Objective magnification = Tube lens focal length / Objective focal length. For infinity-corrected systems with 200mm tube lens: 25× objective has 8mm focal length, 60× has 3.33mm. Total magnification to camera = Objective × (Tube lens FL / Reference FL). Sample size at pixel = Pixel size / Total magnification. Magnification does not affect resolution—only NA and wavelength determine resolution.
Optical Parameter
Magnification
How much larger the image appears
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Definition
The ratio of image size to object size. In microscopy, total magnification is the product of objective and eyepiece (or tube lens/camera) magnification. Higher magnification spreads the same light over more area, reducing signal per pixel while enabling finer sampling.
Technical Details
Simplified
Making things look bigger by projecting the image over a larger area. But here's the key insight: higher magnification doesn't give you more detail—it just spreads the same detail (and the same light) over more pixels. That's why magnification must be matched to resolution and pixel size.
Why It Matters
Magnification determines the sample area each pixel captures. Too low and you undersample (lose resolution). Too high and you oversample (waste pixels on redundant data and reduce signal per pixel). Optimal magnification matches the resolution to the pixel size for Nyquist sampling.
Practical Example
25× objective with 3.7μm pixels: each pixel sees 148nm of sample. 60× objective with 6.5μm pixels: each pixel sees 108nm. Despite different magnifications and pixel sizes, both achieve similar (near-Nyquist) sampling of their respective optical resolutions.