Bright Circles around Dark Objects

[photometry]

Hey guys!

I have recently been taking some glass positives of the sky and when I look at them up close I can see a bright circle surrounding each of the prominent stars on my positive. Has this happened to anyone else? What's causing this and is there a way to fix it? Any help would be appreciated, thank you, guys!

 

[koraks]

Halation, light piping. The fix is a couple of decades of R&D, but you may be able to glean one or two solutions from the antihalation and remjet backings of commercial products. No guarantees that those will be effective on glass plates or that they're feasible in a DIY setting though. I imagine coating a glass plate with a layer of gelatin loaded with a carbon pigment should be doable. What kind of glass plates do you use, are they DIY or do you buy them ready-made? In case of the latter, I don't have much hope for a feasible solution.

 

[AgX]

Halation is a inherent proplem in analog photography:
Light is reflected at the border of layers of diffeent refraction. The strongest at the base/air border. At the image of point light-sources it shows as a circular white ring around it at the positive. Thus the name "Halo", resp. halation.

The halo becomes larger, the thicker the base is. Think of a glass plate in your case.
The introduction of dedicated halation prevent/reducing layers and, dyes added to the layers and the vast reduction of base thickness (from thick glass to flims film) stongkly reduced that problem to practically nonexistant in most cases.


This form of halation must be differenciated from an optical effect inside the taking lens of light unwantedly reflecting there and producing somewhat similar images.

As your handle indicates some interest into the science behind photography, you should look deeper into these matters.


What I myself not understand is your wording in the title: "around dark objects"

 

[AgX]

Halation, light piping.

Indeed the light entering the base can be reflected repeatedly and thus spread laterally in the base. But in general with light piping a predominantly lateral light spreading is meant. As in entering the exposed-to-light film-leader and then spreading towards the part of the fim still covered by the cassette and there entering into the emulsion.