Re: Improved T-Max 400

Richard Knoppow <dickburk@[EMAIL PROTECTED]
> wrote:
> 
> 
>     I think you are refering to log exposure. I am going to 
> have to research this because I don't remember if the 
> ASA/Jones method used the same units (lux seconds) as are 
> currently used. 

Thanks. I think a metre-candle-second is the same as
a lux second. 

I've been trying to get a handle on what the X axis
on the H&D curves means in practical terms.

Here is what I've come up with:

For ISO 100, units are log lux seconds:

-2.3  - Jones point (Old ASA 50)
-2.1  - ISO B&W speed point  (0.1 above base + fog)
-1.05 - where usual light meter tries to put the average
-0.3  - where 100% reflectance goes if meter aimed at grey card
 0    - enough to fully blow highlights on typical slide film

A difference of 0.1 is 1/3 stop. 
A difference of 0.3 is one stop.
Thus for 400 speed film subtract 0.6 from these figures.

I think this (if accurate) is a fairly useful list to
keep in mind when looking at H&D curves.

I know there are theoretical problems with trying to
co-relate camera exposure with the figures on 
the H&D curves, but it seems to me that we are essentially
doing just that whenever we set our light meters
based on the ISO value.  I don't think I've seen
such a list anywhere so I've collected one together myself.

It would be great if someone would point out errors,
or add anything which seems useful.

Peter.
-- 
pirwin@[EMAIL PROTECTED]