Swing/Shift

[Craig Gerard]

I'm playing around with a Novoflex T/S bellows and found the following observation interesting. It won't come as news to most, but I thought it worthwhile uploading.

First image is with no adjustment applied to the bellows.

The second image is the result with swing/shift applied to the camera end of the bellows. Minor but noticable difference.

The third image was taken with swing/shift adjustments applied to the lens end of the bellows.

Canon 50D, SK Apo-Digitar 80/4

Image #1:


Image #2:


Image #3:


Craig

[enricosavazzi]

If I remember my geometry correctly, shift applied to the rear standard (camera end) is completely equivalent to shift applied in a reverse direction to the front standard (lens end), ignoring in this discussion the need to reposition the camera relative to the subject.

If one applies no shift, tilt of the rear standard of course produces different results from tilt of the front standard. This is probably what you are observing in the pictures. However, by combining tilt of the rear standard with shift of either standard one can completely duplicate the effects of tilt of the front standard, within the limits of the available amount of movements.

At least in principle, and in a geometric sense, it is not necessary to have tilt/shift capabilities at both standards, and with sufficient amounts of tilt and shift available at a single point between lens and camera (and equivalent movements available for repositioning the camera-lens complex relative to the subject) one can duplicate the same effects available in a camera with movements at both standards.

It is of course convenient to have movements at both standards - sometimes very convenient.

[Harold Gough]

Craig,

An impressive demonstration.

A question I have to ask myself, having recently invested in such bellows, is, in macro and close-up, as opposed to the scale of buildings, etc., how many times could a similar effect be obtained by a change in position of the camera and/or of angle of the long axis of the lens in relation to the subject?

harold

[enricosavazzi]

Craig,

An impressive demonstration.

A question I have to ask myself, having recently invested in such bellows, is, in macro and close-up, as opposed to the scale of buildings, etc., how many times could a similar effect be obtained by a change in position of the camera and/or of angle of the long axis of the lens in relation to the subject?

harold

I am not sure I understand, but since the DOF in small-subject photography is very limited, with three-dimensional subjects even relatively small amounts of tilt produce a visible change in the inclination of the focus plane, with some parts of the subject going out of focus and different parts coming into focus.

In landscape and building photography, unless something in the field of view is located close to the camera, the whole field of view is usually located at infinity, so introducing a tilt movement causes parts of the subject to go out of focus - but no new parts of the subject to come into focus. Tilt is sometimes used to create a "diorama effect" in landscape photography, but since things in a landscape can only go out of focus (not come into focus) the effect is only similar, not identical to photographing a miniature landscape.

[Harold Gough]

I am not sure I understand, but since the DOF in small-subject photography is very limited, with three-dimensional subjects even relatively small amounts of tilt produce a visible change in the inclination of the focus plane, with some parts of the subject going out of focus and different parts coming into focus.

Yes but might that not be acheived by moving the plane of focus in the camera to the appropriate position and orientation in the three-dimensional vicinity of the subject. I'm not stating that but trying to visualise what happens.

Harold

[elf]

Yes but might that not be acheived by moving the plane of focus in the camera to the appropriate position and orientation in the three-dimensional vicinity of the subject. I'm not stating that but trying to visualise what happens.

This would require moving the camera/lens which will change the perspective, so the answer is no, you cannot get the same image by simply moving the camera/lens.

[Harold Gough]

Yes but might that not be acheived by moving the plane of focus in the camera to the appropriate position and orientation in the three-dimensional vicinity of the subject. I'm not stating that but trying to visualise what happens.

This would require moving the camera/lens which will change the perspective, so the answer is no, you cannot get the same image by simply moving the camera/lens.

Thanks. I really must use the bellows. Then I will understand better. I know about shift, having used it for non-macro but have yet to try tilt.

Harold

[rjlittlefield]

Harold, search on "Scheimpflug principle".

The trick is to get the subject plane, lens plane, and sensor plane to all intersect in a single line. If you can do that, then everything will be in focus.

Tilting the sensor plane will keep you in the sweet center of the lens field but will stretch & keystone the image compared to the non-tilted version.

Tilting the lens plane will move the sensor off-center in the lens field but will retain the original geometry (barring lens distortions). It can also offer a wider range of adjustment, especially at higher magnifications where the lens is relatively much closer to the subject. You can see in this example that the same subject tilt is handled with much less lens tilt (left) than sensor tilt (right)



If you're pushing the envelope of the lens then the best solution might involve tilts at both ends.

Craig, in #2 was the problem that you didn't have enough tilt range to accomplish the focus you wanted?

--Rik

[Harold Gough]

Thanks, Rik.

I'm going to have to find some very understanding subjects!

Harold

[Craig Gerard]

Craig, in #2 was the problem that you didn't have enough tilt range to accomplish the focus you wanted?

Rik,

I was only investigating the swing/shift approach without any particular outcome in mind.


Craig