Does VC paper require 3000k light source from enlarger?

[kingbuzzie]

Sorry, I'm really new to owning own enlarger. Does my light source need to be 3000k for b&w printing?

 

[spijker]

I think that the VC filters are designed for an approx. 3000K light source. If the colour temperature is lower, then all the filter grades become a bit lower / softer. Similar, if your enlarger bulb is higher than 3000K, all grades become a bit higher / harder. Ilford only says "tungsten light" but I think that most enlargers bulbs run at a small overvoltage to get a higher colour temperature.

 

[kingbuzzie]

I think that the VC filters are designed for an approx. 3000K light source. If the colour temperature is lower, then all the filter grades become a bit lower / softer. Similar, if your enlarger bulb is higher than 3000K, all grades become a bit higher / harder. Ilford only says "tungsten light" but I think that most enlargers bulbs run at a small overvoltage to get a higher colour temperature.

Ah thanks for that. My enlarger is designed to use a clear bulb if I install a frosted filter in a slot. I was thinking of upgrading to an LED bulb with a cool white (maybe) that is if I don't get hot spots on the prints.

 

[MattKing]

First, are you planning on printing colour? If so, tungsten or halogen are much more suited to the materials available.
Secondly, do you (as I suspect) intend to use variable contrast materials? If you are working with fixed grades, the answer might be different.
The problem with light sources like LED or fluorescent is that they tend to have discontinuous spectra. So you can encounter "holes" where you might want light.
Can you remind us what enlarger you have?

 

[kingbuzzie]

A durst 606. I have never done color. I could try it for fun, but I would have to come across the color paper cheaply and I would have to stack the filters in a drawer, which sounds like a PITA. I did intend to use vc filters. It was just a thought, I certainly wouldn't use a LED bulb if it gave me too many problems.

 

[MattKing]

Did the thread always have VC paper in the title? If so, sorry I missed it.
If you want to experiment with an LED bulb, I would lean toward a "warm white" version. But you would be well served to try some tests with different contrast filters (and ideally, a step wedge) to see how the system behaves. You may see strange contrast jumps as you switch filters.
Is there a halogen option that would fit? I'll let the Durst users here comment on whether that would create heat problems.

 

[tedr1]

VC papers and filters are designed to operate with traditional incandescent lamps, old-fashioned tungsten, and tungsten-halogen, are the two common types, use these without regard for precision of color temperature, you will be fine. Conversion to LED lamps brings uncertainty over the spectral details which can be avoided by using tungsten or tungsten-halogen types.

I believe the concept of color temperature derives from solar radiation which is a continuous spectrum, and may be extended to other incandescent radiators such as incandescent lamps. LED (and fluorescent) lamps are not incandescent and not continuous spectrum radiators and do not have a color temperature, they may be problematic for VC work.

 

[spijker]

I think that all that matters for VC papers is the intensity ratio of the blue (~450 nm) / green (~530 nm) light. I don't think that holes in the spectrum are relevant. As long as the LED bulb approximately matches the blue / green intensities of the originally intended light bulb, you should be fine colour wise. The various people that designed and built enlarger heads with royal blue & green LEDs do the same. The red LEDs are just a replacement for the under the lens red filter. Huge holes in the overall spectrum but it works fine.

 

[Leigh B]

Color Temperature is a meaningless concept as regards b&w printing.

By definition. Color Temperature expresses the ratio of RED light to BLUE light.
Color Temperature does not evaluate the GREEN light content in any way.

Since no b&w paper is sensitive to RED light, that ratio is of no significance whatsoever.
B&W papers are sensitive to GREEN and BLUE light.

- Leigh

 

[Marco Buonocore]

I'm not sure colour temperature is a meaningless concept with black and white printing. The warmer the light, the lower the contrast. The cooler the light, the higher the contrast. You can test that quite easily with a step wedge.

At any rate, Ilford states that with their VC paper, the filters are designed to work best with Tungsten 2856 - 3000K . This information came from their wonderful technical support staff.

