Ideas for projecting a grid pattern onto a microscope base

[e100]

I have a stereo microscope with a long working distance which makes it difficult accurately place the PCB being viewed in the centre of view before I look down the eye pieces. Essentially I have to look through the microscope and wiggle the board around until I recognise landmarks. Not so easy when one part of the board looks almost identical to some other part of the board. I haven't been able to find an off the shelf LED spotlight with a sufficiently narrow beam to make a centre alignment spot.
Concentric circles or a grid pattern with an outside diameter of about 20mm (3/4 inch) in diameter would be ideal. The light source will need to be at least 10cm away from the point of focus so there is room for my hands and a soldering iron.

I thought about using a 1mW laser to project a centre spot but mixing lasers with magnification runs the risk of eye damage and they have a short life span so I abandoned that idea.
So I thought about the kind of grid pattern that some camera flash focusing lights use, or perhaps something like the $5 clock wall projectors you find on Ebay. I'm guessing that these shine a LED through a LCD display then focusing lens. If it isn't tiny then I could in theory replace the LCD with a grid pattern made from wire.
I'm probably re-inventing the wheel here, so if anyone has already solved this problem I would be interested to know.

Mike



 

[bradleytron]

Not fully sure what your trying to achieve however would it make sense to arrange a rig that allows you to swing a small plate of glass into and out of the optic axis of the microscope. The plate of the glass (acting as a beam splitter, BS) would be at 45 degrees w.r.t. the optic axis when in place to direct a beam from an LED with aperture to control beam diameter. The LED and aperture would be off to the side and perpendicular to microscope optic axis. This would cause the LED beam to be projected down onto the microscope bed. The LED power supply could allow you to adjust the intensity of the beam to a safe level. You could acquire an etched glass plate (expensive) with whatever grid pattern suits you needs or perhaps devise one on your own, e.g., if you don't need the grid pattern over the PCB all the time, that is only when aligning it, then you could Laser print a grid pattern on a sheet of acetate and affix it to the glass BS.

Hope this helps.

[pickle9000]

I'd use lasers like these

http://www.ebay.ca/itm/High-Brightness-5mW-650nm-Red-Laser-Module-Line-/380438513675?pt=LH_DefaultDomain_0&hash=item5893e7080b

and a proximity detector on the microscope to turn them off while you are using it.

...mke

[EEVblog]

I'd use lasers like these
and a proximity detector on the microscope to turn them off while you are using it.

Detector fails and you lose your eyesight. Not smart.
You can get graticules for microscopes, and even eyepieces with a graticule built in.
http://www.ebay.com.au/itm/New-MEIJI-Eyepiece-graticule-100-1cm-19mm-diam-/180886301845?pt=UK_Collectables_Scientific_MJ&hash=item2a1da9ec95#ht_500wt_1413

Dave.

[SeanB]

Cheap laser pointer on the fixed part of thearm and aim it at the centre of the table ( 0.5mW diode) and keep the current low enough ( feed it with 5mA instead of the 30 or so it needs to lase) do the spot is both small and dim. That way you can align the board, and even if the light is left on accidentally there is not much light to begin with.

[sonicj]

+1 for laser crosshairs  WoodRiver-Universal-Drill-Press-Laser-Attachment
-sj

[free_electron]

Simply beam light through one of the eyepieces ...
Shine a strong light through one of the eyepieces. it will appear as a spot on the board. align the board , remove light from eyepiece and off you go.
If you have a stereo microscope with a third port ( like for a camera attachment ) that is where you can put your light source. you can control it with a foot pedal.

I use that principle to align chips under the microscope. you have this big wafer with hundreds of chips and no clue what the lens is now pointd at. shut down primary light source and use the laser guidance beam ( the lasercutter has a normal light beam to set the aperture slits. ) as a guide. once the right chip is under the beam , turn on main lightsource , locate exact spot , switch to aperture slit , align the horizontal and vertival slit to get the correct shape of what you want to fire , focus , power up the laser and blast away. oh , and the eyepieces have special filters that block the UV and green laserlight. So it is safe to watch when firing. That laser is of the type you can see twice in your life ... once with the left eye and once with the right eye ...

