Re: How do you test if camera lenses match?

[P3D John Ohrt <johrt@xxxxxxx>]

P3D Grant Campos wrote:
> 
> Hi,
> 
> This might be a question for John B., but here goes.
> 
> I searched the archives to try and get a definitive answer as to how
> to test if lenses are matched.  I read about taking pictures of grid
> patterns and making sure the diagonal measurements of the grid patterns,
> were within 1% (?) of each other, but then I'd have to use film and I
> don't want to have to do that.


Use a ground glass and measure with calipers.

Really, the simpest way is use film, develop it, and scan it.  Very
accurate too!

> Would it be sufficient to take them out into the sun and compare their
> infinity focus (see how far from the off white paper each one is when
> it starts to burn the paper).  Then if their infinity focus distance
> is within 1 % (0.1 %?) can I use them to make a stereo camera?

The sun isn't a point source, hence a poor reference.  One way is to
perform a foucalt test and measure the distance from the focus plane on
the optical axis to the referenece plane on the back of the lens where
it mates with the camera body.  A pretty trickey test, but it will give
you the accuracy you are asking for.  If you don't want to use film, you
probably will like even less the cost of such a test step!

Frankly, I'd be very curious to here of a simpler solution than shooting
film.  Go to Walmart (or whatever), buy their cheapest film, and have it
developed the cheapest way.  If the only frames are the two shots, you
are only going to pay for two prints and developing!

Good luck,

John

--
John Ohrt,  Regina, SK, Canada
johrt@xxxxxxx


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