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anyone know anything about optical comparators?

RC99

Diamond
Joined
Mar 26, 2005
Location
near Rockhampton, Queensland, Australia
I have a Kodak "contour projector" here I use from time to time.

Today I discovered one of the lenses that directs the light from the light source has cracked into two. When I pulled the assembly apart, well it fell apart with multiple ways to go back together.

Anyone know what does this series of lenses might do as maybe I could cobble something else in there in this day and age. I thought it might collimate the light, but it always threw a larger beam then the objective lens.

Oddly enough, the machine still seems to work without any lens system near the light source.
 
Oddly enough, the machine still seems to work without any lens system near the light source.

If it still works, I'd guess the intensity is not as evenly distributed center to edges?

If so, the assembly had the same function as - ISTR it was called a "condenser?" - found in a darkroom enlarger for general photographic work, pre-digital days. Three pieces of glass, IIRC, at least one of them "heat absorbing" - or heat-spreading more realistically, so as to reduce risk of cracking and such.

Your one may be common with, or close-enough, to one of those that you could adapt it.
 
How many glass lens elements do you have? Any loose spacers, etc? If it a simple condenser it will be two plano-convex elements with the convex surfaces facing each other. If there's a heat absorbing element it will face the bulb.
 
There are four elements and they are all meniscus lens shaped.

The one that has broken is smaller then the others, it went next to the bulb, which I modified from the unobtanium bulb to a halogen one.

I will get some photo's tomorrow.
 
The replacement of the bulb with a halogen bulb likely a primary cause of the lens failure, due to the extra heat output typical of halogen elements. The 4-element meniscus may very well be this design, patented by Kodak:

Patent US2865252 - Wide field objective comprising four highly meniscus elements - Google Patents

You may be able to find something at Edmund that would be close enough to work. I would suggest finding a glass window to mount in front of the halogen element to eliminate the IR spectrum from getting to the lens assembly, whether you replace the broken lens element or not, otherwise you may see a succession of failures. Fiber optic illuminators that employ halogen elements typically have a similar window at the output port to filter the heat, thus protecting the fiber and taking the IR out of the illumination output. I suspect you could find a filter like this at Edmund also.
 
No claim that I "know" about optical compartors but have some experience so some thoughts:

The idea of the optic train in the light source is to provide collimated light.
Unfortunately you need lots of light so some compromises are needed.
Better systems will have a condenser, followed by an adjustable stop and then a collimator.
All such systems are very sensitive to filament placement to work correctly. With the back end so short moving the bulb just a little bit will change the beam a lot.

It is a "shadowgraph", the ideal light would be an infinitely distant point source, the sun comes close to this and produces nice shadows.
Here you don't have a lot of distance to work with and true collimation does not project enough light.
Most will have a adjustable light stop that makes a better beam but dims the screen. Many also have a color filter which dims things but helps the optics.
Multi element designs also help a lot when working with "white" light.

They will make an image with just a bright flashlight.
The test is on round parts in two orients on all four edges (or suspended balls) and the same with a gage block.
Not only should the image look crisp but the parts should also measure correctly in both x and y.

There is also a correction for magnification in the four quadrants of the screen, this is done by adjusting the mirror mounts.
Cleaning and adjusting the light source, magnification and screen alignment is a 2-4 hour job for an experienced tech.

You can get rid of the heat on the optics with a hot mirror. These reflect "heat" while allowing visible light waves through.
This heat has to go somewhere so you have to vent the lamphouse. With or without you will need a cooling fan using halogens and most movie projector bulb type machines already have that built in.

Always turn off the light if walking away even if for minutes.
One way to see the "Bad Bob" come out is to leave your light source turned on at the compartor when you are not using it.

You can get away with a lot of bad things here if your use is limited to certain type parts or measurements and short usage intervals.
A single element with the bulb filament at focal will make a sort of collimated output, one would not want a reflector.
Bob
 
Thanks everyone.

Here is a picture of the lenses.

Also a picture borrowed off the internet of the same model of mine, showing the throw of the light.

20170806_122404.jpg kodak profile projector.jpg

I do not use the comparator for much, it only has a barely readable cross hair on the screen and I just do basic measuring of hard to measure parts.

