Condenser/Diffuser Hybrids

[koraks]

All these things are closed loop additive (like the Heiland LED light sources) .

I don't think the Heiland system is closed loop. Arguably, it doesn't need to be. It's supposed to be perfectly consistent (and I don't doubt it is - even though it may not be perfectly linear).

 

[Sundowner]

I have an 8x10 Zone VI type 2 VC cold light enlarger, a 5x7 Zone VI VC cold light enlarger, a Beseler 45MXT with the 45 Universal VC controller, and finally another Beseler 45MXT with the 45 Universal head setup with the color controller. The Zone VI enlargers have a 10 foot stainless sink, the Beseler units have a wide 7 foot sink.

I have two. That is all. In no way do I have three, nor do I have four. Five is just right out, unless when we say it we actually mean "two". Any number past five - up to and including eight - are not actually numbers, and cannot even be discussed. We will also not discuss the percentage of enlargers that I have that actually work at current, because that discussion would not include a number.

Everything is closed loop so adjusting contrast doesn't (dramatically) change exposure time. Everything is diffusion, easy enough to insert condensers on the Beseler units if needed.

I'm not exactly following the meaning of "closed loop" in this context.

All these things are closed loop additive (like the Heiland LED light sources) .

Additive: that part I get. Probably. Maybe.

Still pretty hard to beat a reliable subtractive head with a incandescent source and dichroic (or acetate) filters. Just not as handy. I've been putting together my darkroom since I was in high school. The only enlarger I bought new was in high school. Everything else was scrounged

Well, the only problem with that is that I'm really good at making them unreliable. I forget to subtract things...or I subtract the wrong thing twice. And all of this is user error, but it still results in complete unreliability of the system.

 

[koraks]

I'm not exactly following the meaning of "closed loop" in this context.

In this context, 'closed loop' refers to servo-controlled systems where a light sensor (usually located in the mixing chamber) monitors light output of the bulb. This signal is fed back into a regulator that controls lamp power. This results in a closed control loop that ensures more or less stable light output regardless of input voltage fluctuations, bulb aging, thermal fluctuations etc.

 

[Sundowner]

In this context, 'closed loop' refers to servo-controlled systems where a light sensor (usually located in the mixing chamber) monitors light output of the bulb. This signal is fed back into a regulator that controls lamp power. This results in a closed control loop that ensures more or less stable light output regardless of input voltage fluctuations, bulb aging, thermal fluctuations etc.

That's a very cool system. Kind of vaguely similar to the Zone VI head with the photodiode, then.

 

[ic-racer]

That's a very cool system. Kind of vaguely similar to the Zone VI head with the photodiode, then.

Yes, same principle but times 3 for the thee colors.

korkas would know about LED intensity stability, but the cold cathode tubes (like in the Zone VI head) were notorious for intensity fluctuation with temperature.

In terms of dichroic heads my experience is cams for color filters can show irregularity. In the early 1980s I was getting some unpredictable results and I tested the output of the magenta filter of my Minolta dichroic enlarger and the graphed curve was bumpy. Close examination of the magenta cam showed a regular series of machining marks from when it was cut at the factory. That is one of the reasons I switched to a closed loop servo controlled filter head.

 

[xkaes]

It's just the two 23s, and that's all. Just those two.

Cross your heart and hope to die?

 

[Sundowner]

Cross your heart and hope to die?

In fact, it's just the one 23, really. Sadly, the other one died a few minutes ago when its head was cut off.

korkas would know about LED intensity stability, but the cold cathode tubes (like in the Zone VI head) were notorious for intensity fluctuation with temperature.

I had that exact problem on my Zone VI-ed Aristo head; a new lamp solved it.

Except, that didn't solve it at all...and the new lamp didn't fit so I had to get a second one that kind of fit. So, I then took everything apart and cleared the thermostat contacts, and checked the resistors; that helped quite a bit.

Except that it didn't help very much at all. So, I then emailed Light-Sources and asked them some pressing questions about the lamp and thermostats; they were extremely helpful and their advice fixed everything.

Except that it didn't; they had no idea what to tell me. So, I then did a bunch of research and replaced the photodiode, and that fixed it.

And that time, it was actually fixed.

In terms of dichroic heads my experience is cams for color filters can show irregularity. In the early 1980s I was getting some unpredictable results and I tested the output of the magenta filter of my Minolta dichroic enlarger and the graphed curve was bumpy. Close examination of the magenta cam showed a regular series of machining marks from when it was cut at the factory. That is one of the reasons I switched to a closed loop servo controlled filter head.

