Microscope Objectives: Achromat vs. Plan Achromat

Microscope objectives are corrected for field curvature and color aberration. The difference between an Achromat and a Plan Achromat microscope objective lens is the degree of the flatness of field.  Because an achromat microscope objective does not have a correction for the curvature of the lens, the very outer edges of the circular image you view through the microscope will be just slightly out of focus.

In a Plan Achromat microscope objective lens, this curvature of lens has been corrected and should result in a crisp clear in-focus image from one side of the circular image to the other.

We decided to test out the National Optical model 162 biological microscope, which can be purchased with either Achromat or Plan Achromat lenses.

This is a pine needle cross section as seen with the Achromat objectives from the National 162 microscope.

This is the same pine needle cross section, using the Plan Achromat objectives from the National 162 microscope.

When looking at the two images, it is a bit hard to recognize a large difference between the Achromat and Plan Achromat lenses. On this particular model of microscope (a high school microscope), our recommendation would be to save money and simply purchase the Achromat lenses. 

Some of the higher end microscope models have a more distinct difference between the Achromat and Plan Achromat objectives.  Especially when using 1000x magnification and looking for micron size particles, the Plan Achromat objectives are preferred and reveal a superior image over the Achromat lenses.

Plan Achromat lenses have an image that is in focus from the center towards its edges and the field is said to be "flat".  In general, the flatter the field of an objective, the more lenses it contains and the more expensive the cost.

Trachea under the Microscope

The trachea is a tube inside the human body that connects the larynx (voice box) with the lungs, allowing passage of air. A trachea is also referred to as a windpipe. The trachea is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus. Mucus lines the cells of the trachea so that it can trap inhaled foreign particles that the cilia then waft upward toward the larynx and finally the pharynx where it can be either swallowed into the stomach or expelled as phlegm.

There are about fifteen to twenty incomplete C-shaped rings made of cartilage that reinforce the anterior and lateral sides of the trachea to protect and maintain the airway. The trachealis muscle connects the ends of the incomplete rings and contracts during coughing, reducing the size of the lumen of the trachea to increase the air flow rate.

Illustration courtesy of Lord Akryl, NIH Cancer.gov.

Trachea captured with a FITC filter using the MT6200H Epi Fluorescent microscope.

 

 

Trachea captured with a TRITC filter using the MT6200H Epi Fluorescent microscope.

DIN Standard Microscope Objective Lenses

"DIN" is an abbreviation of "Deutsche Industrial Normen."   This is a German standard that has been adopted internationally as an optical standard used in most quality microscopes.  The focal tube length of a DIN standard microscope objective is 160mm. A typical DIN standard microscope objective lens has 0.7965" (20.1mm) diameter threads, 36 TPI (threads per inch), and 55° whitworth.

The former standard was RMS ("Royal Microscope Society"), which had a longer tube length (170mm).  Most DIN optics are interchangeable. However, DIN and RMS objectives are not interchangeable. If you have RMS objectives and want to use them on a DIN objective nosepiece you would need to use an adapter, and even with this adapter the microscope would not be parfocaled. You can learn more about how to parfocal microscope objectives here.

50x Oil Objectives

Oil immersion is typically used with the 100x objective lens. However, there are times when using a 50x oil immersion objective lens is helpful. A problem that many users often encounter, is keeping their 40x dry objective from getting oil on it when switching back and forth between the 100x lens and the 40x objective lens. A simple way to solve this problem - and one that is used in many clinical laboratories - is to mount the "dry" 40x objective lens on the opposite side of the nosepiece from the 100x oil immersion objective. This mounting arrangement reduces the likelihood of inadvertently dipping of the 40x "dry" objective into the immersion oil.

40x Dry Microscope Objective Lens

An alternative to avoiding accidentally dipping the 40x dry objective lens into the immersion oil, is to purchase a 50x oil immersion lens. The 50x oil immersion objective will produce better quality, brighter images than the 40x dry lens does. The disadvantages to purchasing a 50x oil immersion objective lens are that this lens is more expensive than the 40x dry lens, and a 50x oil immersion lens is difficult to use with a haemocytometer because the oil can adhere and inadvertently lift off the coverslip.

