Durst 138 / 138S heat filter question

[Mark J]

I have been slowly working through the various steps to get my 138 S ( purchased in approx May ) commissioned in the darkroom.
This is the unit with condenser head.
One minor issue that keeps bothering me is this :
I would like to install a heat filter, either absorbing or reflecting, in the allocated slots in the inside of the head.
Every time I go looking for material , I see that across the board, the glass thickness is around 3mm.
Now the slots in the inside of the light box look like they would not take much more than 1mm thickness.

I went looking through the manuals this evening to see if there was some sort of metal carrier into which the filter is mounted, which then slots into the 'spring-slots' in the head.

Best I could find is this shot from the 138 manual - but it's hard to see.
Does anybody have more hands-on knowledge on this ?

I am just about to talk to the local sub-contractor for optics test gear etc who can help me with some internal parts and ideas for the light-source mounting, so it would be good to get a bit of background info on this part, if we need to add it to the list.

[ic-racer]

If you ask me, the heat absorbing glass is to protect your color filters. If not using filters in the drawer, you would not need the heat absorbing glass.

How about this one:

[Mark J]

Thanks for looking but I will quite likely be using colour filters in the drawer, and that filter is too small, the port in the head is 85 x 75mm, all the bigger filters are 3mm thick.

[Jason Greenberg Motamedi]

The heat absorbing glass is indeed 3mm, and comes mounted on a metal carrier, as you guessed...

What do you need to know? I was confused initially by the two pieces of glass, but from what I have read on this forum it is intentional and helps dissipate heat without a notable effect on light distribution...

[Mark J]

Oh fantastic - thanks !
Isn't that interesting...
In that case I will order some 3mm glass and discuss a holder for it with John.

[Mark J]

Very odd about the two pieces of glass - wonder if it is something to do with either heat expansion or an alignment aid of some sort ?
I will most likely be buying a 'hot mirror' ( dielectric reflect ) for this, so the glass will not get as hot. There are 100mm square pieces you can buy, I can get it cut down to size accurately.

[Drew Wiley]

Hot mirrors are sometimes combined with UV coating on the opposite surface - another option.

[interneg]

The heat filters in the Ilford MG500 dichroic head are also two piece - whereas LPL used 1.

[Mark J]

Hot mirrors are sometimes combined with UV coating on the opposite surface - another option.

Is that a UV reject or a UV AR coating, do you think ?

[dsphotog]

The HAG in the Durst 184 condenser head is also 2 piece.