Point light contact printing

[mbuonocore]

Has anyone ever seen or used a point light source contact printing unit like this? Apparently Gretag manufactured one. I'm wondering where and why it might have been used.

255829

[xkaes]

I don't quite understand the 90 degree "thing". I assume that is to add distance. There are plenty of point light sources that sit on top of the enlarger -- no mirror needed.

[John Layton]

Would love to see a close up rendering of how rays from such a light source direct themselves through and around a films' (both tabular and otherwise) grain structure, plus analysis of visible results - and compare this with such renderings and results utilizing other types of light sources (from single bulb, projected from diffused enlarger head, large soft box, etc.).

[nolindan]

Contacting point sources were for use in pre-press graphic arts, not pictorial photography. Nothing says they can't be used for plain-ole contact prints but there wouldn't be much advantage to it. But, hey, the goal is to have fun so go for it. I have a nuArc graphic arts point-source somewhere but have never used it.

[Drew Wiley]

Arcane. It would ideally need to be a front-surface mirror anyway. Just using a small aperture on an enlarger lens can approximate a point source anyway, if you want to use an enlarger as the luminary. The "Callier effect" can be manipulated in several ways; but all of this can get rather complicated to explain, since different kinds of grain structure exist, not to mention the behavior of dye clouds when contact printing color film. A good rainy month project for someone.

I often use a sheet of frosted mylar in between the contact frame glass and original neg itself, which ironically actually increases the finely "etched" look in the print. This is done in conjunction with manipulating the angle of incidence of the projected enlarger light via both height from the contact frame, and the smallness of the f-stop. I typically use multi-bladed aperture process lenses which can stop down as far as f/90 if needed. ... Complete overkill for ordinary b&w contacts, but useful when making very precise color sheet film dupes and internegatives (or B&W ones). The exact effect can also be manipulated by the thickness and number of mylar sheets. Don't expect me to explain why - it just works, but differently than with a projected image onto paper or oversized film.

[ic-racer]

If one can't get the negative tight up against the paper, a point source will print sharper.

My experience is a 1/2" piece of glass, by gravity, is not strong enough for double weight paper in a dry environment to make any kind of sharp contact print with a diffuse soruce.

[Drew Wiley]

A properly cushioned contact frame does it easily. For 8x10's or smaller, I use my pin-registered Condit masking frame. It's equipped with anti-Newton glass and excellent thick silicone foam cushioning for sake of pressure. Large work can be done using a transparent vacuum blanket for sake of firm drawdown. While ordinary darkroom workers might not be familiar with this kind of gear or how to obtain it, much of it is still readily available. Instead of searching EBay ads in the Photography & Cameras section, go to the Commercial/Industrial section under used printing equipment.

[xkaes]

The original diagram does not include an enlarger or a lens -- and neither are required for contact printing -- but can make things easier, and more controllable.

Point light sources can present a problem, especially with large prints, because the height of the point light source is very tall -- relative to other enlarger heads.

One approach is to put the enlarger on the floor, or use the enlarger straddling two tables with the easel on the floor.

Many enlargers can be turned horizontally to project onto a wall -- similar to the diagram above, but upside-down. If the enlarger cannot be "flipped", it's easy to attach a front-surface mirror under the lens -- just get an inexpensive Spiratone MIRROTACH or similar device. In either case, it's important to get everything aligned exactly as possible.

255847

[Michael R]

Unless there are things missing from the diagram I don’t see how this would work.

I also don’t understand what the benefit of this would be for contact printing (unless perhaps the film emulsion is very thick with high turbidity and super duper high granularity).

[Drew Wiley]

Perhaps a relict fossil from back in the days when window light was used, redirecting it.

[Mal Paso]

I used a point source at least 8 feet above the vacuum frame to reproduce tool masters for integrated circuits on Kodalith film. There was also a pulsed xenon source on a track that rolled in front of the point source for slow emulsions. The point source was recessed in the ceiling so I never got a good look at it. The xenon was so bright in the darkroom I would hit the exposure button and run for the exit.

[Drew Wiley]

Well, a tightly focussed xenon bulb is still a possibility. I recently received an e-mail ad for such an item, or actually, a selection of them, obviously of industrial quality ($2500 to $4500 apiece, per bulb). I don't know why me; perhaps I once bought something else from that company. One would never look into that kind of light; it would blind you.

[Maris Rusis]

Over the last 40 years and maybe 20,000 contact prints I've fallen into the opinion that the last thing I want is a point light source for contact printing.

The fundamental problem with true point light sources is that everything that blocks the beam between the source and the surface of the printing paper can cast a sharp edged umbral shadow and appear in the final picture.
This includes flaws and dust in a contrast filter, flaws and dust on the top and bottom surfaces of a printing frame glass, flaws and dust on the top surface of the negative.

