Detachable coaxial illuminator viewing accessory for flashlights

A conveniently detachable lighted-magnifier accessory for use with a high-brightness, focusable-beam flashlight, that provides true coaxial illumination for shadow-free viewing of a wide variety of subject matter as well as to the bottom of small holes, is disclosed. Light from an attachable flashlight is reflected by a beamsplitter onto the subject matter. An observer views the illuminated subject matter through a beamsplitter through a magnifying lens or clear window.

I claim the priority date of my Provisional Application for the herein 
described invention dated Aug. 16, 1995 and filed under Ser. No. 
60/002463, now abandoned. 
BACKGROUND-FIELD OF INVENTION 
This invention relates to a detachable lighted-magnifier viewing accessory 
for a popular commercially available flashlight that, when used with the 
flashlight, provides coaxial illumination and thereby permits the user to 
see clearly to the bottom of holes, as well as to view detail on surfaces. 
It is well suited for general use by the public, and also for those 
involved in technical and scientific work. 
BACKGROUND-DESCRIPTION OF PRIOR ART 
Drug and hardware stores commonly supply consumers with self-contained, 
battery-operated lighted magnifiers which, although are adequate for 
surface viewing, do not permit the user to see clearly to the bottom of 
holes, or surface detail near large surface irregularities. This is 
because the illumination is incident at a large angle with respect to the 
viewing axis, so it casts troublesome shadows in the viewing area. A few 
specialty flashlights have been manufactured to permit viewing into holes, 
and in some cases, surface detail as well, but they are expensive (because 
the flashlight is an integral part of the device) and lack versatility, 
since they can be used only for viewing objects because the flashlight may 
not be removed. 
Also, the illumination may be only approximately coaxial, and if so, the 
viewing clarity into holes will be less than optimum. These commercial 
designs differ optically from that of my invention as disclosed in this 
patent application. U.S. Pat. No. 4,659,221 to General Electric describes 
a device for hole viewing that is optically similar to mine, but it is a 
specialty device designed for examining holes in turbine blades, and so 
lacks the needed versatility of a device for use by the general public. 
OBJECTS AND ADVANTAGES 
My invention has the following advantages over prior art: 
(a) It provides superior viewing brightness and clarity for both holes and 
surfaces because it combines true coaxial illumination with a 
new-technology, high-brightness, focusable-beam flashlight. 
(b) It can be produced at a fraction of the cost of the specialty 
flashlights now available for hole viewing because it is an inexpensive 
accessory to a very popular flashlight that many prospective users already 
own. All of the hard parts may be quantity manufactured in low-cost 
plastic. 
(c) Because it is a conveniently detachable flashlight accessory, the 
owner's flashlight may be used as an ordinary flashlight with the 
accessory removed. 
(d) Although the preferred embodiment of my invention is for use with a 
high-brightness, focusable-beam, size-AA flashlight, this design can be 
adapted for use with any flashlight. 
SUMMARY 
The reader will see that my coaxial illuminator flashlight accessory 
provides clear viewing to the bottom of small holes because its 
illumination axis is parallel to the viewing axis, so annoying shadows are 
eliminated from the viewing area. When it is used with a high-brightness, 
focusable-beam flashlight, copious light illuminates holes, thereby 
providing a bright view even into holes in dark-colored surfaces. Coaxial 
illumination also provides optimal viewing of surfaces because the light 
is always "aimed" directly at the subject matter. The illuminator is very 
easy to attach and separate from the flashlight because the simple O-ring 
mechanism pinches the flashlight in place, so it simply "snaps" in and out 
of the illuminator housing. Since the design is well suited for 
all-plastic construction, the invention is cost effective to fabricate.

