Reddit mentions of Canon 52mm Soft Focus Filter

Back in the old days they'd put vasline on the lens. This was done in film a lot, especially for shooting glamorous shots of women with that slightly out-of-focus look. Here's a gallery showing some of the look. Another trick photographers use to get in-camera flare on the highlights like that, and a soft focus seen in your shots is a soft-focus filter. Here's one. I have a calumet one around here somewhere. It's a clear plastic square that mounts in a housing in front of the lens. It's slightly frosted looking. Bright spots flare a bit to give a bit of glow, and bright sections of skin do this a bit as well. It also means that even when you're in-focus, everything is just a whisker out of focus, hiding blemishes and smoothing skin tones. People make them in various ways. Too, they tend to kill black areas by allowing light to diffuse over them, and will kind of lightly wash out the contrast in a shot. You can also change exposure either in the camera or when developing the negatives or prints to raise the blacks to gray and blow out the whites a bit.