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Science Forum Index » Optics Forum » Dead Black
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| dbvanhorn |
 Posted: Wed Apr 16, 2008 12:53 pm |
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I'm looking at some cameras which are "high end" machine vision units.
They use M12 lenses, mounted in a plastic lens holder, which screws
directly onto the PCB. The internal surfaces are shiny plastic, shiny
solder joints, etc.
Am I nuts, or should everything that isn't an optical surface within
the optical assembly be coated "dead black"? How bad is this when
they aren't treating the surfaces? |
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| Jonathan Scheuch |
| Posted: Fri Apr 18, 2008 4:31 am |
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On Apr 16, 6:53 pm, dbvanhorn <microb...@gmail.com> wrote:
Quote: I'm looking at some cameras which are "high end" machine vision units.
They use M12 lenses, mounted in a plastic lens holder, which screws
directly onto the PCB. The internal surfaces are shiny plastic, shiny
solder joints, etc.
Am I nuts, or should everything that isn't an optical surface within
the optical assembly be coated "dead black"? How bad is this when
they aren't treating the surfaces?
In most cases the black plastic lens holder screws to the PCB, but
it's square base covers the entire image sensor chip. This base
should block light from the mounting screws and solder joints on the
PCB from reaching the image sensor surface. The inside of the lens
holder may be shiny black plastic which may not be ideal for
attenuation of stray light. However, cost is a driving factor with
these types of components. To get a better optical black finish on
the inside would probably drive up the cost too much. |
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| dbvanhorn |
| Posted: Fri Apr 18, 2008 10:37 am |
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Quote: In most cases the black plastic lens holder screws to the PCB, but
it's square base covers the entire image sensor chip.
That's how it is on these.
Quote: This base should block light from the mounting screws and solder joints on the
PCB from reaching the image sensor surface.
On these, there are solder joints and vias near the imager, under the
housing.
Quote: The inside of the lens holder may be shiny black plastic which may not be
ideal for attenuation of stray light. However, cost is a driving factor with
these types of components. To get a better optical black finish on
the inside would probably drive up the cost too much.
Well, I'm not that cost sensitive, I'm just trying to get a handle on
how much improvement I could get.
I have to use these in everything from barely moonlight to "staring
into the sun, on the snow pack, at noon"
I'm also concerned that there's no real seal between the lens holder
plastic and the PCB, but I can solve that easily enough with some
black paint that will wick into that joint.
I'd use larger lenses too, but we're mechanically constrained from
that. |
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| Marc Reinig |
| Posted: Sat Apr 19, 2008 1:45 pm |
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Quote: I'm also concerned that there's no real seal between the lens holder
plastic and the PCB, but I can solve that easily enough with some
black paint that will wick into that joint.
I'd use larger lenses too, but we're mechanically constrained from
that.
If the seal is to keep out light, you're fine with black paint. However, if
it is for humidity, use an appropriate epoxy or sealing ring and check if
the rest of the lens is hermetic.
Marco
________________________
Marc Reinig
UCO/Lick Observatory
Laboratory for Adaptive Optics
"dbvanhorn" <microbrix@gmail.com> wrote in message
news:85892652-8f7f-4e1a-9c83-6cabc56c7284@e67g2000hsa.googlegroups.com...
Quote: In most cases the black plastic lens holder screws to the PCB, but
it's square base covers the entire image sensor chip.
That's how it is on these.
Quote: This base should block light from the mounting screws and solder joints on
the
PCB from reaching the image sensor surface.
On these, there are solder joints and vias near the imager, under the
housing.
Quote: The inside of the lens holder may be shiny black plastic which may not be
ideal for attenuation of stray light. However, cost is a driving factor
with
these types of components. To get a better optical black finish on
the inside would probably drive up the cost too much.
Well, I'm not that cost sensitive, I'm just trying to get a handle on
how much improvement I could get.
I have to use these in everything from barely moonlight to "staring
into the sun, on the snow pack, at noon"
I'm also concerned that there's no real seal between the lens holder
plastic and the PCB, but I can solve that easily enough with some
black paint that will wick into that joint.
I'd use larger lenses too, but we're mechanically constrained from
that. |
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| dbvanhorn |
| Posted: Sat Apr 19, 2008 2:47 pm |
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Guest
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Quote: If the seal is to keep out light, you're fine with black paint. However, if
it is for humidity, use an appropriate epoxy or sealing ring and check if
the rest of the lens is hermetic.
I'm not aware of anything that's particularly sensitive to humidity,
and this is within a sealed enclosure anyway. |
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