AIEL Shop Tips
The fresnel (freh-NELL) is a staple of the entertainment lighting world,
especially for the theater and television. It is a versatile fixture capable
of a variable soft-edged flood to a spot, in a round or oval pattern.
Typical wattages range from 100 through 2000. Most fresnels are constructed
in a similar manner. Simply modify the instructions here to suit your
manufacturer's fixture. It shall be assumed that the fixture is to be
completely overhauled and will be disassembled. However, you may only
require to do a part of what is outlined here, so simply skip to the
THE FOLLOWING MAY NOT BE REPRODUCED
WITHOUT PERMISSION FROM THE AUTHOR ©
Be aware that neither Atlantic Illumination, nor its owner or
employees will be responsible for any problems encountered as
a result of following or not following the procedures here. This
is strictly a guideline. You must decide the suitability of the
following and be responsible for the results of your work.
Read through this article before starting so you'll have an idea of what
is required. You may find that some procedures are better done out of order
for your particular model. If you are unfamiliar with the particular
model on which you are about to work, make notes or drawings, or have an
assembled fixture available for ease of re-assembly. Also, you may wish to
print this page and use it to check off each step as it is completed.
Set up a work space with proper lighting and the tools required. See
our Work Area Setup article to help with this.
Have some numbered containers or a muffin pan available in which to place
the parts from each disassembly step. This will benefit you when it comes
time to put the unit back together again because no parts will be left out
and you will know the correct order; not to mention the fact that parts in
containers don't get lost. Lay some clean newspapers on the bench to protect
both the bench and the fixture. Their light colour also helps to contrast
small parts which may be dropped during the overhaul operation, and it makes
for a nicer work surface.
You should have the following available:
- Screw Drivers
- Nut Drivers
- Hook Tool (See the reflector re-assembly section.)
- Rubber Mallet
- Electric Drill or Bench Grinder
- Brass Wire-Brush Drill Attachments (Small and Large)
- Emery Cloth (Grade: Fine)
- Sanding Sponges (Grade: Fine)
- Wool Soap Pads (*Not* Steel Wool!)
- Narrow, Metal Paint Scraper
- Fine-Toothed Flat File
- Scrub Brush
- Tooth Brush
- Dish Detergent
- Electrical Tape (White and Black)
- Permanent Marker (*Not* Water-Based)
- Heat Shrink
- Heat Gun
- Spray Paint (Heat Resistant for Metal)
- Alignment Jig and Screen
- Light, Spray Oil
- Spray Silicone Lubricant (Industrial Grade)
- AC Volt Meter
- Varsol (Paint Solvent)
- Methanol or Rubbing Alcohol (To be used with caution -- see text)
- Glass Cleaner (To be used with caution -- see text)
- Distilled Water
- Soft, Lint-Free Tissues
- Suitable Selection of Replacement Parts
- Numbered Parts Containers or Muffin Pan
Remember to keep track of the disassembly by making notes, using numbered
containers or a muffin pan to hold the parts removed during each phase, and
by having an assembled fixture available for reference. Now do the following:
Working with a room-temperature fixture, first remove any clamp or stand
adaptor, and place it aside. Next, take off the yoke. With some models, the
removal of internal nuts may be required to get the yoke off. Some persons
wait to do the above until after the next two procedures. If you wish to
delay, be sure during movement that the still-attached yoke and clamp do not
damage anything on the bench. It's easy for a less-than-tight yoke to swing
unexpectedly and hit something, or to jam a finger between it and the bench
or the fixture itself.
Now remove the lens and lamp. This may be as simple as taking off a
retainer ring and popping the lens out the front. However, some fresnels
require the removal of internal clips with the lens coming out the back
of the lens holder.
When removing the lamp, don't be worried about touching the bulb. You
will be cleaning the lamp before re-insertion during the assembly stage at
the end. Put both the lens and lamp in your safe place as discussed in the
Work Area Setup article.
Now take off the electrical cord connector. Most fresnels allow removal
of the socket/reflector assembly this way. It is done by having the line
cord pull through the body, permitting the socket assembly to be taken out
through the front of the fixture. Should the line cord use a moulded
connector, it will have to be disconnected at the inside end.
Loosen any strain relief where the cable enters the fixture body and any
additional ones inside the fixture. After pulling out the wire and
socket/reflector assembly as discussed next, you will be able to remove the
Unscrew the focus adjustment knob on the bottom or side of the unit. The
socket/reflector assembly should now be able to be removed from the fixture
body by raising it and pulling forward. For those units which employ
external mechanisms to do the focusing, they will have to be disconnected
first. Be sure to keep parts for each in its own numbered container.
For fresnels that achieve focus via a moving lens, meaning the
socket/reflector assembly is stationary, you may have to remove the lens
and its track & mechanism in order to get at the socket assembly.
Remove the lens holder and any remaining brackets. You
should now be left with just the body shell.
