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My microscope has a filter wheel. How is it used?

Filters are used to increase contrast and color correction for visual observations of specimens or slides. They may be used with live specimens as a non-lethal substitute for staining.

Blue is commonly used to correct yellowish or reddish color from incandescent bulbs in illuminators. Other filter colors (green, yellow, magenta, frosted) should be tried with specimens to see if they improve contrast and visibility. Simply turn the wheel to put the filter you need into the path of light from your condenser-illuminator.
What is the difference between achromatic, semi-plan and plan objectives?

Most microscope objectives come in three basic designs: achromatic, semi-plan and plan.

An achromatic objective corrects for color and has a flat field across the central 65% of the image. It’s usually a pair of lenses.

Semi-plan (semi-planar, sometimes called micro-plan) objectives have an 80% flat field. They can either be two lens element achromats or three or more element apochromats.

A plan (or planar) objective corrects better for color and spherical aberration than either the semi-plan or the achromatic objective. Plan objectives have a flat field about the center 95% of the image. They also often have larger working distances. While plan objectives give you flatter fields than achromatic objectives, they also are the most expensive.
What’s the resolution of a microscope? Is this related to numerical aperture?

A microscope’s resolution is its ability to form separate images of lines or dots. It’s defined in terms of the actual distance between the detail on the object. The wave nature of light puts a practical and theoretical limit on the resolution of a white-light microscope as about half a wavelength of visible light, about 250 nanometers or a quarter-micron. This also limits the highest useful magnifications to the range of 1000x-2000x. Resolution depends solely on the objective lens, as the eyepiece just magnifies light from the objective.

The numerical aperture of a microscope lens is a measure of the increase in resolution due to the lens being able to gather a wider cone of light from the specimen. This depends on how close the lens is to the specimen and also if oil or another fluid is used between the lens and the specimen.  Both increase the numerical aperture and the microscope’s resolving power.

Numerical aperture is higher for higher-power objectives because they are used very close to the specimen. Its value for the objective is usually engraved on the barrel and runs between 0.04 for very low-power objectives and 1.4 for very high-power objectives. A typical 40x objective that will be used at 400x with a typical 10x eyepiece has a numerical aperture of 0.65.

A condenser’s numerical aperture should equal or exceed that of the objective lens to effectively illuminate the specimen. Higher powers will need condensers with higher numerical apertures, meaning the condenser lens is closer to the specimen. Condensers with numerical apertures of 1.2 are typical for objectives delivering magnifications of 400x.
Microscopes
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Which are the main features of a microscope?

Before buying a microscope, it's important to keep in mind the following characteristics:
- MAGNIFICATION: the product of eyepiece magnification and lens magnification gives the total magnification power. An increased magnification decreases the field of vision.
- ILLUMINATION: it may be either incident light, meaning from below and particularly useful in a biological microscope, or transmitted light, meaning from above and for a stereoscopic microscope. Some stereoscopic models have both types of illumination.
 
Which are the optional accessories recommended for a microscope?

According to client's needs, in order to increase or decrease the magnification provided, it could be necessary to purchase extra eyepieces and/or lenses.
In a biological microscope, when it isn't included, a small transport table (a square-shaped instrument that allows microscopic movements of the glass plate) and a light to provide the necessary lighting in the observation of the prepared slides, could be useful.
A special graduated micrometric eyepiece could also be useful, in order to measure exactly the dimensions of the prepared slides
 
Can a camera be connected to a microscope?

Yes, but two adapters are necessary: the photo adapter for a given microscope and the T-2 ring for the type of reflex. On a binocular microscope the camera is connected to one of the two eyepieces.
 
Is it always necessary to prepare the items for the observation at the microscope ?  

Using a stereoscopic microscope, whatever is viewed doesn't need preparation. Instead, using a biological microscope, it's necessary to make accurate preparations. The sample must be cut very thin and it must be placed on a glass slide. It could seem a rather complicated process, so if you don't want to do it yourself, Konus has in stock more than 20 series of prepared slides with interesting biological subjects.
 
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Blank Microscope Slides (72 pieces)Blank Microscope Slides (72 pieces)
Concave Blank Microscope Slides (50 pieces)Concave Blank Microscope Slides (50 pieces)
Miroscope Cover Slips (100 pieces)Miroscope Cover Slips (100 pieces)

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