The trick for shooting manual flash is really no trick at all if you're
shooting direct flash. That's the case where you're shooting Chinese
night market shots and where the flash is the main light. That's what
guide numbers are all about. For example, a T32 has a guide number of
104 feet (32 meters) at its high power setting and 52 feet (16 meters)
at its low power setting. The low guide number is half of the high one
but is only 1/4 power, not half power. That's that inverse square law
showing its head again.
To use the guide number just divide the guide number by the distance to
the subject (or read it off the scale most flashes provide on the back).
If you're 10 feet away at full power you divide 104 by 10 and get
f/10.4. Don't worry too much about precision here, just set the
aperture to slightly wider than f/11. If the flash is set to low power
just divide 52 by 10 and get f/5.2. Once again, just set the aperture
to slightly wider than f/5.6. The trick to making this work reliably
and quickly is to always shoot from the same distance, preset the camera
and flash and zoom with your lens rather than your feet. Once set, you
don't worry about exposure anymore.
So, apart from depth of field, how do you choose one power level over
the other? If you refer to Fred Parkers ultimate exposure computer
mentioned the other day <http://www.fredparker.com/ultexp1.htm> you'll
see that he rates "brightly lighted night time streets" as EV 7. But
lighted store fronts he rates as EV 8. Take your choice. If you look up
EV 7 in chart B on that page (assuming ISO 400 film) you'll find that
the non-flash exposure for this scene at f/5.6 is 1/15 second and for
f/11 is 1/4 second. So, if you choose the low power setting at f/5.2
and a shutter speed of 1/30 your foreground subjects at 10 feet away
will be properly exposed and the lighted street background will be one
stop under. One reason to prefer low power to high power is if you need
to shoot quickly. Recycle time at 1/4 power will be much quicker than
at full power.
One caution on the use of guide numbers is that every single flash I
have ever tested with a flash meter fails to meet its guide number,
usually by 1/3 to 1/2 stop but some by as much as 2/3. So, without a
flash meter to test with I think you'd be wise to open up slightly
beyond the guide number's recommendation. Another consideration is the
use of fresh alkaline batteries (1.5 volts) vs. NiMH rechargeables (1.2
volts). While the rechargeables can deliver more current and will lead
to faster recycle times the lower voltage may produce less total light
output... at least for the older 80's and 90's flash units that I have
which appear to have no built-in voltage regulation.
Yes, shooting at parties and other events with lots of people and a
confined space is problematic. But it's problematic more so for the
effects of the inverse square law than trying to determine "proper"
exposure. If folks in front are properly exposed then those behind them
will range from underexposed to severely underexposed... and vice versa.
If your flash has an auto mode then this is the place to use it. The
auto mode will probably give pretty good exposures at from 6-8 feet
which is also probably as much separation as you can reasonably hope to
get in any sort of busy people gathering. The ultimate solution here is
to add more slave flashes to fill the background as well as dragging the
shutter to make use of whatever ambient light is available. This shot
shows the effect of camera mounted flash assisted by two studio flash
units (out of sight to the left) bounced of the inside of the white tent
and the shutter dragged to 1/4 second. Notice motion blur on finger
tips at far left
<http://www.chucknorcutt.com/party.php>
You can also use auto mode for daylight fill flash. First set the
camera at max sync speed and then determine the aperture for a proper
exposure of the presumably brighter background behind your subject.
Then set the auto mode aperture range to suit the aperture set on the
lens and then set the ISO on the flash to one or two stops higher. For
example, if shooting with ISO 100 on the camera set the the ISO on the
flash to 200 or 400 or somewhere in between. I would generally prefer 2
stops for less fill light but that's a matter of preference. Keep in
mind that auto will likely only work well at relatively close distances
of 6-8 feet. But your biggest problem will be trying to take a photo in
bright sunlight at 1/60th second. You'll likely find this impossible
without slow film and an ND filter. That's where your Pen F comes to
the fore with its high speed sync capability.
But you're right. Digital and/or a meter makes the whole thing simpler.