INSPECTION and RECONDITIONING
Look at the body to see if there are any dents or bent parts. Repair as
necessary. To pound out dents, use a wooden form and rubber mallet to
lessen metal damage as compared to a direct hammer blow. Inspect the screw
mounts for the yoke; they should not be worn or damaged. If so, then it
means a trip to the machine shop to have it re-threaded. Note that some
models use a "grab plate" locking mechanism, so the yoke mounts are free
to pivot, thus stripped screw mounts are less likely to have happened.
Do the same for the yoke. Note any burrs that should be filed off, and
then straighten the yoke, using a vice if necessary.
Place the body into a plastic set tub or use rubber mats to protect
an enamel one. Scrub the unit using hot water and dish soap. Use a tooth
brush to get into small areas. Remove rust with a wool-type, soapy scouring
pad. For stubborn rust, use a sanding sponge or emory cloth. Rinse. (A
one-metre length of garden hose with no connector at the output end is
good for this.) Dry with an old towel. Don't use a new one as some rust
will likely come off. Hang the unit up to air dry the inaccessible areas.
Repeat this procedure for the yoke.
For a severely corroded body, and for tarnished hardware, employ a narrow
paint scraper and use a bench grinder with a wire brush to buff the
finish. A brass brush is preferred over steel. If no grinder is available,
use an electric drill with a lockable trigger. Clamp the drill into a vise.
You will likely find that clamping the drill and holding the parts against
the rotating brush works better than clamping the parts. It saves having to
clamp and unclamp each part, and having to put the drill down to do the
re-clamping. Use a pair of pliers, preferably the locking type, to hold
small parts. This will give you more control and also keep your skin away
from the rotating bristles. Work gloves are recommended, as are hearing
protection and goggles or a face shield.
Begin to buff the fixture body. Do not press too hard because the wire
bristles will score the metal. Use the side of the bristles for finer work
with less chance of scoring the metal. You need not take off all the old
paint -- only that which is loose, and of course, surface rust should be
removed, too. Dust the parts off.
(You might now wish to skip to the "Painting" section so that the first
coat on the fixture body will be drying while you continue with the steps
Move to the socket assembly. Remove the socket and inspect the contact
screws. Burnish off any corrosion there and inside the socket, either using
the drill and a small wire-brush attachment or by hand with a stiff scraper.
If the socket remains severely discoloured, you should replace it.
(Discoloured sockets can contribute to reduced lamp life.) If you install
a new socket, replace the insulator wafer underneath if it is damaged,
split, or missing.
If the line cord is attached through a strain relief, remove both and
inspect. Should the cord be melted, frayed, or brittle, it will require
replacement. If it's old and uses asbestos wiring, install a new line
cord. Asbestos conducts electricity when wet and is hazardous to breathe.
Put the wiring into a plastic grocery bag and send to recycle or to your
local Hazardous Waste Facility.
Some line cords may use fibreglass sheaths. Replace or repair as necessary.
If the damage to this is external to the fixture body, you may use electrical
tape or heat shrink. If it's internal, cut off the bad part and slide a good
section inside. Make up the shortfall on the other end with an appropriate
length of sheathing coupled via heat shrink or electrical tape. When the
light is fully assembled, the sheathing should run from the socket assembly,
along the line cord and into the plug at the other end.
If the reflector is attached to the socket mount by bolts, remove now.
If not, and you don't wish to drill out the rivets, you may leave it on.
The instructions here will assume a detached reflector. If the reflector is
metal, place it into the sink and use a wool soap pad with water to clean
the back of the reflector as a scratch test. Use a circular motion. If it
polishes with a minimum of scratches, do the same on the front. You will
have to decide if it's better to have a smooth but tarnished reflector
versus a shiny, scratched one. I vote for the latter if it reflects more
light without too much scatter, rather than leaving it tarnished. Rinse
If the lens does not use a coating, it may be cleaned in the sink with
dish detergent and a very soft scrub brush, or bare hands if it's dirty
with grit. Rinse well before applying any rubbing motion. Be cautious of
chipped sections which may potentially cut one's skin. If the reflector
and lens do have coatings, no glass cleaner or undiluted alcohol can be
used on it. Either can degrade, if not destroy, their optical qualities.
Do not use a brush on coated surfaces -- clean, wet hands only. For very
grimy lenses and reflectors, runse well, then use a solution of 10%
alcohol and water to clean the film off. If streaks appear after drying,
repeat the cleaning and use distilled water as a final rinse.
Clean off the socket/reflector mount and inspect for damage. Recondition
as necessary. If it's rusted, it will have to be scraped or buffed, washed,
then painted with a heat-resistant finish. If painting is required, follow
the steps below for body repainting.
Clean and buff all metal hardware including the pipe clamp or stand
adaptor. Take the clamp apart to do this. Repaint as necessary. Replace
any severely rusted parts if they can't be buffed cleanly by the wire
brush. Coat unpainted, cleaned hardware with a light machine oil.
Should any parts (other than electrical or the reflector) be rusted,
discoloured or have a flaking finish, painting will be required. The usual
colour would be flat black, which I do recommend for all interior parts in
order to minimize unwanted reflections. The interior paint should also be
one which can handle directly radiated heat, such as a barbeque paint.
