# Any Optics gurus out there? **URL:** \ **Category:** Factual Questions\ **Created:** [August 18, 2002, 5:48am UTC](https://boards.straightdope.com/t/any-optics-gurus-out-there/124446 "2002-08-18T05:48:23Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![SenorBeef](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senorbeef/32/2220_2.png) [@SenorBeef](https://boards.straightdope.com/u/SenorBeef)\ **Post date:** [August 18, 2002, 5:48am UTC](https://boards.straightdope.com/t/any-optics-gurus-out-there/124446/1 "2002-08-18T05:48:23Z")
Apparently an optics guru made this post invisible. ---
**Author:** ![happyheathen](https://avatars.discourse-cdn.com/v4/letter/h/b5e925/32.png) [@happyheathen](https://boards.straightdope.com/u/happyheathen)\ **Post date:** [August 18, 2002, 8:12am UTC](https://boards.straightdope.com/t/any-optics-gurus-out-there/124446/2 "2002-08-18T08:12:38Z")
Can anyone direct me to detailed instructions on haw to build a [Camera Obscura](http://brightbytes.com/cosite/sanfran.html) ? More precisely: I know that the head contains a first-surface mirror with a condensor lens assembly below it, and that the viewing table is parabolic. Now the questions: How to determine the formula for the table surface: what do I need to know about the lenses to derive the formula? and yes, a fixed-focus model would be nice. ---
**Author:** ![capybara](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/capybara/32/202_2.png) [@capybara](https://boards.straightdope.com/u/capybara)\ **Post date:** [August 18, 2002, 9:55am UTC](https://boards.straightdope.com/t/any-optics-gurus-out-there/124446/3 "2002-08-18T09:55:24Z")
I asked this some time last year, or something like it-- I’d search but my connection’s wussy. There are some sort of wimpy diagrams out on the web somewhere.