[LargeFormat] 12" Commercial Ektar - lens board extension

[Clive Warren]

At 4:50 pm -0800 12/12/01, Les Newcomer wrote:
>thanks to two prime directives of my life--never throw anything away and
>It's all on my desk, I can provide some usefull data

Big Snip
>
>Accroding to the 16th edtion of Machinery's Handbook, b=c x tan B
>
>  Mr. TI 30 says the TAN of 32 is .6248
>
>2" long tube  x .6248= 1.249 or 3" dia
>
>3        "    x .6248= 1.874" or 3.75" dia
>
>4" long tube  x .6248= 2.50 or 5" dia
>
>5" long tube  x .6248 =3.12" or 6.25" dia
>
>
>Without showing my work
>
>a 12" lens at  14" will focus at 7 feet
>
>            at  16"     """""""   4feet
>          
>            at  18"    ''''''''   3 feet
>
>
>formula:  object distance=  bellows draw  x focal length/ bellows draw -
>focal length
>
>So an extension box that will fit a 4" lens board that's 3" long will
>allow you to focus to about 5 feet without vignetting.
>
>Les Newcomer
snip

Les,

That is absolutely brilliant - thank you very much indeed!

Will have to get some quotes for the work as I know that my old lathe 
will not be a lot of good for cutting the internal threads on the 
extension tube...

Thanks again,
              Clive