BRIEF DESCRIPTION OF THE DRAWINGS 
The preferred embodiment of my detachable coaxial illuminator flashlight 
accessory is for use with an AA-size focusable-beam, high-intensity 
flashlight, such as the MINI-MAGLITE, and it is shown in FIGS. 1 and 2. It 
consists of an opaque plastic housing 10 into which an opaque plastic 
eyepiece body 12 is built. Other suitable opaque materials besides plastic 
may be used for the housing 10 and eyepiece body 12. The eyepiece body 12 
contains a lens 14, but a lens system, or clear window may be used. Lens 
14 is held in place in the eyepiece body by 2 O-rings 16 which are bonded 
to the inner wall of the eyepiece body with rubber adhesive (RTV), but 
other suitable mounting methods, such as a step in the wall similar to 
step 21, or set screws may be used. The eyepiece is cut at a 45 degree 
angle on the end inside the housing, as shown in FIG. 1, and a clear 
plastic (polycarbonate) oval-shaped beamsplitter 18 is bonded to this end. 
Other suitable transparent materials may be used for the beamsplitter. A 
hole 26 in the eyepiece body opposite the 45 degree cut end is provided. 
The flashlight fits into the left side of the housing as shown in FIGS. 1 
and 2, and is held in place by a lubricated O-ring 20, but other suitable 
attachment methods for the flashlight may be used, including a thumbscrew 
or even use of a flexible housing. A small step 21 in the inner wall of 
the housing acts as a stop for the flashlight, but this may be unnecessary 
depending on the design of the lighted end of the flashlight, or some 
other suitable means may be used in place of the stop. A plastic end cap 
22 having a black velvet-like light absorbing surface 24 covers the end of 
the housing opposite the flashlight. A hole 28 is provided in the housing 
directly below the plastic beamsplitter to allow viewing of the subject 
surface 30 below. A small mirror mounted at 45 degrees with respect to the 
axis of the light reflected from the surface 15 placed either below the 
beamsplitter 18 or above the lens 14, may be used to provide right angle 
viewing. The device is normally stored in a plastic zip-lock bag to 
protect the optics from dust and damage, and to preserve the O-ring 
lubricant. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
The flashlight is inserted into the left side of the opaque housing 10 as 
shown in the figures, and is snugly held in place by the O-ring 20, which 
accomodates small variations in size of both the flashlight body and 
opaque housing due to manufacturing tolerances. A small amount of grease 
on the O-ring aids insertion and removal, and the flashlight is removed 
simply by pulling it out of the housing. A small step 21 in the inner wall 
of the housing acts as a stop for the flashlight. This may be unnecessary 
if the flashlight has a suitable feature on its outer surface that 
prevents it from being inserted so far as to contact and possibly damage 
the beamsplitter or eyepiece housing. The flashlight beam is focused for 
the smallest spot size on the subject surface, 30. Light from the 
flashlight 8 enters the coaxial illuminator, and strikes a plate 
beamsplitter 18. The useful light component 13 is reflected off the 
beamsplitter downward in the figure, through the exit hole 28 in the 
housing toward the subject surface 30, while the unwanted light component 
11 transmitted through the beamsplitter 18, and hole 26, is incident on a 
black velvet-like light absorbing surface 24 where it is nearly totally 
absorbed to prevent glare in the view field of the subject surface. Other 
suitable light absorbers may be used in place of the black velvet-like 
material. The user's eye looks down from the top in the figure through a 
simple magnifying lens 14, which may be replaced by a lens system or clear 
window, in the coaxial illuminator and sees the light reflected from the 
subject surface 30 below that is transmitted back up through the 
beamsplitter. The image of the subject surface 30 is brought sharply into 
focus by adjusting the distance between the illuminator and the surface. 
With the subject sharply focused, his is called the working distance, 23. 
Simple lenses of 2.7 to 8.5 inches in focal length, providing 
magnifications of about 3.7 to 1.2 respectively, have been used with good 
results. Lenses of the longer focal length provide a longer working 
distance 23, so one can see to the bottom of deeper holes, but with less 
magnification. If the simple lens is replaced by a suitable lens system, 
both long working distance and high magnification can be obtained. 
Alternately, a clear window permits viewing at any distance to the limit 
of the illuminating power of the flashlight, and has been used with good 
results for viewing up to a distance of about 18 inches for the flashlight 
of this embodiment. (Those persons who normally use reading glasses may 
benefit from their use when viewing through this illuminator if a clear 
window is used instead of a focusing means for lens 14.) A magnifying lens 
performs somewhat better than a clear window because the lens defocuses 
the small amount of glare from the beamsplitter 18 and velvet-like light 
absorbing surface 24, making it less noticeable, when the subject surface 
30 is sharply in focus. A small mirror mounted at 45 degrees with respect 
to the axis of the light reflected from the surface 15 placed either below 
the hole 28 or above the lens 14 as shown in FIGS. 1 and 2 may be used to 
provide right angle viewing. Note that in my invention the viewing axis is 
parallel to the illumination axis (hence, the term "coaxial illuminator"), 
so troublesome shadows are eliminated from the viewing area, and viewing 
even into deep holes is thereby possible.