Replacing the eyepiece on an autocollimator with a CCD

[LowEnergyParticle]

I have a Hilger and Watts TA-6 autocollimator that I use for measuring flatness of machine beds. My eyes get very tired looking through the autocollimater, so I was looking at possibly replacing the existing eyepiece with one of these CCD eyepieces and looking at the image on a computer screen. These CCD assemblies talk to USB ports, and are as low as $100 on ebay:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110272057863

If it works, then it will be a pretty nice setup for $100! I'll have to machine an adapter to fit the CCD eyepiece to the TAI-6 autocollimator, but that's OK.

I'm an EE, my knowledge of optics is embarrassingly small. I've got a couple questions if that's alright?

1. These eyepieces are intended for microscopes. Are the eyepieces for autocollimators different than ones for microscopes? (I've looked into the autocollimator's eyepiece, and it does not seem to have a reticle in it.)

2. This particular one comes with a 0.5x reduction lens. I don't know if that's good, bad, or indifferent. Does anybody know how this compares to an autocollimator's eyepiece?

3. The resolution on this one is 640x480. Like anything else, you can get more if you're willing to spend more! Does anybody have a feel for whether this resolution is enough to enable work that is at least as good as can be done with the naked eye & eyepiece?

Thank you very much for your time and expertise!

David

 

[IRstuff]

1. Possibly, each manufacturer is obviously free to pick and choose his eyepiece, although there may be plenty of good reasons for picking a standard one. The reticle shouldn't be in the eyepiece itself.

2. Unknown to me

3. 640x480 is comparable to broadcast TV quality, but, it's the compression that counts, so you need to know what compression they're using to get the video down the USB port. Hypothetically, since you're free to choose the display size, you might considerable amount of magnification from the display itself, making up for losses in compression. If the software allows you to electronically zoom, that'll be even better.

TTFN

FAQ731-376

 

[LowEnergyParticle]

Thanks very much, IRstuff!

The eyepiece barrel is threaded, so the focusing is done by twisting the entire eyepiece. There is no writing of any sort on the eyepiece: no manufacturer's name, no "power" of magnification, nothing.

I feel like I should be able to tell the CCD vendor more about the existing eyepiece. I can certainly measure the diameter of the lenses at both ends, the end-to-end length, the OD of the barrel, etc. but I have no idea how to tell what the focal length is or the magnification.

Are there any simple means by which I can determine these parameters?

Thanks again!
David

 

[IRstuff]

Not normally, since the eyepiece is usually not run at infinity focus, being the back portion of a lens train that includes the objective elements at the front of the collimator. That said, a typical microscope eyepiece as a back focal length on the order of half an inch.

TTFN

FAQ731-376

 

[IRstuff]

Also, in general, you can get away with gross mismatch of eyepieces, so long as you're not looking for optimum image quality throughout the field of view, which should be the case for an autocollimator, since the reticle is located at the center of the image.

I've gotten tolerable results jamming random optics in place of the eyepiece on a conventional theodolite, whose construction should be comparable to your autocollimator. Once, we stuck a night-vision goggle on the back of our T-3000 theodolite so that we could see a laser spot at night. While the overall image quality was pretty poor, the center of the field of view was quite usable.

TTFN

FAQ731-376