EOS350D/Ring flash.. camera not setting to sync speed

[laika]

Hi all,

 

I've been asked at work to help setup a camera for taking macro shots

of jewelry and its not doing what I think it should be able too. We

are using an EOS 350D(Rebel XT) with a Sigma 105/2.8 EX DG Macro lens

and a Sigma EM-140 DG Macro Ring Flash. As this camera is going to be

used by several people (non camera people) so I want to set it up so

its easy to use. From similar work I've done years ago I would set

the camera in aperture priority mode @ f32, the camera detects the

flash and sets to its sync mode and the camera shuts down the flash

when the correct exposure is reached, tweaks to the exposure are done

via the exp comp dial.

 

Now with the above equipment the camera is mixing the flash with

timed exposures in everything but Auto mode. Its as if the flash

isn't totally compatible with the camera.. I come from a Nikon

background so apologies if its the dopey users not the equipment.

 

Thanks for any help.

[yakim_peled1]

Even with best lenses, diffraction may appear at very small apertures like f/32. I'd suggest f/11.

 

Happy shooting,

Yakim.

[derek_linney]

The camera is trying to balance ambient and flash. The best solution is to set the camera mode to manual and set aperture to f32 and the shutter speed to the flash sync speed - the camera will then manage the flash output to get the correct exposure relying on the flash out put only not trying to factor in ambient light. Incidentally, the aperture setting gets remembered when you switch back to manual mode after using a different mode.

[paul -]

Have you tried changing Custom Function 3 from "0" to "1"? This will force Av mode to use 1/200 when a flash is used.<p>With CF3:0, Av mode will choose the shutter speed based on ambient light so the background (unreached by flash) will be properly exposed.<br>With CF3:1, the forced 1/200 will properly expose the flash-lit subject at the possible cost of an underexposed background.

[mark_chappell]

Like Yakim, I don't recommend using an aperture of f32. At 1:1 reproduction with a lens like

the Sigma (which extends to achieve close focus), that will be an effective aperture of

something like f64. You will unavoidably get image softening due to diffraction, no matter

how good the lens is. An f11 setting will translated into approximately f22 at 1:1, which is

more reasonable.

[steve_dunn2]

<p>You come from a Nikon background, so perhaps this is how Av works with flash in the Nikon world, but not in the Canon world. Av with flash essentially uses ambient light for exposure, with the flash used for fill.</p>

 

<p>M is the best solution to a lot of EOS flash problems. Want to control shutter speed and aperture? M. Pick any shutter speed and aperture you want, and flash will be used automatically as the primary illumination source or as fill, depending on how much ambient light gets past your choice of shutter speed and aperture.</p>

 

<p>The answer to almost any EOS flash question you could possibly have will be found <a href="http://photonotes.org/articles/eos-flash/">in this extensive article</a>.</p>

[laika]

Many thanks all, the CF tip and a few other tweaks have just about got it sorted.

[mark u]

In order to tweak exposure where flash is the dominant source of light, you will need to adjust flash exposure compensation - changing the aperture (as with regular EC) will simply alter the depth of field or degree of diffusion blur, since flash output will automatically adjust to compensate unless you use manual power settings on the flash.