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point-source enlarger theory?

 
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Murray@uptowngallery.org



Joined: 03 Apr 2002
Posts: 164
Location: Holland MI

PostPosted: Mon Sep 10, 2007 4:46 am    Post subject: point-source enlarger theory? Reply with quote

1) I chose this forum because it was the 'least wrong'.

2) I chose this site because it's an old tech question and I'm not getting any bites on other sites.


Anyone know enough about mechanics/optics of point-source enlarging to discuss it?

Basically I'm interested in knowing how critical the lamps are, condenser location and behavior relative to a 'conventional lamp' condenser enlarger.

Lastly, if an enlarger is missing condensers, how critical is specifying/locating replacements? In other words, does a condenser simply have to spread out the light and would pristine generic or surplus ones work (if they fit) ?

I know point-source illumination is fraught with difficulties, but I'm just looking for info beyond all the caveats.

Thanks

Murray
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R_J



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PostPosted: Mon Sep 10, 2007 2:14 pm    Post subject: Re: point-source enlarger theory? Reply with quote

Murray@uptowngallery.org wrote:

Basically I'm interested in knowing how critical the lamps are, condenser location and behavior relative to a 'conventional lamp' condenser enlarger.

Lastly, if an enlarger is missing condensers, how critical is specifying/locating replacements? In other words, does a condenser simply have to spread out the light and would pristine generic or surplus ones work (if they fit) ?

I know point-source illumination is fraught with difficulties, but I'm just looking for info beyond all the caveats.
Murray


Hi Murray,

that's a lot of questions to unpack; perhaps I'll only comment on a few of the issues.

Most of my experience comes from using a diffuser head, and the light source (fluorescent tubes); height from the negative etc are less critically important than for a condenser source. With a condenser source, the type of lamp and its location from the negative plane introduces more printing aberrations relative to a diffuser head for any change in a specific variable.

If a condenser enlarger is missing its lenses and derives its light from a point source, then it follows that a negative cannot be illuminated evenly across its diameter without the condenser lenses. The resulting diffusion effect, with the wrong type of lighting source, introduces its own printing defects (such as loss of contrast in the printed negative) in addition to the above. The function of the condenser lens in most modern enlargers, tends towards condensing (or reducing the diffusing effect of the light source) of the light source, thereby increasing contrast (a characteristic of condenser enlargers), rather than maintaining a standardised and reproducible diffusion of light (such as that from a cold cathode head).

Although it might be onerous experimenting with a broken enlarger (that is, one without its original condensing lenses), any non-factory replacement for condenser lenses will at best, be marked by illumination problems across the diameter of the negative format for which you would print.

Hope that helps.
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Henry



Joined: 09 May 2001
Posts: 1427
Location: Allentown, Pennsylvania

PostPosted: Mon Sep 10, 2007 7:20 pm    Post subject: Reply with quote

Murray, what brand enlarger? There are parts available for a few of the old-line jobs like the Beseler. You might even be able to pick up a junker for parts that match yours.
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Murray@uptowngallery.org



Joined: 03 Apr 2002
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Location: Holland MI

PostPosted: Mon Sep 10, 2007 9:35 pm    Post subject: Reply with quote

No brand. No enlarger. I do things a step at a time, sometime 1 forward & 2 back.

I just started acquiring enlarger lenses. I was looking for 90-100 mm lens & saw an Ektar lens from a 'color printer' with fixed iris. Reading led me to the point-source concept.

It seemed like it was as much or more work to adapt an existing enlarger to point source than start from scratch, because of the lamp movement requirements.

I didnt know if it was possible to generically select a condenser or pair to cover a specific format like it's not hard to find a taking lens to cover a given format.

And it looks like any good enlarger lens could be pressed into point-source service if the rest of the system was there.

I won a 100 mm lens Saturday on eBay anyway (with iris :O).

My original plan was a horizontal one with cold head. Maybe an optical bench type construction will allow me to hack different light sources into the system.

I hope they still make paper by the time I have one running :O(

While R_J is here, back to the cold head idea...

Surplus Shed has inexpensive EK flashed opal glass in 4x5, 5x7 and 8x10. I thought I should hide a piece of each for someday when the next phase 'happens'.

I understand one wants one's existing enlarger condenser lenses to be free of defects or they may show. Does the inherent dififfusion in opal glass give one some leeway for imperfections in the glass or should I specify 'mint condition or never mind' on the opal glass?

