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Re: [OM] is this distortion? what kind?

Subject: Re: [OM] is this distortion? what kind?
From: Acer V <siddim01@xxxxxxxxxxxxxxx>
Date: Mon, 15 Jan 2001 19:44:47 -0800 (PST)
On Mon, 15 Jan 2001, John A. Lind wrote:

>>http://albums.photopoint.com/j/View?u=380427&a=9125406&p=31228289&Sequence=0&res=high
>>note round bottle/jug/whatever it is called at extreme right...it's not
>>round. note edge of shed at right, it is straight! what's going
>>on? cropped from left so you can't see it on that side.
>
>In the extreme right corner, the base of the bottle looks oval, as well it 
>should in an extreme corner.  This is normal rectilinear lens 
>behavior.  The shorter the lens, the more noticeable it becomes.

>However 
>the right vertical edge of the bottle looks to show some pincushion.  I 
>would expect that edge to be straight and just the base with an oval.

yes! now that you mention it, i see it.

>Hard 
>to really tell as it looks like you may not have had the camera level so 
>the lens axis would be perpendicular to the window blinds.  The edge lines 
>do look straight.

again, closer inspection shows i didn't have the camera level (i was
shooting in the dark, guesstimated tripod leveling on uneven dirt,
shooting into a shed, bounced flash from ceiling @f/8 or so.

the more i looke at it, the more the edge seems to bow in; power of
suggestion or staring too much or what? hehehe...

>I believe that pincshion and barrel can be mitigated with the lens stopped 
>down, in which the diaphragm blocks ray paths around the edge of the 
>lens.  Gotta think it through more about what happens optically under those 
>conditions.

lens was definitely at f8 (or f/5.6 or f11) since this was close
distance on 400 speed film (tri x)

>Wayne is right about the possibility of aberrations being introduced during 
>printing and/or scanning . . . something I had not thought of.  We have a 
>scanner at work that tends to tilt images, and one must sometimes rotate an 
>image back to get vertical lines parallel vertical image edges.

dind't think of that... will try to scan a graph paper and see what
happens. scanner is epson perfection 636u

/Acer V
--
dum spiro, spero
http://student.ucr.edu/~siddim01


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