Light meter shutter speed when measuring flash???

DonF · Oct 11, 2017

I have never used a handheld flash meter before and have a basic question.

I just purchased an older Minolta IV F flash-capable light meter in mint condition for a good price. I noticed in the manual, a shutter speed can be set for the corded on non-corded flash modes.

Since the flash is of a very short fixed duration, the camera shutter speed should have no effect on the flash exposure if set longer than the duration of the flash. If there is significant ambient light present as well, the shutter speed would affect that part of the exposure only until the shutter speed became shorter than the flash duration. Correct?

My question is why a flash meter has a shutter speed setting in the flash modes. Does the meter use that setting to measure the ambient light at that shutter speed before firing the flash and adding the detected flash illumination to the ambient value?

My Minolta IV F doesn't have a % flash indication, but does it still calculate and sum the contributions of both ambient and flash separately?? If not, the reason for the shutter speed setting is a mystery to me.

Does the meter also measure actual flash duration and use the shutter speed setting to calculate a reduced light value for the flash if the shutter speed is set to a duration less than the detect flash duration?

Thanks for any help.

Regards,

Don

MattKing · Oct 11, 2017

I've often wondered about that with respect to some of my flash meters.
It may be because you can use them with flash bulbs as well.

DonF · Oct 11, 2017

MattKing said:
I've often wondered about that with respect to some of my flash meters.
It may be because you can use them with flash bulbs as well.

Perhaps that's it. The manual for the Minolta IV F says to set the speed to the sync speed (X or M, I guess), It may simply determine the duration of the measurement window for the flash once the meter triggers it, or the duration after first-light is detected in cordless mode. Setting it to the longer "M" sync speed of the camera would allow all light from a flashbulb to enter.

Don

Mainecoonmaniac · Oct 11, 2017

I used to have a Minolta Flash meter IV. If I remember correctly, the meter can take an ambient and flash reading together. When you take a corded or non-corded reading, the blinking F stop indicator indicates the flash reading and the F stop indicator that is steady is the ambient reading. You can use both readings to see how far apart the brightness between the ambient and flash readings are.

darkroommike · Oct 11, 2017

Studio flash duration can be much longer than the flash duration of handheld "strobes" this may also be part of the reason as might the lower powered systems of the past, e.g. the 200ws Studiomasters, where the modeling light may also affect exposure slightly.

DonF · Oct 11, 2017

darkroommike said:
Studio flash duration can be much longer than the flash duration of handheld "strobes" this may also be part of the reason as might the lower powered systems of the past, e.g. the 200ws Studiomasters, where the modeling light may also affect exposure slightly.

Very true. My Speedotron 102 heads when operated at 2400WS have a long 1/250 duration.

Speedotron 102 Flash Head (MW8QVC 3200WS Tube)
Maximum Power: 2400 Watt-seconds
Flash Duration (watt-seconds per light unit)
300 Ws : 1/1250 seconds
600 Ws : 1/670 seconds
1200 Ws : 1/400 seconds
2400 Ws : 1/225 seconds

So if I were running one head at maximum power, I would need to set the meter no less than 1/225 to get an accurate reading. I'm using old large-format film cameras with Copal leaf shutters, which should sync at any available speed in the "X" setting. In this case, I wouldn't want to go higher than 1/225 on the shutter as I would start to lose some light, but I could go faster at 300WS. I guess I could leave the meter at 1/225 for all power settings, assuming there is no significant ambient light.

Don

mjork · Oct 11, 2017

In my Sekonic meter the reason for setting the shutter time is that it measures both the ambient light and the flash output. It then tells you what percentage of the total illumination comes from flash vs ambient.

wiltw · Oct 11, 2017

DonF said:
I have never used a handheld flash meter before and have a basic question.

I just purchased an older Minolta IV F flash-capable light meter in mint condition for a good price. I noticed in the manual, a shutter speed can be set for the corded on non-corded flash modes.

Since the flash is of a very short fixed duration, the camera shutter speed should have no effect on the flash exposure if set longer than the duration of the flash. If there is significant ambient light present as well, the shutter speed would affect that part of the exposure only until the shutter speed became shorter than the flash duration. Correct?

My question is why a flash meter has a shutter speed setting in the flash modes. Does the meter use that setting to measure the ambient light at that shutter speed before firing the flash and adding the detected flash illumination to the ambient value?

My Minolta IV F doesn't have a % flash indication, but does it still calculate and sum the contributions of both ambient and flash separately?? If not, the reason for the shutter speed setting is a mystery to me.

Does the meter also measure actual flash duration and use the shutter speed setting to calculate a reduced light value for the flash if the shutter speed is set to a duration less than the detect flash duration?

