Dr. Flash says, "you're quite welcome". :-)
Chuck Norcutt
On 5/20/2011 1:11 PM, Walters, Martin wrote:
> When written like that, manual flash doesn't seem quite so intimidating.
> Clearly, practice makes the arithmetic second nature.
>
> Chuck: Please thank Dr Flash for the time and effort he puts into his
> replies.
>
> Martin
>
> -----Original Message-----
> From: Chuck Norcutt [mailto:chucknorcutt@xxxxxxxxxxxxxxxx]
> Sent: Friday, May 20, 2011 10:52 AM
> To: Olympus Camera Discussion
> Subject: Re: [OM] OM TTL flash behaviour
>
> 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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