Interesting defect, for sure; wouldn't have thought to look for something like that, myself.

Question on diffuser material: in my reading, I'm seeing reference to multiple layers of diffusion glass being used back in the day, but the common wisdom these days seems to be that only one layer of diffusion material is needed, and that any more will displease The Old Gods and cause my non-existent friends to disown me...so, what caused that shift in practice? We have more powerful light sources now than we did in the past (to an extent) so why were people okay with those heads using multiple layers, but such isn't really the case now? Manufacturing limitations of the materials at the time, or what?

 

[DREW WILEY]

There are various potential avenues to what might be implied as "closed loop'. On my true additive enlargers, the mixing chamber contains a second array of RGB filters, quite small, which monitor the specific light output and allow the controller box to correctly pulse the programmed respective amounts, all at the same time. It's important to keep these secondary filters clean.

With my conventional CMY colorheads, I don't bother with any kind of feedback. My line voltage is consistent enough that I don't need that. No fancy electronics to worry about.

With my big Aristo cold light, there is simply a probe inserted into the lamp housing detecting the amount of lumen output at any given instance, which varies the timing of its audible "beeps" accordingly. It's essentially an audible light integrator made by Zone VI, but usable on any cold light setup. Therefore if the cold light is appropriately warmed up in advance, any significant variation print to print is solved;
and the sequence of beeps can also be used for timing dodge and burn operations, split printing too.

Per diffusion materials and design, old fashioned opal glass went out of favor long ago because it doesn't allow enough light to pass through. Some enlargers wisely use double-diffusion technique, via thin white acrylic panels, both at the top and bottom of the mixing chamber or mirror box. Fancier options include butyl acetate linear array fresnels or Rosco Opti-Sculpt sheeting, both of which allow a greater degree of light balancing out along with sustantially better light transmission. Shaped true Lambertian acrylic optical domes can also be ordered, provided the lamphouse has been designed for their extra size, and that the system can be appropriately cooled too (more an optical engineering task than DIY). There are all kinds of tricks, which can often be used in combination if necessary.

High light transmission, combined with high lumen output, was quite important in the design of expensive commercial enlargers during the Cibachrome era, since that medium needed far more powerful exposure than RA4 and black and white papers do. Furthermore, supplementary registered contrast masks were also routinely involved, which created even more extra density to print through, sometimes up to 3 stops extra (.90 ND). So any wasted light due to an inefficient diffusion system would have become a detriment. But my more common problem these days is having too much light output !

About the only other thing I can say is that most typical colorhead designs do not in fact come out of the box with an ideal diffusion system, but with something compromised, easy and affordable to mass manufacture. In one way or another, I've somewhat reengineered every one of mine.

 

[MattKing]

FWIW, the terms "condenser enlarger" and "diffusion enlarger" arose in an attempt to describe existing approaches to providing a light source to print from/through a film negative or transparency.
They are mostly descriptive, not determinative.
It wasn't as if things started from a defined category, and then followed by designing something to comply with the category rules.

 

[xkaes]

Same semantic problem with lenses.

Say "wide-angle lens" to a 35mm user, and they think "wide picture angle", while a large format user thinks "wide angle of coverage".

Mention "tele-photo lens" to a 35mm user, and they think -- well you know..........

 

[DREW WILEY]

Not necessarily. Wide-angle still means the same thing in large format usage in terms of the angle of perspective. Size of the usable image circle is something else; and the angle of view itself potentially changes due to the fact that large format lenses are often usable on multiple format sizes. What is a wide focal length for 8x10 becomes relatively long with 4x5, and even longer with respect to roll film backs.

Tele-photo originally meant a lens design configuration allowing a shorter lens relative to the nominal focal length by shifting the nodal point forward. It still technically means that. But yeah, we all know what happens when somebody transposes casual small camera lingo
where it doesn't belong.

 

[mshchem]

I have two. That is all. In no way do I have three, nor do I have four. Five is just right out, unless when we say it we actually mean "two". Any number past five - up to and including eight - are not actually numbers, and cannot even be discussed. We will also not discuss the percentage of enlargers that I have that actually work at current, because that discussion would not include a number.



I'm not exactly following the meaning of "closed loop" in this context.



Additive: that part I get. Probably. Maybe.



