Lens distortion?

[atlcruiser]

The pincushion is due to my heavy handed LR distortion correction. Maybe 5% is needed not the 6% I did on the 2nd image.

But...........some good news. I went out this AM to take some shots and to sort of see if I can replicate this again. I did with my 360 commercial. The issue is not the lens but it is the camera or, better bet, the monkey in back of the camera.

I will post up the scan in a few hours and see what the issue is. I suspect my rear GG or rear standard is wonky. perhaps my level is not up to the task

[EdWorkman]

Fifteen feet sounds "close" to the wall, but then i don't know what format- 240 hardly is wide angle for 4x5..
Perhaps some trigonometry will tell if 6% is "correct".
If the window opening width and heights at each end are known, triangulate the distance from film to inner jamb then film to outer jamb. Or just use a tape measure. The distance to the inner jamb [ say 15 ft] is shorter than the hypotenuse [ which is er, more than 15 ft on the tape] to the outer jamb, so unless the actual vertical dimensions on the wall shown at the edges of the frame are GREATER than those in the middle, [highly unlikely account manufactured windows, brick courses, layout screwups are seldom suymmetrical etc]the edges should seem to "recede"- cuz they actually do.

[atlcruiser]

Hi all,
This image was taken this AM but with my 360 commercial not the 240 as before. I leveled the camera, tripod first, then composed image, leveled with 7" level then lined it all up with the GG. The slats on the side of the building go every which way but the upper, top slat was more or less level on the building and level on my GG. I set the grid line to be on the lower edge of that horozontial line.

This is a traight scan. The upper line bows outward.


1011 BW 810 small-4.jpg by urbanlandcruiser, on Flickr

This is the same image with +3% distortion correction. Looks about right.


1011 BW 810 small-4-2.jpg by urbanlandcruiser, on Flickr

[atlcruiser]

I think I need to get out the real measuring stick and start looking at the back of the camera and how it all is in or not in square.

[johnielvis]

there's distortion, it's a "real" lens, but that's not what you're seeing--it's pure perspective

short lens---and the building has a "nose"

check the courses of bricks how they don't line up at all levels---the camera is level enough for the bricks/buliding--that center column "nose"...see on the bottom...follow a brick line..it don't line up because of perspective..lens level lines up perfect....get higher/lower and it changes.

yeah--THIS is why you want a long lens for 3d objects....shoot the same thing with the"nose" ON ONE SIDE....you'll see...or no "nose" at all..just flat bricks...

this is due to closeness with a very wide lens for 8x10.

this is why I try to use long lenses--PARTICULARLY for stuff like this

you should see less with a longer lens...360...that really ain't that much longer dude...you need to go L O N G E R to see a difference...like DOUBLE .... MORE than double---take your longest lens and unscrrew a cell...get yourself a super long lens then.. and test THAT....you got a plasmat in your set..you can use rear element to see...

[Vaughn]

I think John might be on the right track, and it was my first thought also, With a wide to normal lens and that close to a wall, the center of the wall is significantly closer to the camera then the corners.

I had what might be a similar problem photographing a redwood that was about 300 feet tall. Camera was level with about 1/3 up the tree. It took me awhile to figure out why the tree was fatter towards the middle of the tree. It was just that the middle of the tree was significany closer to the camera than the bottom and the top.

Vaughn

Of course in your case there might be other factors increasing the natural distortion.

[Ken Lee]

Why not scan a piece of graph paper - and see of your scanner has barrel distortion ?

[Frank Petronio]

Photograph a big box office building (don't get yourself arrested by rent-a-cops) from further away to rule out the "too close" argument. My gut tells me that a 240mm on 8x10 isn't that wide, just like a 40mm on 35mm, so it shouldn't be distorting that much.

[EdWorkman]

C'mon you guys- get a tape and measure lens to center of frame on the bldg, lens to edge of the frame on the building. Hey look. it's more to the building part showing at the edge of the frame [than it is to the building at the center of the frame]. Hey that's the same as looking down the row of telephone poles, the second one is farther away than the first, etc, and even though they are the same height, the next one LOOKS SHORTER
IT AIN'T THE LENS [es] IT'S PERSPECTIVE
NO REALLY
NO
REALLY
You want less perspective MOVE BACK so that the dimensions I told you to take are very nearly the same- of course they NEVER WILL BE THE SAME, but if you get back far enough the difference could be smaller than you can reliably measure.
"Gee Miss Farquar how come we gotta learn this-? We'll never use it in real life"
I trust Miss F. gave you D grades.
LOOK AT ME WHEN I"M TALKING TO YOUZ, LISTEN TO JOHN
Go download a free book from Google or Internet Archive about perspective, particularly perspective drawing, and you will see some diagrams that should make it clear.
And don't EVEN remark about "drawing is different from film" Both are recording 3D on a plane in 2D.
IT'S NOT, REPEAT NOT NOT NOT DISTORTION
not in the lens, not in the GG, not in this world

[johnielvis]

yeah...what he said

anyways...there's afamous pic of the empire state building shot with a 40 inch lens I thing....it shows it "in proper perspective"....with teeny tiny houses and such to show the massiveness of it--a german dude shot pics like this...always with the long lenses--because people, with there eyes, are used to seeing the distortion and their brain corrects for it...then when you see it on paper, ?????? what....the brain doesn't re-interpret it the correct way----so it looks screwy.

you cant see it until it's printed...THEN you notice....this is why I got into the longer lenses...and even THEN it don't do that much for lf cause space is thelimitation on the camera--my studio camera is like only 6' long...ONLY...yes only...that aint long enough for me to get what my brain sees....my brain interprets a square grid but the camera doesn't record that due to perspective which the brain compensates for.