I have found out how I think the lens are supposed to go, on the original patent. Two face the same way, then two back to back. https://patentimages.storage.googleapis.com/pages/US2552238-2.png

The patent even generously provides the specs. radius of 33mm one side and 23.4 the other, which measure up to what I have.

Patent US2552238 - Profile projector and optical comparator - Google Patents

Now who makes lenses that are affordable :D
 
Now who makes lenses that are affordable :D

"A" lense. One.

I don't see anything at all wrong with the other three. Little hero threw itself on the heat-grenade. That Halogen light source heat budget needs looked at, as already mentioned, to prevent a repeat.

My guess is that for no more than you use the rig, the damaged lense could be replaced with anything "close". Or maybe even NOT very close.

Time was, film and paper era, hobby gear being constantly abandoned as interests changed, the zone was flooded with used-but-good enlargers going cheap.

Edmund or such may be easier nowadays. Should be cheap enough as far as shipping costs go.
 
OT but title reminded me

No help on the comparator, but the title reminded me of a joke from 50 or more years ago.

A guy it taking a parachute jump, and when he pulls the cord nothing happens. Quickly he tries the reserve, and again nothing.

He's hurtling towards the ground and son of a gun but he doesn't see a guy shooting up towards him. As they get close he yells to the only other possibility, "Do you know anything about parachutes?"

The other guy yells back, "No. Do you know anything about lighting a water heater?"
 
What do you mean "full open"

There are cheap lenses at surplus shed. According to the website Edmond does not as a stocked item carry anything close to my requirement.

It would not surprise me if a camera wide angle lens in reverse would not achieve the same thing.
 
Another parachute story...

So a new recruit is getting ready for his first jump. Sergeant tells him, "Don't worry, just pull the cord. If that doesn't work, pull the emergency cord. When you get down, a truck will pick you up."

So he jumps, and pulls the cord. Nothing. He pulls the emergency cord. Nothing. He shakes his head, and says to himself, "Fuckin' army. I bet that damn truck won't be there, either."
 
ahhh but you have get rid of the heat, the existing fan in the system is obviously not good enough. Or maybe use a LED light, although I think they put out light differently to a globe.

Fans are for convection, heat sinks for transfer by conduction.

Your heat is radiant. LED can help, but is not magical, either.

The "glass" that best handles the job is probably in your kitchen.

Not so good at "transparent", unfortunately.
 
Since you know the radii maybe this helps: (it's a PDF download of the lens maker formula for a thin lens with a sample solution)
https://www.google.com/url?sa=t&rct...ns.pdf&usg=AFQjCNGjPPs_2QpDtONyXAz0rO1tNHl2cw

I found two online calculators and they say around 131mm focal length.

I get out the autocollimator for it's source of parallel light and putting the glued together lens up to it, I can focus the light to a tight spot of sorts at around 70mm.

So which one is right.
 
I found two online calculators and they say around 131mm focal length.

I get out the autocollimator for it's source of parallel light and putting the glued together lens up to it, I can focus the light to a tight spot of sorts at around 70mm.

So which one is right.

If that "glue" was no worse than is used for repairing stone chips to motorcar windscreens... or attaching rear-view mirrors?

Find a way to reduce the heat input, and JF use it, glued. You weren't going to marry the creature, so no need of an intact Virginity Certificate.

A thick, FLAT pane of "heat absorbing" glass ahead of the first element, plus a change to LED source, and short eyes-ready-only "ON" time might do that cheaply?
 
I found two online calculators and they say around 131mm focal length.

I get out the autocollimator for it's source of parallel light and putting the glued together lens up to it, I can focus the light to a tight spot of sorts at around 70mm.

So which one is right.

The actual glass used can have some effect on the focal length due to refractive index differences, and various accumulations of errors (measurement setup for radius, reconstruction of broken lens, etc.) can have some additional effects, though perhaps not in the 50% category. The major result you want to achieve is a less divergent beam headed for the objective, so you have most of the available light for use, and that you overfill the objective's clear aperture, to make sure you have illumination across the field. The uniformity is most likely to be the primary characteristic affected by the "wrong lens".

If you were to substitute LED illumination, I suspect there would be zero need for heat isolation.
 








 
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