Use of Flash Meter for Portraits

[acroreef]

Hello,

I have a Sekonic L-308S-U light meter and am a bit confused re how to use this to determine flash power if I have chosen my other variables. (This is my first go at using a flash meter). I want an F8 aperture on my Sony A7R, with 100 ISO. I'm setting shutter speed above my synch speed to block out all ambient light, at 200. (Synch speed is 1/160 on my camera). My Godox flash supports high-speed synch. I'm not quite sure where to go from here. None of the You Tube tutorials seem to address this or quite possibly I'm missing something.

Any help/suggestions/ You Tube totorials are greatly appreciated.

Thanks in advance,

Dave

[george013]

Hello,

I have a Sekonic L-308S-U light meter and am a bit confused re how to use this to determine flash power if I have chosen my other variables. (This is my first go at using a flash meter). I want an F8 aperture on my Sony A7R, with 100 ISO. I'm setting shutter speed above my synch speed to block out all ambient light, at 200. (Synch speed is 1/160 on my camera). My Godox flash supports high-speed synch. I'm not quite sure where to go from here. None of the You Tube tutorials seem to address this or quite possibly I'm missing something.

Any help/suggestions/ You Tube totorials are greatly appreciated.

Thanks in advance,

Dave

I don't think you can set flash power in hss.

George

[inkista]

I don't think you can set flash power in hss. ...

You can set the flash power in HSS. But most handheld light meters can't measure the flash in HSS. Sekonic released the first one that can this year (L-858D).

Typically, what you do, is that you set the camera how you want (keeping at or below sync speed), throw the flash on at any old power setting, and take a meter reading. However the aperture reading on the meter defers from the actual aperture setting you want to use, you make that same adjustment on the flash's power.

So, for example, you're at f/8, but the meter is reading f/5.6. So you need to increase the flash's power setting by one stop (double what you have set). If you're at 1/4 power, you need to bump up to 1/2 power.

But with HSS, all bets are off. The meter probably can't measure it accurately. You could try and use sync speed and guesstimate, (so in the case of 1/160 vs. 1/200, you need to adjust by an additional 1/3EV), but HSS does eat more power to do all that blinking. How much depends on what gear combo you have.

This is why I like having TTL gear, and a Godox XPro-C trigger with the TCM function. The XPro-O hasn't been announced yet, alas (both the Sony and Fuji versions are already listed for pre-order on Adorama. (sigh)).

[george013]

You can set the flash power in HSS. But most handheld light meters can't measure the flash in HSS. Sekonic released the first one that can this year (L-858D).

Typically, what you do, is that you set the camera how you want (keeping at or below sync speed), throw the flash on at any old power setting, and take a meter reading. However the aperture reading on the meter defers from the actual aperture setting you want to use, you make that same adjustment on the flash's power.

So, for example, you're at f/8, but the meter is reading f/5.6. So you need to increase the flash's power setting by one stop (double what you have set). If you're at 1/4 power, you need to bump up to 1/2 power.

But with HSS, all bets are off. The meter probably can't measure it accurately. You could try and use sync speed and guesstimate, (so in the case of 1/160 vs. 1/200, you need to adjust by an additional 1/3EV), but HSS does eat more power to do all that blinking. How much depends on what gear combo you have.

This is why I like having TTL gear, and a Godox XPro-C trigger with the TCM function. The XPro-O hasn't been announced yet, alas (both the Sony and Fuji versions are already listed for pre-order on Adorama. (sigh)).

Are you sure?
Flash power is controlled by flash duration.
And in hss the flash duration is spread over the total exposure time, meaning starting when the first curtain starts opening and ending when the second curtain is closed.. I don't know how to influence that.

George

[PhotomanJohn]

Dave,

You don't say what the ambient light level is. In general, I would say that you will have better luck overpowering the ambient light with the camera set at its flash sync shutter speed than trying to do it at a higher shutter speed and HSS. The difference between a 1/160s and 1/200s will barely make a difference in the background exposure anyway.

Your meter doesn't display ambient versus flash ratios like its bigger brothers do so make a ambient light reading with the meter set for 1/160 and ISO 100. Next make a measurement with the flash on manual at full power. If the reading with flash is two or more stops higher than the ambient reading then your flash is powerful enough to do what you want. If the reading is greater than needed, drop the flash power down so that the reading is a couple of stops over ambient. Whether you are going to be able to use f/8 will depend on how bright your ambient light is.

John

[Manfred M]

Are you sure?
Flash power is controlled by flash duration.
And in hss the flash duration is spread over the total exposure time, meaning starting when the first curtain starts opening and ending when the second curtain is closed.. I don't know how to influence that.

George

George - the problem with HHS is that the shutter blades are not fully open when the shutter speed exceeds the synch speed of the camera and the amount of light reaching the sensor is dependent on the width of the slit of the two shutter curtains that are in motion. An algorithm to compensate for this has to be built into the flash meter. As Kathy says, this is not commonly found on flash meters.

[Manfred M]

Dave - how significant is the ambient light under your shooting conditions?

