Thread: Optical protractor

Hello,

I just aquired a vintage optical protractor in mint condition for a killer price.

Built in the 80s or early 90s.

0-360 degrees measurement range with 5' resolution.

Besides the obvious, that can measure angles, how usefull is such a tool compared to let's say an electronic protractor?

Thank you



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Never have to worry about EMP or battery problems!

Super nice..could have used that in sharpening and making cutting tools.

In the mean time I found some more info related to this device.

It is a copy of the Carl Zeiss Jena device.

I have no clue if it is a clone or a licensed copy, but the build quality is super nice.

I also found a scanned copy of the original user manual.


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I've got one of these made by Helios. Nice tool. It still has the original inspection sheet showing that the errors in the dividing circle are 10 seconds of arc. The instruction sheet claims that even though the markings are 5 arcminutes one should be able to get 1 arcminute accuracy in reading or setting the scale.

Originally Posted by DLF

In the mean time I found some more info related to this device.

It is a copy of the Carl Zeiss Jena device.

I have no clue if it is a clone or a licensed copy, but the build quality is super nice.

I also found a scanned copy of the original user manual.


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Carl Zeiss Jena found itself in "East" Germany after the war. And when reunification happened 1989/1990 Carl Zeiss Oberkochen (West Germany) managed to support Carl Zeiss Jena with additional funding. CZ-Jena did manage to trade optical products (for example related to photogrammetry) to the West etc.

What you have does not look like the CZ-Jena device.

Could it be a Russian/ East German/ Hungarian etc. Universal Angle measurer … (I.e. not a direct knock off) but maybe both of them have a common ancestor ?

Originally Posted by cameraman

Carl Zeiss Jena found itself in "East" Germany after the war. And when reunification happened 1989/1990 Carl Zeiss Oberkochen (West Germany) managed to support Carl Zeiss Jena with additional funding. CZ-Jena did manage to trade optical products (for example related to photogrammetry) to the West etc.

What you have does not look like the CZ-Jena device.

Could it be a Russian/ East German/ Hungarian etc. Universal Angle measurer … (I.e. not a direct knock off) but maybe both of them have a common ancestor ?

Thenk you for the info.

Like mentioned in the original post, it is a copy. And you are right, it was made in the eastern part of the world, in Romania by a company called Mecanica Fina.

And it looks and functions just like the CZ-Jena device. I figured this ouy after going through the manual.

I just wanted yo know more about the origins of the device.

BTW: I checked it against my precision ground cylinder block. Measures 90.00 degrees spot-on.

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Since I mostly lurk in this forum, I thought that I would try to contribute a bit. So here is a picture of my tool in the box. This one carries the "Helios" brand but was made by Schneider & Kern in West Germany late in 1969. There is a shorter and longer protractor beam which can be inserted.



Here is a close up of the head. The black lever clamps the long arm or short arm in place. These are keyed. The lens is above the lever and has an adjustable focus. The black object to the right of that is a lens cap which I have removed. The knurled knob to the top left is a screw which is connected to a worm gear. When engaged (ein) it turns the gauge by small amount. When disengaged (aus) then the gauge can be turned by hand through large angles.



Here is another view. The knurled ring visible on the side is used to lock/unlock the angular motion. Loosen this before engaging/disengaging the worm, and use it to snug or lock the protractor in place.



Here is a very blurry shot of what one sees through the eyepiece. During a full revolution the angles run 0->90/0->90/0->90/0->90. Each degree is broken up into 3 groups of 4 divisions each, so 12 divisions per degree (each being 5 minutes of arc).



Here are the instructions in five languages (German, English, French, Spanish and Italian). The accuracy of the dividing circle is +- 5 seconds of arc and the overall accuracy is +-30 seconds of arc. The test table shows the error in angle in arcseconds.



Here are the other two languages and the cover page:



Overall a very nice tool, and one that will still be working in 100 years.

Cheers,
Bruce

Originally Posted by ballen

Since I mostly lurk in this forum, I thought that I would try to contribute a bit. So here is a picture of my tool in the box. This one carries the "Helios" brand but was made by Schneider & Kern in West Germany late in 1969. There is a shorter and longer protractor beam which can be inserted.



