calculate magnifications of images and actual sizes of specimens from drawings, photomicrographs and electron micrographs (scanning and transmission)

Sourav PanOctober 28, 2024

Answered

Calculating Magnifications and Actual Sizes

1. Light Microscopy (Compound Microscope) Images

• Given:
  • Objective Lens Magnification (e.g., 4X, 10X, 40X, 100X)
  • Eyepiece Magnification (usually 10X)
• Total Magnification Calculation:
  • Total Magnification = Objective Lens Magnification × Eyepiece Magnification
  • Example: Objective Lens = 40X, Eyepiece = 10X; Total Magnification = 40X × 10X = 400X
• Actual Size of Specimen Calculation (if total magnification and measured size on image are known):
  • Actual Size of Specimen = Measured Size on Image / Total Magnification
  • Example (hypothetical measured size): Measured Size on Image = 10 mm, Total Magnification = 400X; Actual Size = 10 mm / 400 = 0.025 mm or 25 μm

2. Digital Microscope On-Screen Images (including calculations for screen display)

• Given:
  • Objective Lens Magnification
  • C-Mount Adapter Magnification (if applicable)
  • Camera Sensor Size (in mm, e.g., 1/2″ = 8.00 mm diagonal)
  • Screen Size (in mm, e.g., 19″ = 482.6 mm)
• Calculations:
  1. Optical Magnification:
     • Optical Magnification = Objective Lens Magnification × C-Mount Adapter Magnification (if used)
     • Example: Objective = 4X, C-Mount Adapter = 0.5X; Optical Magnification = 4X × 0.5X = 2X
  2. Digital Magnification:
     • Digital Magnification = Screen Size / Sensor Size
     • Example: Screen Size = 482.6 mm, Sensor Size = 8.00 mm; Digital Magnification = 482.6 mm / 8.00 mm = 60.325X
  3. Total On-Screen Magnification:
     • Total On-Screen Magnification = Optical Magnification × Digital Magnification
     • Example: Optical Magnification = 2X, Digital Magnification = 60.325X; Total On-Screen Magnification = 2X × 60.325X = 120.65X
• Actual Size of Specimen Calculation (if total on-screen magnification and measured size on screen are known):
  • Follows the same principle as for light microscopy images.

3. Electron Micrographs (Scanning and Transmission)

• Given (typically provided with the micrograph or in the publication):
  • Scale Bar with Actual Length
  • Magnification (may be directly provided, especially in publications)
• Calculations:
  • If Magnification is Provided:
    • Use the same approach as for light microscopy to find the actual size if needed.
  • If Only Scale Bar is Provided:
    • Measure the scale bar length on the print/image (in mm, cm, etc.)
    • Actual Size of Specimen Feature = (Measured Size on Image) × (Actual Length per Scale Bar Unit)
    • Example (hypothetical): Measured Size on Image = 5 cm, Scale Bar = 1 cm = 1 μm; Actual Size = 5 cm × (1 μm / 1 cm) = 5 μm

Applying These Steps to Your Specific Case

1. Identify the Type of Micrograph: Determine if it’s from a light microscope, digital microscope, scanning electron microscope (SEM), or transmission electron microscope (TEM).
2. Gather Provided Information: Look for magnifications, scale bars with actual lengths, objective lens magnifications, eyepiece magnifications, sensor sizes (for digital microscopes), and screen sizes (for on-screen calculations).
3. Apply the Relevant Calculations: Use the formulas outlined above based on the type of micrograph and the information provided to calculate the total magnification and/or the actual size of the specimen or its features.