What is the purpose of this red light on the lens board?

[slackercrurster]

Photos eBay: Fair Use

 

[JensH]

Hi,

it illuminates the aperture ring.
So you can see what f stop is set in the darkroom...

 

[slackercrurster]

Thanks! In 55 years of photo work, first time I ever saw one.

 

[Ian C]

Clever in theory. Useless in practice.

The one shown in post #1 has the 45º bevel rotated 180º out of position. The bevel should be opposite the lens. The bevel is coated with silver paint that is supposed to reflect the light from the lamp 90º from the tube to the aperture scale. The light reflects from the reflective paint at bottom of the bevel, through the tube, and to the aperture ring.

Here are some photos of Beseler 23C lens boards with the pilot light tube in correct orientation.

https://www.bhphotovideo.com/c/product/4519-REG/Beseler_8037_50mm_Flat_Lensboard_for.html

https://www.bhphotovideo.com/c/product/4525-REG/Beseler_8029_39mm_Lensboard_with_5_8.html

https://www.bhphotovideo.com/c/product/4517-REG/Beseler_8023_39mm_Flat_Lensboard.html

https://www.bhphotovideo.com/c/product/4515-REG/Beseler_8021_39mm_Flat_Lensboard.html

Note the different tube lengths to accommodate the assumed aperture ring distance from the flat part of the board.

 

[JensH]

Thanks! In 55 years of photo work, first time I ever saw one.

Newer seen such, too. I wonder if it can cause problems when doing color enlargements...
Btw, later examples of the Componon-S 135 come with illumination from inside the barrel.