The answer to the problem is to keep everything optically perfect to a clean-room standard (very hard to do) OR use a very diffuse light source.
With a diffuse light source and a reasonable standard of dust suppression any tiny dust between the source and the surface of the printing paper will cast only a broad and weak penumbral shadow which in many cases will pass beneath notice.

I have used point source enlarging for electron microscope images where the atomic number contrast is not enough and the contrast boost from the point source is needed. The technique tends to generate image defects
but they are acceptable when trying to pick out atomic scale details.

By amusing coincidence my photography in an art context was represented to the market for many years by Point Light Gallery in Sydney, Australia.

[Mal Paso]

Well, a tightly focussed xenon bulb is still a possibility. I recently received an e-mail ad for such an item, or actually, a selection of them, obviously of industrial quality ($2500 to $4500 apiece, per bulb). I don't know why me; perhaps I once bought something else from that company. One would never look into that kind of light; it would blind you.

The pulsed xenon was spiral coiled tube 4" in diameter and 8" long. At full power it was brighter than the sun. I think it was chosen over carbon arc because it was vastly cleaner in the darkroom environment. I don't know what the point source bulb was as I never got close enough to see. Most of the work was processing the output from the Gerber Plotter on Kodalith. We ran a 40" dry to dry processor.

[Mal Paso]

Over the last 40 years and maybe 20,000 contact prints I've fallen into the opinion that the last thing I want is a point light source for contact printing.

The fundamental problem with true point light sources is that everything that blocks the beam between the source and the surface of the printing paper can cast a sharp edged umbral shadow and appear in the final picture.
This includes flaws and dust in a contrast filter, flaws and dust on the top and bottom surfaces of a printing frame glass, flaws and dust on the top surface of the negative.

The answer to the problem is to keep everything optically perfect to a clean-room standard (very hard to do) OR use a very diffuse light source.
With a diffuse light source and a reasonable standard of dust suppression any tiny dust between the source and the surface of the printing paper will cast only a broad and weak penumbral shadow which in many cases will pass beneath notice.

I have used point source enlarging for electron microscope images where the atomic number contrast is not enough and the contrast boost from the point source is needed. The technique tends to generate image defects
but they are acceptable when trying to pick out atomic scale details.

By amusing coincidence my photography in an art context was represented to the market for many years by Point Light Gallery in Sydney, Australia.

Yep! Point Source is a PITA. We were making tool masters which had very tight tolerances. We ran test strips several times a day. Air temp was always exactly 68 degrees with the humidity controlled as well.

[bob carnie]

I have one set up in my darkroom above the developing trays so I can do print and film solarizations...

[John Layton]

jeesh...you guys sure are getting technical :confused::rolleyes:

[LabRat]

If you want to experiment on the cheap, you can try using a single LED flashlight, raised high enough where the light output is even across printing surface... It can have a shutter to close off beam in front of light, or a card or hat etc for shutter for the seconds of exposure...

But as mentioned, this hard light can reveal striations in printing glass, emulsion, grain, hard dust/lint shadows etc... Note that when driving at night, distant LED headlights can reveal all kinds of invisible (normally) haze/fog on your windshield, making it hard to see out of... This is a point source also...

The basic theory of how these work for printing is that a diffuse source hits a spot where the broader light spreads the shadow as it is coming from multiple diffuse areas blending the shadow of negative densities, but a "harder" source (condenser or point source) is collimated into to a tighter bundle of direct light that leaves a harder sharper shadow, but also tends to not gradate shadow edges, so things like imperfections, imperfect cleaning/invisible fingerprints, grain, waves in emulsion etc leave harder visible shadows... Note that labs making separation negatives would mount printing frame on a turntable with point source light at an angle while rotating frame to vary the relationship of incidence to shadow areas, and reduce striations (softening to blend areas to overlay easier)...


Steve K

[John Layton]

I suppose one could also mount the point source into a turntable above the easel - and the turntable itself could incorporate a series of mounting points at various radial distances...allowing one to vary the angle of incidence.

Or better yet...a series of point light sources mounted at various radii on the turntable - so the user could choose which to activate, with the further possibility of activating more than one at a time or perhaps even individual lights sequentially during exposure.

To dive in further...perhaps each of the point lights could actually be paired as green and blue - to allow for either variable ratio contrast control and/or split-grade printing - which in concert with angle of incidence controls could allow for even more amazing fine-tuning and refinement! :cool:

[Drew Wiley]

I recommend an otter swimming at a set parabolic formula within a tub of liquid mercury, or some other exotic reflective solution. But to do this, you first need to train a fish to swim that exact pattern, so that the otter will follow it.

[Duolab123]

I recommend an otter swimming at a set parabolic formula within a tub of liquid mercury, or some other exotic reflective solution. But to do this, you first need to train a fish to swim that exact pattern, so that the otter will follow it.

Too much mercury in seafood as it is!
:rolleyes: