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

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GBo

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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.
 
You have to shoot a controlled shot of an accurate grid (like a sheet of graph paper). It's too hard to tell from your shots but I think ~ distortion is very unlikely.

Duane
GBo said:
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.
Click to expand...
 
Duane DeSieno said:
You have to shoot a controlled shot of an accurate grid (like a
sheet of graph paper). It's too hard to tell from your shots but I
think ~ distortion is very unlikely.

Duane
Click to expand...
It was also unlikely that the D7 with some UV filters vignettes only more on the upper left corner than the three others!

I agree to try agrid test (although the D7 would be IN FRONT of the grid and not tilted upwards like in my shots, maybe it's different?).

Look at this one, again a brand new building (french but straight ;-): this is ridiculous!

 
GBo said:
Duane DeSieno said:
You have to shoot a controlled shot of an accurate grid (like a
sheet of graph paper). It's too hard to tell from your shots but I
think ~ distortion is very unlikely.

Duane
Click to expand...
It was also unlikely that the D7 with some UV filters vignettes
only more on the upper left corner than the three others!

I agree to try agrid test (although the D7 would be IN FRONT of the
grid and not tilted upwards like in my shots, maybe it's
different?).

Look at this one, again a brand new building (french but straight
;-): this is ridiculous!

Click to expand...
I am very worried about this asymetric distortion because it is very noticeable and not treatable by software (not a symetric barrel as it should be). I wonder if i need to have my D7 remplaced, but if all the D7 are doing the same thing...

Does your D7 distord like that at 28 mm? (any building pictures?) I'll will try a grid as soon as I can get one large enough for 28 mm!

Maybe the problem comes from a misaligment of the CCD (not exactly in the axis of the lens)?
thanks for your help!
 
GBo said:
I am very worried about this asymetric distortion because it is
very noticeable and not treatable by software (not a symetric
barrel as it should be). I wonder if i need to have my D7
remplaced, but if all the D7 are doing the same thing...
Does your D7 distord like that at 28 mm? (any building pictures?)
Click to expand...
Yes it does. I think this is a quite typical problem of wide-angle lenses - especially zooms. Both wide-angle (24-... mm) SLR zoom lenses I've used had similar distortion - maybe not as bad, but definitely visible in some pictures. I heard someone calling this kind of distortion "gull wing distortion", but I'm not sure if that is the correct term.

For digicam users this is a-never-seen-before problem, because wide angle lenses have been so rare.

Marko
 
GBo said:
Instead, what I discovered is that my D7 has a distorsion a bit
like a " " (tilde). Look at the two pictures below:
Click to expand...
If you look at the review, there is a wide angle shot of the
barrel distortion target that very clearly shows barrel distortion,
but no ~ distortion at all. Granted, this is not a grid, but it
does have a horizontal line at the top and bottom of the image,
which is where the ~ distortion seems to be worse.

It sure seems like it might be a problem with your particular
camera, perhaps a defective lens element or something.

-D
 
GBo said:
GBo said:
It was also unlikely that the D7 with some UV filters vignettes
only more on the upper left corner than the three others!
Click to expand...
I am very worried about this asymetric distortion because it is
very noticeable and not treatable by software (not a symetric
barrel as it should be). I wonder if i need to have my D7
remplaced, but if all the D7 are doing the same thing...
Does your D7 distord like that at 28 mm? (any building pictures?)
I'll will try a grid as soon as I can get one large enough for 28
mm!
Maybe the problem comes from a misaligment of the CCD (not exactly
in the axis of the lens)?
thanks for your help!
Click to expand...
I was going to suggest about the same thing -- I believe it may be a
combination of barrel distortion and axial misalignment. Lens tests
often show centering errors, even with expensive lenses. I have
never seen the effect in a picture, so I can't be sure. The fact that you
see asymmetric vignetting tends to reinforce this conclusion. Whether
you can get the manufacturer to acknowledge the problem is the big
question.

Good luck.
Darrell
 
dear GBO

I can understand your distress but I very much doubt this is a faulty lens because the image is too sharp. Basically, as you know, you have a glorified point and shoot camera with a very wide ranging zoom lens. I don't have a Minolta myself but the lens is never going to be a great performrer in the 28mm mode. What would you prefer? this or a single focal length equiv to 50mm on a 35mm?

Calm down and to put the camera parallel to (as other posters have noted) some sort of grid or graph paper. You know yourself that you are going to get distortions - barrel. pincushion, whatever. The only way you would have much much less is to go out and buy a film camera and buy a prime 28mm lens - not a zoom. Even expensive zooms will be "beaten" by cheap primes.

You know too that your posts are not "architectural" shots; they are impressions of buildings. I know you have paid a lot of money and I haven't yet but look at this way, if you insist on shooting digital then you would have to buy a D30 and a 20mm which is a combination a good 2.5 to nearly 3 times what you have already paid.

I really wouldn't worry about it. You are hoping for a sort of perfection that isn't going to happen at this price point. You don't need us to advise you of this; you already know, I'm sure.
sincerely
jerome y.
 
With all due respect to those who suggest this is normal, I'd be contacting the Minolta service center about this if it were mine.

Regards,
Scotty
GBo said:
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.
Click to expand...
 
