Distance display on 430EX

[jseivert]

Still playing with a week old 430EX and I'm checking out this range display. I've read a ton on guide numbers etc, and see in the manual that at ISO100 & 70mm full output should be 37m. Mine shows 18m. I don't have any FEC or EV dialed in. I've tried different ISO's but it stays the same or less. Lens is 75mm f/2.8.

Is this 37m distance in the book based on f/1? and I need to do the math...what 3 stops? to f/2.8 thus reducing the distance to 18m?

[Curtis N]

Info about guide numbers:
http://photography-on-the.net/forum/showthread.php?t=208520

[PacAce]

Still playing with a week old 430EX and I'm checking out this range display. I've read a ton on guide numbers etc, and see in the manual that at ISO100 & 70mm full output should be 37m. Mine shows 18m. I don't have any FEC or EV dialed in. I've tried different ISO's but it stays the same or less. Lens is 75mm f/2.8.

Is this 37m distance in the book based on f/1? and I need to do the math...what 3 stops? to f/2.8 thus reducing the distance to 18m?

The 37m in the manual is the guide number which is the product of the distance and the aperture. So, distance in your case would be 37m divided by your aperture of 2.8 giving you roughly 18 m.

[jseivert]

I actually read that a couple of times, as I have each of your tutorials. Awesome stuff by the way. I think I'm overloaded on this stuff now.

Here's what I get when I do some math:

ISO Change GN f/ Range

100 ------- 37 ---- 2.8 -- 13.2m
200 1.4 - 52 -----2.8 --- 18.5m
400 2 ---- 74 -----2.8 --- 26.4m

But my range will never show more than 18m. Shouldn't it? Haven't been out to do any real world tests on this to see if it'll actually cover more and it's just not indicating that it will.

Another curiosity question. The distance will change based on what it's pointed at. ~4m if I point it out a window and ~18m if toward a dark section of the room. Is this the flash showing me what it thinks it needs as fill?

[Curtis N]

The distance will change based on what it's pointed at. ~4m if I point it out a window and ~18m if toward a dark section of the room. Is this the flash showing me what it thinks it needs as fill?Tv mode, perchance? Is your aperture changing when you do this?

[PacAce]

I actually read that a couple of times, as I have each of your tutorials. Awesome stuff by the way. I think I'm overloaded on this stuff now.

Here's what I get when I do some math:

ISO Change GN f/ Range

100 ------- 37 ---- 2.8 -- 13.2m
200 1.4 - 52 -----2.8 --- 18.5m
400 2 ---- 74 -----2.8 --- 26.4m

But my range will never show more than 18m. Shouldn't it? Haven't been out to do any real world tests on this to see if it'll actually cover more and it's just not indicating that it will.

Another curiosity question. The distance will change based on what it's pointed at. ~4m if I point it out a window and ~18m if toward a dark section of the room. Is this the flash showing me what it thinks it needs as fill?
Did you check to see what aperture the camera is actually set to? As you change the aperture setting, you'll note that the distance mark changes, too.

BTW, in my first post, I incorrectly stated that 37/2.8 = 18. It should have been 13. I wasn't wearing my reading glasses so the 13 looked like an 18 on my calculator. :o

[jseivert]

Tv mode, perchance? Is your aperture changing when you do this?

Yes, in both Tv and Av modes it'll change the distance displayed.

I think I found the answer on photonotes.org:

"Flash duration (flash output) is determined by the flash metering system. Like Tv mode the camera always works in fill flash mode when in Av mode."

Thus when pointed at a light scene it reduces the output and vise-versa for a dark scene.