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

I've been exposed to Newton's rings before with an old Paterson enlarger, but my question does not involve a near negative-to-glass contact. On my Beseler CB-7 and 45 MXII, the heat-absorbing glass is separated from the upper condenser by a spacer ring -- probably 1/16-1/8" thick. I'm wondering why the spacer is there. I don't see how it would produce Newton's rings if removed. I could run some tests myself, but I thought someone here would have an explanation for the spacers. It is probably just to avoid scratches. Any thoughts?

I'm not familiar with the construction of your enlargers, but I'd speculate that the spacer is not involved with an NR issue, but rather to isolate the warm/hot heat absorbing glass from contact with condenser which may cause optical distortion in the non-uniformly heated condenser. Your description implies that if the spacer is removed, then the h/a glass could come in contact with the condenser. Are you certain your condenser is glass and not (OMG!) plastic?

Thanks for the response. I am sure the condensers are glass. I had not thought about the heat issue with the condensers. I had always thought about the heat-absorbing glass as trying to protect the negatives! They are obviously there for a reason, but can they remove that much heat with a long exposure to make a difference? How much heat -- created by a 100 watt bulb would result in a condenser distortion if the heat-absorbing glass was not there?

Is it there to protect the condenser or the negative/slide? Or both! Curious minds want to know!

If your neg can be warped by as much as a sixteenth or even eighth of an inch, parts of it are going to out of focus too!

Don't know the specifics of the construction but the spacers could be there to create an air space to enhance the heat absorbing effect - the hot air can escape and brings a cooling effect.
Yet another reason that comes to mind is that the condenser is probably not a heat hardened glass and should not be in a direct contact with a heat source - which the heat absorbing glass paradoxically is.

I don't how how the heat could escape, because it's pretty tight.

At this point, the question is:

Is heat absorbing glass used to reduce heat on the negative, the condenser, or both?

Quote:

---

Originally Posted by xkaes

Is heat absorbing glass used to reduce heat on the negative, the condenser, or both?

---

Well, because the condenser is between the film and the heat absorbing glass then logically you have to reduce the heat on the condenser if you want to reduce it on the film.

Why not reduce the heat AFTER the light goes through the condenser if the purpose is to reduce the heat to the negative?

Quote:

---

Originally Posted by xkaes

Why not reduce the heat AFTER the light goes through the condenser if the purpose is to reduce the heat to the negative?

---

Because you don't want to heat the condenser so much as you can heat the HA glass. The condenser is probably not heat hardened glass.
Also, the condenser is a big chunk of glass and you don't want to heat it with a spot heat source, it could crack. The heat absorbing filter dissipates the heat so it hits the condenser in a more uniform way.

I wonder if my Beseler usage makes heat a non-issue. I don't seem to heat anything up that much. I work kinda slow on one neg and one print at a time. Once focused which takes very little time, I futz a bit with paper and then print maybe 10 until I get my print how I want it. Then I make 3 more fairly quickly. Once I like a print I always do 3 more. Just in case. I don't want to come back.

I imagine back in the day CB7's were used fast, hard and hot. Maybe using them for printing spools of medium format? I can't clean glass, dust, insert a 4x5 neg fast enough to have heat issues.

Is heat really a worry for a hobbyist?

I also turn down my bulb voltage...

I have never run across a heat issue either, but my original question was about Newton's rings -- and if that has anything to do with the spacer ring in between the condenser glass and the heat absorbing glass. I still don't know about that. I can run some tests myself, but was trying to avoid spending the time.

A far as I know, none of the other enlargers I have used, before my Beselers, even had heat absorbing glass -- but they all had glass condensers. So far, all I've heard is speculation about whether the heat absorbing glass is there to protect the condensers, the negative, or both. Regardless of the answer, it would seem that any enlarger, especially with a glass condenser, would have heat absorbing glass in it. Is this the case? Seems like a simple, straightforward question.

Beseler is still in business. Have you tried asking them? Sure, it's possible that the designer of the enlargers is long gone and nobody else remembers. But maybe someone there will know.

Quote:

---

Originally Posted by Randy Moe

I imagine back in the day CB7's were used fast, hard and hot. Maybe using them for printing spools of medium format? I can't clean glass, dust, insert a 4x5 neg fast enough to have heat issues.