GBo said:
GBo wrote:
Click to expand...
GBo,

If you give me some situation that I can reproduce, I'll be happy to take a shot for you with my camera. Bryan
 
Bryan Biggers said:
GBo,
If you give me some situation that I can reproduce, I'll be happy
to take a shot for you with my camera. Bryan
Click to expand...
Thanks for your proposal Bryan, very helpful at usual! It would be nice if you could take a 640x480 picture at equ. 28mm of a recent building with perfectly horizontal lines the same way I did in the first posted sample: I was just in front of the building, the D7 tilted upwards. Horizontal lines at the bottom will show the distortion shape.

I've also printed a grid with microsoft Excel (15 columns, 53 lines) on a A3 sheet (european format) with a laser printer, i'll try tonight to shoot this grid and post the result.

I'm convinced that my D7 has an optical or alignment problem but it may be not the only D7 suffering from this. I took already hundreds of pictures without noticing this Wide Angle problem.
regards,
GBo.
 
Hi GBo,

May we call you "G"? ;) Anyway, I took a shot of some siding on a house that I think shows the gull wing distortion quite well. Unfortunately, Photopoint is down, and I can't get ftp to work with my ISP, so I'll have to wait to post it. I could mail it to you if you like, about 120K Bryan
GBo said:
Bryan Biggers said:
GBo,
If you give me some situation that I can reproduce, I'll be happy
to take a shot for you with my camera. Bryan
Click to expand...
Thanks for your proposal Bryan, very helpful at usual! It would be
nice if you could take a 640x480 picture at equ. 28mm of a recent
building with perfectly horizontal lines the same way I did in the
first posted sample: I was just in front of the building, the D7
tilted upwards. Horizontal lines at the bottom will show the
distortion shape.
I've also printed a grid with microsoft Excel (15 columns, 53
lines) on a A3 sheet (european format) with a laser printer, i'll
try tonight to shoot this grid and post the result.
I'm convinced that my D7 has an optical or alignment problem but it
may be not the only D7 suffering from this. I took already hundreds
of pictures without noticing this Wide Angle problem.
regards,
GBo.
Click to expand...
 
Exactly, on some $2k glass!

But the interesting concern coming out of this is what happens when you stick a .55 or even a .7 WA converor on this. I suspect that will really give some interesting distortion (should I say 'creatively useful opportunities').

dh
Bryan Biggers said:
Scotty said:
Scotty
Bryan Biggers said:
Photopoint is back up. Here is the photo. Sorry it is dark, I took
it early this morning. Bryan

http://albums.photopoint.com/j/View?u=785850&a=13692264&p=53517909&Sequence=0&res=high
Click to expand...
Click to expand...
Click to expand...
 
Has anyone seen this with the camera parallel to the subject rather than pointing pointing up? If it is only visible when at an angle to the building, could it be a combination of the barrel distortion with the normal distortion seen in wide angle lenses when the "film plane" is not parallel to the subject?
Tom
Scotty said:
Regards,
Scotty
GBo said:
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.
Click to expand...
Click to expand...
 
Bryan Biggers said:
I think that it is "normal" for the D7. They don't call it
anomalous dispersion glass for nothing. I've seen the gull wing
distortion on other zooms for film cameras. I don't know if it can
be corrected in software or not.
Bryan
Click to expand...
Still curious, why wouldn't have this shown up on the barrel
distortion test target in Phil's review? Is it still possible they
don't all do it? Seems unlikely since two of you have it, but
stranger things have happened.

I don't have a digicam yet, but I've never noticed this on
my Minolta 24-85 zoom that I use on my film camera. I'm
certainly going to check it out, though. Not being digital,
however, I won't know the answer for a while.

-D
 
If you look at the test that Phil runs, I think that he just shoots a box pattern and measures the edges. The edges are actually pretty well corrected. to see this, he would have to shoot a series of concentric boxes. Bryan
David Rosky said:
Still curious, why wouldn't have this shown up on the barrel
distortion test target in Phil's review? Is it still possible they
don't all do it? Seems unlikely since two of you have it, but
stranger things have happened.

I don't have a digicam yet, but I've never noticed this on
my Minolta 24-85 zoom that I use on my film camera. I'm
certainly going to check it out, though. Not being digital,
however, I won't know the answer for a while.

-D
Click to expand...
 
Bryan Biggers said:
If you look at the test that Phil runs, I think that he just shoots
a box pattern and measures the edges.
Click to expand...
Yes, but some of the wavier lines in your photo and the original poster's
photos are very close to the edge (particluarly in yours), unless
the images are cropped.

I do agree, though, that the problem is probably endemic to the
camera. I don't profess to know much about lens design or construction,
but I imagine that with 13 lens groups, many of which must move
relative to others, there will be some variablity in alignment from
one unit to another, so some may have more of the effect than
others.

If you stand back and look at the images, it actually looks like
a combination of barrel distortion and pincushion distortion, with
the centers of the edges barreling and the corners
pincushioning. It's interesting to note that this was
actually a pretty common effect in older, pre- solid state
televisions. The uncorrected deflection coils tended to produce a
pincushion effect. The pincushion correction circuits attempted
to correct for it, but it wasn't perfect, often giving a little too
much correction in the center of the edge and not quite enough
near the corners, resulting in a wavy effect similar to the D7 lens.
 
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