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Since there's only a very small amount of light reaching the lens system of microscopes when on high powers, A special technique (called >>>oil immersion
Not using this technique must be the cause of the problem you are experiencing.
eHow will guide you through the exact procedure of using the oil immersion technique: http://www.ehow.com/how_8431358_focus-high-power-objective-microscope.html
Good luck in exploring the micro world!
most objectives and eyepieces are interchangeable between models of microscropes. There are however a few things that you need to be aware of. On the out side of the objective there are number written on them that look similiar to this:
There maybe more writing then that, but usually at the very least you get this. The first part (100x) is the objective magnification, the 1.25 is the Numerical aperture, the 160 is the tube length (in mm), and the .17 is the cover-slip correctness. What you are most concerned with is the mechanical tube length. There are 3 common ones, 160, 210, and infinity. It is very important that you get an objective with the right tube mechanical tube length, or there is a very good chance it won't work. If you are working with slides, then it is a good idea to get one that is cover slip corrected, otherwise most of the other information is only real important to very specific applications.The other key variable is the threading. Most microscopes use what is call a standard RMS threading, however many educational or high end objectives will not have this.
The eyepieces are pretty straight forward. You just need to find one that that has an outside diameter of the sleeve that will fit the inside diameter of the tube it is going into. Beyond that, most eyepieces are pretty interchangeable amongst brands.
There is probably oil on the outside of the object. You can try cleaning it off with some alcohol and a que-tip. If that doesn't work, the seal of the objective has probably failed and oil has seeped up inside. Otherwise the other problem that can cause it is to many small scratches to the outer lens of the objective. This can happen when the objective lens crashes through a slide.
One thing you can do to protect your objective from this happening, is that most microscopes have some sort of up stop lock, which is designed to prevent the stage from coming past a certain point. On your model, this is most likely a screw that sits just behind the stage.
If the cleaning doesn't work, the usually replacing it is the most economical option. This model has a pretty standard object type, so any object that has a 160mm tube length and has standard RMS threading should work with it just fine.
Since you need to use oil at 100x, there is probably a good chance that there is oil on both the 100x and 40x objective. I see this a lot in my work. Since the working distance of the 40x is so close to the slide, what often times will happen is that it will accidentally get dragged through the oil while rotating to lower magnifications. The 100x is sealed to protect it against the oil, but the 40x is not, and if the oil sits on the objective for any length of time, the objective will act like a wick of a candle and **** the oil up inside of it. At that point it is more economical to buy a new object. The same thing can happen with the 100x, but it takes much longer for it to happen. Basically the seal around the objective tip is just latex chalking, and the oil will break it down over time, thereby causing the same affect as with the 40x.
You can try to clean them. If you are lucky the oil is only on the outside surface of the objective. Try using a que-tip and isophrapoyl alcohol to clean it off.
Unfortunately, if you indeed have water or oil inside the lens it is probably ruined. Obviously the seals have deteriorated away. Objectives are practically irreparable. They cannot be disassembled. Very reasonable new and used Replacements are available at:
Delta Optical Instruments, Inc.
Inquire at: firstname.lastname@example.org
There are two reasons. One reason is that when on high power you are working so close to the glass slide that it is easy to misjudge how much you are moving the specimen toward the lens that you can break a slide before you realize it. The coarse focus moves the stage with the specimen on it very fast and you only have a very very short distance within the focus plane before you run the objective lens into the slide.
Secondly, it is just harder to control the minute adjustments needed at the higher powers with the "coarse" focus knob. If you start at the low magnifications find what you want to concentrate on with the coarse focus knobs and then work your way up to the higher powers, you will have very little trouble moving to the fine focus controls at 40x and 100x while still having control of your image.
There is what is called a "stage stop" screw.
Its purpose is to limit the specimen from rising high enough to contact the objective lens.
The "stage stop" screw is directly behind the black stage platform in plain sight and very easy to access. It is a thumb screw and sits vertically. Simply loosen it a bit to allow the specimen to rise high enough to focus.
If your stage is still in its correct orientation then make sure your objective lenses are screwed in tight as well as the eye piece being secured correctly. Try using different objectives (don't go too high or you may damage your lenses if you ram it into your specimen) and using the fine and course focus. If the you still cant focus using different objectives it's quite possible that your mirrors or lenses inside the microscope have been knocked loose. I would then recommend only having it repaired by a certified microscope technician. If it is still under warranty take it back to the store of purchase or send it back to the manufacturer.
Seing bacteria isn't just about magnification, many
are transparent and need to be stained. Even at X1000, you will see little detail, but can make approximations of shape etc. Here is a good starting point for staining bacteria.
With a toothpick scrape a little plaque from your teeth (size of a pinhead is plenty). Put this in the centre of a slide with 1 drop of water and mix thoroughly. Allow this to dry then pass the sample through a flame three or four times (hot, but not hot enough to burn fingers) Stain for five mins using either Methylene Blue or Eosin. If you don’t have these, Blue or Red fountain pen ink will do for starters. Rinse off excess stain with very slow running water. Blot dry and observe at X400. If you have an oil immersion lens, you must use a cover slip and mount your specimen in balsam first.
If I can be of any further help, please don’t hesitate to ask.