Thanks for any help.

Regards,

Don

ALL shots consist of TWO portions...1) the fraction which is due to flash, and 2) the fraction which is due to ambient.
Usually we choose X-sync (or slower) speed for focal plane shutter cameras, but there are some leaf shuttered cameras that can sync with electronic flash with shutters as fast as 1/1000! So in using a flashmeter like your Autometer IVf , it always considers the two fractions to a single exposure -- even though it does not have the analyze capability, to tell you what fraction of the total is due to flash vs. due to ambient light.

Mainecoonmaniac · Oct 11, 2017

The only exposure control for the flash part of the exposure is the aperture. For the ambient portion of the expoure, is aperture and shutter speed. Since the aperture is set for the flash exposure, the only exposure control for the ambient light is the shutter speed. The slower the shutter speed, the more ambient light exposure. The Minolta IV meter has both so photographers could "balance" the exposure between the two exposures. Some times there are limitations on how fast you can set the shutter because you can cut off the flash exposure in your frame if the shutter speed is too high. But there's no limit on how slow you set your shutter speed for the ambient portion of the exposure.

DonF · Oct 11, 2017

wiltw said:
ALL shots consist of TWO portions...1) the fraction which is due to flash, and 2) the fraction which is due to ambient.
Usually we choose X-sync (or slower) speed for focal plane shutter cameras, but there are some leaf shuttered cameras that can sync with electronic flash with shutters as fast as 1/1000! So in using a flashmeter like your Autometer IVf , it always considers the two fractions to a single exposure -- even though it does not have the analyze capability, to tell you what fraction of the total is due to flash vs. due to ambient light.

So if I understand correctly, in flash mode the shutter speed setting on the meter controls how long the meter measures light, as on a camera. If only the flash is providing light, as in a darkened room, the meter would read the same regardless of the shutter speed setting (up to the duration of the flash). If the ambient light is higher, the meter will sum the same light from the flash plus the ambient light detected during whatever the shutter speed is set to.

Chan Tran · Oct 11, 2017

Old flashmeter only measured the peak intensity of the flash and thus those didn't have shutter speed setting. I believe Minolta was first to introduce the type of integration flash meter. It measures light for the duration of the shutter speed set and taken into account that the light intensity isn't a constant during that duration. So the result is an integral of the light for the measurement period which is the shutter speed setting.
In the example that some studio flash can have duration as long as 1/240 sec or so and if the meter is set at 1/500 and the camera also at 1/500 it will indicate a lower reading which is the correct reading.

Arklatexian · Oct 11, 2017

While I don/t have a reply, I do have a comment. This post is one of the best that I have seen since joining this group and the answers have been just as good. The question was interesting and useful and so were the replies............Regards to all!

DonF · Oct 11, 2017

Chan Tran said:
Old flashmeter only measured the peak intensity of the flash and thus those didn't have shutter speed setting. I believe Minolta was first to introduce the type of integration flash meter. It measures light for the duration of the shutter speed set and taken into account that the light intensity isn't a constant during that duration. So the result is an integral of the light for the measurement period which is the shutter speed setting.
In the example that some studio flash can have duration as long as 1/240 sec or so and if the meter is set at 1/500 and the camera also at 1/500 it will indicate a lower reading which is the correct reading.

Thanks, that's exactly what I needed to know. That means I can use a shutter speed faster than my studio strobes' flash duration and the meter should still give me a correct f/stop setting, as it will only measure the part of the flash discharge active when the shutter is open. That's good information to know. Also that the contribution of ambient light to the total reading is properly calculated.

darkroommike · Oct 11, 2017

DonF said:
Thanks, that's exactly what I needed to know. That means I can use a shutter speed faster than my studio strobes' flash duration and the meter should still give me a correct f/stop setting, as it will only measure the part of the flash discharge active when the shutter is open. That's good information to know. Also that the contribution of ambient light to the total reading is properly calculated.

If you are shooting in the studio why would you need to shoot at a speed faster than flash duration? You are actually "chopping off" part of your flash exposure. AND (big and) most studio cameras have shutter speeds only up to 1/100th-ish to about 1/250-ish until you get to the MF systems. Slower shutter speeds are fine, too, depending on the ambient and modeling light contributions to exposure.

DonF · Oct 11, 2017

darkroommike said:
If you are shooting in the studio why would you need to shoot at a speed faster than flash duration? You are actually "chopping off" part of your flash exposure. AND (big and) most studio cameras have shutter speeds only up to 1/100th-ish to about 1/250-ish until you get to the MF systems. Slower shutter speeds are fine, too, depending on the ambient and modeling light contributions to exposure.

