Originally posted by telly0050 recently i learn about using flash as fill light during daytime.
high speed sync is required since the shutter will be too fast for the flash.
but i been through the menu and didn't find anything related to this.
does the k5 comes with this function? or is it only available on canikon camera?
thanks.
Yes, but its not the "shutter that to fast for the flash" actually the flash is always faster than the shutter (it fires in something like 1/10,000th sec)
The shutter speed will be too fast for the shutter curtains to be fully open across the whole frame when the flash goes off.
You can look up how shutters work but basically its like this.
A curtain comes down to let light into the sensor, when the shutter closes after the time you set (shutter speed) , ANOTHER (2nd) curtain comes down to block off the light to the sensor.
With Pentax the shutters travel across the sensor in a bit less than 1/180th sec. So if your shutter speed is 1/180 then the first curtain comes down and travels whole length of the sensor (so it is fully open across the whole frame) and then just after that the second curtain comes down to block the light off again.
At 1/180s it is only FULLY OPEN for a small instant, and that is when the flash triggers, either just when the first curtain makes it to the bottom or just before the 2nd curtain starts to move. The whole sensor is exposed and the flash lights it all over.
If you have the shutter speed at say 1/4000th sec. Then the first curtain starts coming down to open it and then 1/4000s later the second curtain comes down to block it off again BEFORE the first curtain has travelled fully across. What you effectively get is a small "slit opening" moving downwards across the sensor. Both curtains are still moving at the same speed as they always do but the delay between them is 1/4000s of course.
If you popped the single flash in there you would only get the flash to expose the "slit" that was across the sensor at that time & that's no good.
The answer is the High Speed Sync (as Pentax Calls it) but it works the same on Canikons etc..
The flash has to be able to do it and the camera also has to support it.
What the flash does is to actually spread out its discharge instead of one bright flash for 1/10000s or so, it has to emit several pulses of light that will expose the sensor as that "slit" in the shutters moves down the sensor. The flash is actually emitting pulses of light for about 1/180s total time in order to progressively light the sensor for only 1/4000s shutter speed (sounds odd but it does)
K5 supports HSS and many flashes also do it (mainly the expensive ones). The built in flash does not so you are limited to 1/180 with that one. and if you trigger a external wireless flash optically with the built-in then of course 1/180 is as fast as you go.
Another thing about the HSS mode, I sucks power. Your flash power is reduced alot because of the pulsing light emitting for a longer time instead of just 1 single flash.
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If my shutter explanation wasn't unsderstandable i found this on YT showing a hi speed video of the shutter curtains, could have save myself all that typing above.
its a Canon 5D so at 1/200 the sensor is fully exposed, at 1/1000s you can see there is only a slit moving down
Hope that might be helpful