Light meter help...

Jeff Singer94142 · Sep 6, 2002

I just got my light meter (Sekonic L-358) and I've never used one before. I had a question regarding the results for use in flash mode. In flash mode you can only select and change the shutter speed while in ambient mode you can used either the shutter speed or aperture. I believe this to be because the shutter speed effects the ambient to flash %. So, changing the shutter speed will cause the % of ambient to flash. However, when changing the shutter speed the aperture setting changes. What is confusing me is that I thought with flash lighting the shutterspeed and aperture combination didn't matter. I thought that you can choose f1.4 @ 1/125th and you would get the same exact exposure as you would for f8 @1/125th (just with a shallow DOF). If that is true, does that mean when using the light meeter in flash mode I can ignore the aperture reading and just use the shutter speed to determine my ambient to flash % (i.e, if I want shallow DOF I can use 1.4 @1/125 even though the meeter may say f8 @ 1/125)? Or am I misunderstanding something?

Hope I explained that properly.

Thanks,
Jeff

--
--------------------------------
http://www.photosig.com/userphotos.php?id=17960
http://www.pbase.com/jhsinger
D60, 28-135IS, 50mm f1.4, 75-300IS

Paul Ferrara · Sep 7, 2002

The way you normally do this is to set your camera to it's highest sync speed and set that shutter speed on the meter. Then you adjust your lights until the reading you gets matches the aperture you have your lens set for (say, f8).

Paul
http://www.paulsportraits.com

jsinger986 said:
I just got my light meter (Sekonic L-358) and I've never used one
before. I had a question regarding the results for use in flash
mode. In flash mode you can only select and change the shutter
speed while in ambient mode you can used either the shutter speed
or aperture. I believe this to be because the shutter speed
effects the ambient to flash %. So, changing the shutter speed
will cause the % of ambient to flash. However, when changing the
shutter speed the aperture setting changes. What is confusing me
is that I thought with flash lighting the shutterspeed and aperture
combination didn't matter. I thought that you can choose f1.4 @
1/125th and you would get the same exact exposure as you would for
f8 @1/125th (just with a shallow DOF). If that is true, does that
mean when using the light meeter in flash mode I can ignore the
aperture reading and just use the shutter speed to determine my
ambient to flash % (i.e, if I want shallow DOF I can use 1.4 @1/125
even though the meeter may say f8 @ 1/125)? Or am I
misunderstanding something?

Hope I explained that properly.

Thanks,
Jeff

--
--------------------------------
http://www.photosig.com/userphotos.php?id=17960
http://www.pbase.com/jhsinger
D60, 28-135IS, 50mm f1.4, 75-300IS

Duncan C · Sep 7, 2002

Jeff,

Aperture always affects your exposure, flash or ambient, and affects them both the same predictable way. Go to the next larger f-stop and you double the light. Always.

Shutterspeed is a little more complicated. With ambient light, doubling the shutterspeed gives you 1/2 as much light, since the shutter is open for 1/2 as much time.

Flash doesn't work that way though. Flash is a very short, very bright pulse of light. Shutterspeeds longer than your flash's discharge time will have NO effect on the amount of flash light in the exposure. For studio flashes, this means you can use very fast shutterspeeds with no effect on your light. However, once your shutterspeed gets fast enough to reduce the light, the results become very hard to predict. The light output from a flash is not linear over time. It's simplest to just use shutterspeeds no faster than your flash's discharge times.

Because moderate shutterspeeds (1/60'th to 1/250th, say, or even faster if you're using fast-discharging flashes and a camera with a high sync speed) affect the ambient light in a predictable way, but have no effect on flash exposure, you can use shutterspeeds in this range to reduce the ambient light quite a bit. (note that small battery operated camera-mounted flashes have slower discharge times, so you start losing light from your flashes at much slower shutterspeeds.)

If you want to increase your proportion of ambient light, you have to reduce the amount of flash reaching your subject somehow. If your flashes have variable power, that's easy. Failing that, you can move them further from your subject (flash power falls away with the square of the distance), put them through filters, diffusers or bounces, or use other tricks.

