speedlite

[dioptic]

Hello,

This forum is great.


I have a 20D and want to buy a speedlite. Will a 420EX work with it? What kind of range should I expect? Any tips?

Thanks.

Dioptic

[digibeet]

The 420 EX will work. The range is depending on the lens you are using and the choosen ISO setting.

[dioptic]

Thanks Digibeat.


Let's say I was shooting with ISO 100 and using a 70-300mm lenss. What kind of range do you think I should expect?

[robertwgross]

Flash coverage(mm)
24 28 35 50 70 105

Guide number (for ISO 100, in meters)
23 25 31 34 37 42

So, let's say you have it zoomed to 105mm at ISO 100. That means 42 meters, divided by the f/stop of your best lens. Let's say that is f/2.8. Then 42 divided by 2.8 is 15 meters of range. If you increase ISO to 200, then multiply by 1.4. So, the same range for ISO 800 would be 42 meters. Often you will have much slower apertures, so the range falls off quickly.

---Bob Gross---

[Kostyanych]

Well, would you mind explaining me another situation:
Flash coverage is 24 mm, guide number is 23. Does it mean that the range is 23/2.8 = 8.2 m at ISO 100?
Am I right?

[pierrot]

No you aren't. ;)
It means a range of 23 meters at ISO 100 for a lens opening at f/1.0. Because (nearly) nobody could afford a f/1.0 lens (and they are not available on consumer market), better make the calculation with a f/1.8 for instance.
Then the range (at ISO 100) will be 23/2.8 = 8.2 meters. If you set your lens at f/8, the range will be a bit less than 3 meters, and so on.
And if you double the sensitivity, you double the range. Shooting at ISO 400 would give you a range of 32 meters à f/2.8 and 11.5 meters à f/8.

[tim]

Rule of thumb: it makes dark things brighter, and it's in a different league from the onboard flash. The 550EX is one of the things that's made the biggest difference to my photography, and the 420EX will do the same job 95% as well for most people, IMHO.

[MrChad]

I love my 420EX, but you may want to also look into the 580EX I think it was specifically designed for the 20D. But the 580EX is way pricey vs. the 420EX.

Anyone know if the 420EX works with all the AF points on the 20D?

I know the 550EX only used all the AF points on the Eos3 and higher film bodies.
It works on my Elan 7N but it doesn't activate the vertical points.