Dr. Flash
On 5/20/2011 8:23 AM, Walters, Martin wrote:
> Dr Flash's comments are duly noted and appreciated. I can understand
> that manual works extremely well in a studio or fairly static
> environment (inside or outside). I suspect that it's more cumbersome for
> ad hoc shooting - street shots (e.g., my Chinese night market shots) and
> "parties/gatherings". I can also see how using manual is easier with
> digital than with film.
>
> Lots to think about. Thanks
>
> Martin
>
> -----Original Message-----
> From: Chuck Norcutt [mailto:chucknorcutt@xxxxxxxxxxxxxxxx]
> Sent: Thursday, May 19, 2011 5:55 PM
> To: Olympus Camera Discussion
> Subject: Re: [OM] OM TTL flash behaviour
>
> Hmmm. Dr. Flash avoids all this auto mode and TTL and flash
> compensation mumbo-jumbo by shooting only in manual mode on both camera
> and flash. It's just plain easier that way.
>
> There are a few simple rules to learn about shooting flash.
>
> 1) When shooting electronic flash there are always two exposures. The
> first is the ambient light exposure which is affected by ISO, shutter
> speed and aperture. It's what you'd get by using your light meter but
> with the constraint that the shutter speed used must not be faster than
> the sync speed for the camera. The second exposure is from the flash
> which is controlled only by ISO, the flash's power output and the
> aperture on the camera. Shutter speed has no effect at all. Even if
> you use your Pen F which can sync at any shutter speed the flash
> duration is still much faster than the fastest shutter speed on the
> camera. So the Pen F will make life easier for fill flash (since it
> allows controlling the bright ambient light with the shutter) but that
> 1/500th shutter speed won't affect the flash exposure one bit.
>
> 2) The "depth" of your flash exposure is maddeningly limited by the
> inverse square law. To get a handle on that it helps to keep a few
> numbers clearly in mind... 1.4 (the square root of 2), 2 (the square
> root of 4) and 4. Now, here's how to use those numbers for some flash
> exposure insight. Assume your subject is 7 feet away and you have
> correct flash exposure for that distance. By the time the light from
> the flash has reached 10 feet (7x1.4) it's only gone 3 feet farther but
> is already 1 stop down. By the time the light reaches 14 feet (7x2) the
> light there is already 2 stops down. By the time the light has gone 28
> feet (7x4) the light is down by 4 stops which is getting quickly toward
> black, or no effect at all.
>
> Applying what we just learned we can see that, if flash exposure is
> applied to a near subject then that subject is going to be about the
> only thing that's properly exposed. You don't have to have another
> subject much closer to the flash in order to get serious overexposure.
> You don't have to have another subject much farther from the flash to
> get serious underexposure.
>
> One help (not a solution) is (as discussed here somewhat already) is to
> "drag the shutter" which means to use a slow shutter speed to assist
> with illuminating the scene from the ambient light. That does help
> light the background and is independent of distance from the flash.
> However, the foreground flash exposure still suffers from the effects of
> the inverse square law. But note that, if you're shooting a subject at
> 10 feet rather than 7 feet, light loss doesn't hit one stop until 14
> feet and doesn't hit two stops until 20 feet. The main point is that
> the farther you can get from your subject the more even the illumination
> will be for other subjects ahead of and behind your main subject. But
> there is no free lunch. As you move your flash farther from the subject
> you lose light power and the tiny flash head begins to look more and
> more like a point source of light (like the sun). Just like the sun,
> point sources of light cast rather harsh shadows. The solution for that
> problem is to turn your tiny flash into a very big and broad light
> source. The easiest way to do that is to bounce off a (relatively)
> neutral ceiling or wall or both and use higher ISO and bigger apertures
> to compensate for overall light loss. And, if you want to go whole hog,
> sprinkle some slave flashes around the room to help fill the background.
>
> Doing this with TTL is a bit problematic since you don't really know
> what the camera is going to do. But doing it without TTL on film either
> means that you need a flash meter or else a digital camera so you can
> quickly evaluate the effect of any given exposure.
