Originally posted by Lowell Goudge note that full power duration of the AF540FGZ is not as high as you state,
which is the reason I included the reference for the information I was working from. I'm not entirely sure of the actual duration myself.
Originally posted by Lowell Goudge if you trace back through the forum posts, and also try yourself at full power against a uniformly lit wall, you will start to see a black / darker area at the bottom of the frame as shutter speed is increased to maximum. it disappears at 1/150 but is definitely there at 1/180 (at least it was with the K10D). Perhaps later shutters are a little quicker, but the flash duration at full power of the 540FGZ is actually quite long. I also note that when comparing similar shots when taken using my *istD and switching (day to day or when I have which ever flash available) it appears that shots taken with my AF500FTZ are sharper and do not exhibit the same level of motion blur compared to shots taken when using the AF540FGZ . I have not studied this in detail, it is just an impression but it seems that full power when using the AF540 does not freeze the image in all cases.
Interesting observation, I am more familiar with my Elinchrom studio equipment that has considerably shorter flash durations at 1:1 than hotshoe flashes, but I have noticed that the motion stopping capability of the AF540FGZ is not as good as other flash units capable of similar/greater power output e.g: Nikon SB900 Canon EX 580II.
Originally posted by Anvh However you said clearly that you will see a black bar at 1/250, not that you think you will see one. You've showed nothing to back that claim up so far so i'm confused how you can be so sure?
Because of my knowledge of the mechanics of camera shutter systems. If the the sole light source is flash, and a shutter speed higher than the recommended synch speed is used, a blade of the shutter
will be covering part the sensor while the flash is fired there
will be a unexposed(black)area in the frame. The amount of the frame that will be unexposed depends on how far the recommended synch speed is exceeded.
PS:
As we all know, the hot shoe on pentax DSLR cameras goes cold when shutter speeds higher than the synch speed are used(without HSS enabled flash hardware) so I got my Pentax K5IIs and linked the shutter release remotely to my Nikon D4 which was set at its synch speed of1/250th which in turn triggered my studio strobes. After several attempts, this is what I got from my Pentax K5IIs with my sigma 180mm f/3.5 APO EX and a synch speed of at 1/250th with my Elinchrom BRX 500 fired at a blank wall @ 1:1 power*:
EXIF of this image is intact, I shot several frames some of which were black because of the fact that the shutter lag on the D4 is considerably lower than the K5IIs** - fortunately with the computer control capability of the Elinchrom BRX flash units you can set the flash units to delay firing after the synch signal has been sent for a set time, so using this control I was able compensate for the differential in shutter lag and get the timing perfect. I got some strange looks from my colleagues in the studio when I was doing this.
*Flash duration T.1= 1/520th
**D4= 45ms Vs K5IIs=90ms