Bulb recommendation needed for point source enlarger

[eli griggs]

I mentioned in an earlier thread I want to make my Omega B66 into a point source enlarger and I'm now looking for recommendations for a bulb and socket for this conversion.

I have installed on my bench a switchable, multi-enlarger, dual-analog timer control box built by a skilled, old time photographer that has a built-in voltage regulator to adjust any chosen enlargers' light out-put,(try saying that real fast three times) so I can dial in my illumination intensity, as needed.

Now I just need a suitable light to build my housing around, so what have you used or seen that'll work with AC and where can I find it on line?

Cheers

 

[Claire Senft]

Get a GE BHD or the equivalent. This is a 20v bulb that is somewhat similar in shape and size to the bulbs in auto taillights. To be able to use the bulb in a lamp socket there is an adapter available. The bulb will probably cost you a couple of $. The adapter will cost about $15.00 Not every place that sells the bulb will offer the adapter. The adapter looks like the socket base of of lamp socket with a upward extension of a couple of inches.

This is not the only choice of bulb but it is reasonably inexpensive.

 

[Ralph Javins]

Good morning, Eli;

You referred to "a point source." How close to a "point source" do you need to be to accomplish your purposes with consideration to real life limitations?

And, how much illimination do you need to get the enlarger to work in a reasonable length of time for an exposure?

 

[ic-racer]

Here is one used by some Minox folks:

Also, an interesting article on artifacts exaggerated by point source. Not to discourage you, but point source may be better for technical purposes rather than pictorial. Either way, let us know how it works out!

http://www3.interscience.wiley.com/journal/109896179/abstract

 

[Ian Grant]

When I had a point source enlarger we used a 12v halide lamp in a reflector, same as most modern diffusion enlargers, prior to that we used a photoflood.

That's what I'd designed the head for. It needed precise alignment nad sometime focussing but after that was great.

Ian

 

[eli griggs]

Thanks for the input, a quick search of these seem to indicate that:

1) The BHD is running about $50 @ at http://www.replacementlightbulbs.com where I usually shop, if you know of a cheaper source, please post it here

2) The #1133 is a microscope bulb (?) and that, in general, I should not use VC papers and polycontrast filters for printing with a point-light source. I also need to make sure I have a good negative carrier that will not allow excess light to slip past the negative to spoil the paper with 'hot-spots'.

3) Ralph asks questions that hurt my poor grey head.

Seriously, Ralph, I am only experimenting because I can spend a little time doing so, enabled by several enlargers with different light sources on my bench now, with which I can compare results without disrupting 'normal' enlarging chores. I have few expectations at the moment, I just want to see what I can do and, if it doesn't work, I'll put the B66 back to normal condenser condition and remove the Durst M600 from my bench, or both, if I can find a Focomat Leica 35/medium format machine for free or cheap.

I've seen and enjoyed in the past, the work of some few photographers whom did use point source successfully and that, with curiosity aroused by past conversations read here, ("aroused" is such a nice word, n'est-ce pas?) thought, 'why not give it a try'? Whither or no I am able to make decent enlargements that make it past my darkroom door is not at issue at this early point, only getting a good start on the hardware, which should be affordable on a thin budget and a relatively easy wiring set-up to make.

I'm wondering if these single element white-light, BA9s LEDs might do the trick, with a simple socket wired to my timer/voltage set-up? I'm thinking the 120∘bulb will give a good result? What do you think of these?

Dead Link Removed

Eli

Edited to add link...

 

[Anscojohn]

I recall reading of one photogtapher (was it Harry
callahan?) who used point light source. He souped roll film in modified Stoeckler, for very soft negs--the pls, I assume, boosted the contrast enough for him. For myself, I could not be bothered. It seems to me that contact printing "quality" can only be approached using diffuse light in the enlarger. But what do I know. I'm still ASS u ME ing many of the wretched-appearing images I see nowadays are because most negs and prints don't scan well for posting. I may be wrong.

 

[ic-racer]

I love cool equipment and I am into Omega enlargers, and I have seen the Omega point source and have been curious, like you, as to what it can do. So I am interested in your experiments.

FYI: this is the description of the Omega point source:

The DM Point Light Source heads were created to provide high intensity light sources for special applications such as microfilm, engineering drawings, electron microscope negatives, Ektalith printing, etc. Three different heads were available to accommodate different focal length lenses, and a custom condenser set was required for each focal length. A variable transformer power supply was necessary since the enlarging lens was required to be at maximum opening at all times to prevent colour fringing. The lamp could be adjusted vertically to ensure even light distribution at different magnifications. Using the special BEV lamp, the DM was able to provide up to 60 times the light output of a conventional condenser lamphouse.
It was most often sold with D2, D3, and later, D5 chassis as Omega DM Microfilm Enlargers.

Used Advice: The DM lamphouse is not intended for normal photographic printing, but is useful for high contrast work. One should ensure that a used lamphouse is the correct type and has the correct condenser set for the intended format.

 

[eli griggs]

I forgot to add link to LED site in previous post, here it is: Dead Link Removed

Is anyone aware of other members here currently using a point-source for any work?

Eli

 

[Claire Senft]

Sorry am I for the bad advice. I thought the BDH was only a couple of dollars each.

 

[eli griggs]

No worries Claire, I'm very glad to hear your ideas and have your participation.

