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Re: [OM] Distortion in 35/2.8?

Subject: Re: [OM] Distortion in 35/2.8?
From: Andre Goforth <goforth@xxxxxxxxxxxxx>
Date: Thu, 22 Jan 1998 22:14:56 -0800
Olympians,

Sorry to beat the perspective versus distortion horse but check this out.
If you have the following Oly document.

Larry wrote on top of what Shawn wrote:

>Some on this list have described what you experienced as "barrel
>distortion".  I'd be a little cautious with that diagnosis.

I'd like to second Larry's point.

In Olympus' publication  labeled on the back with " printed in Japan IEMZLG
0380 20MT"(no date but circa late 70s/early 80s), and titled Olympus OM
system Zuiko Interchangeable lens group, there are a couple of interesting
photos to ponder.

On page 22 is photo of a porch with a wooden sailing captain figure. Look
at the weird angles of the columns holding up the roof and the angle of the
roof header versus the porch..  If this photo is what the building really
is like then something must be really wrong with the building!  The wall on
the left is "plumb" but the rest of the items in the photo are not.

On page 27 is a photo taken with the 35 shift. In comparison with the photo
on the next page taken with an ordinary 35 it looks better but there is
something weird about it. Is the whole picture on a tilt to the right? The
lean of the  building at the left edge of the page is patently obvious and
the  left edge of the building in the center is ever so slightly leaning to
the right but its right edge appears to be exactly vertical.  My guess it
has something to do with where the bulk of the object being rectified is
relative to the axis of the camera lens. This must be taken in account as
well as Marco's advise on leveling the file plane with a spirit level.

My guess is that Shawn's unverticals have to do with the relation of the
camera axis to the objects/features in view.

I would appreciate comments from anyone who has this publication. I got it
with my OM1N a long time ago.

Parting words, think of the optical illusions created in carnivals where
the illusion has to do with faking one out in terms of perpective. There is
not patent distortion but a illusion that the room is bigger or tilts up
when it really doesn't.

Shawn, could you put the photo up on your web site? I would like to see it.

Still shiftless in California

Andre
San Carlos, CA
USA

For the record (Marco's advise in a separate email):

Larry wrote on top of what Shawn wrote:

>Some on this list have described what you experienced as "barrel
>distortion".  I'd be a little cautious with that diagnosis.
>
>If you have barrel distortion, it will show up when you photograph
>a grid when the film plane and subject are parallel.  The lines will
>be curved (bulging outward).
>
>Your lens may very well have barrel distortion, but it is much
>more difficult to quantify this if you tilt the camera off axis.
>
>The distortion can vary through the focus range.  You can also
>complicate things by introducing a little distortion from your
>enlarger lens.  Likewise, you can't tell by looking through
>the viewfinder.
>
>Shawn Wright wrote:
>>
>> I just printed an 8x10 shot with my Zuiko 35/2.8 (single coated),
>> with an old church near the centre, and three old lamp posts, one
>> near the centre, and one near each edge of the frame. Upon printing,
>> I noticed the outer lamp posts are leaning inwards toward the
>> centre of the frame.
>
>If they are leaning, but not curved, there may likely be NO barrel
>distortion.
>
>> Since I don't recall them being this way, I must assume this is
>> distortion in the lens, although I don't recall exactly the name
>> for this effect.
>>
>> Is this typical of the 35/2.8, and if so, are there Zuikos in
>> the 24-35 range which are better at controlling this effect?
>>
>> I'm afraid the shot is ruined, as is a vertical of the same
>> church. At least with the vertical, I expected a problem, since
>> I don't have a shift lens. The horizontal shot came as a surprise
>> to me.
>
>Verticals usually just give the subject more room to show the
>leaning, or temp the photographer in tilting the camera even
>more.
>
>Home science experiment:  Cut a perfect rectangle in a piece
>of card stock.  Maintaining the same relationship between
>the eye and the frame you've made, do some tilting at tall
>objects and really examine the frame edges.  This isn't
>a perfect representation of the optics involved, but is
>close enough to get the point across.
>
>Larry



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