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 for the theatre range from 300 through 1000.
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 pertinent section(s).
INFORMATION BELOW MAY
NOT BE REPRODUCED
FROM THE AUTHOR ©
Be aware neither Atlantic Illumination, nor its owner
and employees will be responsible for any problems
encountered as a result of following or not following
the procedures here. This is only a guideline. You
must decide the suitability of the steps given, and
be responsible for the results of your own work.
The fresnel fixture is more complex than a PAR, but less so than an
ellipsoidal. Having said that, there are fresnels with sophisticated
focus mechanisms that will need vigilance during disassembly so as to
keep the parts straight in your head. 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
Read through this article before starting so you'll have an idea of what
is required and the tools needed. You may find that some procedures are
better done out of order for your particular model.
Set up a work space with proper lighting and the tools required. See
our Work Area Setup series of articles
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.
Before you begin with the procedures, determine
which of the items below to make available:
- Small Parts Bottles
- Parts Containers
- Heat Shrink
- Heat Gun
- Paper Towels
- Silicone Lubricant
- Permanent Marker
- Electrical Tape
(White and Black)
- Alignment Cradle
- Alignment Screen
- Test Dimmer
- Screw Drivers
- Nut Drivers
- Diagonal Cutters
- Bench Vice
- Bench Brush
- Hook Tool
- Locking Pliers
- Rubber Mallet
- Crimp Tool
- Cut-Off Garden Hose
- Drill Bits
- Rotary Mini-Tool
- Electric Drill or Bench Buffer
- Variety of Wire Brush
- Goggles or Face Shield
- Fine-Toothed Flat File
- Narrow, Metal Paint Scraper
- Emery Cloth
- Sanding Sponges
- Plastic Soap Pads
- Steel Soap Pads
- Fine Steel Wool
- Scrub Brush
- Tooth Brush
- Dish Detergent
- Fine-Toothed Flat File
- Spray Paint (Heat Resistant for Metal)
- Medium Spray Oil
- Paint Solvent
- Methanol Alcohol
- Soft, Lint-Free Tissues
- Glass Cleaner
- Distilled Water
- Masking Tape
- Cardboard Mask
- Penetrating Oil
- Lubricating Oil
- Oil Station Bin
- Suitable Selection of Replacement Parts
- Numbered Parts Containers or Muffin Pan
Now begin the overhaul itself:
A reminder that if you are new to this to keep track of the
disassembly by making notes. Use the numbered containers
or muffin pan to hold the parts removed during each step,
and have an assembled fixture available for reference.
Now do the following:
- Initial: Working with a room-temperature fixture, first,
take off the yoke. With some models, the removal of internal nuts may be
required to get it off. Some techs wait to do the above until after the
next two steps. If you wish to delay, ensure during movement that the
still-attached yoke and clamp do not damage anything on the bench. It's
easy for an unsecured yoke to swing unexpectedly and hit something, or to
jam a finger between it and the bench or the fixture itself. Now remove
any clamp or stand adaptor from the yoke and place it aside.
- Lens: If your model does not have an internal track/holder
for the lens, but has it secured the front of the fixture, remove the lens
This may be as simple as taking off a retainer ring or bracket 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.
- Lamp: Remove the lamp. Don't be worried about touching the
bulb; you will be cleaning the lamp before re-insertion during the reassembly
stage at the end. Put both the lens and lamp in your Safe Place as discussed
in the Work Space Design article.
- Electrical Components: 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
wiring and socket/reflector assembly as discussed next, you will be able
to remove the strain relief(s).
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 mechanisms with an external lever or knob to do the focusing, these
will have to be disconnected first, and in the case of screw focus units,
the threaded rod will need to be removed. Remember to keep the parts for
each step 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.
- Final Component Removal: Take out the lens holder
and remaining brackets. If not riveted, remove any light baffles, noting
orientation and specific location. Place alignment marks to aid in later
reassembly. You should now be left with just the body shell.
- Body: 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 them re-threaded,
unless you own a tap & die set. 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.
- Yoke: Look at the yoke. Note any burrs that should be
filed off, and if straightening will be needed. The latter can be done
using a vice to squeeze ripples flat, and as a clamp to permit reshaping
- Reflector: Have a look at the reflector. If it's badly
tarnished and can't be improved as described in the "Washing" section, it
will have to be replaced or sent to a metal refinisher.
- Electrics: These will be inspected during the "Electrical"
- Initial Restoration: If the fixture is very dirty, you
may wish to clean off the loose dirt with a bench brush, then skip ahead
to the "Washing" topic. Return here while it is drying to study the next
For a severely corroded body, and for tarnished hardware,
employ a narrow paint scraper and use an electric buffer with a wire brush
to redress the finish. (A brass brush is preferred over steel so as to
lessen the chance of gouging.) If no buffer 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.
- Buffing Technique: 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 marring 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 off the parts.
Do the same for the lens holder, baffles, and metal parts other
than the reflector. Be sure the parts are dust free afterward.
