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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 27 Apr 2015 (Monday) 21:14
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Lets See Your OCF HSS Outdoor Portraiture.

 
golfecho
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Sep 05, 2019 11:50 |  #1021

tim1970 wrote in post #18922048 (external link)
Another reason could be that using ISO 100 would have caused the SS to be increased to ~1/1200. HSS requires more flash power at 1/1200, then 1/600 of a second. Even if the ISO is higher.

Kinda what I was thinking too . . . I also thought (as mentioned above) that ISO 50 was a pseudo-ISO that did not reduce noise (and some say actually increases it).

1/600 or 1/1200 both require HSS, but as mentioned above, could be not enought power at 100 ISO . . .

Just curious . . . Waiting for the reply from the OP . . .


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Sep 05, 2019 12:29 |  #1022

tim1970 wrote in post #18922048 (external link)
Another reason could be that using ISO 100 would have caused the SS to be increased to ~1/1200. HSS requires more flash power at 1/1200, then 1/600 of a second. Even if the ISO is higher.

This would be the very reason I would choose to go with ISO 50 over 100....get the SS down so HSS doesn't suck all the life out of the flash.


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golfecho
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Sep 05, 2019 13:36 |  #1023

idsurfer wrote in post #18922069 (external link)
This would be the very reason I would choose to go with ISO 50 over 100....get the SS down so HSS doesn't suck all the life out of the flash.

Maybe I am missing something . . .

At 100 ISO, the sensor is twice as sensitive to light as at 50, right? So that would mean a faster SS for the same total light. So why would a faster SS require more flash power, since the shutter is only open half the time? It would seem that a more sensitive sensor (at 100 ISO) would need LESS flash power . . .


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Sep 05, 2019 14:38 |  #1024

tim1970 wrote in post #18922048 (external link)
Another reason could be that using ISO 100 would have caused the SS to be increased to ~1/1200. HSS requires more flash power at 1/1200, then 1/600 of a second. Even if the ISO is higher.

This. ISO 50 is not without its issues but they are less of an issue with a flash lit scene. Power drops off rapidly with every stop of SS using HSS.




  
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Sep 05, 2019 14:42 |  #1025

golfecho wrote in post #18922085 (external link)
Maybe I am missing something . . .

At 100 ISO, the sensor is twice as sensitive to light as at 50, right? So that would mean a faster SS for the same total light. So why would a faster SS require more flash power, since the shutter is only open half the time? It would seem that a more sensitive sensor (at 100 ISO) would need LESS flash power . . .

Using HSS your flash power drops off rapidly. Because the pulsing of the strobe only happens for the duration of the shutter opening you lose more flash than you would gain using iso 100. It's all about maintaining the balance between ambient and flash.




  
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Sep 05, 2019 16:40 |  #1026

My experience is that the only non-linear drop in power comes when switching from x-sync to HSS. Typically 1 stop less ‘power’. So changing from x-sync at 1/200th, to HSS at 1/250th results in the appearance of a 1-1/3 stop drop in flash power as the light switches from a single, short burst, to a continuous pulse.

Beyond that, HSS is much like a continuous light source (best to think of it at 1/1 power for this example, but any power below or above x-sync works the same). As the shutter speed increases, the HHS power decreases by an equivalent amount. One stop increase in shutter speed equates to a one stop decrease in the HSS flash power. Where I’ve seen confusion is in the additional loss of ambient. And, that RGB values do not respond linearly to light values.

I tested all this a few years ago by shooting a grey card and reading the RGB values and comparing below x-sync with HSS power and well as continuous vs, flash balance.

Again, it’s been a while, but as I remember it, if you remove the effects of a continuous (ambient) light source, the HSS power is a linear drop. So, I too am confused by the choice of ISO 50. But, I wonder, am I missing something?


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Sep 05, 2019 23:57 as a reply to  @ post 18922002 |  #1027

Yes, less noise in the shadows for shots like this. I try to use 50 whenever possible. I realize there might not be a huge difference between 50 and 100, but I prefer to keep it at 50 and use shutter speed and/or aperture for adjustments. I believe these were taken around 6:30pm and the shadows were getting pretty dark. There are a lot of ways to get a good exposure, light power, aperture, shutter speed, iso... I started with settings I liked, then worked from there as the shoot went on, these were about an hour in.

Another point I should mention, is that this was my first outing with the EOS R and I had set my aperture settings to the lens ring, when I changed to the 135 f/2 I no longer had the lens ring, so I moved the aperture setting to the mode dial, which had been set to ISO. So it was much easier to change the shutter speed and light power than it was to change the ISO.


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Sep 06, 2019 16:48 |  #1028

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Sep 07, 2019 14:32 |  #1029

[GALLERYIMAGE]: embed failed, id not found (image not in gallery any more)


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Oct 28, 2019 08:38 as a reply to  @ post 18626324 |  #1030

Good, creative photo.


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Lets See Your OCF HSS Outdoor Portraiture.
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