 

[Leigh B]

I'm not sure colour temperature is a meaningless concept with black and white printing. The warmer the light, the lower the contrast. The cooler the light, the higher the contrast. You can test that quite easily with a step wedge.

You're misinterpreting parameters.

"Warmer" and "cooler" are human perceptions based on RED/BLUE ratios just like a color temperature meter.
They're based on our brain's assumption that the shape of the luminance curve matches that of an incandescent source.
That is true for any regular light bulb, including tungsten bulbs, as well as candles and bonfires.

That luminance curve defines the amplitude of GREEN based on the RED/BLUE ratio because the shape of the curve is invariant. As our warm/cool perception changes, that curve just moves up or down the chroma scale.

However, when the shape of the luminance curve changes, the implied GREEN amplitude is no longer valid. This happens for example when we use filters to change the print contrast. Color temperature no longer applies in this case.

What does change is the magnitude of the contrast changes with different filter densities.
For example, "10 units of green" depends critically on the color temperature of the light source.

- Leigh

 

[spijker]

For the whole discussion around colour temperature, you need to take the context into account. The recommendation from Ilford comes from the time that almost every enlarger used a tungsten light bulb. For these bulbs, a certain colour temperature automatically meant that the blue/green was at a certain intensity ratio. So nowadays the recommendation wrt colour temperature should be interpreted as "a light source with a blue/green ratio that is the same as the blue/green ratio of a tungsten light bulb with a colour temperature of 2856 - 3000°K."

For the OP; since you seem to be new to enlarging, I would suggest that you start with the opal tungsten light bulb as recommended by Durst and not a LED bulb. Also use fresh/new paper and new VC filters. That way, the only "wildcard" are your skills but not your equipment and materials.

 

[Leigh B]

The recommendation from Ilford comes from the time that almost every enlarger used a tungsten light bulb. For these bulbs, a certain colour temperature automatically meant that the blue/green was at a certain intensity ratio. So nowadays the recommendation wrt colour temperature should be interpreted as "a light source with a blue/green ratio that is the same as the blue/green ratio of a tungsten light bulb with a colour temperature of 2856 - 3000°K."

Absolutely correct.

- Leigh

 

[MattKing]

All of the comments above about colour temperature and LEDs and blue and green and VC papers are correct.
However, if you don't have specific spectral output information about the LED you are looking at (i.e. you are buying it from the corner hardware store), I still would recommend the warm white or daylight ones for your experiment.
This guy uses a high end Cree bulb for his purpose built Omega light sources: http://www.modernenlargerlamps.com/Modern_Enlarger_Lamps/Welcome.html

 

[Arctic amateur]

By definition. Color Temperature expresses the ratio of RED light to BLUE light.
Color Temperature does not evaluate the GREEN light content in any way.

Reference?

To me this sounds like a simplified approach to color temperature (physicist speaking here). The shape of the spectrum emitted from a perfect blackbody radiator is completely determined by the surface temperature of the blackbody, so the ratio of any two wavelength emissions is constant for a given temperature. If you can reasonably assume that your illumination is approximately blackbody-like (for example, an incandescent lightbulb but not an array of RGB LEDs) but of unknown temperature, then you can determine the blackbody temperature (also called the color temperature) from two intensity measurements of known wavelengths.

That luminance curve defines the amplitude of GREEN based on the RED/BLUE ratio because the shape of the curve is invariant. As our warm/cool perception changes, that curve just moves up or down the chroma scale.

Patently incorrect. The shape of a blackbody spectrum is highly dependent on the temperature of the blackbody.


https://en.wikipedia.org/wiki/Black-body_radiation
https://en.wikipedia.org/wiki/Color_temperature

A blackbody is a theoretical construct that completely absorbs all electromagnetic radiation that hits it, heats up, and re-radiates that energy. The temperature of the blackbody determines the spectrum and color of the emitted light.

 

[RalphLambrecht]

Sorry, I'm really new to owning own enlarger. Does my light source need to be 3000k for b&w printing?

No it doesn't just get an halogen bulb or whatever is indicated by the owner's manual.

 

[Leigh B]

To me this sounds like a simplified approach to color temperature (physicist speaking here).

