Incandescent light source contrast differences

[Harlan Chapman]

Picked up a simple Solar 5x7 diffusion head enlarger that uses a 150 watt enlarger bulb (looks like a standard home light bulb). Get wonderful prints using it, they really pop. But the Solar vignettes badly and is shakey so I found a solid no-name diffusion head 8x10 enlarger that uses two 300W pencil type halogen bulbs (the same type used in cheap floodlights).
The 8x10 enlarger doesn't vignette my 5x7 negatives.
The contrast from the two light sources is really different. For example, using the same negative and carrier glass, filters, lens, paper, and developer, split grade printing with the Solar takes 1:1 grade 0:grade 5 time. The 8x10 enlarger takes 1:2 grade 0:grade 5 time to get close to the same contrast.
The real issue though is hard to describe but I'd call it a difference in fine detail contrast. The prints from the 8x10 enlarger are good but they don't pop, they don't have the same apparent high contrast in the fine detail that prints from the Solar enlarger do.
I'm wondering if spectral differences between the light sources might account for the difference. If so, I could build a light head using standard enlarger bulbs for the 8x10.
I'm pretty new to using enlargers. I may be missing some variables. And sometimes it feels like I'm splitting hairs. But I'd like to get the best from my nice 5x7 negatives and do at least as well with the 8x10 enlarger as I can from the Solar.

[Curt]

Harlan, what is the diffusion material in each head?

Curt

[jeroldharter]

Some VC paper is low contrast with cold lights. With my Beseler Dichro 45s halogen light source, my Kentmere paper is quite contrasty. But with my Aristo vcl8100 cold light, the same paper is about grade 1 in the middle of its range. You will probably need to increase you're development times (with a slight decrease of exposure) to get things on track.

[Ken Lee]

"I'm wondering if spectral differences between the light sources might account for the difference"

Your hunch is correct: polycontrast paper is color-sensitive. That's how it works. Even if we can't see the difference (because our eyes adjust quickly), the paper can.

[Paul Fitzgerald]

"The real issue though is hard to describe but I'd call it a difference in fine detail contrast. The prints from the 8x10 enlarger are good but they don't pop, they don't have the same apparent high contrast in the fine detail that prints from the Solar enlarger do."

"Harlan, what is the diffusion material in each head?"

What is the spacing difference between the 2 diffusion materials and the negative? The closer it is, the more the light will scatter in the negative, killing off your fine detail.

"Your hunch is correct: polycontrast paper is color-sensitive. That's how it works."

Exactly right BUT the contrast change should not affect the fine detail.

[ic-racer]

I'm wondering if spectral differences between the light sources might account for the difference. .

The 'standard light bulb' likely is more yellow than the halogen bulbs (stimulating the green emulstion layer more). Halogen bulbs in the other ennlarger could come in many different color temps, so the difference in multigrade printing contrast between the two enlargers could be quite large.

If for any reason you wanted them the same, you could add some blue filtration to the 'standard light bulb' or add some yellow filtration to the halogen lamps.

[Bob Salomon]

The enlarging Edison base (screw-in) bulbs have the makers logo and markings on the side of the glass globe. The household bulb that looks the same has the markings on the end of the bulb. With condensor enlargers when you use a household bulb rather then the enlarger bulb you can get that logo and info to print on the paper.
According to my GE bulb catalog a 150W PH212 enlarger bulb is 3050K with 2800 lumen output and a 100 hour average life at 115 to 125V. If you have lower voltage it will be a different color temperture (it will change antway as the bulb ages), have a longer burning time and lower output.

GE enlarger lamps vary in color, per GE, from 2900 to 3400K depending on the bulb type.

[cowanw]

The 'standard light bulb' likely is more yellow than the halogen bulbs (stimulating the green emulstion layer more). Halogen bulbs in the other ennlarger could come in many different color temps, so the difference in multigrade printing contrast between the two enlargers could be quite large.

If for any reason you wanted them the same, you could add some blue filtration to the 'standard light bulb' or add some yellow filtration to the halogen lamps.

I don't think you can add blue to the mix; filters only subtract colour. While the light may look bluer to our eyes, it will not be bluer to the paper.
To rephrase this; you can not add wavelengths that are not given off from the bulb.
You can however take away blue or green by filtering with yellow or magenta respectively

[ic-racer]

I don't think you can add blue to the mix; filters only subtract colour. While the light may look bluer to our eyes, it will not be bluer to the paper.
To rephrase this; you can not add wavelengths that are not given off from the bulb.
You can however take away blue or green by filtering with yellow or magenta respectively

Of course 'adding blue filtration' will do nothing to a bulb that gives off no yellow light. In this case the 'household bulb' gives off too much yellow light, and is ideally suited to the example.

[cowanw]

Poly contrast paper is sensitive to blue and green, not yellow and magenta. A blue filter is really a minus yellow filter; less yellow light really does not accomplish much if the paper is not sensitive to it.
Similarily a cyan filter does not do much in a colour head used for B&W