View Camera Focusing and the Scheimpflug Principle

[Lon Overacker]

Leigh, of course - the ramp is a flat surface. That building at the end of the ramp though... the plane of focus will only slice through that building and so technically you can not get the entire building and the ramp in focus on the GG (assuming of course you are focusing wide open.) You also assumed that I meant a flat surface such as a vertical wall. Lot's of examples of flat surfaces, such as the ramp, which of course require the use of Scheimpflug.

Of course I agree that it "does not depend on extremely small apertures," - That works when nearly everything falls on or very near the chosen plane of focus. The moment you have elements that extend beyond the plane of focus you need smaller apertures, varying depending on how far away those elements are from the plane of focus.

I was simply trying to answer the question, which seemed to be one of concept rather than technique. Rick's image shows that he applied the concept of the plane of focus by choosing his subject plane carefully, then used the techniques to achieve the desired plane of focus.

Lon

[Leigh]

That building at the end of the ramp though... the plane of focus will only slice through that building and so technically you can not get the entire building and the ramp in focus on the GG (assuming of course you are focusing wide open.)

Another invalid assumption.

I intentionally did not specify the size of the building, nor its distance from the camera.

You made a blanket statement previously which is simply not correct, to wit that the three surfaces must be parallel in order to achieve focus.
Not true with the ramp example.

- Leigh

[federicomar]

...
I did a write up on this that may help - especially since it has examples where you can visualize it much better than any written explanations can do. I'm not a technical photographer really so some of you gurus might find some things that aren't exactly correct, but I did my best and the intended audience is of course someone new to LF. If anyone takes a look and finds something that needs to be corrected, feel free to drop me a note. tx

Hope this helps.

Lon

thank you for the pdf, much appreciated

[tih]

I really like Harold Merklinger's writings on this subject. See http://www.trenholm.org/hmmerk/ for the complete collection. His books go into more detail than most photographers need, but are very interesting if you're so inclined. For an introduction to Merklinger's approach to practial use of the Scheimpflug principle, I'd recommend his articles in View Camera magazine, available from the above site as http://www.trenholm.org/hmmerk/VCFaDOF1.pdf and http://www.trenholm.org/hmmerk/VCFaDOF2.pdf

-tih

[Tim Meisburger]

Thanks Lon. I enjoyed it as well.

[SergeiR]

or you can also just watch video.. Might spot something here

http://www.youtube.com/watch?v=gR4m70xr9mE

[C. D. Keth]

One useful thing to understand about the scheimpflug principle is the volume of the depth of field as movements are applied. When the movements are zeroed out, the depth of field makes a section of a cone with the smaller circle toward the camera, the larger circle away from camera, and the subject plane somewhere between 1/3 and 1/2 of the way in between. Once you account for the fact that your film is a rectangle and the edges of that circle are cut off, that leaves you with a section of a 4-sided pyramid.

If you apply some front tilt with the top of the lensboard away from the film, that volume that is in focus changes. In fact, it changes pretty dramatically. That 4-sided pyramid shape becomes more like a wedge. The sharp edge of the wedge is at the line where the subject plane, lens plane, and film plane intersect. The wedge then goes off from there with about a third of the volume toward camera from the theoretical subject plane and two thirds beyond it. That means that the scheimpflug principle gives you a way to include more and more stuff in focus at it gets further from the camera. You do this by placing that subject plane carefully. Sometimes, you place that theoretical plane itself in clear air but the volume of depth of field that surrounds it is able to encompass what you need to be sharp.

Take for example the theoretical situation that Leigh posed above in this thread. There's a ramp close to camera leading up to an area with some people, and a building beyond that. If you were to place the subject plane so it hits the closest part of the ramp, perhaps flies over the people's head by 6 feet, and then cuts the building about 2/3 of the way up, you very well might be able to get all that in focus once that plane you're imagining expands into a wedge of focused space.

[ic-racer]

Also, I do understand that a 3D plane, as opposed to 2D one, will need a certain amount of DoF to compensate for what can't be brought into tack sharp focus.

3D plane?? Does not exist. A plane, by definition, only has two dimensions. Maybe that is the source of the misunderstanding?

[Ian David]

you very well might be able to get all that in focus once that plane you're imagining expands into a wedge of focused space.

Except that it is not a wedge of focused space, but rather a wedge of acceptable sharpness. There is still only a single plane of true focus, right?

[C. D. Keth]

Except that it is not a wedge of focused space, but rather a wedge of acceptable sharpness. There is still only a single plane of true focus, right?

That's technically correct but it's much easier to explain it as focused space and unfocused space.