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- Aug 14, 2013
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Sometimes it becomes necessary to perfectly center a lens. Other times that is the absolute
worst thing to do.
So let's say you have a "200mW" green DPSS module with a crooked beam that is hitting the
inside of the barrel and causing reflections and power loss. Getting the lens perfectly centered
could only make things worse since the crystal set itself is off center. All is not lost! Moving
the lens around will move the beam in the opposite direction and allow you to send it down the
center of the barrel.
The problem is the expanding lens. It is sometimes positioned incorrectly, causing a reflection
in the barrel of the collimator and power loss. The solution is to move it in the opposite
direction until the reflection disappears.
Other times, you do in fact want a lens perfectly centered. One way to do it is using a mini
"potter's wheel" that can be made from spare parts.
We take an eject motor out of the pile of junk from those old DVD and BluRay drives. It will
have a pulley or gear on it, but it is too small to hold a lens mount. There is a larger pulley that
is the perfect size, but its center hole is too large for the motor shaft. So Spin up the motor and
sand down the gear/pulley until it is just the right size to fit inside the hole in the larger pulley.
Some very course 60 grit sandpaper will get do the joj.
Once it's the right size, glue the larger pulley to the smaller one. It doesn't have to be anything
special. Gorilla glue works just fine. Spin up the motor again while the glue is drying and look
for any wobble. While it's spinning, use your finger to press gently on the pulley until it stops
wobbling. Leave it run as the glue dries and keep checking on it, or else it will move off center
and you'll have to start over again.
Now once the glue dries, we can get started on centering the lens. To do this, the motor has
to spin SLOW! Take a 220Ω 1W resistor and connect it in series with the motor. Then attach
a variable power supply.
Put your lens barrel on top the motor as close to the center as you can get it by eye. Then
spin up the motor very slowly. It is probably going to wobble because it isn't in the exact
center. So take something slick like tweezers and gently touch it until the wobble stops. It
takes a very steady hand, so you may have to brace against the edge of the table.
Once the barrel is centered to your liking, stop the motor and very carefully place the lens on it
without disturbing the barrel. Again, get the lens as close to the center as you possibly can by
eye. Slowly start the motor spinning and do the same with the lens as you did with the barrel.
This is where something very slick is crucial. The lens has so little mass that it will catch on
anything soft and go flying. Hardened steel, smooth stone, or stainless steel should work.
Once it's well centered, it's time to glue it down. Walmart.com has some UV curing glue that
hardens under a black light or 405nm laser.
Lisa Pavelka Magic-Glos UV Resin, 1 oz: Crafts : Walmart.com
worst thing to do.
So let's say you have a "200mW" green DPSS module with a crooked beam that is hitting the
inside of the barrel and causing reflections and power loss. Getting the lens perfectly centered
could only make things worse since the crystal set itself is off center. All is not lost! Moving
the lens around will move the beam in the opposite direction and allow you to send it down the
center of the barrel.
The problem is the expanding lens. It is sometimes positioned incorrectly, causing a reflection
in the barrel of the collimator and power loss. The solution is to move it in the opposite
direction until the reflection disappears.
Other times, you do in fact want a lens perfectly centered. One way to do it is using a mini
"potter's wheel" that can be made from spare parts.
We take an eject motor out of the pile of junk from those old DVD and BluRay drives. It will
have a pulley or gear on it, but it is too small to hold a lens mount. There is a larger pulley that
is the perfect size, but its center hole is too large for the motor shaft. So Spin up the motor and
sand down the gear/pulley until it is just the right size to fit inside the hole in the larger pulley.
Some very course 60 grit sandpaper will get do the joj.
Once it's the right size, glue the larger pulley to the smaller one. It doesn't have to be anything
special. Gorilla glue works just fine. Spin up the motor again while the glue is drying and look
for any wobble. While it's spinning, use your finger to press gently on the pulley until it stops
wobbling. Leave it run as the glue dries and keep checking on it, or else it will move off center
and you'll have to start over again.
Now once the glue dries, we can get started on centering the lens. To do this, the motor has
to spin SLOW! Take a 220Ω 1W resistor and connect it in series with the motor. Then attach
a variable power supply.
Put your lens barrel on top the motor as close to the center as you can get it by eye. Then
spin up the motor very slowly. It is probably going to wobble because it isn't in the exact
center. So take something slick like tweezers and gently touch it until the wobble stops. It
takes a very steady hand, so you may have to brace against the edge of the table.
Once the barrel is centered to your liking, stop the motor and very carefully place the lens on it
without disturbing the barrel. Again, get the lens as close to the center as you possibly can by
eye. Slowly start the motor spinning and do the same with the lens as you did with the barrel.
This is where something very slick is crucial. The lens has so little mass that it will catch on
anything soft and go flying. Hardened steel, smooth stone, or stainless steel should work.
Once it's well centered, it's time to glue it down. Walmart.com has some UV curing glue that
hardens under a black light or 405nm laser.
Lisa Pavelka Magic-Glos UV Resin, 1 oz: Crafts : Walmart.com
