"Richard Knoppow" <dickburk@[EMAIL PROTECTED]
> wrote in message
news:13id6442h4ele76@[EMAIL PROTECTED]
>
> "Peter Irwin" <pirwin@[EMAIL PROTECTED]
> wrote in message
> news:fg5ogt$tnv$1@[EMAIL PROTECTED]
>> Richard Knoppow <dickburk@[EMAIL PROTECTED]
> wrote:
>>
>>> Assuming
>>> the minimum usable gradient is somwehere around log -2.5
>>
>> I had been under the impression that the Jones
>> point for a 200 old ASA film was at log -2.9.
>>
>> I'm not really reliable at math, so I'd be glad
>> if someone would show me if I've gone wrong.
>>
>> If the old ASA speed definition is:
>>
>> old ASA speed = 1/(4xE)
>>
>> then E = 1/(4x old ASA)
>>
>> E = 1/(4 x 200)
>> E = 1/800
>> Log (E) = -2.903
>>
>
> 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. In any case, the Jones method was based on
> an exposure giving a minimum toe gradient of 1.3rd of the
> overall straight line gradient. ^^^^^
Mis typed, should be 1/3rd.
--
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@[EMAIL PROTECTED]
|
