D7 distortion at WA: not barrel, tilde !!!

[Marko Björkroth]

I have some sample pictures online

http://www.pbase.com/mbjorkro/test_pictures

The size of the test target was 600x450 mm, small squares are 50x50 mm. I had to be really close (almost as close as I can get!) when I took the 28 mm picture. I'm not sure if the focusing distance has also an effect on the distortion.

Pay no attention to the colors or illumination. On some pictures the upper edge is brighter and the distortion may look worse than it really is.

Marko

 

[Pabletto]

I'm sorry ... but wouldn't any extreme angle shot at anything other
then 1X magnification do exactly this?

I'm no expert, but I thought this was a simple matter of physics of
optics (concave/convex lenses, etc).

JonW, it is not a simple lens distorsion. It is the wavy pattern that is strange.

--Pablettowww.pbase.com/pabletto(samples taken with the MINOLTA DiMAGE 7)Last update 26 February 2002 (MORE food photos)

 

[John Lai]

Marko

Thanks for the samples. Distorsion at 28 mm seems normal. However the sample posted does not reproduce the context of the distorsion., namely the camera is at an angle (pointing upwards) to a plane containing horizontal lines. Can anyone living near such a building post some shots?
Thank you all.

Regards
John

I have some sample pictures online

http://www.pbase.com/mbjorkro/test_pictures

The size of the test target was 600x450 mm, small squares are 50x50
mm. I had to be really close (almost as close as I can get!) when I
took the 28 mm picture. I'm not sure if the focusing distance has
also an effect on the distortion.

Pay no attention to the colors or illumination. On some pictures
the upper edge is brighter and the distortion may look worse than
it really is.

Marko

 

[Jon W77861]

JonW, it is not a simple lens distorsion. It is the wavy pattern
that is strange.

It just looks like its following the curve of the lens to me.

shrugs

The part of the picture above the center of the lens is distorted like this

-----

and the part below the center of the lens looks like

---- ----

If it looked like

---- --- ---

That'd be unexpected, but it sure seems to be following the curvature of the lens, give or take a slight droop at the top left.

Has anyone found a WA camera that won't do this to a shot at such an extreme angle?

 

[Marko Björkroth]

Marko
Thanks for the samples. Distorsion at 28 mm seems normal.

It might look like typical barrel distortion, but it isn't quite as simple. I've uploaded new, better samples.

http://www.pbase.com/image/1302107
http://www.pbase.com/image/1302109

Lool at the corners and horizontal lines at the upper edge of the image. There's a lot of barrel distortion near the centre of the image, but less in the extreme corners. That's what is causing the weird wave-like distortion, also know as gull wing distortion.

Marko

 

[Jon W77861]

Lool at the corners and horizontal lines at the upper edge of the
image. There's a lot of barrel distortion near the centre of the
image, but less in the extreme corners. That's what is causing the
weird wave-like distortion, also know as gull wing distortion.

Well, at least at the resolution you supplied the samples, I don't see a "wave" effect at all. Basically the whole distortion on the top line(s) of the 28mm shot are contained in just 2 or 3 pixel rows. Perhaps you see it more clearly with the originals?

If the lens or CCD were slightly off center, I'd imagine that would introduce some interesting edge distoration as well ...

 

[Marko Björkroth]

Well, at least at the resolution you supplied the samples, I don't
see a "wave" effect at all. Basically the whole distortion on the
top line(s) of the 28mm shot are contained in just 2 or 3 pixel
rows. Perhaps you see it more clearly with the originals?

You are right, it's hard to see, because the samples as so small. In full size pictures there is more distortion that just 2 or 3 pixels.

However, if you look carefully enough, you'll see that there's a touch of pincushion distortion at the corners. Look at the upper right corner. The vertical black line is bent to the right at the extreme corner.

As a result of the non-uniform distortion (lots of barrel distortion at the centre of the image and virtually no distortion at the corners), all lines are bent away from the centre, but they do not look like perfect circular arcs - they are less curved near the edges of the image.

Marko

 

[John Lai]

Marko,

Thanks for your samples. Their distorsion pattern is the same as Phil's review and Gbo's photo. What I cannot understand is why in GBo's sample, the pattern repeats itself more than once along any given horizontal line and not only once.

I e-mailed http://www.theimagingfactory.com about possibility of correcting this with Debarrelizer. Their reply unfortunately is as follows:

OR> Thank you for your interest in our plugins.
OR> I have looked at the picture and i am afraid this is beyond the capabilities
OR> of Debarrelizer. This type of distortion can only be corrected (if at all)
OR> with Helmut Derschl pano tools, or possibly with LensDoc.

OR> Sorry for being of little help. I saw many people have contributed to the
OR> discussion thread and hopefully they have been able to give you some useful
OR> advice.

OR> Kind Regards,
OR> Oscar Rysdyk,
OR> /////////////////////////////////
OR> http://www.theimagingfactory.com

Regards
John

Well, at least at the resolution you supplied the samples, I don't
see a "wave" effect at all. Basically the whole distortion on the
top line(s) of the 28mm shot are contained in just 2 or 3 pixel
rows. Perhaps you see it more clearly with the originals?

You are right, it's hard to see, because the samples as so small.
In full size pictures there is more distortion that just 2 or 3
pixels.

However, if you look carefully enough, you'll see that there's a
touch of pincushion distortion at the corners. Look at the upper
right corner. The vertical black line is bent to the right at the
extreme corner.

As a result of the non-uniform distortion (lots of barrel
distortion at the centre of the image and virtually no distortion
at the corners), all lines are bent away from the centre, but they
do not look like perfect circular arcs - they are less curved near
the edges of the image.

Marko

 

[Rinus Borgsteede]

I still have the Nikon 990 and with the WC-E63 wide lens attached, that is what it looks like. The older and much smaller WC-E66 did have barrel distortion but that could be fixed with the Debarrelizer http://www.theimagingfactory.com/

The effect of the tilde distortion happens when a lens has a corrective lens element/system installed to undo some of the distortions introduced by a severe wide lens system. The normal wide system often gets barrel distortion do to design limitations like small space or larger f stop requirements. To correct, they add a lens system that corrects partially the barrel distortion. It cannot completely correct because that would require more elements, hence the wavy lines. This is the compromise you'll get. It is not too bad for general photography but a real pain for straight lines, making it completely useless. I Ditched that WC E63 and went back to the highly correctable WC-E66 for my interior photographs.
Rinus

 

[John Lai]

Check this link.
http://www.dpreview.com/forums/read.asp?forum=1014&message=2594050

Best Regards
John

Hi all,
I was very pleased with my camera until I tried to shoot some
buildings.
I was aware that the D7 had some barrel distortion at eq. 28mm, but
I knew also that this can be corrected with some software.
Instead, what I discovered is that my D7 has a distorsion a bit
like a " " (tilde). Look at the two pictures below:

• Is it the same for you or do I have a problem with my lens???
• How is it possible to obtain such an asymetric distortion?
• what about software correction for this specific ugly distortion?

See the lines at the bottom; believe me the beams were perfectly
straight and parallel in this brand new building:





--
thanks,
GBo.