Here's how to make a digital version of a black and white Holga photo. And yes, that's me and the world's greatest big brother.
1. Open your image in Photoshop and crop it square.
2. Now, create a black and white Gradient Map layer. Go to Image > Adjustments > Gradient Map.
3. The photo needs contrast. Go to Image > Adjustments > Brightness/Contrast. Move the sliders to your liking.
4. For a more authentic look, let's add some noise. From your background layer go to Filter > Noise > Add Noise. Adjust the slider to the amount you want. Make sure that the Monochromatic box is checked.
5. If your whites are too bright, adjust them with Levels. Go to Image > Adjustments > Levels and slide your White Output to the left (towards the black).
6. To create a vignette, select the circle marquee from the tool box. Change your Feather to 40px and drag a circle around your image. Go to Select > Inverse.
7. Go to Image > Adjustments > Curves. In the pop-up box, drag the midpoint down (towards the black) until the vignette is as dark as you'd like it to be.