---

I don't see why a CB7 would run hotter than a 45 MX II. The condenser heads are almost identical -- especially the venting. So assuming the same bulb is being used, I would not expect a difference in heat.

Quote:

---

Originally Posted by xkaes

I don't see why a CB7 would run hotter than a 45 MX II. The condenser heads are almost identical -- especially the venting. So assuming the same bulb is being used, I would not expect a difference in heat.

---

You are correct. They are the same design, yet scale is in CB7 favor. More glass, more mass. Larger vents, more area. Bigger enclosure. I use the same bulb.

What is heat absorbing glass? Borosilicate? I have stacks of glass in my Elwoods. Elwood documentation shows they increased the number of heat absorbing glass over time. I think Elwood has plain glass. No condensers.

Perhaps the Beseler upper layer is partly sacrificial and meant to protect expensive condensers from scratches, melted filters, grilled cheese toast...

CB7 is bigger, note the light cones have different paint. Is black better than white paint.

Just so happens I am setting up a new darkroom. Beseler CB7, MXT, 23C III, Elwood 5X7 and a Leica V35. So I am haveing a second look at my inventory.

Adorama has this text, '• The high performance 45M Condenser Lightsource utilizes Beseler's patented "Cone-of Light" variable condenser system to adjust the position of the over-sized 6½" optical glass condensers to maximize the illumination for every size film from 35mm through 4" x 5", yielding exceptionally short exposure times, a cooler film stage and less negative buckling than with conventional condenser heads.'

https://farm5.staticflickr.com/4583/...c1dd348d_n.jpgIMG_0464 by moe.randy, on Flickr

https://farm5.staticflickr.com/4570/...2c936480_n.jpgIMG_0465 by moe.randy, on Flickr

https://farm5.staticflickr.com/4532/...89a22e8b_n.jpgIMG_0468 by moe.randy, on Flickr

[QUOTE=Randy Moe;1415440
What is heat absorbing glass? Borosilicate? I have stacks of glass in my Elwoods. Elwood documentation shows they increased the number of heat absorbing glass over time. I think Elwood has plain glass. No condensers.

Perhaps the Beseler upper layer is partly sacrificial and meant to protect expensive condensers from scratches, melted filters, grilled cheese toast...[/QUOTE]

My heads are slightly different that yours, but that is inconsequential. As to the heat absorbing glass, it looks like typical window glass, but I have to assume that it is there to absorb heat from the bulb since it is on the TOP of the condenser assembly. If you look closely around the edges, you will see a thin brass spacer ring on either head. It's easy to assume that it is more than plain window glass, but that would be a guess on my part. Maybe plain glass accomplishes the task! And since it is built-in, it has got to accomplish more than just "scratch/dust" protection.

Does the heat from a 100 watt bulb actually pose a threat to a glass condenser? Curious minds want to know!

I'm out.:)

Quote:

---

Originally Posted by xkaes

My heads are slightly different that yours, but that is inconsequential. As to the heat absorbing glass, it looks like typical window glass, but I have to assume that it is there to absorb heat from the bulb since it is on the TOP of the condenser assembly. If you look closely around the edges, you will see a thin brass spacer ring on either head. It's easy to assume that it is more than plain window glass, but that would be a guess on my part. Maybe plain glass accomplishes the task! And since it is built-in, it has got to accomplish more than just "scratch/dust" protection.

Does the heat from a 100 watt bulb actually pose a threat to a glass condenser? Curious minds want to know!

---

If your enlarger still has its original heat absorbing glass then it does not resemble window glass and there is only one correct side that has to face the light source for the glass to work properly to protect your film from excessive heat to reduce popping. However, to get optimal performance from your enlarger and lens the enlarger must be properly aligned at all three stages, negative, lens and baseboard. The film must be in a glass carrier, the lens must be used within its optimal magnification range and at its optimal aperture.

Additionally the film stage must be within safe temperature range and that is why you need heat absorbing glass, if required, and the proper wattage lamp.

Quote:

---

Originally Posted by Bob Salomon

The film must be in a glass carrier, the lens must be used within its optimal magnification range and at its optimal aperture.

---

That's odd. Beseler only sold one 4x5 glass negative carrier -- that I know of -- for 4x5". I have Beseler carriers from Minox to 4x5" and all of them are glass-LESS.

