E61 Paper Towel Tubes and BFL

This week we talk about making your own lenses, why Back Focal Length is meaningless to Ethan, and how to play around with loose achromat lens elements to make your own, homemade lens.

The formula: Formula:

F = (f1 x f2) / (f1 + f2 - d)

BFL = (f2 x (d - f1)) / (d - (f1 + f2))

f1 is the front lens,

f2 is the back lens,

d is the distance between the lenses.

F is the focal length,

BFL is the distance between the back lens and the recording media (film, sensor)

A link to a spreadsheet with the formula in it: https://docs.google.com/spreadsheets/d/1yQ3dsD0Rs-HflRcnPYHSmK0soLXtykGAPl8pdZcrBpM/edit?usp=sharing

Special thanks to Erik Mathy (https://www.instagram.com/erikhmathy/ @erikmathy).

We first heard about this formula on an episode of the Large Format Photography Podcast (https://largeformatphotographypodcast.podbean.com/)

We also talk about a modified Adolescent Crown Graphic Nick's working on.

Ethan mostly tells Graham his formula is wrong.

Graham mostly tells Ethan he names his products after rodents and wonders when the Cameradactyl Chipmonk is coming out.

Graham offers to give away a bunch of darkroom equipment to someone in Northeastern Florida (Jacksonville to Ocala, Daytona to Gainesville). Email Graham@homemadecamera.com if you are interested.

Warning, Graham swears at the very end. If this had been edited by Simon of the LFPP and Classic Lenses, there would have been a gap where you guessed what Graham said but because Graham edited the show, you hear a bunch of F-words in a row.

Finally, we may be taking the month of November off from recording. Don't worry, we'll be back by the Winter Solstice when things are darkest.