Autocollimator vs ground glass in setting infinity focus

[L David Tomei]

That is not very expensive, but sending it to me would cost several times more than the price of the faceplate.
Now it states in the description that "They are used in CRT's, camera tubes, CCD coupling, and image intensifiers."
So it came to my mind I could look in some old CRT computer monitors. Am I wrong and if not, where exactly to look?
In a different formulation: Does every CRT contain such a part?

That funny... When I started using the 3:1 FO taper 20 years ago, it cost $3000. Mine was a flawed reject made of fibers with black glass cladding. These days, the price is very reasonable. David

 

[hanskerensky]

Having worked with 3 auto-collimators now (Franke&Heidecke, Zeiss/Voigtländer and Gokosha) i know that you can run in trouble with these instruments if you neglect to calibrate just before you do a test. This calibration is usually done on a flat surface mirror under the lens.
You need calibration for 2 things :
1) If your auto-collimator has a focus adjustment . To check the infinity focus of the instrument.
2) To adapt the occulair to the state of your eye-vision at that moment just before the test
is conducted.

Usually in an auto-collimator measurement your eye is part of the optical system as the image coming from the occulair is projected on your retina. So, if the occulair is not well adapted to your eye-sight you'll have an error in the focus adjustment of the test object.

However a properly calibrated auto-collimator is very exact and is just a very covenient instrument because you litterary can check the infinity focus of cameras night and day.

Bringing a groundglass in the filmplane and observing the image projected on that is also a very good way to go as, even when using a magnifyer to see that image, the focus distance will not shift because of eye-sight. This method was also used in the "old-school" camera repair shops but the infinity target was usually a collimator, not a tree in the distance.

Both type of measurements can only be accurate if you bring the groundglass/mirror exactly in the filmplane and that is also a point were errors are easily made as even the slightest difference (i.e. gap) will ruin your infinity adjustment.

Here an image of a vintage professional groundglass type focus tester :

And here the vintage Collimator which was used in combination with the focus tester above :

 

[Steve M.]

Careful if you go rooting around in a CRT monitor. I'd imagine they're like color TV's and have quite a charge stored and waiting for a ground to discharge to.

Thanks for the tip of scotch tape on a CD. I normally just stretch the tape across the rails and hope I don't hit it w/ the loupe when focusing. As an alternative, I have an old, shattered 4x5 GG that works fine as well. Normally, doesn't matter whether it's a 35mm camera or LF, I generally set focus on the neighbor's antenna pole about 150' away. Never had any unsharp photos using this method.

 

[Eugen Mezei]

Steve, I'm avare of loaded capacitors and be careful. But still need to know where to look for these fiber boundles.