(Photographer speaking here)
It certainly IS a simplified description of color temperature, as is totally appropriate for photographic use.
It evaluates ambient light color components as appropriate to the sensitivities of film emulsions.

As a reference, the Minolta Color Meter IIIF measures light using three sensors, RED, GREEN, and BLUE.
The color temperature is calculated and displayed by comparing the magnitude of the RED and BLUE channels.

The GREEN channel amplitude is displayed as a separate number, identified as "CC".

Quoting from page 24 of the Minolta Color Meter IIIF user manual:
"The CC index provided by the Color Meter IIIF indicates the nominal density of the green (G) or magenta (M) CC filter required. Both of these filters adjust the quantity of green in the illumination; since magenta is the complementary color of green, it can be thought of as "minus green". Indications for other CC filters are unnecessary, since the light-balancing filters adjust the quantities of red and blue in the illumination."

- Leigh

 

[pentaxuser]

No it doesn't just get an halogen bulb or whatever is indicated by the owner's manual.

For the OP this one sentence sums it up superbly. The Durst is designed for a tungsten bulb and to withstand the heat generated for the few seconds it is on. Remember there were no other bulbs when the Dursts were produced so they work as they should.



pentaxuser

 

[TheFlyingCamera]

If you are set on using an LED light source, look for one with the highest possible CRI - I forget what CRI stands for as an acronym, but what it means to you is the relative fidelity to daylight for accuracy. As mentioned before, some light sources (most noticeably fluorescent and sodium-vapor) are discontinuous - they have gaps in their spectral output. The fact that fluorescent is notably peaky in green would make it a bad light source for variable contrast printing, as it would skew really badly in favor of low contrast. I don't know what the gaps in LED output are, but they tend to go very blue/white, which would suggest they would favor high contrast.

 

[Dan0001]

Ah thanks for that. My enlarger is designed to use a clear bulb if I install a frosted filter in a slot. I was thinking of upgrading to an LED bulb with a cool white (maybe) that is if I don't get hot spots on the prints.

Your Durst 606 was not designed to work with a clear bulb but a 75(PH-211) or 150 watt opal bulb(most enlargers with condensers use opal bulbs). If you acquired this enlarger with a clear bulb the previous owner substituted the wrong bulb. Be sure to get an opal bulb specifically for an enlarger--no printing should show up on the outside glass.

 

[tezzasmall]

I first started with a Paterson 35mm enlarger at home that took a florescent light. I don't know where that lies on the colour temperature scale?

Terry S

 

[Dan0001]

Your Durst 606 was not designed to work with a clear bulb but a 75 or 150 watt opal bulb(most enlargers with condensers use opal bulbs). If you acquired this enlarger with a clear bulb the previous owner substituted the wrong bulb. Be sure to get an opal bulb specifically for an enlarger--no printing should show up on the outside glass.

I have to correct myself somewhat. I did look up the original manual for the Durst 606 and it does reference the opal bulb(PH-211)as its primary source of illumination but it also mentions use of a "projection lamp" can be used as a substitute with a "opal filter". Why bother with that when the opal bulb is the prefered and most common way to go.

 

[kingbuzzie]

Thanks for the opinions. I'll try to find a led bulb that lists its color temp and experiment just for fun (after making sure I have the basics down with an opal bulb and fresh paper). I actually got the idea from here:

http://www.faikee.net/?p=5493

 

[MattKing]

I don't care for your snark.

Ralph is an acknowledged expert with one of the best books in the market on darkroom work. However, since his serious heath problems, he has difficulty typing. You shouldn't mistake brevity for snark - I am sure that he didn't mean to offend.

 

[Dan0001]

If your experimenting with a LED bulb becuase of a concern for overheating the negative I think a tungsten 75 watt bulb in a Durst 606 would not be a problem-they distribute heat well. Bear in mind even if the negative stage is warm or hot the glass negative carrier(the most common one) would prevent negative popping. If your doing this to save money on electricity, the amount would be miniscule. If your doing this just for the hell of it, go for it. My guess is that you will go back to the original recommendation of a tungsten opal bulb. Just my two cents.