[e100]

+1 for laser crosshairs  WoodRiver-Universal-Drill-Press-Laser-Attachment
-sj

Looks exactly what I'm looking for. As far as I can tell it projects two sheets of light that run through the axis of the thing you want to align.
It's $45 from the US, but Australian customs will seize any laser gear if the recipient doesn't have an import license (I have experienced this first hand).
So, to buy the exact same thing from an Australian supplier will cost $97 (http://www.woodworksupplies.com.au/prod489.htm). Someone is making a lot of money.

The irony is that it only consists of two $5 laser pointers each with circular rod lens and a plastic mounting bracket to keep them in position.

[e100]

Simply beam light through one of the eyepieces ...
Shine a strong light through one of the eyepieces. it will appear as a spot on the board. align the board , remove light from eyepiece and off you go.

Works great, I didn't think of that.
My microscope doesn't have a third tube, so I need to figure out an elegant way of mounting an LED torch so it can be temporarily made to point down one of the eye pieces then rotated away.

[e100]

I'd use lasers like these
http://www.ebay.ca/itm/High-Brightness-5mW-650nm-Red-Laser-Module-Line-/380438513675?pt=LH_DefaultDomain_0&hash=item5893e7080b

These look like the lasers used in the Woodriver alignment tool mentioned by sonicj.
As I mentioned in another post finding an Australian supplier is the hard part as it's impossible to import lasers into Australia without an import license.
Locally I can get <1mW laser pointers so I might try to cobble together something using a glass rod as the diverging lens to create a sheet of light.

[SeanB]

How about the cheap laser pointer with the hologram display that you screw on the front. Take a star shape and use it as an aim point.

[XynxNet]

If you are worried about the laser (which is perfectly reasonable in my opinion), just get a led and a condensor lens. You don't need a laser to generate a light spot.

If you have one of those el cheapo laser modules at hand you propably can retrofit it by replacing the laser diode with an led. Almost all cheap semiconductor laser modules do have a condensor lens built in.

[sonicj]

So, to buy the exact same thing from an Australian supplier will cost $97 (http://www.woodworksupplies.com.au/prod489.htm). Someone if making a lot of money.

Dang! My drill press was around $100 USD (on sale) and came with laser alignment. 
-sj

[e100]

If you are worried about the laser (which is perfectly reasonable in my opinion), just get a led and a condensor lens. You don't need a laser to generate a light spot.

I can focus an LED through a 30x magnifying glass to produce an image of the LED chip complete with bond wire which is about 8mm wide at the required distance. It might do the job. I'll have a look at the $2 lenses on Ebay.

[CampKohler]

The 99-cent Only stores we have here sell red laser pointers for uh, 99 cents. They are sold as toys to play with pets (they love to chase the dot), so you can bet that the power is so low there will be no eye damage, even with magnification. You could pull the batt out and connect the laser to a wall-wart of the appropriate voltage (probably 3v DC left plugged in (unless you are worried about not getting your full 99 cents worth out of the laser's life). A push button on the scope allowing you to turn on the laser only when positioning the board should solve all the problems.

[Bored@Work]

The 99-cent Only stores we have here sell red laser pointers for uh, 99 cents. They are sold as toys to play with pets (they love to chase the dot), so you can bet that the power is so low there will be no eye damage, even with magnification.

Famous last words. These things are so cheap for a reason. Parts of unknown origin, and any safety mark faked. There could be anything in this pointers, whatever someone found on a shop floor in China.

For years dodgy laser pointers appear withing the EU. Class 3R and 3B, but even class 4 lasers have been found. Pen style, torch style, key fob style, doesn't matter. Same with laser sights for soft air guns, lasers in leveling tools, even in child toys.

[e100]

I tried focusing an LED but gave up because of the 3 dimensional mechanical mounting complexity, so I found an Australian supplier of laser line levels on Ebay and purchased 2 for $30 including postage which is less than cost of the Woodriver tool in the US and a third of the cost of the same thing in Australia.

I just hold the levels to the microscope base using double sided sticky tape. The beams run through the optical axis of the microscope and intersect at about 60 degrees which isn't ideal, but good enough.
The lines are very dim and about 1.5mm wide which is just about perfect for my needs as the field of view is about 3mm in diameter.
I plan to add a momentary switch for alignment, firstly for safety and secondly so the monochromatic light doesn't affect the colour balance when looking through the eye pieces.
From an eye safety point of view, the lines are so dim that they are almost invisible under a fluoro work lamp.


Mike