However, you may consider another colour for the exterior to dress the
light up or to better identify your lights from those belonging to others,
and to give your show a uniqueness. Even so, try to stay with a darker
colour to minimise external reflections. For the exterior, I recommend a
satin (semi-gloss) finish regardless of the colour chosen, but some prefer
even the external colour to be completely flat, especially around the lens
and gel frame holder. Now, gather your paint materials as per the preliminary
list near the start of this article and do the following:
Re-inspect the body of the fresnel. Remove any rust not gotten by
washing or buffing, then clean. Be sure it is dry. Mask anything to not
be painted such as screw threads and electrical stickers. Leave a tab of
tape to facilitate removal by folding a bit of the sticky side back on
to itself. Place the body in your paint booth or area, as discussed in the
Work Space Setup.
Shake the can well, and in a well-lit area, spray in even strokes,
releasing the nozzle at each end of the pass. Repeat for the yoke, hanging
each to dry in a non-dusty area. Keep the coats thin and allow to dry
between coats as per instructions on the can. Use paint solvent to clean
overspray. Allow to dry. Realise that dry paint can still be soft
underneath, so handle carefully. It is best to wait over night so as to
achieve a fully cured, hard coating.
If the exterior is to be a different colour, after the interior has
dried, coat it using the technique above. Keep overspray out of the
interior. You may have to touch up the inside after the exterior has
been completed. Allow to dry. After each painting phase, blow out the
paint can nozzle by turning it upside down and spraying until only
propellant comes out. To lessen waste, I always do this onto one of
the lights I am in the process of painting.
REASSEMBLY and LUBRICATION
Being careful of your new paint job, replace the socket, wiring, and/or
reflector, as necessary. Remember to place the insulator wafer under the
socket. Regarding the paint, it may feel dry, but can take a day or so
for the new finish to harden completely, hence the caution when handling.
Reinstall the reflector/socket assembly along with any strain reliefs
and pull the cable through the body. Attach the plug. Ensure that the
wire to the socket's button (center contact) goes to the hot (brass) screw.
Use the black lead. Wrap the wire around the screw in a clockwise direction
to keep it under the screw during tightening. White goes to neutral (silver
screw) and green goes to ground (green screw). (These colours are for
Canada -- they may be different in your country.)
If the wiring is from elsewhere, do the above as per the electrical
colour coding of the country involved. Make sure the outer covering or
sheathing goes inside the plug's strain relief and tighten all body and
strain relief screws. Adjust the sheathing, if the unit uses it, so that
the slack goes inside the fresnel body and up to the socket. Tighten the
socket strain relief, if one exists.
Replace any internal brackets or fittings.
Restore the reflector to its mount, if it was removed. If it's a
slider style of focus, use silicone lubricant on the slide parts. Replace
the reflector/socket assembly back into the body and attach any controls,
but do not tighten or adjust just yet. With the assembly fully forward,
tighten the fresnel body strain relief through which the line cord passes.
Check to see that the sheathing reaches the socket.
Now adjust any mechanism used for focusing and tighten as necessary to
allow it to function normally. If it's only a simple slider focus, then
for the time being, tighten it in any position to stop it from moving.
Replace the lens holder and any closure mechanism/fittings.
Restore the lens and lamp, being sure to clean the bulb with methanol
alcohol to remove finger oils. Ensure that the lens is loose! Do not place
retainer clips or rings hard against them. The lens must have room to
expand during operation. This goes for glass reflectors, as well.
With a light oil, lubricate any hardware not already done, and for any
parts that rub one another, spray with silicone. Keep oil and silicone off
any parts not intended. This is especially true for the lenses, reflector,
and lamp. Keep these different lubricant types apart from one another, too.
In addition, keep them off your bench. An oil/silicone soaked bench is not
a good environment for lighting fixtures because it will work its way into
areas where it is not wanted.
Do the final assembly using the remaining parts, but you may elect to
leave the yoke and pipe clamp off until after the alignment is done.
This requires a stand or jig which will support the fresnel. It may
be made of wood or metal but should have the cradle lined with cloth, rubber, or carpet to prevent scratching the
fixture body. Alternatively, one can use a pipe on to which to clamp the
light. Also, a screen or flat white wall is required for proper alignment.
A bonus is if the screen or wall can have a center dot and concentric
circles at half-metre intervals.
Test the light. Shine it on to the screen and check the focus. The
beam pattern should be even and free from hot spots or "ring shadows". If
not, the reflector will have to be adjusted. Few fresnels have such an
adjustment, but if yours does, rotate the screws until the reflector gives
the brightest and smoothest beam at all beam angles.
Some cheaper units have no adjustment screws but do allow its metal
reflector to be bent gently forward and back. Take a hook tool, which is
a slender rod with a crook on one end, and reach in through the vent holes
behind or above the reflector. Hook the top of the reflector and push or
pull until the beam is at its brightest and most smooth. Test for all focus
angles and readjust as necessary to give the best beam at all angles.
You now have a clean, operating, properly aligned
fresnel fixture ready to work for you. ENJOY!
But wait... don't enjoy too much. You have all
the rest of your lights to overhaul. (-:
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