Set your camera to manual and select the ISO, aperture setting and shutter speed at synch speed and take a shot. The resulting image shows you the impact of ambient light conditions.

Unless you are shooting in extremely bright conditions, you may find that the impact of ambient light is negligible.

[acroreef]

Thanks to all for your helpful advice. I wanted to "black out" all ambient light and use only flash to light my subject. Assuming the light doesn't bounce off of anything too close to my subject, shouldn't I be able to set the shutter speed above the synch, until it blocks all ambient out, and then just light with flash? (My flash will shoot above synch speed). I was attempting to use a light meter to get an exact determination re my flash exposure once I set in ISO, shutter speed and aperture. Instead of trial and error.

[george013]

George - the problem with HHS is that the shutter blades are not fully open when the shutter speed exceeds the synch speed of the camera and the amount of light reaching the sensor is dependent on the width of the slit of the two shutter curtains that are in motion. An algorithm to compensate for this has to be built into the flash meter. As Kathy says, this is not commonly found on flash meters.

I thought I explained that. Normaly the flash is a short illumination of the subject of something 1/1000s, just to say something. In hss the flash acts as a continuous light. The flash is divided over the time between the start of the first curtain and the ending of the second curtain. I don't know how to influence that little power that's left, except with the normal tools as diaphragm and shutter speed.

George

[Manfred M]

Thanks to all for your helpful advice. I wanted to "black out" all ambient light and use only flash to light my subject.

Is this a theoretical approach, i.e. you need to confirm that there is no ambient light or is a practical approach where the ambient light level is so low that it has no noticeable impact on the subject? For standard portraiture work, I cannot see why you would want to use HSS. This is something that is generally reserved for shots where the subject is moving so quickly that the short duration of the flash will not freeze the shot.

I find in most situations where I use flash, unless I drag the shutter, the ambient light has no noticeable impact on the image. HSS is something I have played with, but have never needed in any of my "real world" shooting.

Unless you have a flash meter that supports HHS (mine does not and only Sekonic's current top of the line meter does so), it will have to be trial and error.

[Manfred M]

I thought I explained that. Normaly the flash is a short illumination of the subject of something 1/1000s, just to say something. In hss the flash acts as a continuous light. The flash is divided over the time between the start of the first curtain and the ending of the second curtain. I don't know how to influence that little power that's left, except with the normal tools as diaphragm and shutter speed.

George

With HSS (or Auto FP for us Nikon shooters), one is effectively shooting the same way that one would be using ambient light, so the usual variables of shutter speed, ISO and aperture have to be used to get the exposure correct. The easiest way to get a "correct" exposure is to use the integration of flash to the camera metering system. This works reasonably well when shooting with a recent flash produced by the camera manufacturer, but may or may not work well with third party flashes. A top of the line Sekonic flash meter, i.e. the one that Kathy references will work, as will trial and error.

If one is shooting with a third party flash or using other third party devices, like radio triggers that do not integrate with the camera's metering system the choices are a high end flash meter or trial and error as these tools cannot be integrated with the camera's metering system.

[dje]

Thanks to all for your helpful advice. I wanted to "black out" all ambient light and use only flash to light my subject. Assuming the light doesn't bounce off of anything too close to my subject, shouldn't I be able to set the shutter speed above the synch, until it blocks all ambient out, and then just light with flash? (My flash will shoot above synch speed). I was attempting to use a light meter to get an exact determination re my flash exposure once I set in ISO, shutter speed and aperture. Instead of trial and error.

Hi Dave

One thing you need to remember with HSS is that the light intensity put out by the flash in this mode is considerably lower than in normal flash mode. This limits the distance from flash to subject that can be used. The general consensus seems to be that HSS is really only useful for wide aperture fast shutter speed fill flash use in bright sunlight or for freezing fast motion (with significant limitations in subject distance). This Scantips article goes into a lot of detail.

Depending on the circumstances, you may be able to achieve what you are trying to do with HSS but not necessarily any more effectively than using normal flash. You could experiment with both.

George

You can adjust the power level in HSS (at least on my Nikon gear) and i believe what happens here is that the light intensity rather than the duration is controlled by the electronics in the flash unit. I have no detail though on exactly how this works.

Dave

[rpcrowe]

This method may be awkward but it works for me. I meter the ambient light either with the cameras meter or with a hand held meter.

Then I use the ETTL to determine the flash power. I adjust that power by the + or - flash compensation.

I don't have portable studio lights so I use my hotshoe flashes outdoors. Most of my hotshoe flashes have both HSS and ETTL capability....

[george013]

This method may be awkward but it works for me. I meter the ambient light either with the cameras meter or with a hand held meter.

Then I use the ETTL to determine the flash power. I adjust that power by the + or - flash compensation.

I don't have portable studio lights so I use my hotshoe flashes outdoors. Most of my hotshoe flashes have both HSS and ETTL capability....

Can you adjust the flash power in hss?

George

ps.

I just tried it and must say it works on my D700 and SB700. Must be something as Dave wrote. Or the flash duration is changed.
I tried again. Only in TTL

George