If nothing else, this has been (another) educational adventure. Other than one hound lens I naively bought (Rodenstock EL-Omegar 75 mm) before I really researched, the others are good ones.

Thank you both (and any upcoming posters). Dan, too, in anticipation of any forthcoming harassment :O).
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Dan Fromm



Joined: 14 May 2001
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PostPosted: Mon Sep 10, 2007 9:44 pm    Post subject: Reply with quote

Murray, why does a fixed aperture enlarging lens want a point source?
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Murray@uptowngallery.org



Joined: 03 Apr 2002
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PostPosted: Mon Sep 10, 2007 9:53 pm    Post subject: Reply with quote

Well, I'm told that an aperture has no useful effect with a point source light source and that exposure times are adjusted by varying light intensity (which has color temperature issues) or ND filters.

Because that 108 mm Ektar lens I saw was fixed aperture, some said one possible origin for it may have been a point source system. But someone else tod me that the color printers were sometimes for fixed sizes, sometimes had interchangeable fixed apertures.

But since people use whatever normal enlarger lens they have on things like Durst 138's when they go point-source, that Ektar is looking less attractive.
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R_J



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PostPosted: Tue Sep 11, 2007 10:58 pm    Post subject: Reply with quote

Hi Murray,

Not sure why I'm finding myself thinking how remote cold head diffusion is, when compared to lensless point source light enlarging.

There is a marked difference in the final print from both methods: classically, a cold cathode enlarger endows prints with a contact print quality, with none of the harshness characteristic of condenser enlargers. The condenser-diffusers take a middle-ground compromise rendition between a diffuser and a condenser.

Perhaps most modern heads fall into this middle category, however the cold light cathode enlargement is an aesthetic which seems to be sidelined as more photographers assume that split-grade printing (which overcomes the inherent problems with variable contrast papers) is oddly superior in any way to a completely different printing technique with graded papers. The point source enlarging practice, fits on the same side of condenser-enlarging practice, away from diffuser-enlarging practice. Your project could come up with some fascinating results. I'm curious: how would a cold head diffuser, with the opposite extreme, of a single point light source alter print characteristics - what would the prints look like

Quote:

I understand one wants one's existing enlarger condenser lenses to be free of defects or they may show.


Yes; the condenser lens accentuates visual characteristics of grain and sharpness and condenser lens aberrations will distort the focussed light at the nodal point of the enlarging lens.

Quote:

Does the inherent dififfusion in opal glass give one some leeway for imperfections in the glass or should I specify 'mint condition or never mind' on the opal glass?


With respect to a diffuser, the opal glass acts as a diffuser and does not require the critical condition of the condenser lens. What you say also follows in relation to a diffuser vs condenser: even if the diffuser is in the plane of the light source and the negative, the diffuser's function is less critical than that of a condensing lens with respect to focussing parallel light onto the negative at the lens' nodal point.
Quote:

I just started acquiring enlarger lenses. I was looking for 90-100 mm lens & saw an Ektar lens from a 'color printer' with fixed iris. Reading led me to the point-source concept.


As Dan comments, not all fixed aperture 'enlarging' lenses were destined for photographers' darkrooms. Printers' lenses do not require such refinements as f-stop aperture controls.Fixed iris' enlarging lenses seem to be more popular in printing houses than with individual photographers and some caution in acquiring these at relatively low cost might be required, since their purpose is alien to that of your project yet freely abundant.

The best of the 'fixed iris lenses', which mostly are iris-less lenses, can take modern 'waterhouse stops' i.e. a circular disc cut out sandwiched or screwed into a virtual space between the front and rear elements of the enlarging lens. Neither is there an absolute requirement for this disc to be circular either (most enlarger apertures are not, at the optimum aperture).
Rodenstock manufacturered it's top line of Apo-Rodagon-N lenses for LF work along this principle, however the cost for printers of these lenses were a mere fraction of the same lens in an iris.

The challenge with a small fixed aperture lens when used with a single point light source, is that the intensity of the heat must be overwhelming especially when focussed on a nodal point at a negative, particularly at the longer printing times required as a result of the decreased light transmission. Even if you undertake a modest 4x5" negative enlargement, pin-point heat burn effects on the negative from the heat, in addition to negative shape distortion/expansion and light intensity outclassing a 300 Watt bulb will all become issues to contend with. None of these issues are insurmountable, however the issues with single point light source enlarging does dissuade anyone but the most ardent enthusiast. It is hard work, Thus the results.

