Why do my Beseler enlargers have a spacer between heat absorbing glass and condenser?

[xkaes]

My two genuine Beseler CB7 heat absorbing glasses are 1/8" thick (AKA Double-Strength). To me, the color looks just slightly greener than plain window/framing glass (3/32"). One is factory installed, the other not. Neither has a mark or dot, of any color, alone the edges. Both are slightly smaller in diameter than the condenser tube -- about 1/16" -- which would allow for expansion -- although it is held in place by four metal tabs that would make expansion difficult. (I'll check into that aspect.)

When I get around to it, I'll add it to the top of my condenser assembly while maintaining some space between the two heat absorbing glasses -- there is plenty of room in the condenser structure.

[Tin Can]

https://www.edmundoptics.com/optics/...sorbing-glass/

Custom sizing available.

Not free.

Mounting position could be closer to source.

Please explain your project scope and parameters.

20 minute wide open enlarging may be interesting.

[xkaes]

[url]20 minute wide open enlarging may be interesting.

Thanks for the link.

No, I do not use my point light source with a lens wide open for 20 minutes exposures. I only use long exposures with my diffusion light sources with filters with the lens stopped down for mural-sized prints. I can easily have one minute exposures for 11x14" prints. I don't see why it is surprising to some that a VERY long exposure would be needed for an eight FOOT print -- that might be made from a cropped section of the negative -- really a portion of a 24 foot print! (I'm sure somebody will respond, "You can't do that!", or some other nonsense.)