Clean immersion oil off the objective
The materials list puts lens wipes next to the oil for a reason. Learn which objective the oil is for, what a paper towel does to a coated lens, and why oil left overnight is a different problem.
- Only one objective is built for oil: The 100x objective is made to work with its front lens in oil. The others are not, and they are not made to be cleaned of it either.
- A lens surface is coated and soft: Objective lenses carry thin coatings. Anything abrasive drawn across one leaves marks that stay in every image the instrument makes afterwards.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Now handle the two mistakes that cost a microscope rather than a slide.
A student finishes at 100x under oil and rotates the 40x objective round for another look. What is wrong with that?
Reviewed- A.The slide will be pushed out of position by the larger lens
- B.The 40x gives a lower magnification, so it is a waste of time
- C.Nothing at all, since the 40x objective simply will not focus through oil anyway
- D.The dry objective is dragged through oil it was never built for
Show the worked solution ▾
Answer: D. The dry objective is dragged through oil it was never built for
- Step 1: Ask what the turret does: Swings the next objective across the same spot the last one was in.
- Step 2: Ask what is sitting in that spot: The oil you just put there.
Why it's right: Turning the turret sweeps the next lens through whatever is on the slide, and right now that is oil. The dry objective picks it up, and it is not a lens built to be cleaned of oil.
- A: The objective does not push the slide about. What it does is collect the oil that is lying there.
- B: Going back to lower power is a normal thing to want, and the problem is the route the lens takes rather than the magnification it gives.
- C: Whether it focuses is beside the point. The damage happens on the way past, before anybody looks through it.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
There are no lens wipes left at your station. Which of these is an acceptable substitute?
Reviewed- A.The corner of your shirt, which is softer than paper
- B.A folded paper towel, so long as a clean part of it is what touches the glass
- C.None of them, so tell your teacher rather than improvise on a coated lens
- D.A tissue from your bag, used gently
Show the worked solution ▾
Answer: C. None of them, so tell your teacher rather than improvise on a coated lens
- Step 1: Ask what they have in common: All three are made of fibres coarse enough to mark a coated lens.
- Step 2: Ask what a scratch costs: Every image that microscope makes from now on.
Why it's right: Clean is not the same as safe here. All three substitutes are abrasive at the scale of a lens coating, and a mark left on an objective stays in every image the instrument produces afterwards.
- A: Fabric feels soft to a hand and carries grit and thread ends that a lens coating cannot survive.
- B: A clean paper towel is still wood fibre, and gentleness does not change what it is made of.
- D: A tissue is designed for skin, not optics, and the same fibre problem applies however carefully it is used.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
- A student lifts the slide straight down and away rather than rotating the turret with oil in place.
Fill these in as you work through the lesson.
- Immersion oil (sits between slide and the 100x lens):
- Objective (the lens closest to the slide):
- Lens wipes (the only thing that touches a lens):
- Abrasive (what a paper towel is, at this scale):
Immersion oil is for the objective only. Clean it off with before the microscope goes away, because oil left on a lens collects and thickens. Never swing a objective through the oil.
- Say why the lens wipes appear in the materials list.
- Explain what happens if the 40x is rotated through the oil.
- Describe why a paper towel is not a substitute.
You finish with the 100x, lift the slide away, and wipe the front of the objective with a lens wipe until it is dry. The scope goes back with a clean lens, so the next student's first view is sharp.