Front tilt?

[Sean Galbraith]

This is a shot I took last year (the first, and so far only, time I've shot LF... until my new gear arrives). I noticed in the scans that the top of the building in the corners was a little soft. Could this have been fixed with a little front tilt? Or would that have introduced problems elsewhere?

http://farm4.static.flickr.com/3615/3457660370_aa4951a4a9_o.jpg

[Sascha Welter]

If you want everything sharp in this picture, tilts won't help. You basically have a deep box here, where we see all the sides (except for the top). Tilting/Scheimpflug basically helps when you can reduce the areas you want sharp to become something around a slice.

You'd have to stop down the lens for this one. But given the scale I'd say it should be doable.

[rdenney]

Tilting the lens tilts the plane of sharp focus. So, the answer to your question depends on what you want to be in focus. If you left the lens board vertical and just used the rise to correct perspective, the focus plane should be vertical. Then, it would depend on what you focused on. If the buildings are in focus at the edges in the middle of the frame, and if you didn't use tilts, then the upper corners should be equally in focus.

So I don't think that's your answer.

I suspect that you found the edges of the coverage of the lens you used. Some lenses, particularly older designs, go a bit soft before they go dark. Some of the newer wide-angle designs try not to do that, but still do to some extent.

Check to make sure you didn't use tilts accidentally. Are the lens and film planes square on your camera? Sometimes, a strong rise with a wide lens will twist the bellows such that it fights back and throws the camera out of square.

Rick "who would not use tilts for an image like this" Denney

[Sean Galbraith]

The lens plane and film plain were square (Sinar F1 with bag bellows), and only front rise was used. The lens was a 90mm Grandagon N, and I shot at f22.

[rdenney]

The lens plane and film plain were square (Sinar F1 with bag bellows), and only front rise was used. The lens was a 90mm Grandagon N, and I shot at f22.

What did you focus on?

The out-of-focus areas that are still nominally within the depth of field might show a little curvature, depending on the situation.

And, as the owner of a Sinar F with an F2 front standard, I can say with some certainty that it's eaiser to push the F1 front standard out of whack than it seems like it ought to be. But the bag bellows should have minimized that.

At what magnification do you see the loss of sharpness?

Rick "running out of ideas" Denney

[Sean Galbraith]

I can see a change in focus in the scan above, even without magnification. I've also scanned it on an imacon and printed it at about 28x36, and it is noticeable. (the scan above is a reduced version of the imacon scan).

I was focusing on the foreground rubble pile line.

[Don7x17]

First of all, either the building nearest you was tilted outwards (doubtful)
or
your rear standard wasn't exactly perpendicular to the ground (its an easy check -- take the picture and put it in powerpoint then draw a square...)....your back was tilted slightly forward from perpendicular.

Since its a grandagon-n 90, the edges aren't soft (I have one) or you dropped it....
So presuming the front standard is near vertical or even parallel to the rear standard
and
that your depth of focus was set looking at the ground (top of the groundglass) and infinity, then you'd need just a bit more depth of focus at for the upper corners of the building which are at the bottom of the groundglass.

You wouldn't see this if you stopped down just a bit further. Or squared up the back to the ground(and verticals in the building)

try it with powerpoint or some other drawing tool that provides boxes....even photoshop...you'll see the verical nearest to you isn't parallel to the sides of the image.

[Sean Galbraith]

The lens was a rental, so I have no idea if anything happened to it previously. It at least looked in great shape. I'm going under the assumption this was entirely operator error. :-)

Thanks for the advice! I'm looking forward to putting it into practice.

[ki6mf]

I agree with the advice here Tilt for DOF should be avoided with tall fore ground objects because the near focus is tilted and a tall object sticks up into the our of focus part of the shot. I have not had this problem with my Grandagon 90MM either. Could it be you were near the edge of the focus circle and with the aperture was getting some softness?

[Sean Galbraith]

It is entirely possible, though I have no idea if that is the case.

[Sean Galbraith]

Why would a front tilt backwards not work for this?

(I'm thinking the opposite of a front tilt forwards, like is used in landscape photography for large depth of field)

[Don7x17]

Tilt on front and back isn't just an issue for tall vertical items in the near region (like trees and buildings and telephone poles, etc)

Two other cases of problems are often seen in images....

1) At a deep hole in the ground, like the Grand Canyon, users standing on the rim will tilt front(or back) to make the near edge of the canyon and the top of the distant edge in focus. They later notice that the bottom of the canyon is now out of focus in the negative/chrome.

2) With near distant mountains, like photographing the Tetons from the Jackson Lake, users will tilt to focus on mountain top and the near shore/water surface. Later they notice the the base of the mountains is out of focus in the negative/chrome.


Always stop down and check your image with a loupe to ensure you don't get nasty surprises much later in the resulting chrome/negative.

We've all done it at one time....

[Don7x17]

Why would a front tilt backwards not work for this?

(I'm thinking the opposite of a front tilt forwards, like is used in landscape photography for large depth of field)

If you were to tilt backwards, the plane of critical focus could be placed from the top of the building to the middle or lower part of the distant building, but then you'd drop out the focus on the bottom of the near building.....so you've just moved the problem.

Stopping down the lens a little further would solve all of these problems, at the expense of a little diffraction as you move beyond f22.

[mdd99]

I would at least try back tilting the front frame, slightly, so that the plane of focus is about 1/3 the way from the top of the near buildings and about 1/3 up from the bottom of the rear building.

See if that doesn't reduce the amount you have to stop down compared with a straight shot with no tilt.

[Sascha Welter]

People are too afraid of the "ghost of diffraction" that goes around and slaps unwary photographers on the hands if they stop down too much. I bet you won't be able to actually see any diffraction at f:32 or even at f:45. But you will see the out of focus areas when you try to tilt to get everything in focus with a wider open diaphragm.

The use of a proper DOF scale like this one on the site we're on (http://www.largeformatphotography.info/fstop.html) can help to avoid the fear of diffraction.

[Thom Bennett]

I would venture to guess that you did in fact have a little tilt on the front standard and did not realize it. That would throw the top corners out of focus. As someone else mentioned, it is very easy to knock the front standard out of whack just enough to affect this.

[Rick Olson]

Sascha ...

Agreed!! I am often in the "ghost diffraction" area of f32-64 to get my complicated 5 x 7 images sharp. I use what it takes to get the shot. To me diffraction is a ghost - I don't see it. Of course, I don't have a scanning electron microscope to check my negatives, so maybe it is there.

Rick




People are too afraid of the "ghost of diffraction" that goes around and slaps unwary photographers on the hands if they stop down too much. I bet you won't be able to actually see any diffraction at f:32 or even at f:45. But you will see the out of focus areas when you try to tilt to get everything in focus with a wider open diaphragm.

The use of a proper DOF scale like this one on the site we're on (http://www.largeformatphotography.info/fstop.html) can help to avoid the fear of diffraction.