Rise/shift the same as raising the camera or relying in lens geometry distortion?

[Helge]

I'm a bit confused about the exact physics/geometry/optics of this often tooted feature of LF cameras.
It's not very well explained anywhere I can find. And the explanations that is there, is often contradictory.

- Is it due to geometric "distortion" of the lens. As in that it gets easier to do with wideangle lenses?

- Or is it due to actually moving the image circle? That is, you simply get to see a diffrent part of the projected image?

Some old folding cameras have front rise with a normal lens. Patent Etui for example.
That speaks for the latter. Geometry distortion can't be that great with a normal lens as to warrant such a feature.

I have a hard time wrapping my mind around what is going on.
Of course it wouldn't be like just moving the camera a few inches higher. That much is empirically evident and logically deducible. But is it equivalent to moving the camera up a meter or three (or lowering it)?
Any helpfull visualisations or analogies?

 

[brbo]

Of course it wouldn't be like just moving the camera a few inches higher. That much is empirically evident and logically deducible. But is it equivalent to moving the camera up a meter or three (or lowering it)?

Yes.

 

[Helge]

Yes.

Thinking a little more about it, that would be impossible, since the geometry changes according to viewpoint.

 

[JPD]

- Or is it due to actually moving the image circle? That is, you simply get to see a diffrent part of the projected image?

That's how I use it, so I can keep the camera straight and, for example, get the top of a building within the frame and keep the walls straight. The lens and film plane is kept parallel. Since the other part of the image circle is used it's sometimes a good idea to stop down a little more for better corner sharpness.

 

[AgX]

Raising the camera changes viewpoint (typically only unless having some ladder at hand), but keeping front/rear standard relation.

Raising just front standard keeps viewpoint but changes perspective (typically strongly), due to change in front/rear standard relation. But by keeping them still parallel, a pseudo-frontal perspective is achieved, which is unnatural, but nonetheless often reagarded as benefitial.

 

[Helge]

Raising the camera changes viewpoint (typically only unless having some ladder at hand), but keeping front/rear standard relation.

Raising just front standard keeps viewpoint but changes perspective (typically strongly), due to change in front/rear standard relation. But by keeping them still parallel, a pseudo-frontal perspective is achieved, which is unnatural, but nonetheless often reagarded as benefitial.

That is what I don't get.
Thinking even more about it, even if a lens has a certain focal length written on it, it still has to be wider to accommodate the larger image circle.
It has to be the typical wide image distortion that introduces the correction for for example buildings. Even if it isn't as much as with a "serious" wide.

 

[Mr Bill]

I'm a bit confused about the exact physics/geometry/optics of this often tooted feature of LF cameras.
It's not very well explained anywhere I can find. And the explanations that is there, is often contradictory.

Hi, to clarify for other readers, the feature being a rise/shift of the lens. This can be used when photographing a tallish building without the sides appearing to tilt in at the top.

One way to understand this is, I think, to take a conventional type of camera in front of the building. First tilt the camera pointing up in order to include the top of the building. You should see, in the viewfinder, that the sides of the building are beginning to converge near the top.

The next step is to change to a wider lens (a zoom is fine). This time set the camera level while shooting from the same position. Hopefully the lens is wide enough to include the top of the building. This time the sides of the building should remain parallel; no converging at the top. If you now make (or just imagine it) an optical print using an enlarger, you can crop the image so that only the building shows. The result should be the same as having used a rising lens stage on a view camera.

Having done this experiment you can probably now see the view camera with a rising lens as simply a more efficient way of getting the image. Instead of throwing away the part of the negative that is not used, the view camera essentially places the film in the area that you want to use, optically.

Now, the question as to why this converging effect happens - it is a consequence of the film plane not being parallel to the face of the building. Now, I haven't specifically tried this, but you can probably sketch out some lines on a sheet of paper to confirm what is happening. Just pretend that it is a pinhole lens to simplify the "ray tracing."

Fwiw the print should ideally be viewed from the same position as the lens had with respect to the film. This is sort of a more complicated sort of thing (or maybe not). This is well-explained, at least in my view, by Rudolph Kingslake in his book "Optics in Photography," in the section on perspective. I think this entire chapter can be seen in preview on Google books. The concept of "center of perspective" is the important part.

