What is the difference between Achromatic, Semi-Plan and Plan objectives?

Microscope objectives come in many different designs. Three of the most common are achromatic, semi-plan and plan. In an achromatic objective, which is the most common type, there is one achromatic lens. Achromatic objectives correct for color and have a flat field in about the center 65% of the image. This is not to say that the outer 35% of the image will be blurry- this just means that if there are aberrations, they occur in the outer 35% of the image. A semi-plan, or semi-planar objective, is an intermediate between the achromatic and the plan objective. Semi-plan (sometimes called micro-plan as well) objectives have an 80% flat field. 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. While plan objectives give you flatter fields than achromatic objectives, they also have a higher price.

What is the difference between Huygenian, Wide Field, and Periplan eyepieces?

Eyepieces for both microscopes and telescopes come in varying optical designs. The major differences between the three microscope eyepiece designs we carry is listed below:

• Huygenian eyepieces consist of two plano-convex lenses placed with both convex faces towards the object. Designed for use with low power achromatic microscope objectives, Huygenian eyepieces tend to have an average eye-relief and are very economical.
• Wide Field microscope eyepieces consist of one achromatic doublet and one plano-convex lens with the convex side facing the doublet. Ideal for high power achromatic microscope objectives, wide field eyepieces have a long eye relief and are moderately priced.
• Periplan eyepieces consist of three lenses: one achromatic doublet and two plano-convex lenses with the convex lenses facing each other just below the doublet. Best used with plan and semi-plan microscope objectives, periplan eyepieces have an average eye relief and tend to be more expensive than either huygenian or wide-field eyepieces.