A microscope game
PARFOCAL
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For the best experience, please use a PC browser
Parfocal is built for a big eyepiece and a real focus knob, turned with a mouse or keyboard. On a phone the controls crowd the view and fine focus is hard to control.
Open parfocal.vercel.app on a laptop or desktop for the full game
A daily microscope game · focus is everything
↑↓ choose · Enter open · QE microscope · Esc back
10x locked
GREAT JOB!!
↑↓ focus · Shift coarse · ←→ stig X · Shift+←→ stig Y
−+ mag · 1–4 scan · R reduced · A ABC · Enter photo
On the image: drag ↔ to focus, Shift-drag to stigmate, scroll to zoom
Brightfield
1000 points if you're right now
Specimen 1 of 5
It sharpens as you wait. Answer early for more points. 1–4
Daily identify
Today's slide
What was on the slide
An objective collects a cone of light from each point of the specimen. Its half-angle θ is set by the numerical aperture, NA = n sin θ. A wider cone resolves finer detail but squeezes the depth of field, which is why 100x is so twitchy.
At 100x even a slow 10° nudge of coarse moves about 15 times the depth of field, and a fast spin drives the lens into the slide.
Focus carries over when you swing objectives, so 40x and 100x need only a small turn of fine focus.
The front lens has to sit in the oil. Without it the usable NA drops to about 0.95 and the image stays dim and soft.
The top of the coverslip sits 170 µm above the smear. Specks up there come into focus first.
Depth of field is the range where the image already looks sharp. So you're scored on the blur you can actually see on screen: a few microns off at 10x is invisible and costs nothing, while a quarter-micron at 100x shows and counts.
A smear isn't flat: cells sit at slightly different heights, and thick patches can't all be sharp at once. Each field is measured against the sharpest plane it allows, and the verdict draws that curve with where you locked.
