P3D The "rule" is not a rule at all.

[Tom Deering <tmd@xxxxxxxxxxx>]

Boris Starosta wrote:

>The 1/30 rule is a pet peeve of mine.

Mine, too.

>>From: "Jeff Toman" <jtoman@xxxxxxxxxxxxxxxx>
>>splitter is hyperstereo, with a base of 112mm.  Using my 50mm focal length
>>lens, my near subject must be several feet away (approx. 11) by the 1 in 30
>>rule.  Nevertheless, the composition is not a problem.

>I have seen more shots ruined by the 1/30 rule than
>I care to remember.  In folios, exhibitions, on the web... I see either
>subjects photographed from too far away, or I see nearby subjects
>photographed with an insufficient stereobase - with the authors pointing
>out that they adhered to the rule.

This thing about it being a "rule" is a little bit embarrassing. 
Like the Sunny 16 "rule", it is more "exception" than rule.  The 
old-timers know that, but the myth somehow perpetuates itself.  A 
simple rule can't begin to address the complexities of either subject.

For the folks who are just getting started, the "1/30 rule" is not a 
"rule" at all.  It's a wives tale, like the one that says aspirin and 
Coke will get you drunk.

For many kinds of shots, the "rule" is way, WAY off.  It's about 
useless for macros and slidebars.  If you happen to be shooting a 
certain scene, with a certain camera, you might get lucky.  But with 
other cameras, different composition, it is simply way off.

Let's use Jeff Toman's 115mm beamsplitter example above.  He could 
get *much* closer than the 11 feet the 1/30 "rule" suggests.  Let's 
say he's in a room where nothing is farther away than 12 feet.  Under 
these conditions, the 1/30 "rule" would render a flat, pointless 
stereo slide.  Turns out, he could bring objects as close as 6 feet 
away with no problem.  Most people would find such a slide much more 
interesting.  6 feet, not 11.

For details, see http://www.deering.org/basis.html.  It makes sense 
if you think about it: For a Realist camera, the "rule" says you 
can't bring your subject any closer than 7 feet.  So, why does the 
camera focus down to 2 feet?  Maybe because the 1/30 "rule" is 
baloney?

But what is the alternative to the 1/30 voodoo?  It doesn't take a 
PhD.  There are a couple of ways to get the right numbers.  Me, I use 
a programmable calculator.  You can use a spreadsheet to make a 
chart. There are web-based calculators.  Or you can put a printed 
calculator in your camera bag, like 
http://www.deering.org/curves.html.

There are those who disagree.  Perhaps they like randomly flat stereo.

Tom

PS: As always, I suggest you shoot a test roll.  That will lay the 
matter to rest.