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What is Base Fog?

OK, don’t freak out—all film has base fog. What?! Yep, it is called “film base plus fog” or “FB+F.”

“Base” is the density of an unexposed, processed area of film. It is a section of the film that has been developed, yet never exposed to light—the space in between each frame, for example. And “fog” is the silver halide within the film that has received no exposure to light, yet gains a slight amount of density during development.

Base fog, although always present, is a problem when it increases to the point where it produces a noticeable reduction in contrast.

Side Effects of Base Fog:

Example of a Base-Fogged Scan:

A base-fogged scan of a
toddler and baby

Base Fog in an Exposure Reference Sheet:

An exposure reference sheet
showing base fog

Thanks to our handy-dandy Exposure Reference Sheets, increased base fog is easy to spot. Notice how this Exposure Reference Sheet lacks tonal range throughout and has increased gray tones in between each frame? This is a red flag for base fog.

Normal Exposure Reference Sheet:

A normal exposure reference sheet

Now, see how this Exposure Reference Sheet has a wide tonal range with a deep black point in between each frame? This is what you want to see!

Base Fog can increase due to a number of factors:

So, how can you avoid base fog?

How can you correct base fog in post?

What do you do once you have received your scans from base-fogged negatives? You captured some seriously sweet moments and would hate to see those images live the rest of their life in the trash bin on your computer. Depending on the severity of your Base Fog, you have various editing options:⁠

If the Base Fog is mild, consider adjusting the images’:

If the Base Fog is more severe, consider these editing tips from @amandaoliviaphoto :

“This shot was something special, I knew I had to find a way to deliver it to my client. To edit, I converted the image to black and white and increased the clarity and contrast and used dehaze in Lightroom. Obviously, the image is incredibly grainy, but I really loved it and wanted to deliver it. I felt that at least this way it looked more like a pushed black and white Delta3200 image!” — Amanda Olivia

Edited Scan

A black-and-white photograph
with notable film grain, picturing a toddler and baby