What does 100% zoom mean in Lightroom, and how does it relate to magnification?
Asked 1/18/2021
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Photo editors like Lightroom show zoom as a percentage, but I’m unsure how that relates to optical magnification or focal length. For example, if I shot a photo at 30mm and view it at 100% zoom, what does that correspond to in terms of magnification or equivalent focal length?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
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The percentage is the scaling applied to render the image onto the display. The size of the image on screen will therefore depend on your screen size. Conceptually this can be thought of:
- 100% means that each pixel of the image is shown as 100% of a pixel on screen.
- 200% is zoom in because each pixel of the image takes 200% of a screen pixel which is 2 pixels vertically and 2 pixels horizontally, so 4 pixels in total.
- 50% zooms out because each pixel is represented by a 1/2 screen pixel, so 4 image pixels get mapped to a single screen pixel since image pixels are scaled 50% horizontally and vertically.
For those who take issue with the simplification of the above list, strictly speaking the mapping can be more complicated to provide a clearer zoom but in terms of scale, that is what happens.
The percentage zoom is unrelated to focal-length. It is simply a pixel-to-screen scaling.
Originally by user1620. Source · Licensed CC BY-SA 4.0
user1620
5y ago
0
Generated from our catalog & community — verify before relying on it.
In Lightroom and similar apps, zoom percentage is a display scaling value, not an optical magnification or focal-length equivalent.
At 100% zoom, the image is typically shown at 1 image pixel to 1 screen pixel. At 200%, each image pixel is drawn larger on the screen; at 50%, multiple image pixels are combined into fewer screen pixels.
That means there is no single conversion from “100% zoom” to “X times magnification” or to a focal length like 60mm or 120mm. The apparent size depends on factors such as:
- your camera’s sensor size and pixel density
- the image resolution
- your monitor’s size and pixel density
- any display scaling in the system/software
So a photo taken at 30mm is still a 30mm photo. Viewing it at 100% in Lightroom does not change it into another focal length; it only changes how large the recorded pixels are displayed on your screen.
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