Cheers

 

[richard ide]

The most important factor with a point source is the filament area for efficiency. I have an Opticopy camera/enlarger head which I use for 8 x 10 and smaller. I checked the lamp and the coiled filament is about 3/16" x 5/8" with no reflector. For even illumination you should reposition the lamp whenever you change the magnification factor so that the condenser focusses the filament image at the lens nodal point. This is easy to do by using a simple magnifying glass in front of the enlarging lens and adjusting magnifier and lamp positions until you get a sharp image of the lamp filament on your easel. For pictorial work I have only used an opal enlarger bulb so far but will be trying the point source in the next few days. I have used it in the past for document reproduction with amazing results. It is also very fast. I can remember making 48 x 96 positve film with an exposure of less than 30 seconds which gave a film Dmax of 4+. Film type and speed was similar to Kodalith (ASA 6). I have looked for information on this kind of setup but so far haven't found anything significant to add to my knowledge.

 

[jon koss]

I wonder if the LED might broadcast in the UV also. If so it might not be safe for use with a grain focuser.

Best of luck, J.

I forgot to add link to LED site in previous post, here it is: Dead Link Removed

Is anyone aware of other members here currently using a point-source for any work?
Eli

 

[Nathan Potter]

I use a homemade point source on my old Omega D2V. Use it occasionally for B&W and Ilfochrome prints from 35mm and 4X5. It uses a halogen 12 volt bulb in a ceramic socket bought from home depot. The housing is home made from plywood and sheet metal. The bulb can be adjusted vertically in the housing such that the condensers in the D2 can illuminate the full 4X5 field. The D2 variable condenser is removed. As some others have said the cone of light thru the enlarging lens is less than the maximum aperture of the lens so the lens stop is inoperable. At about f/11 the stop starts to clip the edge of the 4X5 image on the board so I tend to use the lens wide open and control the exposure dose using the timer. I drive the bulb with a voltage controlled DC 12 volt supply from Radio Shack - its rock solid in reproducibility.

Printing with a point source produces a very hard and contrasty image. This is understood by considering the optical path of the illumination. All of the light arriving at the negative or positive original comes from a single direction and so is delivered to the print from that single direction. This is in contrast to light from an extended source such as a diffusion head where light arriving at the negative comes from a wide angle direction and is replicated onto the copy from the same wide angle. Thus in the case of point source projection there is virtually no cross modulation of light from each point on the negative. Visually this results in an extreme resolution of grain in the print as well as any defects such as scratches and dust. I work in a laminar flow hood to control the contamination. However the sharpness obtained in the projected image is rather astounding when viewed for the first time.

For a degree of additional contrast control I fitted the custom lamphouse with an aperture just below the bulb. I use a series of black painted stops (like waterhouse stops) with a ground glass diffusive screen which I call a psuedo point source. These vary from about 1/4 inch to about 1.0 inch in diameter and allow me to vary the size of the point source for a range of contrasts. This amounts to varying the f/no. of the light source. The actual halogen bulb filament is probably about 1/16 X 1/8 inch in size so is not a classic scientific point source but it does the job.

Nate Potter, Austin TX.

 

[eli griggs]

Thanks for sharing Nate, some interesting stuff here. Do you have any point source printed images you can share or direct us too online?

How are you controlling heat/ventilation with your lamp unit or is it not a problem with your set-up?

I have yet to take a decision on a light source, LED or otherwise, so this is useful for me to know.

As a side note, I worked out how to access and control the built-in voltage regulator on my monster timing unit while building/tweaking my magnetic stirrer, so I can now control my light output on a selected enlarger, etc.

The only thing about it, (the timer) I might change, at some distant point, is the old swinging needle, analog voltage readout dial. Sorry APUG but this is one area where digital IS better, at least where repeatability is a concerned.

Cheers

 

[Nathan Potter]

eli, I don't have a scanner or any images on line so can't send any by computer yet. Soon though. But actually from what I've seen of images here the real detail in true point source images will not be transmitted via scanning. If I could more properly describe the effect of a true point source image it would be to say it is more akin to a litho process where very fine dots are employed. On very close examination mostly only high density grains of silver (or dye couplers in the case of Ilfochrome) are visible. Their size depends on the the resolution of the enlarging lens to a first approximation. There is little or no tonal modulation between grains. As one backs away from the print the eye fails, increasingly, to resolve the fine detail and so the appearance of the print begins to resemble more a conventional condenser enlarger print; that is to say a more modulated aspect where the eye acts as the integrator.

The bulb I use is 12 volt nominally and I run it at about 2 amps at 12 to 14 volts (24 watts total) so the amount of heat generated is small. The bulb is in a metal can part of the head so the metal gets warm. As a guide, my darkroom notebook says at a 33 inch lens to board distance the reflection intensity off a white board is about 80 lux (7.5 foot candles) from just the halogen point source. Plenty of light to do critical focusing. In fact one can focus down through the dye layers in the film and actually choose which layer for maximum sharpness. Of course the intensity is greatly reduced with the psuedo point source aperture/diffuser in place as I originally explained. I see in one example for Ilfochrome I used a 4X neutral density filter with an exposure of 24 sec. for a reflection intensity of 80 lux (without the ND filters).

It's a very interesting technique and I recommend you pursue it. Keep us posted.

Nate Potter, Austin TX.