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Re: Tolerance

  • From: Edward Meyers <aghalide@xxxxxxxxx>
  • Subject: Re: Tolerance
  • Date: Thu, 29 Apr 1999 07:57:14 -0400 (EDT)


On Thu, 29 Apr 1999, Robert Durn wrote:

> I have just taken some test shots with my new home made "Roboscope 2"
> camera! It uses 120 film stock and a 24mm Nikon lens. The image measures
> 152mm on the negative for a full 360 degree. Using the 2 x focal length x Pi
> rule it should be 150.796mm. Is this within tolerance? The images are
> sharp-ish but I'm not sure if the lens is mounted at the correct distance to
> the film. Should it be 46.5mm for Infinity?. Any thoughts?
> 
> Rob Durn.
> 
> Also at Robert.Durn@xxxxxxxxxxxxxxxxxxx   
> 
No problem. Marked focal lengths are rarely true. Manufacturers
like to round off the numbers and fudge on the side that's more
desireable. This is why Erickson of Florida, USA, uses zoom
lenses. After the camera is complete he makes tests at slight
focal length variations to find the right one for the "disc".
Ed