For studio work, I usually use shutterspeeds fast enough to bring the ambient light down to near zero unless I want motion blur. I then set my flash meter to that shutterspeed (my camera and flash meter will both sync up to 1/500th of a second, and I get no measureable loss of flash light at that speed.) I use my desired depth of field to determine my aperture, and then set up my lighting for proper exposure at that aperture. (My studio flashes have variable power settings.)

For flash metering, you usually set the shutterspeed on the meter, then fire the flash(es) and the meter tells you the proper aperture to use for that light level. If you're settnig up multiple lights, you often want different amounts of light from each one, so you can meter them separately, then take a final meter reading with all your lights on to check your total exposure. (Lighting ratios is whole topic of conversation on it's own.)

For ambient metering, you can set the meter to a certain shutterspeed and have the meter tell you the proper aperture, or set the aperture and the meter gives you the shutterspeed. (shutter priority and aperture priority, in TTL metering terms)

I hope that helps. I didn't attempt to explain everything, but rather to clarify the question of shutterspeed, f-stop, and their effects on ambient light and flash (strobe) light. There are several links in these forums to good tutorials on studio lighting. I suggest you hunt down a couple.

Duncan Champney

-------

jsinger986 said:
I just got my light meter (Sekonic L-358) and I've never used one
before. I had a question regarding the results for use in flash
mode. In flash mode you can only select and change the shutter
speed while in ambient mode you can used either the shutter speed
or aperture. I believe this to be because the shutter speed
effects the ambient to flash %. So, changing the shutter speed
will cause the % of ambient to flash. However, when changing the
shutter speed the aperture setting changes. What is confusing me
is that I thought with flash lighting the shutterspeed and aperture
combination didn't matter. I thought that you can choose f1.4 @
1/125th and you would get the same exact exposure as you would for
f8 @1/125th (just with a shallow DOF). If that is true, does that
mean when using the light meeter in flash mode I can ignore the
aperture reading and just use the shutter speed to determine my
ambient to flash % (i.e, if I want shallow DOF I can use 1.4 @1/125
even though the meeter may say f8 @ 1/125)? Or am I
misunderstanding something?

Hope I explained that properly.

Thanks,
Jeff

--
--------------------------------
http://www.photosig.com/userphotos.php?id=17960
http://www.pbase.com/jhsinger
D60, 28-135IS, 50mm f1.4, 75-300IS

Girish Jadav · Sep 7, 2002

Hello Duncan,

You mentioned for the flashes, you set both lights' f# seperate and then take the common reading. I have two 550EXs with a ST-E2.I set the first one on manual and fired. The reading I got was f8.0. I set the second on manual but 1/2 powered instead of 1/1 and fired. The reading I got was 5.6. Then, I left both on and fired together, and I got a reading of f8.0. My question is, is the reason for not getting the shadow that one flash is more powerful than the other? Please help me set up the angles.

I have a D30, which I left on ISO400 (shutter speed 1/125). The maximum sync flash is 1/200. How do you make the ambient light go near zero?

Thanks,

GJ

Duncan Champney said:
Aperture always affects your exposure, flash or ambient, and
affects them both the same predictable way. Go to the next larger
f-stop and you double the light. Always.

Shutterspeed is a little more complicated. With ambient light,
doubling the shutterspeed gives you 1/2 as much light, since the
shutter is open for 1/2 as much time.

Flash doesn't work that way though. Flash is a very short, very
bright pulse of light. Shutterspeeds longer than your flash's
discharge time will have NO effect on the amount of flash light in
the exposure. For studio flashes, this means you can use very fast
shutterspeeds with no effect on your light. However, once your
shutterspeed gets fast enough to reduce the light, the results
become very hard to predict. The light output from a flash is not
linear over time. It's simplest to just use shutterspeeds no faster
than your flash's discharge times.

Because moderate shutterspeeds (1/60'th to 1/250th, say, or even
faster if you're using fast-discharging flashes and a camera with a
high sync speed) affect the ambient light in a predictable way, but
have no effect on flash exposure, you can use shutterspeeds in this
range to reduce the ambient light quite a bit. (note that small
battery operated camera-mounted flashes have slower discharge
times, so you start losing light from your flashes at much slower
shutterspeeds.)

