I've got that Canon model, and I'm using it with a Promaster 7500DX flash. The flash appears to support TTL light metering, but I can't find any way to make the camera recognize this. Consequently, when I use the flash, I have no idea how to set the parameters for proper lighting. I know this is possible, but it's so nice to have the camera give you a clue about exposure before you take the shot, and without having to do a calculation.

So, does anyone know if the camera supports this, and if not, some tips for getting the right lighting without it?

  • \$\begingroup\$ Is the Promaster flash the Canon-dedicated version? \$\endgroup\$
    – mattdm
    Dec 25, 2012 at 0:06
  • \$\begingroup\$ I didn't know that there could be a Canon-dedicated version. How can I tell if it is? \$\endgroup\$ Dec 25, 2012 at 2:36
  • \$\begingroup\$ I forget how to tell with that model, but you'll definitely need the right one — each TTL protocol is different. \$\endgroup\$
    – mattdm
    Dec 25, 2012 at 2:53
  • \$\begingroup\$ Also: a quick Google search indicates that this camera is also known as the Canon 300D, the first in the digital Rebel line. Correct? \$\endgroup\$
    – mattdm
    Dec 25, 2012 at 15:01
  • \$\begingroup\$ Yes, it's a digital rebel a.k.a. EOS. \$\endgroup\$ Dec 27, 2012 at 14:25

1 Answer 1


Yes, the 300D supports E-TTL according to the specs

And it appears that the Promaster 7500DX is compatible with your camera, as long as you have the Canon version of the Flash. The manual says it works in TTL mode for older cameras, and E-TTL for later models.

The Canon version has the letters "CN" at the bottom of the back side of the flash, near the on/off button. You can see this in the user manual (PDF).

To use in TTL Mode

Set the flash to TTL mode, and the camera can be in Program, Manual, Aperture or Shutter priority modes. The camera should do all the work.

To use in Manual Mode

If you cannot get TTL to work, set camera ISO to 100, shutter speed to something under the sync limit, say 1/125th, set the flash to Manual, start at full power (1/1) and use the Guide Number from the manual.

So with a 50mm lens , full flash power (1/1) the guide number is 102 (ft). So if you subject is 10 feet away, 112 ÷ 10 = 11, so set the camera aperture to f/11. Or you can set the flash power to 1/4 power, guide number from the chart is 56, so now at 10 ft subject distance you would set the aperture to 56/10 = f/5.6

If you're unfamiliar with Guide Numbers, there is an explanation here: How can I calculate the effect of non-TTL flash on exposure


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