Re: focusing in monochromatic light

[T3D john bercovitz <bercov@xxxxxxxxxxx>]

John Merritt wrote:

> John B wrote about yellow glasses and monochromatic light.  I 
> suspect these glasses are not monochromatic, but rather a blue 
> cut-off filter.

You suspect correctly.  It's hard to tell minus blue from yellow 
by eye!  Over the weekend I put different filters in front of my 
Gossen Luna Pro F and then added some yellow glasses used in 
ventilation of wood products.  I found no change in red, yellow or 
green but an 0.3 stop drop in blue (#47 Wratten).  Nice call, 
John.  Still makes my eyes buggy.  Maybe it's subtracting the blue 
that my eyes use to balance against the red?

John B


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