A plain incandescent light source may be more appropriate for your use than fluorescent cold cathode tubes, otherwise your enlarging printing times will run into the next century. Unless you plan to use graded papers?

I presume that this project of a single point light source intends for the final print output to be razor sharp and contrasty?

Kind regards,

RJ
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Murray@uptowngallery.org



Joined: 03 Apr 2002
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Location: Holland MI

PostPosted: Wed Sep 12, 2007 3:00 am    Post subject: Reply with quote

Thanks for the detailed answers. Not that I'm qualified to gauge it, but you're obviously a skilled writer too.

I guess the short answer is that what I've read of PS performance makes it a 'must-see' if at all practical.

Burning the negative with a lamp sounds like my luck. Thanks for the warning.

Murray
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Murray@uptowngallery.org



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PostPosted: Thu Sep 20, 2007 7:41 am    Post subject: Reply with quote

I got a dose of reality with the Durst Latico/Lacon condensers - I let an 85 and 130 pass, thinking they were on the small side; they closed on eBay at US$36 and 41 each & seller wanted $25.40 each to ship.

Next I saw a pair of Lacon 380's, and realized there were people with deeper pockets than me. They closed at US$301 + 48# shipping weight. Winning bidder had a Japanese name - I'll just imagine they have to be shipped to Japan.

I realized there were alot more issues that just getting the parts...

I found a Dejur condenser 6.5" diameter fairly cheap, bought-it-now, then realized the Dejur 4x5 has two lenses...and I do not .

I >thought< I read somewhere that a second condenser allows the condenser ass'y to be closer to the negative to minimize enlarger height.

I hope a single condenser can be made to work and isn't just half the function...or I have another useless item to go with some of the others.



Murray
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paxety



Joined: 10 Sep 2003
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PostPosted: Thu Oct 25, 2007 4:35 pm    Post subject: Reply with quote

You might PM Donald Miller on APUG. He converted an enlarger to a point source. IIRC, he used a 1000w bulb and had to build a fan to cool it.
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djon



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PostPosted: Sun Aug 24, 2008 1:20 pm    Post subject: point source Reply with quote

I've did a lot with "point source" ... about 30 years ago.

I don't recall the specific nomenclature, but the lamp that is/was used in Durst, Beseler, and Omega was literally a Volkswagen dome lamp (actually a 2" tubular l2V non-quartz amp that was used in many automobile brands)

There is/was an adapter socket that screwed in to replace the conventional light bulb socket in those three enlarger brands.

The 12V lamp naturally required a 12V source...that was available expensively from the enlarger manufacturer or cheaply from a junk store in the form of a variable voltage model train transformer (I used an ancient Lionel transformer). A fixed voltage 12V converter would be just as good because the variable transformer had to be used at full voltage to avoid strange optical effects as a result of the strange color that happens with lower voltage.

Aperture is crucial...it must be FULL aperture, eg. f2.8 with a 2.8 lens or f4 with an f4.0 lens. Stopping down produces crazy effects ...the diaphragm blades scatter light remarkably....presumably a waterhouse stop would be good...as you know, process lenses were never stopped down for the same reason, but they did use waterhouse stops...diaphragm blades do themselves inherently hurt resolution vs waterhouse stops.

Exposure is a matter of timing, not aperture...I don't recall typical exposure times, but I do recall them being critical.

Professional Dursts had excellent condenses for point source use.
Hobbiest Dursts did not, except for older versions such as 606 and my 609..I doubt subsequent hobbiest Dursts were comparably good.

Omega and Beseler had inferior condensers so they required optional condensers, part of their expensive point source kits (optically coated condensers, lamp, lamp adapter, transformer).

Focus is critical..slight out-of-focus is unusable...strange color effects are projected when slightly out of focus and the faintest abrasions on back of film become exaggerated.

I don't recall what film holder I used..I relied heavily on glass carriers that were standard with Durst..I used anti-newton on back and clear on the emulstion side (emulsion has its own texture to avoid newtons rings).

I also had glassless carriers, but rarely used them and the inevitable film curvature probably (don't recall) made strange effects away from the focus point...PERHAPS I focused off-center, just as I do with Nikon scanner, which is also focus-critical but not nearly so extremely.

What are the results? Remarkably high detail resolution..the best possible from any given lens. Strange print tonality...interesting...as "realistic" as B&W ever is, but startling, distinctive. Increased difficulty with dust and scratches, just as with 4000ppi Nikon scans without Ice.
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