Light position affect aperture?

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I think I might be overthinking this, but as I'm still waiting for my lights to turn up I thought I may as well ask the question.

So, using a Flash Meter I will get an aperture to set on the camera, but does that assume the camera is located exactly where the flash head is? Does one have to compensate at all if the flash head off axis - say 45 degrees? Or does the aperture setting I get from the flash meter suffice irrespective of the camera's position in relation to the strobes?
 
Yes.
And no.

Yes, because if the meter isn't pointing directly at the light then of course it won't give an accurate reading.
But this applies ONLY if the meter is fitted with a flat receptor, which very few are (flat receptors are mainly used only in professional applications where flat artwork is lit) and if you have the normal dome reflector, which accepts light from a very wide angle, there's no need for the meter to point directly towards the light.
 
I thought you pointed the meter towards the camera when taking incident readings?:shrug:

At least now I have something to blame my crap exposures on.
 
Ah cool. Thanks.

So the fact it's a domed receptor means it captures the light irrespective of direction.
 
LJR said:
Ah cool. Thanks.

So the fact it's a domed receptor means it captures the light irrespective of direction.
Click to expand...

With the greatest of respect to Garry, he's a bit not quite right on that point :D

If you face it towards the light source you'll get a correct reading so your highlights don't blow, the farther you turn it away from the light source the more ambient light will be measured, and if the ambient is less (as it usually is in a studio) you'll increasing start to overexpose your highlights

Try it and see

DD
 
DiddyDave said:
With the greatest of respect to Garry, he's a bit not quite right on that point :D

If you face it towards the light source you'll get a correct reading so your highlights don't blow, the farther you turn it away from the light source the more ambient light will be measured, and if the ambient is less (as it usually is in a studio) you'll increasing start to overexpose your highlights

Try it and see

DD
Click to expand...
I definitely will try it when the kit arrives, just trying to get my head around the theory of it though too.

So, if by pointing the meter at the flash I get an aperture reading which is based on no, or little, ambient light then when I set the camera to that aperture wouldn't that slightly underexpose because the camera is not in the same position as the flash head. Sorry if I'm being a bit dense here. I'm sure the penny will drop eventually
 
DiddyDave said:
With the greatest of respect to Garry, he's a bit not quite right on that point :D

If you face it towards the light source you'll get a correct reading so your highlights don't blow, the farther you turn it away from the light source the more ambient light will be measured, and if the ambient is less (as it usually is in a studio) you'll increasing start to overexpose your highlights

Try it and see

DD
Click to expand...

I'm waiting for my lightmeter to arrive, so I'm particularly interested in this. What about if you have 2 lights ? If you meter off one does that mean that you are actually metering off less light than will actually hit the subject ?
 
Lasagne said:
I'm waiting for my lightmeter to arrive, so I'm particularly interested in this. What about if you have 2 lights ? If you meter off one does that mean that you are actually metering off less light than will actually hit the subject ?
Click to expand...

:thinking: hmm that's why I thought you pointed it at the camera :thinking:
 
LJR said:
I definitely will try it when the kit arrives, just trying to get my head around the theory of it though too.

So, if by pointing the meter at the flash I get an aperture reading which is based on no, or little, ambient light then when I set the camera to that aperture wouldn't that slightly underexpose because the camera is not in the same position as the flash head. Sorry if I'm being a bit dense here. I'm sure the penny will drop eventually
Click to expand...

If you're using a very harsh directional light, then yes certain parts of your subject could be underexposed - but that's normally the point when using harsh light, to get a great range from light-to-dark

If you want to exposure for the shadows though, you'll blow your highlights and in most cases that'll not be attractive at all

With anything like a brolly or softbox, exposing for the highlights is THE way to do it as there's always enough light wrapping around the subject to light it nicely. I often shoot with my key light at between 30-60 degrees, I point the meter AT the key light for a reading so the highlights are fine, and shooting anywhere from 0-60+ degrees is fine. The more the angle the more shadows start to appear, but as these give form to the face, that's the point of creating them

DD
 
DiddyDave said:
With the greatest of respect to Garry, he's a bit not quite right on that point :D

If you face it towards the light source you'll get a correct reading so your highlights don't blow, the farther you turn it away from the light source the more ambient light will be measured, and if the ambient is less (as it usually is in a studio) you'll increasing start to overexpose your highlights

Try it and see

DD
Click to expand...

That's if you've got one of them thar fancy meters which can measure flash and ambient at the same time. Or are we still talking about the difference between flat and domed diffusers?
 
Lasagne said:
I'm waiting for my lightmeter to arrive, so I'm particularly interested in this. What about if you have 2 lights ? If you meter off one does that mean that you are actually metering off less light than will actually hit the subject ?
Click to expand...

You meter from your key light, the other is then metered 1-3 stops less as fill

As I said - try it

DD
 
Kev M said:
That's if you've got one of them thar fancy meters which can measure flash and ambient at the same time. Or are we still talking about the difference between flat and domed diffusers?
Click to expand...

All flashmeters read both at the same time regardless of diffuser

DD
 
DiddyDave said:
All flashmeters read both at the same time regardless of diffuser

DD
Click to expand...

I thought that would be the case but Sekonic market the L358 as being capable of measuring flash and ambient simultaneously but not the L308s which I have. Hard to imagine how a light meter would only measure the flash and not pick up on the ambient during a sample but it's strange the way it is worded on the different meters.
 
DiddyDave said:
If you're using a very harsh directional light, then yes certain parts of your subject could be underexposed - but that's normally the point when using harsh light, to get a great range from light-to-dark

If you want to exposure for the shadows though, you'll blow your highlights and in most cases that'll not be attractive at all

With anything like a brolly or softbox, exposing for the highlights is THE way to do it as there's always enough light wrapping around the subject to light it nicely. I often shoot with my key light at between 30-60 degrees, I point the meter AT the key light for a reading so the highlights are fine, and shooting anywhere from 0-60+ degrees is fine. The more the angle the more shadows start to appear, but as these give form to the face, that's the point of creating them

DD
Click to expand...
Perfect! That makes a whole lot more sense to me now. Thanks
 
DiddyDave said:
With the greatest of respect to Garry, he's a bit not quite right on that point :D

If you face it towards the light source you'll get a correct reading so your highlights don't blow, the farther you turn it away from the light source the more ambient light will be measured, and if the ambient is less (as it usually is in a studio) you'll increasing start to overexpose your highlights

Try it and see

DD
Click to expand...

Yes, try it and see.
A dome receptor (cardioid response) - allows a large influence on the reading by the sideways illumination and a disk (or shielded dome; cosine response) allows little or no influence by the sideways illumination.

The old advice, back in the day when all receptors produced a cosine response, was to take a reading from the key light, then take a reading from the fill light (which of course is where the camera is) and to use those two different readings as information on which to base a decision, i.e. to use the meter as a measuring tool and not as a magic gizmo that must be obeyed.

But cardioid response (domed) receptors have changed that, at least for portrait photography and the dome can generally get it right, regardless of whether it's pointing at the camera or the key light. Maybe Dave, who knows that I'm a sad old B***** who likes using rim lighting, where the angle is too extreme for cardioid response to give an accurate response, is saying that my answer is wrong because it's often wrong for me:lol:

The ambient light level is rarely high enough to have any effect on the exposure at any normal shutter speed, say 1/125th. Something else to try and see; just set up the exposure to suit the flash and then take a shot using ambient only and see whether anything at all registers.
 
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