Plus, my heat-absorbing glass on both my CB7 and 45MX II are factory installed and don't appear any different to me than plain thick glass.

Thanks for the info, but I guess I'm on my own.

Quote:

---

Originally Posted by Bob Salomon

The film must be in a glass carrier,

---

Beseler's (glassless) NegaFlat for 4x5 is fantastic - way better than the glass carrier. The glass carrier IMO is great for if you want to scream in frustration as you see your print yet again covered in dust spots after meticulously cleaning it for the 3rd time trying to make just one decent print. Perhaps you have a hermetically sealed darkroom with a phalanx of air purifiers and filters but for a mere mortal like me I chucked the glass carrier in the bottom of a drawer and never looked back. After really going after alignment on my 45MX earlier this year I can say with confidence that the glassless carrier didn't make any difference compared to the NegaFlat for 4x5 and none of the smaller carriers had any noticeable sag when used properly. I printed some negatives and saw it myself.

Quote:

---

Originally Posted by Corran

Beseler's (glassless) NegaFlat for 4x5 is fantastic - way better than the glass carrier. The glass carrier IMO is great for if you want to scream in frustration as you see your print yet again covered in dust spots after meticulously cleaning it for the 3rd time trying to make just one decent print. Perhaps you have a hermetically sealed darkroom with a phalanx of air purifiers and filters but for a mere mortal like me I chucked the glass carrier in the bottom of a drawer and never looked back. After really going after alignment on my 45MX earlier this year I can say with confidence that the glassless carrier didn't make any difference compared to the NegaFlat for 4x5 and none of the smaller carriers had any noticeable sag when used properly. I printed some negatives and saw it myself.

---

The Negaflat can not totally ptrevent popping. But more importantly, if you are so plagued by dust then you still have dust on your film rather then on your glass. By placing your glass carriers in a drawer does not make your darkroom dust free, you would be better off, if possible, in spending some time reducing the dust in your area, do a through damp cleaning on all surfaces. Repaint, if possible with a quality gloss or semi gloss washable paint, cover dust emitting surfaces with a sheet of plastic, install a quality fan that can make your enlarging room a positive air pressure area, make sure all windows and doors are properly sealed,

Now what was my original question?

Oh yeah, I almost forgot, somehow!

Do you think the spacer ring between the heat absorbing glass and the condenser on my Beseler enlargers is to prevent Newton's rings?

No.

Quote:

---

Originally Posted by Bob Salomon

No.

---

+1

Quote:

---

Originally Posted by Randy Moe

CB7 is bigger, note the light cones have different paint. Is black better than white paint.

---

Thanks for the pictures. It tells me that Beseler's enlarger heads evolved over time. That's not really surprising, but there might be some minor differences that some users might be interested in. One difference, for example, is the height of the condenser head -- some are much taller than others -- which is important if you have a darkroom in the basement, as I do!

My 45 head is black, not blue like yours, and looks more like your CB7 head. It is black on the inside, like yours. My CB7 head is gray, not black like yours, and a little taller than yours, and like yours, is white on the inside. Who knows if mine are earlier or later than yours!

The white on the inside should create more light, and I wonder if it makes more even light! But I have enough things to think about.

If the heat absorbing glass rests against the condenser, and the light is left on too long, for instance 2+ minutes to crop and focus, the condenser is likely to crack. Ask me how I know.

Quote:

---

Originally Posted by Jim Noel

If the heat absorbing glass rests against the condenser, and the light is left on too long, for instance 2+ minutes to crop and focus, the condenser is likely to crack. Ask me how I know.

---

Thanks for the tip. I wasn't thinking of removing the heat absorbing glass or laying it on top of the condenser. However, it did cross my mind to the POSSIBLE benefit of adding an additional heat absorbing glass, since I do a LOT of long exposures -- like 20 MINUTES -- and avoiding the problems that you have experiences!

Quote:

---

Originally Posted by xkaes

Thanks for the tip. I wasn't thinking of removing the heat absorbing glass or laying it on top of the condenser. However, it did cross my mind to the POSSIBLE benefit of adding an additional heat absorbing glass, since I do a LOT of long exposures -- like 20 MINUTES -- and avoiding the problems that you have experiences!

---

Why a 20 minute exposure for an enlargement?

