420 ex focal length

[timmyk]

OK I've got a 420Ex and a digital rebel. The 420 zooms based on te hfocal length of the lense, it works fine.

but the focal length has to be multiplied by 1.4 as its on adigital SLR, the 420EX doesn't seem to compensate for this, does this mean I'm not getting the full power as the flash beam won't have been focussed in enough - are there any other disadvantages ?

[PacAce]

Yes, you are getting the full power out of the flash(when required) but, like you said, they won't be as concentrated on the subject compared to if the flash took your 1.6x mag-factor into consideration. However, if you take a look at your flash, you'll notice that the head zooms to specific focal lengths. It doesn't zoom variably as you zoom the lens. So, even if the flash did take the mag-factor into consideration, you would still "lose out" if you used the zoom lens at focal lengths other than what's marked on the flash.

The only flash that currently takes the crop factor into consideration is the 580EX. And it only works with the newer cameras like the 20D, 1D(s)2 and the DREbXt.

In short, I wouldn't worry about the 420EX not adjusting for DSLR sensor sizes.

[scottbergerphoto]

I've been using a 420EX for more then 5 years and the zoom/crop never has been an issue.
Scott

[2goldens]

:) I have the 420EX and it works great with my Digital Rebel.

[DaveG]

OK I've got a 420Ex and a digital rebel. The 420 zooms based on te hfocal length of the lense, it works fine.

but the focal length has to be multiplied by 1.4 as its on adigital SLR, the 420EX doesn't seem to compensate for this, does this mean I'm not getting the full power as the flash beam won't have been focussed in enough - are there any other disadvantages ?

About the only time that there could be an issue is if you are using the flash at the end of your aperture/distance rating and the flash defaults to a "too wide" setting. Lets say that on maxium power (and I'm making this up) your flash gives you this: five meters at f11 with ISO 100 and you are using a 50mm lens. The zoom head needs to be at the 80mm setting (not that your flash has one but ...) so the flash's cone of light is concentrated and gives you 100% power at that distance. If the flash's zoom stays at 50mm, the flash cone is widened and weakened, and then it may only provide f8.X and you could underexpose.

The odds of that happening is negligible and if you check your histogram you will see the underexposure and can either select f8.X or force zoom the flash head to compensate.

I really think that the camera specific zoom in the 580 is more hype than function. In some circumstances it could even hurt. For example if you were using the 580 in a camera rotating bracket with a very wide angle lens. The flash's orientation hasn't changed, it's above the lens and is making a horizontally shaped flash pop. That means that there's good flash coverage left and right, but not as much up and down. But if your camera is now vertical, the camera WANTS up and down coverage.

With the 580 one presumes that you will get the correct flash cone when you shoot with the flash horizontally and the camera horizontally, so the cone is going to be too narrow when the flash is horizontal and the camera vertical. With the older 550 you are going to get a "sloppy" cone and more than you need for the horizontal/horizontal shot, but it might just save you for the horizontal flash/vertical camera shot.

Anyway I wouldn't worry about the 420 and I wouldn't pay a premium for this feature in the 580.