Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,852   Posts: 1,582,904   Online: 1043
      
Results 1 to 5 of 5
  1. #1

    Join Date
    Oct 2009
    Location
    Central Florida, USA
    Shooter
    Multi Format
    Posts
    4,071

    Omega D-2 and D-II, defused or condenser?

    I've been wondering about this....

    I have an Omega D-2 and D-II with standard lamp housing and condensers. One has the variable kind and the other is the fixed kind.

    I understand the TRUE condenser enlargers have a naked (non-frosted) point source lamp and condenser under it. The True defused kind has a side mounted lamp and mixer box, and reflected light hits the negatives.

    Then, what do I have? The lamps are frosted and top mounted. I am assuming just about everyone knows these legendary enlargers well so that I don't need to describe it in detail.

    I ask this because Kodak's literature on film/developers state its timings are based on "defuser enlarger" that when one is using condenser kind, should reduce timing by 20%.

    I am not asking this to debate personal preference and timing and such. I'm curious as to how to classify my enlarger.
    Develop, stop, fix.... wait.... where's my film?

  2. #2
    Rick A's Avatar
    Join Date
    Mar 2009
    Location
    north central Pa
    Shooter
    Multi Format
    Posts
    6,237
    Images
    34
    They are still condenser enlargers even with frosted bulbs. The frosted glass of the bulb serves to mask the shadow the post and filament would cast on the image.
    Rick A
    Argentum aevum

  3. #3

    Join Date
    Feb 2009
    Shooter
    Large Format
    Posts
    673

    Hybrid Condenser-Diffusion Enalrgers

    Modern condenser enlargers that use an opal diffusion layer deposited inside the bulb’s glass envelope are best described as a Hybrid Condenser-Diffusion enlager.

    Here is what John S. Carrol has to say of the matter:

    Callier Effect (p33)

    (Excerpt from out of print 1976 Amphoto Home Darkroom Course by John S. Carroll)

    If you have ever made both contact prints and enlargements from the same negative, and especially if you have used the same paper for both, you probably noticed that your enlargements seemed to have a little more contrast than the contact prints from the same negative. This is not an illusion, but comes from a property of the silver image itself, first described by André Callier and known as the Callier Effect.

    The Callier Effect is the result of the granular structure of the silver image: if the image were perfectly homogeneous, this effect would not occur. What happens is that the individual grains of silver block some of the light while most of the remaining light passes between the grains. That is, the individual grains are opaque, and the differences in light transmission in the image result from the amount of light blocked by the grains as compared with the amount of light that passes between them. Even this would not matter if it were not for a further occurrence. Some of the light rays that strike the edge of a grain are reflected from their normal paths and go off at odd angles; the total effect of the various light rays is called scattering, and it is this scattering that causes the Callier Effect.

    The scattering is least where there is little silver deposit, and most where there is the most silver. The deflection of the light is small but becomes significant in the case of a projected image. In an enlarger, much of the scattered light is deflected sufficiently to miss the lens altogether; if this occurred uniformly in all negative areas, it would make little or no difference, but the amount of deflection actually depends upon the way in which an enlarger is built.

    Enlargers

    The earliest enlargers were built like slide projectors; they had small, highly concentrated light sources and large lenses, called condensers, to direct the light through all areas of the negative and then to the enlarger lens. In the absence of a negative, the light rays traveled in straight lines from lamp to lens to paper. A system like this was highly efficient but difficult to adjust; every time you focused the lens, the lamp and condensers had to be adjusted also.

    Another type of enlarger did away with the condensers altogether; instead it used a sheet of highly diffusing material, such as opal glass, to assure uniform illumination. The problem with this system was that the opal glass absorbed a good deal of light, hence powerful lamps were needed or else exposures were inconveniently long.

    These are the two extreme types of enlargers and are known as condenser enlargers and diffusion enlargers. A hybrid type of enlarger is used by most workers today—it contains condensers for better light efficiency but uses a large opal glass lamp bulb. Thus we have some diffusion right at the source, then the light is picked up and directed by the condensers and directed through the negative in the normal way. This improves the efficiency as compared with a pure diffusion-type enlarger, while eliminating any need to adjust the lamp and condensers once they have been set up at the factory.

    Each type of enlarger has a different effect on the contrast of the enlarged print as compared with a contact print from the same negative. In the case of the contact print, there being no appreciable distance between negative and the paper, any light scattered by the silver grains of the negative reaches the paper before it has departed from its proper area. Thus all printing light reaches the paper except the amount absorbed by the silver grains of the negative, and the print has the same contrast as the negative.

    Condenser and Diffusion Enlargers

    The condenser enlarger represents the opposite extreme. Where there is little silver in the negative, as in the shadow areas, light rays from the condensers travel in a straight line directly to the enlarger lens. In the middle tones, only those rays which pass directly between grains can travel to the lens undeflected; any light scattered by the image never reaches the lens. In the highlights, there is more silver, more scattering, and an even larger proportion of light fails to reach the lens.

    Summing up, light from the shadows reaches the light in toto; some of the light from the middle tones is lost by scattering; and still more light is scattered and lost from the highlights. Thus the projected image definitely has a higher contrast than the negative itself.

    In a diffusion enlarger, the scattering still takes place in the negative, but there is also some random scattering in the diffuser. This does not change the situation in the middle tones and highlights, where scattering still takes place as before; it does, however, result in some loss of light due to scattering in the shadows, where little silver image is present. There is still more loss in the highlights and the middle tones than in the shadows, so the projected image will have some increase in contrast, but the increase will not be as great as with the condenser enlarger.

    These are the extremes; the enlarger that uses and opal glass bulb combined with condensers will show some gain in contrast—more than a diffusion enlarger, but less than a true condenser enlarger. There is little to choose between the totally diffusing machines and those which use a diffused light source with condensers. The general belief that condenser enlargers produce grainier images is not really true, though the increase in contrast may sometimes cause graininess to appear a little more evident. This is easily proved by making a print on softer paper; you will notice that it is no grainier than a print made on harder paper using a diffusion enlarger.

    Newer Diffusion Enlargers [Dichroic color and VC enlargers]

    As mentioned, the main fault with older diffusion-type enlargers is the great loss of light in the opal-glass diffusing medium. A newer type of diffusion enlarger is becoming popular now, in which diffusion is accomplished by reflecting the light back and forth from the walls of the lamphouse. As a result of multiple random reflections, most of the light eventually finds its way through the negative and lens, and there is far less loss of illumination.

    The chief advantage of this system is that several light sources of different colors maybe used; the diffusion housing acts as a mixing chamber, resulting in a highly uniform illumination and complete color control. Modern lamphouses of this sort utilize dichroic filters, which do not fade under heat; a single light source and three variable filters allow complete color correction capability.

    (p36) Thus if you wish to buy the best at the beginning, you may install a color enlarger [lamphouse], since it will be equally useful for black-and-white printing. On other grounds, there is little to choose between diffusion and condenser lamphouses of different makes; they produce minor differences in image contrast, but if a good enlarger lens is used, prints will be equally sharp with any of them. The graininess question is trivial.

  4. #4

    Join Date
    Oct 2009
    Location
    Central Florida, USA
    Shooter
    Multi Format
    Posts
    4,071
    Thanks both.
    Develop, stop, fix.... wait.... where's my film?

  5. #5
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,382
    It is "point source" head that has the non-frosted bulb. That has the most collimated light.

    I like the last paragraph. This should be the emphasized with todays marketplace which is full of used color enlargers for little money (or free sometimes).

    Thus if you wish to buy the best at the beginning, you may install a color enlarger [lamphouse], since it will be equally useful for black-and-white printing



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin