Optics Engineering
Optics Engineering
(OP)
Hello,
I have an application where I need to linearly move a focusing lens (1mm diameter, 37.5 mm long) about the x, y, and z axis, as well as provide rotational freedom within a tube with an ID of 37.5mm (same as focusing lens length). I've looked at all the optics companies websites and they offer combination linear/rotational units, but at very steep prices. I was wondering if anyone knew of an inexpensive means of performing the above, possibly through the use of worm gearing, rack and pinion, etc. There needs to be fine adjustment with this, so that the user can lock in the correct focal length when the focusing lens is in the correct position. Any help on this would be greatly appreciated.
Kevin
I have an application where I need to linearly move a focusing lens (1mm diameter, 37.5 mm long) about the x, y, and z axis, as well as provide rotational freedom within a tube with an ID of 37.5mm (same as focusing lens length). I've looked at all the optics companies websites and they offer combination linear/rotational units, but at very steep prices. I was wondering if anyone knew of an inexpensive means of performing the above, possibly through the use of worm gearing, rack and pinion, etc. There needs to be fine adjustment with this, so that the user can lock in the correct focal length when the focusing lens is in the correct position. Any help on this would be greatly appreciated.
Kevin





RE: Optics Engineering
Most lens adjusters like in a telephoto will have a triple start thread so that the lens will move the full travel with one rotation of the adjuster ring. Will the client be setting the focus once and leaving it or will they need to have adjustment available continuously?
Harold
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Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
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RE: Optics Engineering
> What resolution and accuracy do you need?
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RE: Optics Engineering
Kevin
RE: Optics Engineering
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RE: Optics Engineering
We keep cost down by designing the fixturing (adjustments) out of the product. If this is an installation that won't be re-adjusted after set-up then the lens can be positioned at the factory so that it is not skewed. The key will be keeping the optical center (as opposed to the mechanical center) aligned with the system axis as it moves. That is why adustable lens assemblies travel without rotation. We typically design custom dedicated mounts for optics instead of buying catalog adjusters. The exception being for test benches or fixturing.
To keep the lens on axis, mount and secure it within the lens tube using tangent locating surfaces instead of the O.D.. If the system is super sensitive you might need to align the lens and then glue it in place.
To keep the assembly on axis as it moves you might consider using a slip fit with a sleeve that is split so that it can be locked down after adjustment. We have also had good results using a "V" groove locator that is constructed by having one off axis bore that is slightly larger than the lens mount and another off axis radius that creates two lines of contact. Lock the lens assembly in place with a set screw. The better your pre-alignment and lens positioning the less impact lens adijustment will have on the final alignment.
Harold
SW2009 SP4.0 OPW2009 SP2 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600
www.lumenflow.com
RE: Optics Engineering
Nearly everything can be compensated for by design.
While doing so might appear to more expensive, up front, the apparent savings is vaporous, and you'll spend far more in technician and customer time unnecessarily tweaking and adjusting in the field, where you cannot have anywhere near the control and instrumentation you have in the factory.
If the focus point is changing during adjustment, it's a problem in the construction of the entire optical train, so a well-designed assembly process will minimize that; we've designed systems where the repeatability of boresight over the focus range is way better than 50 microradians, and we've even purchased off-the-shelf optics that can achieve better than 150 microradians of boresight retention.
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RE: Optics Engineering
Kevin
RE: Optics Engineering
Also have you looked at helical focusing elements for cameras. One of many at SK Grimes. There other components used on large format cameras that might be interest, like the rack and pinion focusing mechanism and the element that will allow you to skew, for lack of a better word, the image.
http://www.skgrimes.com/thisweek/1_5/index.htm
RE: Optics Engineering
Kevin
RE: Optics Engineering
Another way would be to use a worm and pawl arrangement, like on the older level wind fishing reels to drive the tube. There would be a little lost motion but not if you were driving in one direction or the lost motion could be compensated for as you mention with a spring.
RE: Optics Engineering
Are you sure about those lens dimensions? 1mm diameter (.039") is pretty small to be 25.4mm (1.0") from the LED source. The only lens I could imagine Doric providing in that small of diameter would be a ball lens. By any chance would the diameter be the 37.5mm dimension? Unless you have a collimating optic on the LED it seems like you would lose a lot of the output by squeezing it through that small of an aperture and the output would change as the lens is repositioned.
When IRStuff is asking about resolution and accuracy I assume he is refering to the system sensitivity and that would be driven by the lens specifications.
Positioners like the assembly from SK Grimes (nice link unclesyd!) are the tube in a tube with a thread you are considering. The fixed tube is typically the "C" Mount which will have slots cut into it; the lens tube will be mounted in a threaded tube that has material removed to match the slots in the "C" Mount; the threads are the triple (or more) start threads that I mentioned previously; the female threads are cut into an outer sleeve that when turned will move the lens assembly. Take a look at Schneider optics "C" Mount lenses for an idea on how the lock the focus after adjustment.
The accuracy requirements (system sensitivity) will drive the machining tolerances for the sleeves and tubes, etc.
For extremely sensitive systems we have used guide rods instead of the slots but that requires more space and tight tolerances. To get the data on the triple start thread I use the thread calculator program ME ThreadPal.
Harold
SW2009 SP4.0 OPW2009 SP2 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600
www.lumenflow.com