- Hardware Refurbishing: Clean and buff all hardware including
the pipe clamp or stand adaptor. Take the clamp apart to do this. Schedule
these for repainting as necessary. Replace any severely rusted parts if they
can't be buffed cleanly by the wire brush.
Be cautious not to distort smaller parts by over-tightening
the plier locking mechanism. If locking pliers are unavailable, use
snub-nose pliers and grip them tightly as you manipulate the item being
buffed. Too loose a grip will see parts go flying due to the speed and
torque of the rotating brush.
- Hardware Protection and Lubrication: After buffing, protect
metal hardware with a thin coating of light machine oil, but use a
medium oil for threaded parts.
Keep oil from soaking into your work bench. A greasy bench is
not a good environment for lighting fixtures because oil will work its way
into areas where it is not wanted. As such, it is suggested to buy a
medium-sized plastic bin such as a dish pan to employ as an oil station.
To soak up excess lubricant, cover the bottom with one layer of an old
towel. Oil all metal components in the pan, turning them to assure full
coverage. Leave parts there until needed for reassembly, being sure to keep
the parts clustered into the same divisions as were in the individual
containers. If the bin is too small to do this, then only buff and oil each
section of parts just before reassembly.
For parts that do not have dust or built-up grime and so
don't need washing, you might now wish to skip to the
"Painting" procedures so that these first items will be
drying while you continue with the steps below.
- Main Parts: Place items requiring a wash into a plastic
laundry tub or use rubber mats to protect an enamel one. Scrub the units
using hot water and dish soap. Use a tooth brush to get into small areas.
Remove rust with a soapy scouring pad. For stubborn rust, use a sanding
sponge or emory cloth. Rinse. (A one-metre cut 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.
- Metal Reflectors: (You may have to first read the
"Electrical" section if the reflector is part of the socket assembly.)
Place the reflector into the sink. Hose off the main dirt first. Use a
plastic soap pad to clean the back of the reflector as a scratch test.
Move the pad with a motion that follows the reflector's shape. If it
polishes with no scratches, do the same to the front. If scratches appear
from the test, you will have to decide if it is better to have a 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. If the pad is not suitable, substitute a clean, soft cloth or
sponge with lots of dish soap. Rinse and dry.
If severely tarnished to the point that it may not be usable,
you can attempt to polish it with actual steel wool soap pads, or with
automotive rubbing compound. The worst ones will have to be taken to a
professional metal refinisher or be replaced.
- Glass Components: If the reflector is glass, and it and
the lens do not use a coating, each 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. Glass cleaner
or methanol alcohol may be used to remove streaks after drying. Soft
tissues can be used as applicators.
If the reflector and lens do have coatings, no glass cleaner
or undiluted alcohol can be used on them. These cleaners 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, rinse 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. Allow to air dry.
While components are drying, you may move on to
restoring the electrical parts you removed earlier.
- Socket: Remove the socket and inspect the contact screws.
Burnish off any corrosion there and inside the socket. You may do this by
hand with a stiff scraper, or use the drill and a small wire-brush
attachment. An option to the latter is a miniature rotary tool. If the
socket remains severely discoloured, you should replace it. (Discoloured
sockets can contribute to reduced lamp life.) Should you install a new
socket and it uses an insulator wafer underneath, replace it if damaged,
split, or missing.
- Line Cord: If the 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.
- Reflector: If the reflector is still 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. Follow the instructions in the "Washing"
section father back.
- Reflector Mount: Clean off the socket/reflector mount and
inspect for damage. Recondition as necessary. If it's rusted, it will have
to be scraped and/or buffed, washed, and then painted with a heat-resistant
finish. If painting is required, follow the next procedure.
Paint Choices: If there are parts that are rusted or
discoloured (other than electrical or the reflector), painting will be
required. The usual colour would be flat black. This is recommended for
all interior body surfaces in order to minimize unwanted reflections. The
paint chosen should be able to handle directly radiated heat. Barbeque
paint is a good choice. Buy a test can first! Some barbeque paints have
a flat black cap, but actually dry with some degree of shine.
For the exterior, you may want a different colour. This might be to
dress up the light, to better identify your lights from those belonging to
others, or to give your show a uniqueness if you like to have visible
fixtures. Even so, endeavour to stay with a darker colour to minimize
external reflections. A satin (semi-gloss) finish is recommended regardless
of the colour chosen.
Now gather your paint materials as given
in the preliminary list near the start
of this article and do the following:
- Preparation: Mask any things not to be painted such as
electrical stickers, screw threads, or lens barrels that must slide without
guide tracks. To facilitate tape removal, leave a tab by folding a small
bit of the sticky side back on to itself. Place the items onto newspaper
in your paint booth or area, as discussed in the
Work Space Setup.
- Painting Procedure: Follow the instructions on the can
regarding optimal temperature and for re-coating. Shake the can well, and
under good lighting, spray in even strokes, releasing the nozzle at each end
of the pass. Blend each line of paint with the previous in a manner that
does not leave gaps of excessively thin coats or ones that are too thick.
