Glass disc in front of filters in Chromega D enlarger head

iandvaag · Jan 2, 2017

I recently picked up a Chromega D4 enlarger locally quite inexpensively. It was really quite dirty and had not been used for many years. It seems to work fine and now that I've cleaned it up it looks ok. The most obvious broken part I've discovered is a glass "filter" that goes in front of the coloured filters. It doesn't seem to be a lens or anything. They both seem to be made of two glass semi circles in a metal ring. These metal housing rings are too large to be attached to the bolts on the enlarger, it seems as though someone replaced them and could not find the right size. What are these glass discs for? Is it just for protection of the coloured filters?

Thanks.

Sirius Glass · Jan 2, 2017

Check with

http://www.darkroomdoctor.com/,
http://www.khbphotografix.com/,
http://www.classic-enlargers.com/ or
http://www.pdf-manuals.com/enlarging-lenses-accessories-omega-1965-841-instructions

removed account4 · Jan 2, 2017

i've never seen a D4 before, but my D3V has a glass disk
made of heat absorbing glass that goes between my light source and
negative stage, maybe this is the same sort of thing ?
i was able to get a replacement at my local glass-shop

good luck ! ( and all the best for the NEW year )
john

AgX · Jan 2, 2017

Looks like a heat absorbtion filter.

darkroommike · Jan 2, 2017

The color gives it aways, heat absorbing glass. Not sure the item was a stick part or an add on. Though cracked they may still work.

Leigh B · Jan 2, 2017

A word of caution regarding heat-absorbing glass...

Never touch it with your are bare hands/fingers, not even briefly.
The oil on your hands transfers to the glass, causing a thermal discontinuity.
This will encourage the glass to fracture at that point when heated.

This is the same caution that applies to handling halogen lamps.

Always wear gloves.

- Leigh

AgX · Jan 2, 2017

darkroommike said:
Though cracked they may still work.

But they seem not to be cracked primarily.

I know a lot of glass filters that are split to enable free expansion, though I never have seen such in a lighting path in an optical system.

ic-racer · Jan 2, 2017

AgX is right. I'd keep using them. However, realize that color head does not have Dichroic filters. So, I'd be more interested in the condition of the color filters.

If I had that head, and I was to use it for B&W, I'd replace the Yellow filter with an Ilford #00 and replace the Magenta filter with an Ilford #5. The Cyan filter is not used in B&W printing.

ic-racer · Jan 2, 2017

Also, that head does not use quartz/halogen lamps, so keep an eye on the conventional lamps and replace them when they get black splotches on them.

mgb74 · Jan 2, 2017

ic-racer said:
AgX is right. I'd keep using them. However, realize that color head does not have Dichroic filters. So, I'd be more interested in the condition of the color filters.

If I had that head, and I was to use it for B&W, I'd replace the Yellow filter with an Ilford #00 and replace the Magenta filter with an Ilford #5. The Cyan filter is not used in B&W printing.

Is this applicable to any colorhead that has bad (original) filters? My Chromega D5 head is all but missing the yellow filter.

Sirius Glass · Jan 3, 2017

mgb74 said:
Is this applicable to any colorhead that has bad (original) filters? My Chromega D5 head is all but missing the yellow filter.

See post #2

removed account4 · Jan 3, 2017

Leigh B said:
A word of caution regarding heat-absorbing glass...

Never touch it with your are bare hands/fingers, not even briefly.
The oil on your hands transfers to the glass, causing a thermal discontinuity.
This will encourage the glass to fracture at that point when heated.

This is the same caution that applies to handling halogen lamps.

Always wear gloves.

- Leigh

hi leigh
i have put in and removed my large rectangular slab of heat absorbing glass
many times without gloves in the past 25 years. i opted to put it in the auxillery filter tray
rather than drop it down into the round spot it originally was in ... i've never had trouble with
fractures &c you warn about. is this caution for heat absorbing glass the same for ALL heat absorbing glass ?
the glass man who sold it to me handed it to me wrapped in newsprint, and i watched him wrap it up with bare hands too.

thanks for the warning !
john

Leigh B · Jan 3, 2017

jnanian said:
hi leigh
i have put in and removed my large rectangular slab of heat absorbing glass
many times without gloves in the past 25 years. i opted to put it in the auxillery filter tray
rather than drop it down into the round spot it originally was in ... i've never had trouble with
fractures &c you warn about. is this caution for heat absorbing glass the same for ALL heat absorbing glass ?
the glass man who sold it to me handed it to me wrapped in newsprint, and i watched him wrap it up with bare hands too.

thanks for the warning !
john

Hi John,

If your hands were recently washed, there might not be enough oil on them to cause a problem.
Or, the alternate location for the glass might reduce the amount of heat impinging on it. Don't know.

The cautions are universal for heat-absorbing glass, being a consequence of the high induced stress when heated.
The same caution applies to halogen bulbs, which operate at over 800 degrees F.

