Some questions after opening the scope boxs

[len]

Hi,
I recently purchased a microscope from AmScope (model B390A) and have some newbie questions.
1. I have 4 objectives, 4x and 10x show sharp image but 40x(S) and 100x(S,Oil) are very blurry, I guess that I need to use oil with the 100x(S,Oil) but why does the 40x(S) looks bad?
2. In photo (item #1) how do I use those color filters and when should I use them?
3. I received a small mirror (item #4) I guess that since I have an electric light I don't need to use it?
4. If I want to watch a non transparent object such insect head how do I illuminate it from above, Does that mean darkfield?

[Olympusman]

The 100x objective will require immersion oil.
The 40X may not be as sharp because you may have to adjust the condenser for Kohler illumination.
The blue filter is an 80B and was usually used to color correct the halogen lightsource for daylight film when shooting with a film camera.
The green filter is used to shoot black and white images with cheap achromat objectives, which yield better sharpness with green light.

[Olympusman]

To shoot non-transparent objects you will probably have to purchase a fiber optic light source. Because of the close working distance of microscope objectives, it is difficult to get light under the objective. You might also try half of a ping pong ball as a diffuser dome with a high intensity lamp or LED flashlight.

[Pau]

Just to add some points to the former posts:

- The 40X (40 0.65 160/0.17 I suppose) can only be used with glass covered microscope slides : 0.17 refers to the standard coverglass thickness, so this kind of optics are not adequate for other subjects than traditional microscope slides. Otherwise it will deliver very poor image due to spherical aberration. And as Olympusman says the right use of the condenser is very important to get a good image. (this kind of microscopes usually don't allow Köhler illumination but critical one, but this isn't very important to begin)
- The 10X and 4X can be used with or without coverglass despite being marked 160/0.17 or 160/- because of its lower NA they are not really sensible to coverglass thickness. And because they have longer working distance they may be adequate for opaque specimens with incident light. Some LED lamps (like Ikea Jänsjo) would do the job. Darkfield is very different technique.

- For halogen illumination I recommend to use the blue filter all the time: it is much more pleasant and also may improve just a little bit the resolution.

- As you guessed the mirror is for external illumination like sunlight or lamp, usually not very practical if you have electricity at home.

- Your scope seems a chinese copy of the Olympus CH, not a bad thing. I have a lot of similar ones at work and they are not great but fairly useful and resistent.

[len]

Thanks for the help.
My primary usage is for examining insects so unless watching dissected parts it's a bit of a problem to cover them with glass

Objectives 10x0.25 vs 40x0.65 (No glass cover, condenser adjusted, photo by cellular phone)


After a some reading I understand that my condenser is 1.25 N.A. and should be higher than my objective N.A. but the slides themself should be added to the objective N.A. value?
I tried to use another slide glass as a cover but found it's two thick for the 40X working distance (0.632mm) so I'll get a proper cover and try again later.

Pau, I was wondering about your suggestion to use external light, doesn't I need a condenser to illuminate the object how can I use normal LED lamps?

[Olympusman]

As Pau said, you need to use cover slips because they are part of the optical path. You cannot use a another slide as a cover slip because it is too thick and the working distance with high magnification objectives is far too close to use something as thick as a slide. As`Pau said, the lower power objectives are far more forgiving. Also bear in mind, that if you are viewing a drop of water with no cover slip, you are adding another plano/convex lens to the optical path and optically everything will go to hell. It's like putting another condenser on top of your slide.
All objectives that require cover slips have the thickness noted on the barrel. As I myself and many others have found, that when your put a micrometer or digital caliper on the cover slips you have, the thicknesses may be all over the place or you may have a mix of objectives that require different thicknesses. Charlie Krebs recently had a resource for consistently high quality cover slips for a reasonable price.
As for illuminating opaque objects, even with the dual gooseneck fiber optic illuminator I have, getting light under an objective higher than 20x is pretty much impossible without axial illumination, which your scope does not provide.