Official Pentax K-5 Specs !

Started Sep 19, 2010 | Discussions thread
ant_ds Junior Member • Posts: 32
Re: 1/250

sir_bazz wrote:

Stig Vidar Hovland wrote:

Explain to me why 1/2EV stop faster flash sync. time is so important. The difference between 1/250 and 1/180 is really small and high speed sync is the solution anyway if you want fill flash outdoors.

Suppose it is a bright day. The meter says 1/180 and f16 (sunny rule @ ISO200)
I want to use my flash, a Metz 48 with a GN = 48, so the reach would be

1/180 f 16 -> reach 48/16 = 3 mt

Imagine my Pentax istDS had 1/250 sync I could do:

1/250 f 13 -> reach 48/13 = 3.7 mt

So it looks as if the difference is not that big, just 1/2 stop.

BUT if I WANT to go to 1/250 with my flash, we enter HSS territory,
and sadly,at 1/250 the my flash GN is already down to about GN=24. So,

1/250 f13 -> reach 44/13 = 1.8 mt

So the comparison is not between 3 vs 3.7 mt of reach.
For those who want 1/250 in those circunstances, it is between
1.8 (having to use HSS) and 3.7mt (full flash power).
That about 2 full stops.

I dont care about the 1/180 or 1/250 of the new K5. As I said
I still use a istDS so I'm used to live with obsolete specs.

Just wanted to explain why some users could use 1/250 sync to their
great advantage.

It's 1/3 of a stop and I don't get it either.

I shoot at x-sync on my 645N, (1/60sec), and have no problems as the flash is the mechanism that freezes the action.


Actually, it is closer to 1/2 stop

log2(250) - log2(180) = 0.47 (closer to 0.5 than to 0.33)


PS: Of course I could be all wrong.

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