Lens Convergence?

[Sirius Glass]

These are two photographs that I took learning to correct for convergence. The negatives were quickly flat scanned saved; then GIMP was used to reverse the images and adjust the contrast so that they would be viewable.

Both negatives were taken with a Schneider-Kreuznech Angulon f6.8 90mm lens. In both photographs I thought that I had corrected for convergence, but on the right of both of them there is convergence. The one of Haper's Ferry has slight convergence and the one of the church has a larger convergence.

Are the convergences an artifact of the lens or an Operator Assisted Failure [OAF]?

Steve

[Darin Boville]

>>but on the right of both of them there is convergence.<<

And on the left, too. :)

Image #1 has obvious convergence all over, not just on the right. Image #2 looks like it is just on the right side but it also looks like the horizon is not level. One you "level" the image you'll have convergence all over, just like image #1.

--Darin

[Sirius Glass]

Image #2 was aimed slightly uphill. Thanks.

[Darin Boville]

Image #2 was aimed slightly uphill. Thanks.

To my eye the whole image is tilted leftward. If you correct it by rotating the image back to the right a tad that "right only" convergence" will look like "all over convergence."

Just what I see at a first glance...

--Darin

[Walter Calahan]

OAF, for sure.

Best solution is to get a carpenter's angle finder to place on the ground glass to make sure it is parallel to the building.

[engl]

To me it looks like you did not have the camera level when taking the shots.

Correcting for convergence is easy. Use a level to make sure your camera back standard is level (left to right) and perfectly vertical (front to back). That is all you need to make sure that lines that are vertical in the real world will be vertical in your photo.

For even better results, a ground glass with a grid should be used to verify and fine-tune the back orientation. You could skip the levels and just rely on the ground glass grid, but that can be difficult if there are few (or perhaps even no) straight vertical lines in the shot.

[E. von Hoegh]

OAF. Get a GG with a grid. Speaking for myself, my little brain seems to "correct" for the convergence when I'm composing. Convergence doesn't reappear until the negative is almost dry.

The easiest solution is to use a GG with a grid. There's a reason architectural photographers won't do without one.

[E. von Hoegh]

Image #2 was aimed slightly uphill. Thanks.


Use the front rise, keep the camera level.

[TheDeardorffGuy]

Square that back to the building !!! The back controls perspective and therefore convergence.

[Cor]

Use the front rise, keep the camera level.

The best solution, only that he has a 6.8/90mm Angulon which has barely enough coverage for 4x5..a f8 or even better a f5.6 90 SA would work..

Best,

Cor

[engl]

Not only the best solution, it is also the only solution for getting a negative without vertical convergence. The 90mm Angulon does give a fair bit of rise at F32 with corner sharpness suffering, although I agree a Super Angulon, or one of the similar lenses from competitors, would be a much better bet for taking pictures like the second one posted.

[jnantz]

...

[Sirius Glass]

Next time I will shoot several different variations of a building. Obviously, doing it correctly with one photograph the first time out using rise is a bit ambitious.

Steve

[Michael E]

Next time I will shoot several different variations of a building. Obviously, doing it correctly with one photograph the first time out using rise is a bit ambitious.

It's not about the number of shots. It's about the precision of your work. Learn to use a level the way engl described:



Correcting for convergence is easy. Use a level to make sure your camera back standard is level (left to right) and perfectly vertical (front to back). That is all you need to make sure that lines that are vertical in the real world will be vertical in your photo.

I use one of those hot shoe bubble spirit levels, I always have it in my pocket. I put it against the ground glass, against the lens board, on top of the ground glass frame. Never rely on levels elsewhere on the camera or the tripod. There is enough that can go wrong within the camera's structure.

After the camera is level, I use the front rise to control the composition.

Good luck!

Michael

[TheDeardorffGuy]

I'm not sure where I posted this question: "Do you always use your cameras swings and tilts?" . It seems here that they were needed. Now is it a "natural thing to do". Meaning, when you set up your camera do you automaticaly square the back to your subject? You really should. I've been to Harpers Ferry many times and it is nearly impossable to find a level surface untill you look at the roof lines, window sills, edges of buildings, some of the phone poles...See what I mean? I had a nice yearly job taking pictures of Toll road payment booths. I could do it without stopping traffic and not show a single car. (use two #4 neutral density filters and really long exposures)
I'd be up on a hillside looking down (camera movement term) Square up on a light pole rear swing as needed and front movements to pull the plane of foci. This should become second nature!! Good luck next time.



These are two photographs that I took learning to correct for convergence. The negatives were quickly flat scanned saved; then GIMP was used to reverse the images and adjust the contrast so that they would be viewable.

Both negatives were taken with a Schneider-Kreuznech Angulon f6.8 90mm lens. In both photographs I thought that I had corrected for convergence, but on the right of both of them there is convergence. The one of Haper's Ferry has slight convergence and the one of the church has a larger convergence.

Are the convergences an artifact of the lens or an Operator Assisted Failure [OAF]?

Steve

[E. von Hoegh]

Next time I will shoot several different variations of a building. Obviously, doing it correctly with one photograph the first time out using rise is a bit ambitious.

Steve

Not at all ambitious. Use the grid on the ground glass and you cannot go wrong. Levels are good, but what if your subject is square but not perfectly level and/or plumb??

The GG shows you precisely what you will get on the negative.

[Ari]

I've been struggling with this lately...
http://www.largeformatphotography.info/forum/showthread.php?t=78766

A level helps get you in the ballpark, but adjusting the back, with the gridded screen, is the final say.
Being low to a building makes things more difficult to square up as well.

[jnantz]

steve,

get a post level ... they cost less than 1$.
keep it in your pocket, and put it on the center of
your camera's box when you set it up.


you won't have trouble with converging lines as long as the bubble
shows you the back is level. if you turn the camera just make sure you
check the bubble again.

make a grid on your computer or download one, and go to a copy store
and have them print it on clear acetate, and just slide it on top of your ground glass.
you don't need anything fancy, and you don't need to mark your glass with pencil &C.

you will be able to SEE everything is straight up + down with the grid,
and if you want keystoning, you will be able to see that too ...

if you like photographing buildings, you might consider getting a view/ field camera
that allows you to adjust the film plane after you tilt the camera...


good luck !
john

[Sirius Glass]

I have a six inch spirit level that is in the camera bag when I go out shooting. The best place to set up the camera for the church picture was lower down than the base of the church. I thought that I had corrected the camera position with the rise. If I had the back of the camera vertical then I would not have had enough rise to get the top of the tower.

[Kirk Gittings]

Schneider-Kreuznech Angulon f6.8 90mm lens

If I had the back of the camera vertical then I would not have had enough rise to get the top of the tower.

That lens IME does not have a large enough image circle to properly shoot architeture.

[Sirius Glass]

That lens IME does not have a large enough image circle to properly shoot architeture.

I will keep that in mind and look for another 90mm lens. Thanks

[Darin Boville]

I've been struggling with this lately...
http://www.largeformatphotography.info/forum/showthread.php?t=78766

A level helps get you in the ballpark, but adjusting the back, with the gridded screen, is the final say.
Being low to a building makes things more difficult to square up as well.

Just to underline this further. There are times when the camera may be perfectly level but, due top the topography, things look a tad slanted. You may want to "correct" for this and tilt the camera left or right. The screen is all tat matters in the end, unless you are doing some sort of scientific survey...

--Darin