about light source and duration of exposure

chris77 · Jun 24, 2018

ave apug!
is it my personal observation or can others confirm that more lumen make for a punchier print? of course there is shorter exposure, therefore less stray light in the room and the emulsion layer, but is this all there is to it?
or is it the difference in temperature, using a standard opaque bulb in a 100w condenser enlarger vs blasting a 100w (equals approx. 1000w) led floodlight (cool) with 2 diffraction layers on top through the same condenser?

as i print rather large we are talking about 200 vs 20 seconds here.
printing on fomaspeed emulsion, fixed grade, so no filters involved.
would be interesting to to hear your thoughts.

avb · Jun 24, 2018

Light intensity increases with a decrease of the distance of the light source to paper. When I enlarge from 8x10" to 4x5" (and account for exposure differences) I don't see any difference in the punchiness of the print, even though light intensity increased. My guess is that the difference is in the light source colour temperature is causing the difference in the punchiness of the print.

tedr1 · Jun 24, 2018

Yes that is my thought also the light sources are different not only in brightness but also in color spectrum and the paper (fixed grade) may be responding to this. To find out for certain if this is true would need another experiment with the LED source reduced in brightness, perhaps by a filter of some sort? In other words there may be more than a single variable here.

If you prefer the punchier print everything is good yes?

MattKing · Jun 24, 2018

There may be issues of reciprocity failure involved with the low intensity, long exposure.

Sirius Glass · Jun 24, 2018

Contrast is somewhat stronger with condensers than with diffusers as light sources, but then sometimes one can get the printing on the light bulb to show up on a print made by a condenser. I use a condenser because I want to print black and white and color with a color head and frankly because that is the way the enlarger came.

chris77 · Jun 24, 2018

in my case i use a condenser, but with somewhat diffused bulb or led lamp.

Pieter12 · Jun 24, 2018

chris77 said:
ave apug!
is it my personal observation or can others confirm that more lumen make for a punchier print? of course there is shorter exposure, therefore less stray light in the room and the emulsion layer, but is this all there is to it?
or is it the difference in temperature, using a standard opaque bulb in a 100w condenser enlarger vs blasting a 100w (equals approx. 1000w) led floodlight (cool) with 2 diffraction layers on top through the same condenser?

as i print rather large we are talking about 200 vs 20 seconds here.
printing on fomaspeed emulsion, fixed grade, so no filters involved.
would be interesting to to hear your thoughts.

I use a halogen bulb instead of the regular one in my Omega D5. This results in sharper grain and punchier prints, indeed. I think part of it is the light source is smaller, giving some of the effect you might get with a point-source.

chris77 · Jun 24, 2018

thanks everybody for sharing!

Lachlan Young · Jun 24, 2018

I'd be inclined to properly test your safelight before haring off after light sources as a source of variation...

I take it that it's the Foma liquid emulsion you're talking about? If it is, it's sensitive to safelight colour & duration of exposure - if you're running over a couple of minutes exposure you really need a properly red safelight - potentially a Kodak #1 or #2 (which is really dark). Only then should you begin to consider other possible factors.

M Carter · Jun 25, 2018

Lachlan Young said:
I take it that it's the Foma liquid emulsion you're talking about? If it is, it's sensitive to safelight colour & duration of exposure - if you're running over a couple of minutes exposure you really need a properly red safelight - potentially a Kodak #1 or #2 (which is really dark). Only then should you begin to consider other possible factors.

I've used the Foma emulsion with those "superbright LED" red bulbs that are popular here, for coating (2 coats), exposure and processing - no issues. It's nice to have all that light when coating!

chris77 · Jun 25, 2018

Lachlan Young said:
I'd be inclined to properly test your safelight before haring off after light sources as a source of variation...

I take it that it's the Foma liquid emulsion you're talking about? If it is, it's sensitive to safelight colour & duration of exposure - if you're running over a couple of minutes exposure you really need a properly red safelight - potentially a Kodak #1 or #2 (which is really dark). Only then should you begin to consider other possible factors.

my whites are white as can be
but thanks.