If you want to increase your proportion of ambient light, you have
to reduce the amount of flash reaching your subject somehow. If
your flashes have variable power, that's easy. Failing that, you
can move them further from your subject (flash power falls away
with the square of the distance), put them through filters,
diffusers or bounces, or use other tricks.

For studio work, I usually use shutterspeeds fast enough to bring
the ambient light down to near zero unless I want motion blur. I
then set my flash meter to that shutterspeed (my camera and flash
meter will both sync up to 1/500th of a second, and I get no
measureable loss of flash light at that speed.) I use my desired
depth of field to determine my aperture, and then set up my
lighting for proper exposure at that aperture. (My studio flashes
have variable power settings.)

For flash metering, you usually set the shutterspeed on the meter,
then fire the flash(es) and the meter tells you the proper aperture
to use for that light level. If you're settnig up multiple lights,
you often want different amounts of light from each one, so you can
meter them separately, then take a final meter reading with all
your lights on to check your total exposure. (Lighting ratios is
whole topic of conversation on it's own.)

For ambient metering, you can set the meter to a certain
shutterspeed and have the meter tell you the proper aperture, or
set the aperture and the meter gives you the shutterspeed. (shutter
priority and aperture priority, in TTL metering terms)

I hope that helps. I didn't attempt to explain everything, but
rather to clarify the question of shutterspeed, f-stop, and their
effects on ambient light and flash (strobe) light. There are
several links in these forums to good tutorials on studio lighting.
I suggest you hunt down a couple.

Duncan Champney

-------

jsinger986 said:

I just got my light meter (Sekonic L-358) and I've never used one
before. I had a question regarding the results for use in flash
mode. In flash mode you can only select and change the shutter
speed while in ambient mode you can used either the shutter speed
or aperture. I believe this to be because the shutter speed
effects the ambient to flash %. So, changing the shutter speed
will cause the % of ambient to flash. However, when changing the
shutter speed the aperture setting changes. What is confusing me
is that I thought with flash lighting the shutterspeed and aperture
combination didn't matter. I thought that you can choose f1.4 @
1/125th and you would get the same exact exposure as you would for
f8 @1/125th (just with a shallow DOF). If that is true, does that
mean when using the light meeter in flash mode I can ignore the
aperture reading and just use the shutter speed to determine my
ambient to flash % (i.e, if I want shallow DOF I can use 1.4 @1/125
even though the meeter may say f8 @ 1/125)? Or am I
misunderstanding something?

Hope I explained that properly.

Thanks,
Jeff

--
--------------------------------
http://www.photosig.com/userphotos.php?id=17960
http://www.pbase.com/jhsinger
D60, 28-135IS, 50mm f1.4, 75-300IS

Click to expand...

Duncan C · Sep 7, 2002

GJ,

You said:

Girish Jadav said:
I have a D30, which I left on ISO400 (shutter speed 1/125). The
maximum sync flash is 1/200. How do you make the ambient light go
near zero?

My camera has a max sync speed of 1/500th of a second. In average room light, that speed makes the ambient light quite dark. With lots of flash power, the ambient light gets so blasted by the strobes that I can pretty much ignore it. I've also had decent luck shooting in manual mode at shutterspeeds faster than 1/500th when I needed to freeze high-speed action, but I wouldn't recommend that. The results are too unpredictable.

Girish Jadav said:
You mentioned for the flashes, you set both lights' f# seperate and
then take the common reading. I have two 550EXs with a ST-E2.I set
the first one on manual and fired. The reading I got was f8.0. I
set the second on manual but 1/2 powered instead of 1/1 and fired.
The reading I got was 5.6. Then, I left both on and fired together,
and I got a reading of f8.0. My question is, is the reason for not
getting the shadow that one flash is more powerful than the other?
Please help me set up the angles.

