Replacement Heat Absorbing Glass For Omega Super Chromega D Dichroic II

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Born2Late

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Hello,

I have had this enlarger for quite a while. I'd like to put a new heat absorbing glass in it; I don't know if the existing one is bad, but given the age it wouldn't hurt. The glass is a disk about 1" in diameter and is located in a "top hat" shaped flange on the side of the mixing chamber. I've done internet searches and found none listed for this enlarger; not even at KHB. I have found heat absorbing glass disks in the right size, but don't know if there is a specific grade that is correct for this application.

Can anyone help me with this question?

Thanks
 

Sirius Glass

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Give KHB a call or message, I've found they have more than is listed on the web site. Worth a try.

Plus product knowledge that we do not possess. I have the same enlarger.
 

Donald Qualls

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Give KHB a call or message, I've found they have more than is listed on the web site. Worth a try.

You know, I should do this, too. Mine is missing the grid out of the attenuator (blocks about 75% of the light to get longer exposures without color shift). That's the only thing I'm missing to put mine into service.
 

ic-racer

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Probably not hard to figure out your requirements. Assuming the existing glass is bad. Is it etched from fungus?
Either way, the halogen lamp gives off considerable IR as seen here. This is manifest as heat. Thus the need for the fan.

Screen Shot 2022-11-17 at 3.47.27 PM.png
 

ic-racer

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Good news is the dichroic reflector lets much of the IR pass outward to the Chromega head assembly and focuses mostly visible light to the light multiplier window. See the green line in the graph.
dichroic.jpg
bulbs.jpg
 

ic-racer

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This is a graph of some of the IR filters of which you were inquiring. As you can see, the bulk of IR has been cast aside by the dichroic reflector. I suspect you will be fine with KG5, 3 or 1.
IR filters.jpg
 

ic-racer

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Here is the sensitivity of Ilford paper. So, your filter will have little effect on your prints, but may help keep the lightbox lasting longer by blocking unwanted IR and heat to the diffusion material.

Which, you might want to inspect to see that it is still bright white and has not yellowed.

MGIVFB_web.QXD - 2011427105150454.pdf.png
 
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Born2Late

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You know, I should do this, too. Mine is missing the grid out of the attenuator (blocks about 75% of the light to get longer exposures without color shift). That's the only thing I'm missing to put mine into service.

You can buy the perforated metal from McMaster Carr. It is a little pricey, but you will have enough to make plenty of them. You may be able to find some elsewhere cheaper.
 

Donald Qualls

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You can buy the perforated metal from McMaster Carr. It is a little pricey, but you will have enough to make plenty of them. You may be able to find some elsewhere cheaper.

I've got a piece of 50% mesh (I was planning to use two offset layers to get 75% reduction) and some high temperature RTV, but it looks like I'll have to disassemble the filter assembly in the head to install that, vs. just pressing in the "hat" shaped original type carrier.
 
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Born2Late

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Here is the sensitivity of Ilford paper. So, your filter will have little effect on your prints, but may help keep the lightbox lasting longer by blocking unwanted IR and heat to the diffusion material.

Which, you might want to inspect to see that it is still bright white and has not yellowed.

View attachment 322031

Thanks for all of all of the info. I think I can interpret it okay; my color blindness makes colored charts a bit of a challenge, that is why I work in black and white!
 

xkaes

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You know, I should do this, too. Mine is missing the grid out of the attenuator (blocks about 75% of the light to get longer exposures without color shift). That's the only thing I'm missing to put mine into service.

Would a typical ND filter solve this? That's what I use on the infrequent occasions that I need/want longer exposure times.
 

Donald Qualls

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Would a typical ND filter solve this? That's what I use on the infrequent occasions that I need/want longer exposure times.

I thought about that, but I was concerned about heat build-up. For that matter, I'd have to look again to be sure the heat-absorbing glass is present in mine, haven't looked inside it in a while.
 

ic-racer

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I don't see why a disk with a hole in the middle (like an aperture) would not work. The Durst attenuator is adjustable and functions like that. Screen Shot 2022-11-18 at 10.00.10 AM.png
 

xkaes

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I thought about that, but I was concerned about heat build-up. For that matter, I'd have to look again to be sure the heat-absorbing glass is present in mine, haven't looked inside it in a while.

I wasn't clear. I use mine on the lens.
 

xkaes

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I have seen them etched by fungus, but I have never replaced one for that reason. I just clean it and put it back.

Besides fungus, how could the glass itself "go bad"? A colored glass filter can fade, but how can heat-absorbing glass lose it's ability to absorb heat?
 

Donald Qualls

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I don't see why a disk with a hole in the middle (like an aperture) would not work.

I thought I had understood that a center aperture could affect color mixing (the filters slide into the light gradually to give more or less color filtration).

I wasn't clear. I use mine on the lens.

Ah. That surely would work. Still need to check my IR block glass, though...
 

ic-racer

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I thought I had understood that a center aperture could affect color mixing (the filters slide into the light gradually to give more or less color filtration).



Ah. That surely would work. Still need to check my IR block glass, though...

Yes, excellent point! You do need to have the entire aperture open. I looked again at the Durst and it uses a variable slit 90 degrees to the filter paths.

I only used a D5 Chromega head briefly, but it seemed to never be too bright. Having mentioned that I'm a proponent of getting all the functionality of an enlarger working, even if the functions are only rarely used.
 

Donald Qualls

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I looked again at the Durst and it uses a variable slit 90 degrees to the filter paths.

Hmm. A slit parallel to the filter movement (which is on an arc, but I can get close enough) might well do the job. This is an on-off attenuator, so I don't need the slit to vary width. And I do have some aluminum tape around, made for furnace ducts, so it should take the heat. Now the question is whether I can install it without disassembling stuff I don't want to have to put back together.
 

ic-racer

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The smallest perforated aluminum sheet McMaster Carr sells is like 24x24" and is pretty expensive. Something from the Kitchen utensil section might work. I also suspect aluminum oxide mesh sanding disks are heat stable.
Screen Shot 2022-11-18 at 10.35.56 AM.png


Ha47d8a7e14c94adc85d77cc193aa63a4M.jpg
 
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