You are right, it makes no sense to do so. I guess it was an academic point to help understand how the meter worked. I would simply dial back the Speedotron power, which would shorten the flash duration.

wiltw · Oct 12, 2017

DonF said:
So if I understand correctly, in flash mode the shutter speed setting on the meter controls how long the meter measures light, as on a camera. If only the flash is providing light, as in a darkened room, the meter would read the same regardless of the shutter speed setting (up to the duration of the flash). If the ambient light is higher, the meter will sum the same light from the flash plus the ambient light detected during whatever the shutter speed is set to.

Correct

wiltw · Oct 12, 2017

DonF said:
Thanks, that's exactly what I needed to know. That means I can use a shutter speed faster than my studio strobes' flash duration and the meter should still give me a correct f/stop setting, as it will only measure the part of the flash discharge active when the shutter is open. That's good information to know. Also that the contribution of ambient light to the total reading is properly calculated.

Yes, but it would be an extreme rare combination of events that allows the combination of flash duration > 1/100 and shutter speed needed is < 1/200...the shortest flash duriation one generation sees is about 1/400 at full power output, and even the film SLRs of the 1990s generally are limited to 1/200 to be fully open curtains compatible with flash.

DonF · Oct 12, 2017

One further and related question comes to mind regarding the difference between the meter's corded and non-corded flash modes. The meter integrates all light detected during the speed set. In corded mode with a sync cable connected to the flash (or a wireless trigger), the meter likely triggers the flash at the beginning of the time set and continues measuring until the end of the window.

In non-corded flash mode, the meter must have to detect the rapid spike in light output to know when to start the measurement window. Curves I have seen for flash output show the light output rises to maximum very rapidly and decays relatively slowly. In non-corded mode is there an issue with degraded accuracy over corded mode, as the light output of the flash has already begun to build before the meter can detect it and begin the measurement period? Some light from the flash must be unmetered. Is the loss significant?

Long ago I built an optical slave trigger from scratch. The circuit used an inductor or coil as a sort of high pass filter to remove the effect of continuous background light and only trigger on a rapid change in illumination. I now use a similar commercial two-pronged optical slave to sync my two Speedotron studio strobe power packs together. The flash meter must use a similar circuit.

Best regards,

Don

The exposure time is set to 1/125 for both examples below. The difference is the point relative to the flash where the measurement begins.

M Carter · Oct 12, 2017

darkroommike said:
If you are shooting in the studio why would you need to shoot at a speed faster than flash duration? You are actually "chopping off" part of your flash exposure. AND (big and) most studio cameras have shutter speeds only up to 1/100th-ish to about 1/250-ish until you get to the MF systems. Slower shutter speeds are fine, too, depending on the ambient and modeling light contributions to exposure.

Wondering how you define a "studio camera"? when I shoot commercially in the studio:

Nikon film SLRs or DSLRs: 1/8000th shutter.
Cambo 4x5 Monorail: 1/400th
Mamiya 6x7: 1/400th
Leaf backs: whatever you have 'em attached to.

My only cameras that max at 1/100th or 200th are folders from the 1940's.

wiltw · Oct 12, 2017

M Carter said:
Wondering how you define a "studio camera"? when I shoot commercially in the studio:

Nikon film SLRs or DSLRs: 1/8000th shutter.
Cambo 4x5 Monorail: 1/400th
Mamiya 6x7: 1/400th
Leaf backs: whatever you have 'em attached to.

My only cameras that max at 1/100th or 200th are folders from the 1940's.

135 and medium forma film SLRs of the 1960s and 1970s were mostly 1/60 X-sync with focal plane shutters; even 135 film cameras with the Copal Square vertical metal shutters were limited to 1/125; it was not until the EOS was launched that 135 film cameras could achieve 1/200.

MattKing · Oct 12, 2017

The exception would be the leaf shutter SLRs like the Retina Reflex.

darkroommike · Oct 12, 2017

M Carter said:
Wondering how you define a "studio camera"? when I shoot commercially in the studio:

Nikon film SLRs or DSLRs: 1/8000th shutter.
Cambo 4x5 Monorail: 1/400th
Mamiya 6x7: 1/400th
Leaf backs: whatever you have 'em attached to.

My only cameras that max at 1/100th or 200th are folders from the 1940's.

Your Nikon DSLR and SLR's have a top speed of 1/4000th (true) but will not sync with studio flash at those speeds. And so called FP flash is not very effective
If your flash duration is 1/250 with your Cambo and you set shutter to 1/400th your flash duration is longer you are chopping off some light again.
Ditto Mamiya.
Don't know what a leaf back is this is the analog forum.