Well, the only problem with that is that I'm really good at making them unreliable. I forget to subtract things...or I subtract the wrong thing twice. And all of this is user error, but it still results in complete unreliability of the system.

The Holy Hand Grenade of Antioch!

 

[mshchem]

I have a couple Stopclock Vario and Metrolux II timers that control the cold light heads, work great. I just need to pray these things last longer than I do. I have backups for the Beselers.

The guy I got the Zone VI stuff from bought this stuff from Calumet in 01, never used it, I rarely use it so should be fine

 

[Sundowner]

Per diffusion materials and design, old fashioned opal glass went out of favor long ago because it doesn't allow enough light to pass through. Some enlargers wisely use double-diffusion technique, via thin white acrylic panels, both at the top and bottom of the mixing chamber or mirror box. Fancier options include butyl acetate linear array fresnels or Rosco Opti-Sculpt sheeting, both of which allow a greater degree of light balancing out along with sustantially better light transmission. Shaped true Lambertian acrylic optical domes can also be ordered, provided the lamphouse has been designed for their extra size, and that the system can be appropriately cooled too (more an optical engineering task than DIY). There are all kinds of tricks, which can often be used in combination if necessary.

I haven't used Opti-Sculpt before, but I've used Optix LD in a similar project; at that time, I thought it would be an ideal candidate for diffusion material. I had also wondered about a Fresnel sheet of some variety, and possibly the least-opaque of the white acrylics...but after reading several threads on diffusion heads, it seems that the "only one diffuser" method prevails.

High light transmission, combined with high lumen output, was quite important in the design of expensive commercial enlargers during the Cibachrome era, since that medium needed far more powerful exposure than RA4 and black and white papers do. Furthermore, supplementary registered contrast masks were also routinely involved, which created even more extra density to print through, sometimes up to 3 stops extra (.90 ND). So any wasted light due to an inefficient diffusion system would have become a detriment. But my more common problem these days is having too much light output !

Yeah, that last part is what's getting me: since I'm now getting deeper into the forest with my 23/45 project and better understanding how to accomplish my goals with it, a diffusion head that's not a vintage Aristo has become a possible solution...and it seems like it's really easy to over-illuminate, given the light output of modern LEDs. I need to find some way to accurately measure what the standard 23 condenser is producing, and then check that against an Aristo or two...but I don't have measuring devices for that kind of thing.

About the only other thing I can say is that most typical colorhead designs do not in fact come out of the box with an ideal diffusion system, but with something compromised, easy and affordable to mass manufacture. In one way or another, I've somewhat reengineered every one of mine.

I feel like I'm doing a lot of reengineering, myself, except that I don't know what I'm doing.

FWIW, the terms "condenser enlarger" and "diffusion enlarger" arose in an attempt to describe existing approaches to providing a light source to print from/through a film negative or transparency.
They are mostly descriptive, not determinative.
It wasn't as if things started from a defined category, and then followed by designing something to comply with the category rules.

That's...huh. That's a very solid point you make, there. I'll have to give that some thought.

 

[DREW WILEY]

A basic Sekonic lux meter doesn't cost all that much, and is fine for simple comparisons of the intensity of light.

When I referred to linear array fresnels, don't confuse these with typical concentric ring fresnels; they have a completely different pattern.

 

[Sundowner]

A basic Sekonic lux meter doesn't cost all that much, and is fine for simple comparisons of the intensity of light.

I have a light meter or three, but none that will actually tell me lux without me having to do math...and I'm just as allergic to math as I am work. I'll look up what Sekonic has to offer; thank you.

When I referred to linear array fresnels, don't confuse these with typical concentric ring fresnels; they have a completely different pattern.

I wondered if a circular fresnel would cause problems. Also, I realized that I have used Opti-Sculpt in the past; I think I tried a 30° panel and a 40°/60° reversible. I don't recall which I ended up staying with, but I can probably figure it out if I look back through my data on all of that stuff. I do recall that it worked really well, but I've had my darkroom packed up for so long that I can't remember what was used where.

 

[ic-racer]

This table is from a Sekonic user's manual, but it applies to any meter.

 

[Sundowner]

This table is from a Sekonic user's manual, but it applies to any meter.

Well that's useful. The only meters I have are A) the questionable meter app on my phone, and 2) a little Digisix that I bought years ago, and which has been much loved. Hopefully one of those will be close enough.