>
> If I were going to do what you're about to I'd use the Pen F and its
> fast shutter speed sync in daylight (for fill flash) and the OM in the
> dark (for the larger film format). I'd also get a flash meter and a
> different flash unit that offers good manual control with multiple power
> levels. Ken's Vivitar 285 is a nice flash unit offering both manual and
> auto modes but it's about a stop less powerful than a T32 or the modern
> system flash units for the major brands. I recommended to Moose last
> year that he add a Canon 540EZ to his gear which he did. The 540EZ was
> Canon's cat's meow TTL flash... for film. It don't know how to do TTL
> on digital so they are not in high demand except by the newbies who
> don't know it don't know digital TTL. :-) You can buy one in BGN
> condition from KEH for about $80 or as low as $60 with patient waiting
> on ebay (assuming the newbies aren't there bidding the price up to $140)
>
> Of course, you don't have to have a 540EZ. It could be some other,
> similar flash unit. It doesn't do TTL except on Canon film EOS cameras
> and it doesn't do auto mode on anything. But it does have 7 power
> levels, a bounce and swivel head and power zoom on the head from
> 24-105mm plus a 17mm pull out diffuser (which also makes a handy bounce
> card). Get a meter and a more versatile flash.
>
> Dr. Flash
>
>
> On 5/19/2011 10:42 AM, Walters, Martin wrote:
>> In spite of the eloquence and expertise of Dr Flash and others on the
>> list, flash remains something of a "black art" for me. As I rarely use
>
>> flash, my usual approach is to simply put my non-Oly dedicated flash
>> on TTL and fire away. For info, the flash is a Braun 340 SCA (full
>> TTL with the correct adapter shoe), in auto it has two selectable F
>> stops (F4, F8), a swivel/bounce head with zoom (28-50-100). The filter
>
>> set includes a diffuser (coverage for 21mm), ND4, and coloured
> filters.
>>
>> So, I'm taking a flash 101 course, which looks to cover pretty much
>> all the topics. I'm in an interesting position as the only film
>> shooter in the group (we're 8-10). Some of the CanNikon gang appear to
>
>> have serious gear, and some of those camera/flash combinations are
>> probably more intelligent than I am.
>>
>> After a couple of courses it's obvious that I'll have some challenges
>> and some of the concepts will be theoretical rather than practical
>> (e.g,, flash compensation, though the instructor lent me an EOS to
>> work with; varying sync speed). My dedicated flash has some
>> significant limitations, especially no or only very basic power
>> control (filters on the flash). That being said, the instructor was
>> quite intrigued that I had full TTL capability both on and off camera.
>>
>> One of the things we've looked at is compensation (both exposure and
>> flash). So, this weekend I'm planning to spend some time test shooting
>
>> to see what happens with various setups under TTL. In the meantime,
>> I'd be grateful for some info on how exposure compensation on an OM2N
>> affects TTL flash. I assume that it will affect both metering and
>> flash, which is controlled by the meter (I believe modern N*kon
>> bodies, for example, treat the two independently). Is this correct?
>> However, that brings up another question: if exposure compensation is
>> active, how does the OM actually compensate, when it automatically
>> fires as 1/60 with a dedicated flash?
>>
>> As a third question, AG and Dr Flash have talked about underexposing
>> the background by 1 or 2 stops. One method mentioned was to set the
>> aperture for 1/30 exposure, and letting the OM fire at 1/60. I
>> understand the concept - and here my ignorance is showing - but does
>> this work in straight auto or in TTL as well?
>>
>> In anticipation of suggestions to get a different flash.... Yes, I've
>
>> thought about a T32, though it appears only slightly more flexible
>> than the Braun, and a Vivitar 285, which doesn't do TTL but allows
>> control of flash intensity. However, the lazy side of me doesn't want
>> to throw away TTL.
>>
>> As far as sync speed is concerned, I could always get out my Pen F,
>> which syncs at all speeds. Of course, no TTL, and life is probably too
>
>> short to deal with other challenges!
>>
>> Martin
>>
>>
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