Re: Lens Alignment

[T3D Sam Smith <3dhacker@xxxxxxxxxxxxx>]

John wrote:

>I'm not 100% on what's meant by "alignment" in this context.  
>I suspect that it means whether or not the lens' axis is 
>perpendicular to the film plane.  Let me know if I'm wrong.
>If I'm right, then you should be able to tell by taking a
>picture of a grid or of radial lines leaving a central point.  
>If the lens is tilted, then you will have two opposite areas 
>out of focus and at 90 degrees to them, you will have two 
>areas in focus.


Yes, John, I did mean whether the lens' axis lined up with the film plane.
The problem arises when you don't have a lens that is sharp at the edges
when wide open. That means all edges are fuzzy no matter what angle the lens
is put ( within reason). Stopping down for the lens also increases the depth
of field, which really screws things up.


Rather than a grid, I was wondering if points of light might give me a
better idea. Is there a certain pattern in the aberrations or circles of
confusion that might give me a hint?



Bob's explanation sounds intriguing, although I am limited in my optical
theory. Lens coverage or focal length isn't my main concern, as I do have
ways of testing these to a degree. In a grid test, would the grid lines fan
out from in the direction the lens is tilted ? ( If the lens was on a square
board, would the corner or side farthest from the film plane show
magnification on the image?


Sam


------------------------------