David Brown · Jun 25, 2018

chris77 said:
or is it the difference in temperature, using a standard opaque bulb ... vs. a ... led floodlight (cool)

probably ...

halfaman · Jun 25, 2018

LEDs emit naturally in the blue spectrum, even "warm" LEDs have some blue component not present in halogen or tungsten lamps. B&W paper is specially sensitive to this spectrum, so it is very typical that LEDs give significantly less exposure time and increase contrast than standard lamps with the same light intensity.

Mainecoonmaniac · Jun 25, 2018

Even though if you have a high lumen light source for a "Punchier" print, your light source can be so bright you can't stop down your lens enough for your exposure, or it would make burning and dodging impossible. To control punchiness, my guess is you either use a condenser enlarger or print with a higher grade, or find a film, developer and process that will give you punchier negatives. If you use VC paper, the color of light will control the contrast too.

Doremus Scudder · Jun 25, 2018

I'm going to question whether you are really seeing a change in contrast or if the print made with the brighter light source and shorter exposure time is simply more exposed.

If there's really a change in contrast, I doubt it is due to the color temperature of your light source, but rather something else like changes in the paper response due to reciprocity failure or desensitization of the emulsion due to prolonged exposure to red light (Herschel Effect; Google it using this site as a limiter and find Ian Grant's discussion of this).

And, if you have a real contrast change caused by light source and exposure time, you now have an additional contrast control for your graded paper! That's only good in my estimation.

Best,

Doremus

MattKing · Jun 25, 2018

chris77 said:
my whites are white as can be
but thanks.

You don't necessarily lose whites because of a safelight problem.
The first sign of safelight fog is a reduction of contrast.
The pre-and-post exposure test in the Kodak safelight test will reveal that problem: https://www.kodak.com/uploadedfiles..._motion_products_filter_K4_Safelight_1106.pdf

ic-racer · Jun 25, 2018

Your fog level is proportional to the ratio between the intensity of lamphouse leak and baseboard illumination.

chris77 · Jun 25, 2018

baseboard is pitch plack and matte, light leak is from the enlarger is zero, walls are black (enlargers are in a separate little room, condenser and diffusor)

its either due to:
-difference in color (incandescent vs cool led)
-intensity of light (lumen)
-reciprocity failure caused by long exposure (guess it doesnt make sense)
-fog from safelight (guess not)

however it is, its great. somewhere between half a grade and a grade. especially useful when working with graded paper.

regards and thanks for input,
cheers apug

Lachlan Young · Jun 25, 2018

chris77 said:
-reciprocity failure caused by long exposure

If it isn't the safelights, this is the most likely cause - especially with Foma materials in my experience - speed and contrast drop off once you get into the multiple minute range (even Ilford MG papers seem to begin to behave a bit less linearly in emulsion speeds between the fast & slow emulsions at fairly long exposures on big enlargements - which can make dodge & burn an interesting adventure). You really want to get your times down to 60-120s at maximum if you can - at least that's my preference when making big (70cm & up) prints. No real substitute for raw power, be it halogen or LED equivalent - and if tuned to the specific sensitivity of the materials you use, you could potentially shorten exposures even more - and as you leave the reciprocity problems behind, of course things will seem perceptibly 'sharper' etc as you are no longer losing contrast to reciprocity - and contrast is critical to perceived sharpness. Realistically, you need upwards of 5-600w, ideally 1200-2400w of halogen or LED equivalent. Yes, it's expensive, but it will make your life much, much easier.