M Carter · Oct 13, 2017

darkroommike said:
Your Nikon DSLR and SLR's have a top speed of 1/4000th (true) but will not sync with studio flash at those speeds. And so called FP flash is not very effective

If your flash duration is 1/250 with your Cambo and you set shutter to 1/400th your flash duration is longer you are chopping off some light again.

Ditto Mamiya.

Don't know what a leaf back is this is the analog forum.

The quote I was questioning was "most studio cameras have shutter speeds only up to 1/100th-ish to about 1/250-ish".

I owned a studio for a decade, and still rent studio space; much of my shooting was in daylight studios. I guess I could say "I shot a gig with a kodak brownie", but really I'm thinking of professional cameras.

I also was an art director with JCPenney for a decade, and the common cameras used by the people I hired and supervised on-set were various 8x10 and 4x5, Mamiya RB/RZ, Nikon and Canon AF, Pentax 67, and various 645 systems, depending on on-figure apparel or tabletop apparel/jewelry. None of those maxed at 100th-250th shutter speed, and I'd say they were all "studio cameras".

The years I shot stills/film commercially (I'm primarily digital video now), my flash sync was from 1/250th - 1/400th. I never had an issue with packs (and this was pre-profoto ubiquity) that had longer flash durations than my synch could handle. My entire film-shooting career was with various speedo packs, not the fastest durations out there.

Just seems like a very misinformed statement, or we're actually talking "Studios" of the 1920's or something?

DonF · Oct 17, 2017

Well, my Graflex Graphic View II certainly qualifies as an old-school "studio camera". It uses a 210mm lens with a Copal #1 shutter. The maximum speed on the Copal #1 is 1/500. At lower powers, my Speedotron 2400ws pack syncs up fine, as do modern low-power speed flashes.

My used Minolta IV F arrived. I was pleased to find it was in mint, almost unused condition. For $89.00 USD, it seems like a good deal. I found a somewhat battered but seviceable 10 degree reflected light spot meter attachment for $28.00 or so. As the meter was missing the little 40 degree reflected light accessory disk, I needed something for landscape shots.

I was pleased to find that the corded mode will happily fire either of my 2400ws Speedotron Blackline studio power units. One has a trigger voltage of 75 volts, the other (newer) pack is 61.5 volts. My Wien optical slave dongles with the two prongs must be polarized correctly to work with the packs. However, the Minolta IV F happily fired either pack with the sync cord inserted in either polarity. Nice.

I ran a test to see the effect of setting the IV F to a shutter speed greater than the published Speedotron flash duration at full power (1/225 at 2400ws).

The pack/tube is rated as follows:

Speedotron 102 Flash Head (MW8QVC 3200WS Tube)
Maximum Power: 2400 Watt-seconds
Flash Duration (watt-seconds per light unit)
300 Ws : 1/1250 seconds
600 Ws : 1/670 seconds
1200 Ws : 1/400 seconds
2400 Ws : 1/225 seconds

I set the IV F to ISO 3 at the following speeds with the flash at full power (2400ws) with a constant flash distance to test subject, The room was darkened so the light was coming predominantly from the flash. The low ISO setting should have eliminated ambient light as a factor.:

1/60 f/22.7
1/90 f/22.6
1/125 f/22.4
1/180 f/22.1
1/250 f/16.9
1/350 f/16.5
1/500 f/16.4

The meter starts to lose light at 1/250, as expected. The flash duration is listed at 1/225 for full power.

However, increasing speeds further on the meter hardly affected the exposure much at all. There is sort of a step function going on.

The only explanation that occurs to me is that the flash puts out most of its light very quickly after triggering, with a rather slow ramp-down at full power. Even at the higher speeds, the majority of light is discharged quickly enough to be captured. The relatively minor light during the ramp-down is the only light eliminated by the shorter shutter speeds.

Regards,

Don

DonF · Oct 18, 2017

You know, looking at my numbers, there is no "step function". The fractional portion of the f/stop reading on the meter represent fractions of a stop. The steps in f/stop for the various times are proportional, indicating the flash is measuring all but a small portion of the flat area of the logarithmic output decay curve, even at the higher shutter speeds. The output duration is typically specified using the t.1 method which measures the time needed to reach the maximum output for the selected power setting plus the time needed to trail off to a point equal to 10% of that peak.

That means that even at the highest sync speed my Copal #1 can handle, 1/500, I can only restrict the light output of the flash by 1 stop at the packs' highest output (1/250 rated duration).

Don

Light meter shutter speed when measuring flash???

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