Here is a close up of the head. The black lever clamps the long arm or short arm in place. These are keyed. The lens is above the lever and has an adjustable focus. The black object to the right of that is a lens cap which I have removed. The knurled knob to the top left is a screw which is connected to a worm gear. When engaged (ein) it turns the gauge by small amount. When disengaged (aus) then the gauge can be turned by hand through large angles.



Here is another view. The knurled ring visible on the side is used to lock/unlock the angular motion. Loosen this before engaging/disengaging the worm, and use it to snug or lock the protractor in place.



Here is a very blurry shot of what one sees through the eyepiece. During a full revolution the angles run 0 ->90->0->90->0. Each degree is broken up into 3 groups of 4 divisions each, so 12 divisions per degree (each being 5 minutes of arc).



Here are the instructions in five languages (German, English, French, Spanish and Italian). The accuracy of the dividing circle is +- 5 seconds of arc and the overall accuracy is +-30 seconds of arc. The test table shows the error in angle in arcseconds.



Here are the other two languages and the cover page:



Overall a very nice tool, and one that will still be working in 100 years.

Cheers,
Bruce

Ahhh the images didn't lay up now they do !

That's super interesting will study those.

Just realised that my photo has the protractor upside-down in the case. For the record here is how it should look.



When my father died and I went through his tools, I discovered that the ones which were not in cases or boxes were rusty, corroded, or in poor shape. The tools in boxes were all in much better condition. So for me, a well-fitted wooden storage box does a lot to increase the long-term value of a tool.

One thing I do not understand.

My protractor has a small cap to protect the optical visor.

The cap has a small opening which allows reading and the manual states that it permits reading with a 1 arcminute precision. I attached the corresponding manual paragraph (german only).

How can this be possible considering the scale has 5 arcminute divisions?

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Originally Posted by DLF

The cap has a small opening which allows reading and the manual states that it permits reading with a 1 arcminute precision.

Actually it says that parallax errors are below 1 arcminute. Here is a translation:

Sealed against dust and humidity. The ocular has a protective cap and has a field of view which is so small that there can not be more than 1 minute of parallax error. This ensures parallax-free readings.

On the instructions for my scale it says that the markings are 5 arcminutes apart which makes it possible to estimate within about 1 arcminute of the correct value.

Originally Posted by ballen

Actually it says that parallax errors are below 1 arcminute. Here is a translation:

Sealed against dust and humidity. The ocular has a protective cap and has a field of view which is so small that there can not be more than 1 minute of parallax error. This ensures parallax-free readings.

On the instructions for my scale it says that the markings are 5 arcminutes apart which makes it possible to estimate within about 1 arcminute of the correct value.

Hi ballen,

I can read german. But I did not quite understand the parallax error thing.

After some more reading, here is my version (in simpler terms): the small cap will not increase the instrment's precision, but will improove the operator's capability of reading the scale. If not for the cap there would be a wide viewing angle of the scale which would result in slightly different readings depending on the viewing angle.

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Resolution may be one arc minute but accurate no way.
Think about this number, the device and touching it on to a part in the real world.
On a half inch part this is just over a tenth. My 100, 300 and 500 power systems are pressed hard to do this and they are not a touch/feel device as this is.
Most certainly a great measuring tool for it's intended use.
Bob

Originally Posted by CarbideBob

Resolution may be one arc minute but accurate no way.
Think about this number, the device and touching it on to a part in the real world.

On a half-inch part I agree. But if you are using the 200mm (8") blade against a ground or machined surface, then 1 arcminute corresponds to about 0.06mm (0.002") at the end of the blade. That is easy to see/feel/measure.

In post #1 last image, if that’s the view I’d get with jewelers glasses on you can divide inside of 5’, one minute would be a stretch though. I think it’s a parallax resistant feature. The one in post #8 I’m not so sure, prolly just the camera.

Nice lookin’ tools though, & sure beat the crap out of my 80’s era japanese hardware store version.

Good luck,
Matt

Hi Matt,

My eyes are not very good, but my right eye is nearsighted. So if I take off my glasses and adjust the focus correctly, I can easily resolve if the indicator line is aligned with one of the scale marks, or 25%, 50%, or 75% over. So I am confident that I can split that 5 minutes of arc into four roughly equal parts. Not nearly as accurate as my Talyvel 4, but nevertheless useful.

Cheers,
Bruce