Heat dispersing / dissipating glass

dogzbum · Jul 2, 2006

How necesary is heat dispersing / dissipating glass?
I bought a second hand Durst Lab G139 that came without the HD glass for the filter tray. Somebody suggested that as the Ilford multigrade filters are acetate they won't melt.
Considering the filters will be about 5cm (2 inches) from the uncooled 300W bulb I am not going to test this until I get a second opinion.
Does anyone run this type of setup without the HD glass?
If the glass is necesary, any idea where I can get some (very cheaply) in Australia as nobody seems to have heard of it?

Roger Hicks · Jul 2, 2006

If you find out, let us all know -- I could do with some too.

I've not tried the setup you suggest but I'd be very nervous too.

Cheers,

Roger

Clueless · Jul 2, 2006

HAG

I bet FocalPoint (Mike) would know or "be" the supplier with the goods. In the larger Dursts there is a slide-out "just" for the HAG (heat absorbing glass).

Donald Miller · Jul 2, 2006

I converted my 138S (same head as the 139) to a fan cooled 1000 watt point light source and I use the heat absorbing glass in mine. I have used the 300 watt Thorn lamp prior to conversion without the HA glass.

In the conversion to point light, the lamp envelope is about 1 1/2 inch from the HA glass. Without fan cooling I have melted the HA glass.

My filters are glass sandwiching acetate filters. I have not had problems with filters but I have cracked diffusion glass when I use it on long exposures. (Rarely)

Claire Senft · Jul 2, 2006

Dow Corning, I beleive, is one firm that makes this glass. You have certainly got yourself one fine enlarger. I hope you enjoy it.

Donald Miller · Jul 2, 2006

I have found a source locally, here in Phoenix, for HA glass it has thermal capabilities to 1400 C. It is really expensive.

The 1000 watt lamp that I use is putting out 985 C.

Claire Senft · Jul 2, 2006

There is an item on ebay for a piece of heat absorbing glass for a Durst L138 S enlarger. My recollection is that your enlarger uses many of the L138 components. It is 1/4x4x4 inches. I went to the Dow Corning web site and I guess they do not make heat absorbing glass.

dogzbum · Jul 5, 2006

Thanks all for your answers. My intention now is to set up a fan that forces air from the front (where the filter box is) and see if one of the multigrade filters melt. I will probably start with the 00 filter. I prefer high contrast anyway

Donald Miller · Jul 6, 2006

dogzbum said:
Thanks all for your answers. My intention now is to set up a fan that forces air from the front (where the filter box is) and see if one of the multigrade filters melt. I will probably start with the 00 filter. I prefer high contrast anyway

The 138 head, I assume the 139 is the same, has an opening for fan cooling directly above the lamp location. There are elongated openings that are baffles for exhaust air dissipation on each side of that opening. It may be that your opening is blocked off with a plate. Most of them are. Two small fasteners should open it up for you.

The fan that Durst calls out has a CFM rating of 70 CFM and the fan is downflow in it's operation. I came up with an alternative fan that moves over 100 CFM with the higher wattage lamp that I have. The fittings for the opening, to allow the fan to connect can be made up from PVC fittings available at Lowes. I have not melted anything down on the PVC with prolonged usage with the fan.

I sort of figured that it was foolish to reinvent the wheel on the air flow design. So I utilized what Durst designed. Good luck.

Kino · Jul 6, 2006

I am suprised that no one thought of Edmund Scientific:
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How big must the filter be?

Be sure to check the wattage limits on the heat filters; you may have to use a hot mirror:

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Heat dispersing / dissipating glass

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