Tilia Under a Fluorescent Microscope

Tilia is a genus of thirty species of trees native throughout most of the northern hemisphere. Tilia species are large, deciduous trees reaching 65-130 feet tall.

Tilia Tomentosa, Morton Arboretum (Chicago), photo Bruce Marlin.

The Tilia's trunk is sturdy and stands like a pillar, as the branches divide and subdivide into numerous branches with thick twigs attached. 

Tilia Leaf - photo Roger Griffith.

The leaves of Tilia are heart-shaped and most are asymmetrical. Aphids are often attracted to the rich supply of sap.

This cross-section of Tilia was captured using the MT6200 epi-fluorescence microscope and the ProgRes Speed XT5 microscope camera. The fluorescence image was captured using a TRITC filter.

Larynx under the Microscope

The larynx (also known as the voice box) is an organ located in the neck of amphibians, mammals and reptiles. The larynx is involved in breathing, sound production and protecting the trachea against food aspiration. The larynx houses vocal folds.

Diagram of larynx courtesy of Olek Remesz.

 

Larynx captured at 100x magnification under a biological microscope.

Larynx captured at 400x magnification using a CCD microscope digital camera.

Weevil

A weevil is a beetle that is small in size (usually 6mm or less). Many weevils damage crops including cotton and wheat. In an unfortunate case, if you have some old flour in the pantry, weevils may have invaded it and you may have been introduced to this insect in an unplanned case of having to retrieve new flour from the store.

Weevil captured with a biological microscope using the MW5.1 CCD microscope camera.

Weevil image courtesy of Joaquim Alves Gaspar

Examining Stomates Science Project

Stomates are tiny openings (or pores) in plants that are used for gas exchange. Plants require both water and carbon dioxide for photosynthesis. The challenge for a plant is to conserve water while permitting carbon dioxide to enter the leaf where photosynthesis will occur. Stomates are the adaptation that permits carbon dioxide to enter the leaf while allowing most of the leaf to be covered with a waxy cuticle that will conserve water.

For this project you will need to use a stereo microscope and/or a compound microscope along with a Zebrina plant. A Zebrina plant can be obtained from an garden store and the great part is - once you use it for the science project the plant should live all year in a classroom or home.

Zebrina plant photo courtesy of Ruestz.

Take a single leaf from a Zebrina plant (these plants work well because they have purple pigment in the leaves) and place it under your stereo dissecting microscope. Older leaves will have the best stomates on them. Place the leaf so the bottom side faces up. What do you see under the microscope? The stomates should be visible in green patches. They stand out against the purple background of the leaf. As you slowly increase magnification notice the details in the stomates. Why do you suppose the stomates are located on the underneath of the leaf?

Stoma captured under a high power microscope by Peter Halasz.

Next use the compound high power microscope to examine the Zebrina leaf. Start at the lowest magnification and make sure the underside of the leaf is facing the objective lenses. Do you notice that each stomate is surrounded by two long, thin guard cells? These guard cells can either open or close the stomate, depending on the availability of water.

Draw a diagram of the stomates you view and label both the stomates and the guard cells. Once you have seen stomates in the Zebrina plant, try locating them on the underside of other plants. It can be more difficult to view stomates in plants that do not have a purple background, but with a bit of practice you will be able to locate them.

Teachers and parents - if you would like a copy of this Examining Stomates lesson plan you can download it for free here.

Ken-A-Vision PupilCam

The PupilCam is a fairly inexpensive way to adapter your microscope to either a computer, TV monitor, or multimedia projector. Ken-A-Vision makes two types of PupilCam cameras - one with a rubber eyepiece adapter that fits securely over the existing microscope eyepiece, or one that includes a built-in 10x eyepiece that will replace your existing microscope eyepiece.

PupilCam 1400 series USB digital microscope cameras.

PupilCam 1400 series video cameras.

 Connecting the PupilCam to an existing microscope is easy.