Quoting from this Wikipedia page: https://en.wikipedia.org/wiki/Halogen_lamp
"A 300 watt tubular halogen bulb operated at full power quickly reaches a temperature of about 540 °C (1,004 °F)"

My enlarger uses two 500-watt halogen lamps. That's a lot of heat.
Of course the glass is blocking radiated heat, not conducted heat, but the source temperature is as stated.

Unfortunately it's all too common to find folks not using proper safety techniques.
Sometimes they don't know about the precautions in the first place, and sometimes they don't care.

If an enlarger uses regular incandescent bulbs, the temperatures would be much lower.

- Leigh

MattKing · Jan 3, 2017

Further to Sirius' suggestion, KHB has a lot of useful information that is specific to your enlarger here: http://www.khbphotografix.com/omega/Enlargers/D4.htm
I'm guessing that you have the earlier, non-dichroic filter colour head.
The Accessories list makes reference to three different versions of "Tri-sected Heat Absorbing Glass", which I would guess are what you are concerned about.
If yours is the original Chromega head, here is their take on it: http://www.khbphotografix.com/omega/Chromega/Chromega.htm

Hilo · Jan 3, 2017

Leigh, your warning is excellent !

It reminds me of the chrome columns of the Focomat 1c that we should not touch with our bare hands, as the chrome will deteriorate because of the substance that our hands transfer. With chrome it is sufficient to clean it well with something like white spirits or naphtha and then apply vaseline . . .

For my Durst L1000 I have a similar heat glass between the lamp house and the filter drawer. That one is called Taucalo and I am not sure if I touched it or not. Any advise how to clean that?

Michael

AgX · Jan 3, 2017

I never heard that warning of touching on heat absobing filters.

In contrast to that on halogen bulbs. BUT after handling a lot of used ones of these I never ever found traces of charcoal at them.
Another theory(?) is that salts on the glass surface can induce crystalisation and thus stress.

Also IR-heaters that got tungsten helicals in thin, long glass tubes often got these filthy.

removed account4 · Jan 3, 2017

Leigh B said:
Hi John,

If your hands were recently washed, there might not be enough oil on them to cause a problem.
Or, the alternate location for the glass might reduce the amount of heat impinging on it. Don't know.

The cautions are universal for heat-absorbing glass, being a consequence of the high induced stress when heated.
The same caution applies to halogen bulbs, which operate at over 800 degrees F.

Quoting from this Wikipedia page: https://en.wikipedia.org/wiki/Halogen_lamp
"A 300 watt tubular halogen bulb operated at full power quickly reaches a temperature of about 540 °C (1,004 °F)"

My enlarger uses two 500-watt halogen lamps. That's a lot of heat.
Of course the glass is blocking radiated heat, not conducted heat, but the source temperature is as stated.

Unfortunately it's all too common to find folks not using proper safety techniques.
Sometimes they don't know about the precautions in the first place, and sometimes they don't care.

If an enlarger uses regular incandescent bulbs, the temperatures would be much lower.

- Leigh

thanks
i'll be more careful when i reinstall + use my condenser head... !

paul ron · Jan 3, 2017

see if a manual has the information. since those filters do not align with the mounting screws, they may have been a user adaptation for the original parts.

manuals here,........

http://www.jollinger.com/photo/cam-coll/manuals/manuals.html

.

ic-racer · Jan 3, 2017

mgb74 said:
Is this applicable to any colorhead that has bad (original) filters? My Chromega D5 head is all but missing the yellow filter.

The light path in an Omega D Chromega II dichroic head (which is different than what is shown in the original post of this thread) is pretty narrow when it reaches the filter. A plastic filter might melt. You could try it and see. You could get quite a few little filters out of a single 6"x6" sheet of "00".

iandvaag · Jan 3, 2017

Thanks so much for all the replies! Yes, the head is the non-dichroic regular chromega. I notice that KHB recommends against using this head (or at least outlaying cash to acquire it). I consider it to have came free with the purchase of the rest of an enlarger (I paid $50 for the whole setup). It looks like a dichroic head could be had from ebay for several hundred dollars if this doesn't work out. It came with two sets of replacement filters and several bulbs. Do the filters fade in the dark, or just from use? It appears as if I won't be able to get the proper heat absorbing filters, so I guess I'll clean these ones off and reinstall them.

Leigh B · Jan 3, 2017

Hilo said:
I am not sure if I touched it or not. Any advise how to clean that?

Hi Michael,

Any good glass cleaner that leaves no residue should be satisfactory.

The problem is any contamination that changes the thermal characteristics of the local surface.
That can cause differential expansion, i.e. local stresses that can break the glass.

- Leigh

paul ron · Jan 3, 2017

denatured alcohol

Glass disc in front of filters in Chromega D enlarger head

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