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[OM] Artificial light, was: OM Gear FS

Subject: [OM] Artificial light, was: OM Gear FS
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Mon, 29 Jul 2013 11:44:35 -0400
The biggest single thing to realize with artificial light (flash or 
anything else) is the unremitting nature of the inverse square law. 
<http://en.wikipedia.org/wiki/Inverse-square_law>  As you can see in the 
diagram in the wiki link the light rays at distance 2r are covering an 
area that is 4 times as large as that at distance r.  That means the 
intensity of the light at distance 2r is only 1/4 (2 stops less) of what 
it was at distance r.  In practical terms for flash or any other 
artificial light that means if the exposure at 4 feet is f/8 the 
exposure at 8 feet (twice the distance) is f/4.  Stated another way, if 
the camera is set at f/8 things at 4 feet will be properly exposed and 
things at 8 feet (not much further) will be 2 stops under-exposed.  At 
distance 1.4r (the square root of 2) the intensity will be down only 1 
stop instead of 2.  You can also see these relationships in the f/stops 
on your camera... 1.4, 2, 2,8, 4, 5.6, 8, 11, 16, 22, 32, etc.

The situation gets worse the closer the subject is.  If the subject is 
at 2 feet whatever is at twice that distance (only 4 feet) is also 
underexposed by 2 stops.  The reverse situation occurs too.  If you're 
properly exposing for a subject 8 feet away anything only half that 
distance is bound to be overexposed by 2 stops.  Yikes!  That's a big error.

These are the simple laws of physics and can't be directly defeated. 
But they can be mitigated.  You can keep multiple subjects together at 
the same distance.  If you can't do that then increase the distance.  If 
the main subject is at 12 feet rather than 4 then the light doesn't fall 
off by 2 stops until the distance gets to 24 feet.  Unfortunately, 
increasing the distance also narrows the apparent diameter of the light 
source which (like the 1/2 degree angular diameter of the sun) causes 
harsher shadows.  Larger diameter sources (think diffusers, umbrellas 
and soft boxes) soften the shadows.  Bounce flash is a good thing since 
the angle up to the ceiling and back down or the angle off the side to a 
wall and back both increases the distance (less variation in brightness) 
and dramatically enlarges the apparent diameter of the light source 
(softer shadows).  Other forms of mitigation include multiple lights 
which may be at different distances and hidden behind objects so the 
source itself is not visible.

Dr. Flash (who is also stymied by flash at times)



On 7/28/2013 4:15 PM, Johnie Stafford wrote:
> Thanks Chuck. Artificial lighting has always been a black art to me. I've
> always struggled with it.
>
> Johnie Stafford
> McKinney, TX
> jms@xxxxxxxxx
> twitter | LinkedIn
>
>
>
>> -----Original Message-----
>> From: Chuck Norcutt [mailto:chucknorcutt@xxxxxxxxxxxxxxxx]
>> Sent: Sunday, July 28, 2013 12:46 PM
>> To: Olympus Camera Discussion
>> Subject: Re: [OM] OM Gear FS
>>
>> I should have mentioned that using a T-32 off-camera with T-cables and a
>> non-OM body requires a TTL auto shoe cord.  Alternatively one can use a
>> standard PC cord but it will require a PC to hot shoe connector on the
> flash
>> end and possibly a hot shoe to PC cord connector on the camera end if the
>> camera doesn't have a PC connection.
>>
>> Radio slaves are certainly the easiest way but also require some sort of
> hot
>> shoe arrangement on the flash end that's compatible with the radio slave.
>> My favorite is the Paramount Cords female hot shoe to miniphone
>> connector.
>> <http://www.paramountcords.com/proddetail.asp?prod=PW-
>> MHSF1&cat=85>
>> Very ruggedly built.  Fits PocketWizards and some other radio slaves such
> as
>> my Alien Bees units.  These Paramount cord connectors are expensive but
>> I've managed to find 2 of them on ebay for about $20 each.
>>
>> An even easier solution if you're using at least 2 flash units indoors it
> to
>> mount the fill flash light on the camera and then use an inexpensive
> optical
>> trigger to fire the main light (or any others) which are off-camera.
>> <http://www.ebay.com/itm/SEAGULL-SYK-3-Hot-Shoe-Flash-Light-Remote-
>> Optical-slave-Trigger-for-Canon-Nikon-
>> /250888270544?pt=Camera_Flash_Accessories&hash=item3a6a1b32d0>
>>
>> These things are very cheap, very sensitive and very reliable.  I have
> some
>> that look exactly like what you see in the link that I've been using for
> some
>> 12-15 years.
>>
>> Chuck Norcutt
>>
>>
>> On 7/28/2013 2:46 AM, Chris Barker wrote:
>>> Thanks, Chuck.
>>>
>>> Chris
>>>
>>> On 27 Jul 2013, at 19:39, Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
>> wrote:
>>>
>>>> Try it.  It's not hard.  You can use radio slaves or even
>>>> T-connectors and cables if you have them.  No other OM gear required.
>>>
>> --
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>
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