Reticles

Reticle Nomenclature and Distinctions

• We only supply “NiChrome-On-Glass” designs, due to sharpness, contrast, and durability.
• We distinguish between “Top-Reading” and “Bottom-Reading” versions. This has always made more sense to us, in that, the alpha and/or numerics “read” correctly when referring to the surface on which the “etch & fill” material is placed.  As such, the reticle labeling reads correctly for a “bottom-reading” version when the disc is viewed from above and the lower surface has the deposited pattern.
• The field stop of an ocular defines the field of view limits. As such, it should always be in sharp focus when viewing through the ocular.  Further, the field stop is the least inner diameter of the eyepiece.  For “positive” designs, the field stop is ordinarily located outside (below) the lens components.  Should the eyepiece design be “negative”, the field stop will be found within the lens components, ordinarily between the eye lens and the field lens.
• Since the intermediate, real image from the microscope is to be projected exactly at the plane of the ocular field stop, it’s imperative the correct version of reticle be chosen and, further, placed correctly:
  • Most field stop designs project inward from the ocular wall, with the beveled edge indicating the field edge.
  • If the bevel is upward, a “bottom-reading” design is placed on top of the field stop.
  • If the bevel is downward, a “top-reading” design is placed on the underside of the field stop.
• There are different mounting approaches available. Some are with reticle “carriers” which hold the reticle onto a shoulder and then screwed into place, against a field stop (ordinarily, this would be a “top-reading” design from below.  Note: Occasionally, this carrier also serves as a field stop.  In that case, it would call for a “bottom-reading” design, seated on top of the carrier’s shoulder, with the carrier then screwed into place.
• All of the above ensures that the pattern is simultaneously in sharp focus with the intermediate image. Focusing eyepieces can assist with needed correction for eyesight, but should not be used to bring into focus an incorrectly placed reticle.  Doing so, would generate loss of parfocality among the objective suite.

Steps for Purchasing the Correct Reticle

1. Determine the pattern needed – i.e., measuring, sizing, counting, alignment, etc.
2. Determine the style of eyepiece (“positive” or “negative”) for locating the field stop
3. If there’s no reticle carrier, measure the inside diameter of the barrel using a metric caliper. Should there be a reticle carrier, measure the I.D. of the shelf where the reticle is to rest.  Note: Graticules, Ltd. in the United Kingdom provides numerous reticle size matches for different manufacturers and eyepiece models.  This information can be found at:  https://www.graticulesoptics.com/technical/reticle-size-match
4. Next, determine if the reticle location calls for a “top-reading” or “bottom-reading” design, based on the previous information. The following diagram should assist with this process: