Lina Bessonova
Analog Photography
I was lucky to be among those who got the Intrepid Enlarger for review, and in this video I am unboxing the prototype and testing it, mainly for black-and-white contrast control, also explaining how the multigrade system works.
LIGHT SOURCES & MULTICONTRAST
DISCLAIMER: THIS IS A SIMPLIFIED EXPLANATION! A proper one would require a huge article and more illustrations than I can make :)
Multicontrast papers consist of three layers, but for the sake of simplification, two are united. Silver halides in one layer are sensitized to blue light only, and in other two, which in the image are "compressed” to one - to both blue and green. The blue light hits the blue-sensitized silver halides and creates a high contrast image. A green light hits only the layer with green sensitizer, and the image is softer. So, to create higher contrast, the light source should be bluer, and for softer contrast - greener.
A traditional light bulb emits a very even color spectrum. The contrast filters work by cutting off the opposite of the desired colour. For example, to let only blue light through, green is being shut off by the magenta colour of filter 5. To let only green through, a yellow/orange filter, which stops the blue spectrum, is used. As you can imagine, a lot of light power gets wasted, because only a small part goes through and reaches the paper. The Multigrade filters, through many years of research and refinement, were tailored to the specific spectral sensitizers in Ilford papers. Other brands have their own filters, but usually they work same.
In order to not trigger green-sensitized silver halides, the blue spectrum has to peak somewhere around 430-450 nm, as only then it gives a pure grade 5.
The approach with two LED lights is dramatically different: it is using pure blue and green lights in different proportions, creating all the steps in between filters 00 and 5, from deadly flat to harsh and contrasty. So even if the light source is smaller and less powerful, the efficiency and exposure times are equal to a traditional light bulb.
But the biggest problem in this whole story is a high quality, controlled, pure blue LED light. I tested at least a hundred light sources in my life, and much of the search was dedicated to finding an LED that would go over to 440nm, and only one theoretically did. This is something you should simply be aware of, when buying ANY LED enlarger, for any price. An old light bulb is harder to find, heats up, needs changing, the enlarger head has to be big for diffusing light, but it guarantees to give you the highest contrast in return.
An LED light source is slim, doesn’t heat up, lasts forever, needs no gelatin filters, uses minimal electricity, but you sacrifice the highest grade. But honestly, how often do you reach to a filter 5 anyway? This must be quite a badly exposed negative. By all the characteristics, LEDs are the lights of the future, we just need to study them better for darkroom use.