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How to build the finite microscope

Task-oriented. You want the classical ("160 mm tube") microscope with the real 4× objective and proper gear focusing.

The 4× objective is a finite-corrected objective: it forms a real intermediate image at a fixed distance (160 mm mechanical tube length, printed on the barrel) which the eyepiece then magnifies.

Magnification: M=Mobjective⋅Meyepiece=4⋅250 mmfeyepieceM = M_\text{objective} \cdot M_\text{eyepiece} = 4 \cdot \frac{250\,\text{mm}}{f_\text{eyepiece}}

✏️ TODO — Benedict

Insert the focal length / magnification of the Ramsden eyepiece shipped in the CoreBox (e.g. "10×, f = 25 mm" → total 40×). The old docs never state it.

The finite microscope in action.

What you need​

  • Z-stage cube with the 4× objective screwed in
  • Sample holder cube + sample
  • 50 mm lens cube, insert rotated 90°, or the Ramsden eyepiece cube (viewing from above)
  • 1× 45° mirror cube
  • 2–3× empty cubes
  • 10–12× puzzle base plates
  • Torch with holder

Parts and base-plate layout.

The plan (side view)​

Sample → 4× objective (on Z-stage) → empty cubes create the 160 mm tube → mirror → eyepiece.

Steps​

  1. Click 5 base plates in a row; put the sample holder at the front.

  2. Assemble the objective cube: thread the 4× objective into the Z-stage insert and close the cube around it.

    Which of the two RMS threads?

    The Z-stage has two threaded positions offset by 5 mm. If a puzzle plate sits between the Z-stage cube and the neighbouring cube, use the thread closer to the edge; without a plate, the inner one.

  3. Place the objective cube next to the sample, then 2–3 empty cubes (they form the tube), and at the end the 45° mirror cube, mirror face up.

  4. Lock the row with base plates on top.

  5. Put the eyepiece on top of the mirror cube — mind its orientation (wide lens down).

  6. Illuminate the sample with the torch from some distance, look into the eyepiece, and focus by turning the Z-stage gear. For coarse adjustment, slide the objective in its holder or move the sample slide.

Focused result through the eyepiece.

What you should notice​

  • Higher magnification, smaller field of view than the infinity build — 4× objective instead of 2×.
  • Distance is not optional here: unlike the infinity design, the tube length is fixed at 160 mm. Shorten or stretch it and the image degrades — that's the fundamental difference between the two architectures, explained in How a microscope works.
  • The numbers on the objective barrel (4x / 0.1, 160/0.17) all mean something: see Parts and parameters.