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).
All these things are closed loop additive (like the Heiland LED light sources) .
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.
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.
All these things are closed loop additive (like the Heiland LED light sources) .
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
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.
That's a very cool system. Kind of vaguely similar to the Zone VI head with the photodiode, then.
It's just the two 23s, and that's all. Just those two.
Cross your heart and hope to die?
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.
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.
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.
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.
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.
This table is from a Sekonic user's manual, but it applies to any meter.
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