[pure-silver] Re: estimating filter factor: gray card?

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <pure-silver@xxxxxxxxxxxxx>
  • Date: Mon, 2 Oct 2006 17:07:25 -0700


----- Original Message ----- From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx>
To: "PureSilverNew" <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, October 02, 2006 2:57 AM
Subject: [pure-silver] Re: estimating filter factor: gray card?


The square root function is not used to turn filter factors into f/stops or
visa versa? I think this has caused some confusion before.

The conversion can be done using the following:

x = 2^N
log(x) = log(2)*N
N = log(x)/log(2)

where x is the filter factor and N is the amount of stops.





Regards



Ralph W. Lambrecht

http://www.darkroomagic.com

Stops are definitely square and square root functions. One can do roots in log form by multiplying or dviding by the root required, that is 2^4 can be found by taking anti-log of (Log 2 *4) and roots by deviding the log by the root required. The (2) factor in your equations above are square and square-root functions. Most calculators do exponentials by means of log look up tables.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 

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