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cruzyn56
9th of January 2005 (Sun), 19:55
Hi all,

A question about the pop up flash on the 20d. I am relatively new to dslr. I have owned film slr's, old and pretty much manual, up until buying a digital p&s 1 year ago. My old film slr had a shoe mounted flash. When taking flash pictures I basically set the shutter speed at 1/125 and the aperature at whatever the flash said was appropriate for the ISO of the film.

I am confused with the settings I am seeing with the pop up flash on the 20d. The camera has the 18-55 zoom lens. In auto at about 40MM the settings are 1/60 and fstop of 5.0. In program mode the same. In shutter priority at 1/60 the fstop is flashing and doesn't stop until I roll back to a shutter speed of 1/8. I was able to bump that up to 1/25 by setting the exposure compensation to -2. In aperature priority it wasn't happy until 1/20 at 5.0 and a -2.

With ttl metering why wouldn't the camera adjust the flash strength so that the shot would be possible at 1/60? Or does that only happen in auto mode? I took pictures of the same subject from the same spot and they are all pretty close.

Would I get better results with a shoe mounted flash?

I was taking pictures of different color water bottles that sat on a table underneath 5 60 watt bulbs in a chandelier. Without the flash opened, in shutter priority, the camera wanted a shutter speed of 3 seconds to get the 5.0 fstop, so it looks like the camera recognizes when the flash is to be used.

robertwgross
9th of January 2005 (Sun), 21:02
I am confused with the settings I am seeing with the pop up flash on the 20d. The camera has the 18-55 zoom lens. In auto at about 40MM the settings are 1/60 and fstop of 5.0. In program mode the same. In shutter priority at 1/60 the fstop is flashing and doesn't stop until I roll back to a shutter speed of 1/8. I was able to bump that up to 1/25 by setting the exposure compensation to -2. In aperature priority it wasn't happy until 1/20 at 5.0 and a -2.

That sounds pretty normal.


With ttl metering why wouldn't the camera adjust the flash strength so that the shot would be possible at 1/60? Or does that only happen in auto mode? I took pictures of the same subject from the same spot and they are all pretty close.


The camera probably WILL adjust flash somewhat for range at 1/60. This all sounds pretty normal. Where is the confusion?

You have read the standard EOS flash information, haven't you? The camera may show you ambient lighting settings prior to the flash shot, but then look to see what it actually used after the flash shot.

---Bob Gross---

iof
9th of January 2005 (Sun), 21:19
In both TV and AV modes the camera meters for ambient light and uses the flash(pop-up or shoe) as fill. The EOS flash sticky does a pretty good job of explaining this

http://www.photography-on-the.net/forum/showthread.php?t=46599

[edit]

also see

http://photonotes.org/articles/eos-flash/
http://photonotes.org/articles/eos-flash/index2.html

scottbergerphoto
10th of January 2005 (Mon), 06:27
In all modes, all the time, the camera meter measures ambient light. It doesn't know or even care that you have a flash attached, except for P Mode. In P mode, the camera is programmed not to go slower then 1/60 with the flash attached to avoid blurry pictures from camera shake. In Tv, Av when the aperture or shutter speed flashes, the camera is just telling you that it cannot adequately expose the ambient light with the Aperture(Av) or Shutter Speed(Tv) you have selected. It doesn't tell you anything about the flash exposure which is controlled by ETTLII.
Regards,
Scott