Keep the overall coating thin. Allow it to dry, between coats as per
instructions on the can. Use paint solvent to clean overspray. Then do a
second coat, and a third one if necessary. Repeat for the yoke, hanging
each item to dry in a non-dusty area. 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
Be careful of your new paint job. It may feel dry, but can take a day
or so for the new finish to harden completely, hence the caution when
handling components as you put them back together. Replace any baffles
and internal parts that are not part of the focusing mechanism while
keeping an eye on their correct orientation.
- Socket Assembly: Orient the socket and its wiring to
the mount for the reflector and focusing assembly, if it's the slider
type. Attach the wiring to the socket by following the colour coding
discussed in the "Electrics" section next. Remember to place the insulator
wafer under the socket, if one is required. (These components might be
mounted to the body if they do not move during focusing.)
- Electrical: 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 on the body or focusing mount). These colours
are for Canada -- they may be different in your country.
You may wish to use metal crimp connectors that have rings
which go under the screws. These make for a more secure connection. Be
sure these crimp connectors have no insulators as they will melt, and
that they are short enough not to extend beyond the insulating wafer.
If the wiring is from outside Canada, 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. If you are not confident
with your wiring skills, you may now elect to do a continuity test as
described in the "Electrical Testing" section.
- Restoring the Focusing Mechanism: Replace a glass
reflector into it mount. Do not overtighten; it must be loose enough to
provide expansion room when it gets hot. Replace a metal reflector
back onto its mount, if it was able to be removed. If the unit uses a
slider style of focus, use silicone lubricant on the slide parts. Replace
the reflector/socket assembly back into the body and attach any focusing
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.
If there is a lever or screw focus adjustor, it will have to
be installed, along with its components, when the above is placed into the
body. Lubricate the lever pivot or screw threads with medium oil. If you
have found that this evaporates due to the heat when the fixture is in
service, completely clean off all oil and then replace with industrial
- Tensioning the Focusing Mechanism: Position 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. Lever and screw focus mechanisms
however, usually require tension to prevent them from moving after being
set. Tighten this just enough to allow adjustment by the user, but not so
much that the focus moves on its own when the fixture is tilted to extreme
angles. The order of hardware, especially lock washers, is critical to
keeping the tension adjusted properly. Be vigilant when reassembling.
- Remaining Internal Parts: Replace the lens holder and any
- Restore the Lens and Lamp: Before the lamp goes in, clean
the bulb with methanol alcohol to remove finger oils. Replace the lens into
its mount. As directed earlier regarding a glass reflector, ensure that it
is loose! Do not place retainer clips or rings hard against the lens. It
must have room to expand during operation.
- Additional Lubrication: Use oil on any hardware not already
done, but for parts that rub against one another such as slider focus
mechanisms, spray with high-temperature 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.
- Final Assembly: Install any remaining parts, but you may
elect to leave the yoke and pipe clamp off until after the alignment is
- Continuity Test: Use the `ohms' setting of your multimeter
to confirm a continuous electrical path from plug to socket. Check the
neutral and ground paths, as well. `Zero' ohms should be the reading.
Diagnose and fix any problems.
- Shorts Test: Test for shorts between hot and neutral, and
from each conductor to the metal fixture housing. If the meter reads
anything but "infinity", there are problems. Diagnose and fix before moving
- Lamp Test: You may elect at this point to install the
lamp as an additional test, but can wait if more parts have yet to be
placed. Do a lamp continuity test before putting it in. If all is
well, move on to the alignment.
- Alignment Cradle: This is 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
- Reduce the Voltage: Plug the fixture into a dimmer and
set it to the lowest position that still produces a bright circle. Lowering
the voltage is done to lessen the chance of lamp burnout during possible
rough movement as its alignment is adjusted.
- Testing and Adjustment: Shine it on to the screen and check
the focus at various beam angles. 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 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. (Some fixtures will require a rear baffle
to be removed to do this procedure.) 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
- Date Tagging: This is an important step because the tag
will give an indication of lamp service life. If the time period is less
than expected, there may be a problem with the fixture, its location, or
its input voltage.
Make a date tag by using white electrical tape which will be
placed onto the inside of the yoke. Make the date tag twice the required
length so that at the next lamp replacement, there will be room to write
the new date. This way, the date tag only need be replaced every second
If a new lamp is installed, mark the current year (four
digits) and month (two digits or three letters) on the tape. Should
the old lamp be used and its installation date is unknown, write the
current year and month along with `P.I.S.' This stands for "Previously
in Service". Otherwise, copy the date from the old tag, or reuse the old
tag if its condition is good.
Stick the tag to the inside of the yoke on one of its
vertical surfaces -- usually the one opposite the tilt-lock knob. Be
consistent so that you and your crew will know exactly where to look.
Don't use the underside of the top of the yoke because heat here will be
greater than along the sides when the fixture is hung in its typical
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. (-: