Diffusion Filters: Night Fog vs. Black Fog vs. Soft Glow
In cinematography, the final 10% of effort is what separates a good image from a truly great one. Filtration is a huge part of that final polish. The right diffusion filter can subtly alter contrast, bloom highlights, and soften skin tones, adding a layer of texture and emotion that a clean lens alone cannot provide. But with so many options, how do you choose the right one for your scene?
In this Cinematography Tip of the Day, DP Shane Hurlbut, ASC, showcases on-set filter testing. He puts three popular Tiffen diffusion filters—Night Fog, Black Fog, and Soft Glow—through their paces, demonstrating their unique characteristics on both wide and telephoto lenses. This article explores that process, designed to help you understand the personality of each filter and choose the right tool for your story.
What You Will Learn in This Article:
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The Testing Methodology: “Break It to Find the Sweet Spot”
Shane begins with his core philosophy for testing filters: always start with the strongest grade to “break it.”
“If you go too little,” he explains, “then you really don’t know what the true effect of this filter is.”
By applying the heaviest strength first, you can clearly see the filter’s maximum impact on the image. This gives you a strong baseline, from which you can then dial it back incrementally to find that perfect “sweet spot” where the effect is present but not overpowering.
Filter Breakdown on a Wide Lens (21mm Optimo Prime)
The test begins on a 21mm lens to see how the filters perform on a wider field of view.
Tiffen Night Fog:
Shane describes this filter as “specular,” acting similarly to a White Pro-Mist. It aggressively blooms highlights and lifts the shadows.
| Strength 2 & 1 | These were immediately identified as “too heavy,” creating a dense, foggy look perfect for a San Francisco night but too extreme for a subtle effect. |
| Strength 1/2 & 1/4 | Still a bit too milky, lifting the blacks into a “chalky gray tone.” |
| Sweet Spot (1/8) | At this strength, the filter provided a nice, subtle chalkiness in the blacks and a beautiful bloom in the highlights, even creating a slight star-like striation on point sources. Shane also notes that the Night Fog tends to add a slightly cool tone to the image. |
Tiffen Black Fog:
This filter has a different character. Instead of a white, milky haze, it feels more like “black dust,” retaining deeper blacks while still blooming highlights.
| Strength 2 & 1 | These were still too heavy for a subtle look, though Shane noted the strength 2 Black Fog was comparable to the 1/8 Night Fog in its intensity. |
| Strength 1/2 | This was getting close, providing a nice bloom and beautifully softening the contrast on skin tones without being overpowering. |
| Sweet Spot (1/4) | At this strength, the effect was subtle but impactful. “I love the bloom, I love how it’s creating that slight haze,” Shane notes. It’s perfect for adding a sense of humidity or moisture to the air without heavy smoke, rounding out the contrast beautifully. |
Tiffen Soft Glow:
Shane compares this filter to Glimmerglass, noting its subtlety.
| Strength 5, 4, & 3 | Even at these higher numbers, the effect was gentle. The filter subtly blooms highlights, fills in shadow detail, and knocks down overall contrast without making the image feel foggy. Shane points out how it adds “depth and dimension” to the deepest blacks by catching the ambient glow from light sources, preventing them from being a flat, empty void. |
Filter Breakdown on a Telephoto Lens (100mm Optimo Prime)
Shane reiterates a crucial rule of thumb:
“Wider lenses, higher number. Longer lenses, smaller number.”
Because a telephoto lens magnifies a smaller portion of the glass, the diffusion effect is amplified, requiring a much lighter grade.
TIFFEN NIGHT FOG |
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| Strength 1/2 & 1/4 | Immediately “too milky” and extreme on the 100mm, causing the ping in the actor’s eyes to lose focus. |
| Sweet Spot (1/8) | This was the perfect strength, taking the hard edge off the contrast, smoothing out skin tones beautifully, and filling in shadows under the eyes. |
TIFFEN BLACK FOG |
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| Strength 2 & 1 | Far too heavy on the telephoto lens, creating an overwhelming bloom. |
| Strength 1/2 | Still a bit too heavy, with the highlight bloom haloing the subject’s face. |
| Sweet Spot (1/4) | This strength provided the perfect subtle touch. “This is what you’re looking for with filtration,” Shane advises. “You don’t want to hit it so hard… you want to feel that slight change in the contrast.” It beautifully softened the image without showing its hand. |
TIFFEN SOFT GLOW |
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| Strength 4 | Even the Soft Glow was too heavy at this grade, milking out the blacks and creating too much of a glow. |
| Sweet Spot (3) | This strength was the perfect choice, barely lifting the blacks while doing beautiful work on the skin, subtly softening contrast, and wrapping the highlights for a polished, dimensional look. |
The Bottom Line: Choosing the Right Tool for the Feeling
This head-to-head comparison reveals the distinct personality of each filter.
Night Fog is your tool for a heavy atmospheric effect, aggressively blooming highlights, and lifting shadows for a foggy or dreamlike state.
Black Fog is a more subtle choice for adding atmosphere and softness while protecting your rich blacks.
Soft Glow is the most delicate. It’s a finishing filter that adds a subtle polish, depth, and dimension without a heavy haze.
The key takeaway is that filtration is a nuanced art. It requires testing, understanding the relationship between focal length and density. And it’s about always choosing the filter and strength that best serve the emotion of your story.
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