Halation has been observed from the earliest days of photography, but became more common upon the introduction of glass plates.

In the ferrotype and similar processes there was no transparent support, so the only form of halation was the reflection or spreading of light within the emulsion, which was not great.

On the introduction of the wet plate, a more aggravated form of halation was encountered, due to the reflection of light from the back of the glass support to the under side of the emulsion. This, however, was not as great as the halation of the dry plate, for the color of the iodized collodion emulsion of the wet plate acted as a filter and cut out much of the light which would otherwise have been reflected.

The emulsion of a dry plate being more transparent, there is more halation, and the chief cause is the reflection from the back of the glass support. The extent of halation depends upon the extent of the reflection, which is determined by the thickness of the glass and the angle of the rays of light which enter it. The refractive index of the glass also plays a small part - but this is of minor importance.

From An Artura Iris Print By A. P. Bradley New York.

From An Artura Iris Print By A. P. Bradley New York.

From An Artura Iris Print By A. F. Bradley New York.

From An Artura Iris Print By A. F. Bradley New York.

How To Avoid Halation StudioLightMagazine1917 19

Fig. 1.

Figure 1 shows a ray of light entering a glass plate at A and the reflection of this ray of light at B. The space from A to B shows the breadth of the line of halation, for there is sufficient diffusion to fog the space between A and B and to show a vignetted blur or fringe of fog beyond the point B.

How To Avoid Halation StudioLightMagazine1917 20

Fig. 2.

Figure 2 shows the same ray of light entering the emulsion of a Portrait Film. The support of the film is so thin that our diagram cannot show the reflection of the ray of light after it has passed through the film emulsion and support. The amount of reflected light is therefore practically negligible. There is practically no halation in Portrait Film other than that which is due to the spreading of the light in the emulsion itself, known as irradiation or lateral spreading of light, and this cannot be considered, for it is present in all emulsions and is due to the scattering of the light by the silver grains.

Halation in glass plates increases with the thickness of the glass and it also increases with the angle of the rays of light entering the glass. The extreme margins of the plate will show the greatest amount of halation and the center of the plate the least.

The most noticeable halation is that around windows, for there is always a very bright light in contrast with a deep shadow. It shows most where it blurs the dark line of the shadow, but it is present throughout the entire window.

Because a shadow is not large in area or dark enough, or a line is not sharp or regular enough to make the halation distinctly noticeable is not an indication that there is no halation. In fact, halation is often most destructive where it is least distinguishable. Its inroads on true quality have been so persistent that the negative without halation is the exception rather than the rule.

In portraiture, the eye sees detail in the whitest drapery. There is no highlight so strong but what the ground glass will show it interwoven with minute shadows - and these are quickly destroyed by halation. There is a brilliancy and roundness to this ground glass image which you are never able to truthfully reproduce in your glass negative and your print.

From An Artura Iris Print By A. F. Bradley New York.

From An Artura Iris Print By A. F. Bradley New York.

You have come to look upon this loss of quality as unavoidable. You reproduce as nearly as possible and attribute any error to the deficiencies of the photographic process.

If this is the case you have not used film. You have not known what the elimination of this degrading influence of halation will add to your results.

This is especially true in portraiture where the texture of flesh is of greatest importance and where every strong point of light on a face as well as the gradations of the half-tones are preserved in all their brilliancy in the film negative.

Bright spots of light, such as windows, when out of focus, show more halation than when their images are sharp. And as they are usually in the margins of the picture the halation is further accentuated by the light rays reaching the margins of the plate at a greater angle.

Film cannot sharpen lines that are out of focus but it will largely do away with the halation, and when windows or similar light sources can be focused sharply the reduction of halation is so great that there is no comparison between the plate and the film result.

Those who work for soft effects with soft focus lenses or other means of diffusion are often disappointed because the effect they see on their ground glass is not what they get in their negative. Halation has upset their calculations and intensified the effect of diffusion.

The commercial photographer is especially concerned with halation and has found it necessary to use double-coated or backed plates in much of his work. But commercial workers are adopting film and find it better in every way and less expensive.

Note again the greatest cause of halation, Fig. 1, and the remedy, Fig. 2. Then prove it to your complete satisfaction by a trial of Portrait Film.

Please Specify

The stock-houses have asked us to emphasize the fact that Azo K paper is now being made in two contrasts - Soft and Hard - instead of one only - Hard - as was the case until October last. Please specify in your orders whether you want K Soft or K Hard, thereby enabling your dealer to give prompt service without delay or disappointment.

From An Artura Iris Print By A. F. Bradley New York.

From An Artura Iris Print By A. F. Bradley New York.

Please Specify StudioLightMagazine1917 25Half tone Cut 233 Price, 60 cents.

Half-tone Cut 233 Price, 60 cents.

A better cut for a high grade of printed matter, such as booklets, folders, announcements, etc., that are printed on a coated paper.

This cut is not suitable for use in newspaper advertising. Order the line cut on opposite page for all but the best of printing on the best of paper stock.

Artura Print, From An Eastman Portrait Film Negative By Dudley Hoyt Nee York.

Artura Print, From An Eastman Portrait Film Negative By Dudley Hoyt Nee York.