Re: [Leica] Testing rangefinder

[Nathan Wajsman <nathan.wajsman@euronet.be>]

Richard,

Thanks. I think I that on my initial series of test shots, the focus error at 1m
was my fault. However, I have since discovered that when I focus on something
that is 1m away from the film plane (as measured with a tape measure), the focus
indication is 1.1m on the lens barrel. Same result with two different lenses,
indicating something amiss in the rangefinder. On the other hand, I suppose the
bottom line is that images that appear sharp in the viewfinder are also sharp on
film, whatever the lens barrel indication, and that appears to be the case.

Perhaps I should stop testing the camera and just take pictures...

Nathan

rurmonas@senet.com.au wrote:

> The closest focus has the smallest DOF so focus errors will be most obvious.
> A constant positional error (i.e. a misalignment) will however give the
> largest error at infinity.
>
> I am surprised that there is an obvious error at 1m, but there is no
> observable error at 2m.  At 1m a focus offset of 10cm represents a huge
> error.  The most likely explaination for this is incorrect focus on your
> part.
>
> Test photography can be useful to determine the behaviour of the
> camera/lens and/or photographer.  It is important to devise tests
> which minimise the influence of "one off errors".  In the case of
> your test I would recommend photographing at 1m, 2m, etc. then
> returning to 1m and repeating the tests.  This would give two
> well seperated focusings at each distance.  An equal error on the
> two photographs at the same distance would then more clearly indicate
> an equipment problem.  Note that focussing at 1m then rephotographing
> immediately afterwards is not as strong a test as seperating the two
> focussings.
>
> Richard Urmonas
> rurmonas@senet.com.au



- --
Nathan Wajsman
Overijse, Belgium

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