I can't see it being a problem specific to any of: colour of light source; output of light source; thickness of paper emulsions, other than how the first two relate to exposure time & consequent reciprocity issues.

alentine · Aug 6, 2018

Lachlan Young said:
If it isn't the safelights, this is the most likely cause - especially with Foma materials in my experience - speed and contrast drop off once you get into the multiple minute range (even Ilford MG papers seem to begin to behave a bit less linearly in emulsion speeds between the fast & slow emulsions at fairly long exposures on big enlargements - which can make dodge & burn an interesting adventure). You really want to get your times down to 60-120s at maximum if you can - at least that's my preference when making big (70cm & up) prints. No real substitute for raw power, be it halogen or LED equivalent - and if tuned to the specific sensitivity of the materials you use, you could potentially shorten exposures even more - and as you leave the reciprocity problems behind, of course things will seem perceptibly 'sharper' etc as you are no longer losing contrast to reciprocity - and contrast is critical to perceived sharpness. Realistically, you need upwards of 5-600w, ideally 1200-2400w of halogen or LED equivalent. Yes, it's expensive, but it will make your life much, much easier.
I can't see it being a problem specific to any of: colour of light source; output of light source; thickness of paper emulsions, other than how the first two relate to exposure time & consequent reciprocity issues.

Thanks Lachlan Young,
Having a contrastier(but normal) negative, does it help?
Maybe toning selenium will produce more contrast to compensate for the the problem?
Or maybe developing for a higher contrast film initially for this type of giant prints?
Just asking.

RalphLambrecht · Aug 6, 2018

Lachlan Young said:
I'd be inclined to properly test your safelight before haring off after light sources as a source of variation...

I take it that it's the Foma liquid emulsion you're talking about? If it is, it's sensitive to safelight colour & duration of exposure - if you're running over a couple of minutes exposure you really need a properly red safelight - potentially a Kodak #1 or #2 (which is really dark). Only then should you begin to consider other possible factors.

a truly 'safe' safelight makes a huge difference in print quality!

Nodda Duma · Aug 6, 2018

halfaman said:
LEDs emit naturally in the blue spectrum, even "warm" LEDs have some blue component not present in halogen or tungsten lamps. B&W paper is specially sensitive to this spectrum, so it is very typical that LEDs give significantly less exposure time and increase contrast than standard lamps with the same light intensity.

There are all kinds of LED’s... you should clarify which ones you are talking about. White LED’s as used for a hacked enlarger? What is the color temperature? The color temperature refers to the blackbody emission spectrum, which tells someone fairly accurately what the spectral content of a broadband light source is. Typical tungsten and halogen lights have spectral output across the visible spectrum including blue and UV (think traditional blacklight). The data can be easily googled.

Science: http://www.techmind.org/colour/coltemp.html

In fact I’ve found that white light LED’s make terrible indoor light sources for basic (UV and blue sensitive) emulsions. Traditional halogen and tungsten bulbs are better. Flourescent lighting and specifically UV LEDs are the best.

Single-color LED’s — like red LED’s that would be useful for safelights — only emit the specified wavelengths. So your statement is simply incorrect for those ... hence why you need to clarify.

halfaman · Aug 6, 2018

This LED bulb

http://www.lighting.philips.com/pro...s/corepro-ledestandar/929001892402_EU/product

That has this spectrum

I

Lachlan Young · Aug 6, 2018

alentine said:
Thanks Lachlan Young,
Having a contrastier(but normal) negative, does it help?
Maybe toning selenium will produce more contrast to compensate for the the problem?
Or maybe developing for a higher contrast film initially for this type of giant prints?
Just asking.

Here are the facts as I see them: if you want to make big prints, don't cheap out. Get the most powerful enlarger you can relative to format etc. Mucking around with changing negative contrast etc is not going to help as much as wattage will. There are differences in contrast behaviour as enlargement goes up, but they're not that drastic - grade/ grade and a half perhaps? And even then, there are ways to solve those problems, not to mention various contrast masks etc.

What are you trying to enlarge & to what size?

chris77 · Aug 7, 2018

Lachlan Young said:
Here are the facts as I see them: if you want to make big prints, don't cheap out. Get the most powerful enlarger you can relative to format etc. Mucking around with changing negative contrast etc is not going to help as much as wattage will. There are differences in contrast behaviour as enlargement goes up, but they're not that drastic - grade/ grade and a half perhaps? And even then, there are ways to solve those problems, not to mention various contrast masks etc.

What are you trying to enlarge & to what size?

i am making prints 70x55 cm up to 140x75.
And i use a 100w led panel (approx 1000w).
exposure times are around 20-35 seconds.
works out pretty well

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