modes is that photos taken in dimly lit areas usually end up with black or poorly lit backgrounds."



The 20D exposes differently for flash photography foreach mode setting (ie Av, M, P etc), and this is explained at the above site in detail:

"In Av, night and Tv (shutter speed priority) modes the camera meters for ambient (existing) light and fills in the foreground subject using the flash. It does not assume that the primary light source is the flash, and therefore the shutter speed it sets is the same as it would set if you weren't using flash at all.



Good luck and hopefuly this helps.









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Old Jan 5, 2005, 8:08 AM   #7
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Wow, I have had a totally different experience? However I am using the 550EX but I would not think this made such a difference?

The image below was from a conference I just did, using bounced flash, and both flash and 20D on program as I just picked up the camera that morning!!!!

You might disagree but I think their is great tonal value, this is improving all the time the more I experiment.
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Old Jan 5, 2005, 11:06 PM   #8
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BobA wrote:
Quote:
BTW, why does the same object get the proper exposure without using AE lock with a straight-on flash?
Check the 'AE Lock Effects' section in your manual, but without using AE lock the camera is in evaluative metering (unless you have selected otherwise), and the camera 'evaluates' the whole scene averaging its exposure while AE lock metered only around the active AF point - which is centered on the white manual -> the meter 'thinks' this is brighter than the whole scene actually is...

Your test results show this as well when the flash was bounced except the light is now more diffuse -> less variation between AE lock and non-AE lock
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Old Jan 5, 2005, 11:55 PM   #9
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Thanks TimmyB,

It's a very good article. Another one that I have found to be valuable is:

http://www.photoworkshop.com/canon/EOS_Digital.pdf

For my second, admittedly "more careful" test that I posted after my first post I wanted to see if perhaps the problem was due to P-Auto selecting between flash illumination and using fill flash (which is why I selected manual mode for one test). I also wanted to see what would happen if I used an object that had a large 18% grey area.

For the 8 pictures I took in the series above the center focus point that lights up when you press * was on the 18% grey card (not on the color patch side of the book).

I would have thought that no matter what I did the pictures should have turned out about the same for this particular test. I think I'll try again ... this time shooting only the grey card.



Regards,



Bob
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Old Jan 6, 2005, 12:00 AM   #10
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Nice pic Grant ... just the type of exposure I'm looking for! I've been able to get a few shots to look good, but not consistently. Using C.Fn-14=1 + bounce without using AE lock seems to work well, however I stillwould like to master (be a competent noob )the technique of using AE lock.

Regards,

Bob
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