Guide to Pressroom
Optics, Microscopes, and Magnifiers
National Offset Warehouse offers the most diversified line
of magnifiers and microscopes for the graphic arts and printing professional.
The optics presented are industry benchmarked for
excellence. National Offset Warehouse optics are the
highest quality obtainable. Many
feature achromatic and color corrected lenses as well as flat fields to reduce
Listed below is some helpful technical information about optics. Use this guide in addition to the
magnifier Recommendation Chart, located below, to help you choose the correct
magnifier for your needs.
Types of Lenses
Positive Lens - A single piece of optical glass or acrylic with two convex
surfaces (curved outward). Designed for low magnification.
Negative Lens - A single piece of optical glass or acrylic with two concave
surfaces (curved inward) used in conjunction with positive lenses.
Lens - A positive simple lens cemented to a negative simple lens. Achromatic lenses are corrected for two
colors and produce flatter fields of view at higher powers.
Lens - Two simple lenses used as a system but not cemented together. This system produces a far superior
image than a simple lens.
- The number of times a lens or lenses multiplies an image with respect to the
original size. Low power is
recommended for scanning large surfaces. Higher powers are generally used for inspecting small areas.
of View - The maximum area seen through a magnifier. The entire field of view may not be in
focus. See Flatness of Field.
of Field - Due to the physical laws of optics, the outer part of the image
formed by a lens may be out of focus. The greater the power and curvature of the lens, the more pronounced
this problem becomes. Magnifiers
with multiple lenses can reduce this problem. The visible area that appears in focus is the flat field.
Distance - The distance from the magnifier lens to the object being
viewed. As magnification power
increases, the working distance decreases.
- This is distortion caused by the lens. Spherical aberration is distortion of the image, as explained in
Flatness of Field. Chromatic
aberration is distortion of colors being viewed, as explained in Color
Distortion - Lenses produce a prism effect, which causes the image to
develop false color fringes. This
is due to the fact that different colors focus at different points. Achromatic
lenses correct this problem by focusing many colors at the same point.
Parallax is the apparent misalignment of two different items when viewed from
an angle. It is the cause of
improper registration when stripping multiple color jobs. Parallax is eliminated when viewing
straight down on registration marks instead of from a slight angle.
Lens - A coated lens helps to minimize or eliminate color distortion caused
by different colors focusing at different locations. Optimum color viewing is obtained from coated achromatic
x 1" Linen tester (6X)
||General-purpose work. The graphic arts most popular magnifier.
Round Stand Magnifier
||Large 60 mm field-of-view is ideal for viewing color transparencies on a slide sorter or light box
Plastic Base Loupe
||Excellent working distance, wide field and clear base makes this unit best suited for darkroom and stripping areas.
|10X & 12X LithoMags
||Sufficient working distance to be used in stripping department for touch-ups. Achromatic lens system is perfect for press checks.
||Higher magnification shows some spherical aberration. Reduced working distance. Best suited for camera focusing, registration checks, slur and gain checks.
Swivel Base Loupes
||Moderate working distance allows unit to be used in stripping department. Use in pressroom for registration checks.
Swivel Base Loupe
||Achromatic lens system. Reduced working distance due to high magnification. Lens shows some spherical aberration. Adjustable focus lens with locking ring. Best suited for critical camera focusing, registration checks, dot gain and slur checks.
50X, 75X and 100X Pocket Microscopes
||Used for close-up inspection of small areas. Pen-style makes them handy to keep in your shirt pocket.
- 200X Stand Microscopes
||Used for the most critical checking of register and dot structure. Should be used to view printed circuit boards and bar codes.
|8X Econo Loupes
||General inspection work in pressroom and camera department. Clear plastic skirt prevents working under lens, so they are not recommended for stripping.
||Large format for viewing 120/220 film, focusing on ground glass of cameras