Microfilm reader as optical comparator?

Discussion in 'Horological Tools' started by karlmansson, Jun 14, 2019.

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  1. karlmansson

    karlmansson Registered User

    Apr 20, 2013
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    Hello!
    I just found a new second hand store in town and in it an old, German made microfilm reader with a busted bulb. It was Minox K6 if I'm not mistaken.

    I've tried to read up a bit on optical comparators and I think I've understood them pretty much. The key lies in having an beam line that is perfectly straight from the work as to not create distortion, and have optics with a known focal length at a high accuracy to be able to make measurements.

    Could a microfilm reader be converted into an optical comparator? The bare a striking resemblance in many ways. They project an enlarged profile of an object onto a screen onto which drawings can be attached.

    Regards
    Karl
     
  2. karlmansson

    karlmansson Registered User

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    Sorry, that should be microfiche reader.
     
  3. etmb61

    etmb61 Registered User
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    I would think the mirror and reticle are probably just as important as the optics. You could certainly get an enlarged view, but probably not much accuracy. Interesting idea though. I'll have to pull out that old overhead projector I have.

    You might be able to do better with a USB microscope.

    Eric
     
  4. DeweyC

    DeweyC Registered User
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    Karl,

    What is your application? As you know, I find it invaluable when I need it; but I got it very cheap here in the US and I know tooling is dear in Europe.

    If you want it as a profile projector, then you might consider an old opaque projector. As Eric pointed out, you will need a way to verify/adjust parallelism of the projected image to the drawing, but I doubt this will be an obstacle for you.

    For optical measurement, while you cannot get the resolution of an optical comparator at 100 or even 20x, I have found a good quality scope (Nikon, American Optical, Bausch, Olympus, etc) with a reticle meets most needs. Most of our work requires being able to interpolate to .005mm which is very easily done with a reticle graduate in .01mm.

    The downside, of course, is the field of view (about 50 mm at 10x) which makes it impractical for plates.

    In my opinion, an opaque projector will be easier to adjust than a reader. Talk to the guys in the audiovisual dept. They likely have one taking up space.

    I suppose if you determined the projections' scale, you could even take measurements off the image with a caliper and divide. This would certainly reduce measurement error compared to direct measurement if you were certain of the parallelism. It would like be picking off measurements from the optical comparator screen with a caliper (why anyone would do that I do not know, but...)
     
  5. Dushan Grujich

    Dushan Grujich Registered User

    Jun 20, 2003
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    G'Day Karl!

    I would not go down the path of converting microfiche reader. Based on work that I have done over years repairing and adjusting various optical instruments, I do not believe that it would work in a satisfactory manner. With a little patience, knowing what to look for, one can easily and affordably get all the specialised equipment needed for one's workshop.

    Myself, I was unable to find an affordable optical comparator, nor a shadow projector. However, I came across Carl Zeiss Stereo Microscope Projector - Plastival 50 which serves as an optical comparator quite well, although it lacks angle measuring capability. These microscope projectors appear now and then on eBay.de, I have even seen one sold on eBay.co.uk. People do not know much about these devices so they get sold fairly cheap. I got mine years ago at the cost of some EUR 300, IIRC. It came with complete set of accessories, it can be used for observation of objects with transmitted or reflected light, or the combination of the two. Plus it is small and does not require half of the workshop space to place it at unlike most of the optical comparators discarded by the industry. Light source is a 50 W halogen bulb located at the back of the device and the object is illuminated by the use of fibre optic cables, I have unit shown on a web page with basic description and few optical diagrams showing essentials, click here.

    Carl Zeiss Plastival 50 is smartly designed and it allows one to take accurate measurements by comparison, it can magnify objects 8x, 12.5x, 20x, 32x and 50x, projecting accurate and non distorted images onto a frosted screen 160 mm in diameter and 120 mm high. I do not use it every day, but when needed it is irreplaceable. It works well in combination with an old single axis measuring microscope, not a modern stuff, but it works quite nicely, click here, and it can not be beaten by anything cost-wise. The little thing measures with resolution of one micrometer and I paid for it only EUR 100.

    Cheers, Dushan
     
    DeweyC likes this.
  6. karlmansson

    karlmansson Registered User

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    Application is, as ever :), watchmaking, clockmaking and toolmaking for the previous two. Being able to inspect parts after manufacture and see how they compare to drawings and nominal dimensions. Opaque projector, wouldn't have thought of that. I think I'll eventually go down the microscope route, or the one suggested by Dushan below.

    Thank you for the suggestion! I seems a lot more reasonable. The microfiche reader was about the size of a standard CRT TV and just about as heavy. Shop space is limited. I'll be on the lookout for the Plastival!

    Thank you to everyone who showed an interest in this thread! On starting it, I was seeing much more possiblities than problems. The microfiche reader was even on sale (at the thrift store...!) at about 20 dollars. I may have been able to cobble something together from it but for checking precision parts I think cobbled up is not good enough. I do find enjoyment in making things from other things but my experience from making an engraving vise from a discarded bowling ball has taught me that not every such project is as enjoyable as one might think. I mean, the vise works, and pretty nicely at that, but sawing the ball apart with a hand saw didn't make me want seconds.

    Best regards
    Karl
     

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