157m flash range?!?!? That can't be right

[Tomsk]

OK, I have a 300D and 550EX flash. I'm about to buy a Sigma 70-200 f2.8.

It's been a while, but from what I remember a GN of 55m@ASA100 means that my 550ex can illuminate a subject at 19.64m using f2.8 (55/2.8 )

Does this mean at ASA1600 the flash can illuminate at (1600/100/2)*19.64m = 157m

That's as far as my car headlights. :shock:

[robertwgross]

GN 55m @ ISO 100
= GN 220m @ ISO 1600
(each ISO stop increase gives 1.4x the effective distance)

Then divide by f/2.8 is about 80 meters.

---Bob Gross---

[Tomsk]

Damn! I was hoping to strap the 550ex on to my car for the dark winter nights! :D

[robertwgross]

Tomsk, you can do that, but you better drive slowly.

You'll have to set the 550EX to Stroboscopic mode. That ought to get some attention.

---Bob Gross---

[Scottes]

I'm not so sure that oncoming drivers would like it so much.. :twisted:

[PacAce]

I'm not so sure that oncoming drivers would like it so much.. :twisted:

Well, you can always yell out, "Smile and say cheese!". :mrgreen:

[ron chappel]

at least you'd get well lit pictures of the inevitable crash! :shock:

[CyberDyneSystems]

Still.. 80 meters... thats pretty far. :shock:

[Chazs]

Still.. 80 meters... thats pretty far.

I would say at least this far. I used the popup flash on the 300D at a high school football game on Friday from the bleachers and illuminated the players on this side of the field, I'd say about 40+ yards. Of course this was also at 1600 ISO and pushing the flash to +2 FEC).

[Curos]

I'm with cds, 80m is pretty good, IMO.