Quote:

---

Originally Posted by Bob Salomon

Why a 20 minute exposure for an enlargement?

---

I guess you don't do murals.

Quote:

---

Originally Posted by xkaes

I guess you don't do murals.

---

Biggest one I ever did was an aerial of the ground from Shaw AFB, SC to Moses Lake, WA. But we never had exposures anywhere near that long.

Quote:

---

Originally Posted by xkaes

I do a LOT of long exposures -- like 20 MINUTES

---

If you'd use a real enlarger lamp rather than a flashlight, you wouldn't have that problem.

I guess flashlights are the only lights you can use without heat absorbing glass.

Buy some proper equipment and learn how to use it.

- Leigh

Thanks for all your "help". Maybe I can repay the favor someday.

switch to a cold light or led bulbs, then heat is a non issue.

Quote:

---

Originally Posted by Paul Ron

switch to a cold light or led bulbs, then heat is a non issue.

---

Thanks. I have a cold light source for my CB7, and a color diffusion head for my 45 MXII, which I use for most of my B&W enlargements, but they require longer exposures for large prints and can't produce the higher levels of contrast that I sometimes want.

Quote:

---

Originally Posted by Randy Moe

Just so happens I am setting up a new darkroom. Beseler CB7, MXT, 23C III, Elwood 5X7 and a Leica V35. So I am haveing a second look at my inventory.

---

Randy,

If your CB7 happens to have a filter holder in the filter draw, and you don't want it -- I might make it worth your while. I'm in the process of making one. If so, send me a personal message.

Quote:

---

Originally Posted by xkaes

Randy,

If your CB7 happens to have a filter holder in the filter draw, and you don't want it -- I might make it worth your while. I'm in the process of making one. If so, send me a personal message.

---

I do have one, but I am keeping the set together. Sorry.

Continuing this sad saga, I've used my CB7 with a point light source. The lens is always used WIDE open, but that has no impact on heat -- just the time the bulb is ON. And it is VERY hot. It has fried a couple of Kodak test Step wedges in no time at all. This puppy needs extremely short exposures for a typical negative -- which is a problem. Sure, I can add ND filters, but then the negative gets fried with the longer exposure time.

The heat absorbing glass has never cracked. The condenser cells have never cracked -- despite long exposure to the point light source.

ALL of this is with the heat absorbing glass in place. My thought was that an additional heat absorbing glass would help. It probably won't help, but I'm not expecting much from this Forum either. Any non-dismissive responses would be appreciated.

Quote:

---

Originally Posted by xkaes

Continuing this sad saga, I've used my CB7 with a point light source. The lens is always used WIDE open, but that has no impact on heat -- just the time the bulb is ON. And it is VERY hot. It has fried a couple of Kodak test Step wedges in no time at all. This puppy needs extremely short exposures for a typical negative -- which is a problem. Sure, I can add ND filters, but then the negative gets fried with the longer exposure time.

The heat absorbing glass has never cracked. The condenser cells have never cracked -- despite long exposure to the point light source.

ALL of this is with the heat absorbing glass in place. My thought was that an additional heat absorbing glass would help. It probably won't help, but I'm not expecting much from this Forum either. Any non-dismissive responses would be appreciated.

---

Is the proper side of the heat absorbing glass facing the light source?

I have one factory installed, and one not. Both sides looks exactly the same to me. If it's my lucky day, you can inform me of the difference.

A second heat absorbing glass with a spacer to keep it from touching the first glass could help.
The basic principle of the heat absorbing glass strategy is that the glass absorbs infrared on one side from the lamp. The glass then becomes very hot and re-radiates the heat energy in all directions. In effect the glass sends half the heat energy back towards the lamp and the other half toward the condensers and the negative. A second heat absorbing glass could reduce the heat load by half again. Heat absorbing glasses have been known to shatter under stress if mounted with no room for thermal expansion. The traditional heat absorber is greenish high iron content glass and a second glass could introduce a significant (?) colour change in the enlarger beam.

Quote:

---

Originally Posted by xkaes

I have one factory installed, and one not. Both sides looks exactly the same to me. If it's my lucky day, you can inform me of the difference.

---

Usually there is a round dot on a corner or edge of the side that faces the lamp.

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.

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.

Quote:

---

Originally Posted by Randy Moe

[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.)