I'm not exactly sure what you're asking. Your setup sounds reasonable though. I gather you're aiming for a 1:2 lighting ratio (main light at f8, shadows 1 stop less at f5.6.) Are you not getting the shadows you're after? What type of reflectors are you using on your main and fill light? And what angles are you putting your lights at? You might need to separate them more. You might also want to try a simple reflector on your main light and a soft box or umbrella for your fill light. That will cause fairly stark shadows from the main light, filled softly with the fill. (make sure to use a flash meter to set your lighting ratios in this case though, since the umbrellas will cause extra light loss beyond the lower power setting on the fill flash.)

How you angle your lights depends on the effect you are after. I could write a novel on studio lighting techniques, and still not explain it as well as others already have done.

I am fairly new to studio lighting myself, and don't want to present myself as an expert ion the subject. I was just trying to explain how aperture and shutterspeed affect flash and ambient lighting, since the previous poster seemed a little confused.

Duncan C

Girish Jadav · Sep 7, 2002

Thanks,

GJ

Duncan Champney said:
You said:

Duncan C said:

I have a D30, which I left on ISO400 (shutter speed 1/125). The
maximum sync flash is 1/200. How do you make the ambient light go
near zero?

Click to expand...

My camera has a max sync speed of 1/500th of a second. In average
room light, that speed makes the ambient light quite dark. With
lots of flash power, the ambient light gets so blasted by the
strobes that I can pretty much ignore it. I've also had decent luck
shooting in manual mode at shutterspeeds faster than 1/500th when I
needed to freeze high-speed action, but I wouldn't recommend that.
The results are too unpredictable.

Duncan C said:

You mentioned for the flashes, you set both lights' f# seperate and
then take the common reading. I have two 550EXs with a ST-E2.I set
the first one on manual and fired. The reading I got was f8.0. I
set the second on manual but 1/2 powered instead of 1/1 and fired.
The reading I got was 5.6. Then, I left both on and fired together,
and I got a reading of f8.0. My question is, is the reason for not
getting the shadow that one flash is more powerful than the other?
Please help me set up the angles.

Click to expand...

I'm not exactly sure what you're asking. Your setup sounds
reasonable though. I gather you're aiming for a 1:2 lighting ratio
(main light at f8, shadows 1 stop less at f5.6.) Are you not
getting the shadows you're after? What type of reflectors are you
using on your main and fill light? And what angles are you putting
your lights at? You might need to separate them more. You might
also want to try a simple reflector on your main light and a soft
box or umbrella for your fill light. That will cause fairly stark
shadows from the main light, filled softly with the fill. (make
sure to use a flash meter to set your lighting ratios in this case
though, since the umbrellas will cause extra light loss beyond the
lower power setting on the fill flash.)

How you angle your lights depends on the effect you are after. I
could write a novel on studio lighting techniques, and still not
explain it as well as others already have done.

I am fairly new to studio lighting myself, and don't want to
present myself as an expert ion the subject. I was just trying to
explain how aperture and shutterspeed affect flash and ambient
lighting, since the previous poster seemed a little confused.

Duncan C

Bill(y) · Sep 11, 2002

Girish Jadav said:
Hello Duncan,

You mentioned for the flashes, you set both lights' f# seperate and
then take the common reading. I have two 550EXs with a ST-E2.I set
the first one on manual and fired. The reading I got was f8.0. I
set the second on manual but 1/2 powered instead of 1/1 and fired.
The reading I got was 5.6. Then, I left both on and fired together,
and I got a reading of f8.0. My question is, is the reason for not
getting the shadow that one flash is more powerful than the other?
Please help me set up the angles.

I have a D30, which I left on ISO400 (shutter speed 1/125). The
maximum sync flash is 1/200. How do you make the ambient light go
near zero?

The part above lost me too, maybe Duncan covered it below though. Are you wanting shadows?

Meanwhile, let me chime in that the max flash sync for the D30 with a 550EX is not 1/200 it's like 1/4000.

You need to change the 550EX to FP (high speed sync mode). Hold two of the buttons on the flash down simultaneously (see the manual, I forget which two). After that, automagically, the D30 will allow faster shutter speeds. Way faster. And more imporatantly, the 550 will keep up.

Bill

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