Question about movements

[Jack Dahlgren]

I did go to the library today and spent 2 hours, but what I did find, really skimmed the topic and didn't explain it in a way I understood. But, I'll try again to see if there is anything else on-line I could read that may help.

Edit
Thanks for the link!

You can just think about it.

First - the film is a plane. If the lens axis is perpendicular to that plane, then there is a corresponding plane on the other side of the lens which the lens will focus onto the film plane. Everything on that plane will be in focus (there is some simplification here as lens can have some distortion - but they generally aim to be planar). Aim your camera at a wall keeping the film plane parallel to the wall and the whole wall will be in focus. Things sticking out of the wall towards you, or objects behind the wall will be out of focus in amounts varying with their distance from the plane of the wall.



Tilting the lens will tilt that plane of focus. So if the wall were instead a brick walkway, the whole plane of the brick walkway could be in focus, but things above the walkway, or below it would be out of focus.

If a person is on a stage, the difficulty is choosing which plane you want to be in best focus. Is it the front of the person (implying a vertical plane) or is it the foreground, the person's head and perhaps the upper scenery behind them (implying a tilted plane)

Stopping the lens down works to diminish the amount of focus lost as objects become further from that plane of focus. Stopping down a lot maximizes the amount that would be in focus, but also causes diffraction which softens the overall image.

Balancing focus plane, depth of field and sharpness can be calculated, but it may be easier to just stick your head under the dark cloth and see how it works on the ground glass.

[Leigh]

Tilts or swings control the plane of focus.

Aperture controls how "thick" that plane is, i.e. how far from the plane objects can be and still be "in focus".

- Leigh

[Brian Ellis]

Tilts or swings control the plane of focus.

Aperture controls how "thick" that plane is, i.e. how far from the plane objects can be and still be "in focus".

- Leigh

Not exactly. Only one plane can be "in focus." Everything in front of and behind that plane is out of focus. Those things may appear "sharp" despite being out of focus depending on a number of variables such as degree of enlargement of the print and viewing distance.

[Leigh]

Everything in front of and behind that plane is out of focus.

Hi Brian,

I intentionally avoided using terms like "in front of" and "behind" because they're not relevant to a tilted plane of focus.

What I said was the aperture controls how "thick" the plane of focus will be, meaning distances measured perpendicular to the plane.

- Leigh

[laroygreen]

Ok, I think I understand now. Basically, I can only decrease my f-stop to get a larger DOF, where as movements will determine the orientation of that DOF.

I guess my problem was that I had made assumptions about movements even before I read anything about it.

Thanks all for the help, and rest assured, I'll be back with more questions soon!

[E. von Hoegh]

Not to mention the difference between "depth of field" and "depth of focus".................

[Leigh]

Not to mention the difference between "depth of field" and "depth of focus".................

Depth of field is on the subject side of the lens.

Depth of focus refers to the image at the film plane.

- Leigh

[E. von Hoegh]

Depth of field is on the subject side of the lens.

Depth of focus refers to the image at the film plane.

- Leigh

Thank you. Too many toss the " DOF" abbreviation about; it isn't always apparent which they mean.

I think the OP was putting a hypothetical case, he's made it apparent that he's just getting off the toe of the learning curve. When I was getting into LF in the mid 1980's I had endless confusion arising from misunderstanding jargon and so on.
Another lesson I needed to learn was that LF isn't always the correct tool. For commercial work the "use the smallest format that will do the job" rule is important.
The smaller the reproduction ratio the less DOF (focus) is available.

[Leonard Evens]

You have to understand the geometry of the depth of field region. If the standards are pa rallel, it is a slab perpendicular to the lens axis which extends infinitely up and down and to either side. Its size depends on the camera position and the f-stop. The further bakc you get, the large it will be.

In your case, you don't want to stop way down to increase the depth from front to back of the DOF region because you would then have to use long exposure times and subject motion might be a problem.

If you tilt the front relative to the back, the geometry changes. The DOF region lies between two half planes which meet somewhere below the lens. The line where they meet is called the hinge line. The vertical extent in focus is narrow close to the lens and expands as you move further from the lens. As you focus, the whole DOF region swings about the hinge line, which depends only on the camera position and the fstop. It is conceivable in some special circumstances, that you could include everything that is needed in focus with an appropriate tilt, but usually that won't be the case. It won't be the case, if there is considerable vertical extent needed in focus which is relatively close to the lens. It may be worth a try, but don't be surprised if it doesn't work.

[Bob Kerner]

Rather than treat it as a hypothetical, can you take your camera and actually do it?
Some of this stuff only begins to make sense by seeing it on the ground glass.