What Is The Difference Between Achromatic Semi Plan And Plan Objectives

What is the difference between achromatic, semi-plan, and plan objectives?

Are you planning to purchase a microscope? But the wide variety and featured overwhelm you?

It is easy to make the wrong purchase on an unsuitable microscope type. Knowledge of the different kinds of microscope components will help make you are not so microscopic investment fruitful.

The most functional unit of a microscope’s system is its objective. We will elaborate on the different types of objectives in this section.

What is the importance of an objective in a microscope?

The quality and how clear the specimen’s final image are, largely depends on the microscope’s objective. It is the closest element to the specimen in the microscopy.

The objective of your microscope’s lens is what gathers the incoming light rays. When focused, these light rays produce the real image that you see through your eyepiece.

The complexity of your microscope’s objective lens makes it essential to understand their manufacturing process. Most objective lenses have a multi-elemental design.

An objective lens can be primarily differentiated based on its quality and design. The lens has several functions.

The function of an objective lens includes preliminary image formation, image quality, magnification, and resolution. To choose the best type of objective, it is essential to understand the difference.

The three basic types of microscope objectives

The quality of an objective lens cannot be stressed enough for accurate microscopy. This lens encompasses a peculiar phenomenon called the superposition of lens.

The superposition of lens in an objective is responsible for reducing the aberrations to a bare minimum. The lens can be divided into semi-plan, plan, and achromatic types.

The semi plan objective lens

The rated field of view for a semi-plan objective is 80 percent. These lenses are also called micro plan objectives.

There can be two achromats or three apochromatic elements in a semi-plan lens. These lenses do not produce high-quality images.

This is one of the crucial reasons why they are avoided for microscopy. For specimens such as in urology, some intricate details can go missing if you use semi-plan objectives.

The Plan Objectives

The plan objectives have a greater number of stacked or superimposed lens. The higher the stack of lenses, the better the image quality.

It is for this reason; a plan objective can offer a clear image on the entire surface. Irrespective of the type of specimen, you are sure to better image quality with these objectives.

You will appreciate the uniformity in the overall image, which is also sharp around the edges. However, some experts might avoid the lens due to the increase in contrast after employing it.

The plan objectives do give you a better field of view for your image. They are also pricier because of this property.

The Achromatic objective

As the name suggests, an achromatic objective is designed for colour correction. They correct the spherical aberrations.

Such objectives are considered the ideal choice for viewing black and white specimens under the microscope. If your objective does not have a label, it is more likely the Achromatic type.

These objectives offer a flat field of view of 65 percent. This simply entails that your image will have fewer aberrations.

The optical aberrations in microscopy

The error caused due to physical limitations in an objective lens is a common problem. There are two basic types of least ideal lens outputs- the spherical and the chromatic aberrations.

These aberrations are naturally the discrepancies caused while observing under a microscope. Modern manufacturing techniques do help reduce these inconsistencies. But we have a long way to go for perfection.

Spherical aberrations

These conditions occur when the light rays passing through the edges of the lens are not focused. The beams in the centre of the objective lens are refracted the least.

The waves passing at the edges experience a higher degree of refraction. This is one of the more critical issues. The seriousness of the condition occurs because the specimen is somewhat expanded and not in focus.

The resolution of a lens makes spherical aberrations a critical phenomenon. You can reduce the exposure of the lens edges to light. This will help reduce the aberrations to a minimum.

Chromatic aberrations

Chromatic aberrations are due to the multiple wavelength property of white light. When light rays travel through a convex lens, different wavelengths get refracted.

The refraction is subject to the frequency of each wavelength. The blue light refracts the most, followed by a green and red light.

Chromatic aberration is a classic inconsistency in an objective lens. This is better explained through the lens makes formula.


  1. Olympus Life Science
  2. Celestron
  3. WPI Inc
  4. Microscopyu
  5. Long Way Yueping