Welcome to the SSV Community Web Page on
Making a Large Image Safe Solar Viewer (LISSV)
The original web page for the LISSV had
details for making the viewer with lenses that were
difficult to obtain or simply no longer available. This
web page offers a simple approach but the original
information is archived here for those who wish
to access it.
Making a LISSV is a little more
challenging than one projecting a smaller image because
the supports must be more robust and getting the
alignment of the lenses correct and keeping them that
way requires more effort. Still, such a viewer can be
made in a woodworking shop with modest equipment or
using another simple method.
Some members of our community with
access to 3-D printing facilities have printed their
entire viewer except for the lenses and obtained
excellent results. With that approach the alignment of
the lenses is almost automatic.
Choosing the Objective
People have had trouble finding a
suitable objective for the LISSV until now. The
objective lens needs to be of sufficient size and focal
length to do the job. Fortunately Surplus Shed had
listed a new SSV package that is perfect for a LISSV.
That lens is a 71.9 mm x 700 mm achromat that is offered
with a suitable −19 mm Barlow for only $23 plus
Even though these lenses are
achromatic, there will be chromatic aberration (a blue
fringe around the solar image) from dispersion just as
there is with the smaller SSVs with the lenses we
recommend. Even if you find an achromatic Barlow lens,
the combination will not produce an entirely color-free
result. I treat the blue fringe as both a teaching
opportunity and means of adjusting the lens alignment.
If the objective and Barlow are both
parallel to the screen, the blue fringe will be uniform.
If it is not, then slightly adjusting the tilt of either
or both of the lenses is necessary. With an SSV made of
cardboard, we simply flex the cardboard hold the
objective lens to adjust its tilt. With the Barlow
adjusting the tilt of the Barlow holder up and down or
left and right does the trick.
When anyone inquires about the blue
fringe during a solar viewing session, I present a short
optics lesson about dispersion, prisms and lenses. If
you are concerned about chromatic aberration, then the
finding a lens with a higher f/ratio than f/10 will
theoretically show less of the effect but also make your
In constructing your LISSV, know that
the distance from the objective to the Barlow is almost
the same as the focal length of the objective. The
location of the Barlow changes very little in a LISSV
with a small image compared to one with a larger image
but the projection distance will be longer with
increasing solar image size.
Our tests with the new Surplus Shed
71.9 mm objective gave an image size of about 8.5 inches
in a LISSV measuring 48 inches from the objective to the
screen. A longer device would produce a bigger solar
image but that image would be fainter. It is a matter of
personal taste as to how bright the image must be.
One caution should be observed with
any LISSV. Since the objective lens is necessarily
larger with these viewers, the greater light gathering
power of these objectives will make the concentrated
sunlight striking the Barlow hot enough to ignite paper
and char wood if the beam drifts off the lens and onto
the holder. For that reason we suggest covering the face
of the Barlow holder with aluminum foil that is attached
by some means. We use double stick tape.
As with the 2-lens SSV, the best image
will result when the screen, the Barlow holder and the
objective holder are kept parallel and the Barlow is
centered on the optical axis defined by the objective.
For other details in making a LISSV, please refer to the
pages on making the 2-lens SSV.
Image Screen Surface
With a larger solar image it is
important for the projection surface to be perpendicular
to the optical axis and as flat as possible. Copier
paper will ripple. With the regular SSV we have used
heavy card stock and others in the community have been
successful with poster board. We have tried a sheet of
one brand of AV projection screen material with adhesive
backing. Applying it required skill that we did not
possess. We simply could not get the sheet to adhere to
smooth plywood without bubbles or ripples. We think
white card stock or poster board works well, but you may
have better ideas and, if you do, let us know so we can
|Back to the