 

[Helge]

Hi, to clarify for other readers, the feature being a rise/shift of the lens. This can be used when photographing a tallish building without the sides appearing to tilt in at the top.

One way to understand this is, I think, to take a conventional type of camera in front of the building. First tilt the camera pointing up in order to include the top of the building. You should see, in the viewfinder, that the sides of the building are beginning to converge near the top.

The next step is to change to a wider lens (a zoom is fine). This time set the camera level while shooting from the same position. Hopefully the lens is wide enough to include the top of the building. This time the sides of the building should remain parallel; no converging at the top. If you now make (or just imagine it) an optical print using an enlarger, you can crop the image so that only the building shows. The result should be the same as having used a rising lens stage on a view camera.

Having done this experiment you can probably now see the view camera with a rising lens as simply a more efficient way of getting the image. Instead of throwing away the part of the negative that is not used, the view camera essentially places the film in the area that you want to use, optically.

Now, the question as to why this converging effect happens - it is a consequence of the film plane not being parallel to the face of the building. Now, I haven't specifically tried this, but you can probably sketch out some lines on a sheet of paper to confirm what is happening. Just pretend that it is a pinhole lens to simplify the "ray tracing."

Fwiw the print should ideally be viewed from the same position as the lens had with respect to the film. This is sort of a more complicated sort of thing (or maybe not). This is well-explained, at least in my view, by Rudolph Kingslake in his book "Optics in Photography," in the section on perspective. I think this entire chapter can be seen in preview on Google books. The concept of "center of perspective" is the important part.

You can do the basic empirical experiments with an iPhone with three lenses.
The mystery to me was/is how it is possible to do rise shift with a normal lens too?
The answers so far seems to be that the normal lens is really not normal, once you get out of the standard image circle.
Then it begins to exhibit the geometry correcting/distorting traits of a wide lens.
Am I totally wrong?

 

[AgX]

That is what I don't get.
Thinking even more about it, even if a lens has a certain focal length written on it, it still has to be wider to accommodate the larger image circle.
It has to be the typical wide image distortion that introduces the correction for for example buildings. Even if it isn't as much as with a "serious" wide.

By no word I had it about angle of coverage resp. circle of coverage.

But of course a lens applied at shifting must yield these as too big for the format. And of course such lens at a larger format woul be a wider-angle lens. But this all has nothing to do with the pespective effects at raising the front standard.
You are completely astray with your thougt.


There are two kinds of "wide-angle distorsion"
-) bending (curving) of straight lines. (A lack in lens design, which of course would apply at raising the front standard too)
-) weird scale ratio between front and background due to going nearer to the subject than with a standard lens, to keep scale of one of them.

 

[brbo]

Thinking a little more about it, that would be impossible, since the geometry changes according to viewpoint.

Yes. My answer was simplified and in spirit of why are rise/fall movements used at all. If I had an infinitely long ladder that would fit in my pocket, that would solve 100% percent of rise/fall adjustments (for me!). But let's see if someone can present a scenario when rise/fall is better that moving the camera. For me, I'm willing to accept that I'm only getting a crop from a larger circle, because the change in camera position is just not possible.

 

[Helge]

Yes. My answer was simplified and in spirit of why are rise/fall movements used at all. If I had an infinitely long ladder that would fit in my pocket, that would solve 100% percent of rise/fall adjustments (for me!). But let's see if someone can present a scenario when rise/fall is better that moving the camera. For me, I'm willing to accept that I'm only getting a crop from a larger circle, because the change in camera position is just not possible.

I am almost positive that you wouldn’t get the same result from a super high tripod or a ladder.

It would seem to me, that one way of thinking of shifting/rise, is that it is almost like combining the best of two focal lengths. Wide in the height, and normal in the width.

 

[Helge]

By no word I had it about angle of coverage resp. circle of coverage.

But of course a lens applied at shifting must yield these as too big for the format. And of course such lens at a larger format woul be a wider-angle lens. But this all has nothing to do with the pespective effects at raising the front standard.
You are completely astray with your thougt.


There are two kinds of "wide-angle distorsion"
-) bending (curving) of straight lines. (A lack in lens design, which of course would apply at raising the front standard too)
-) weird scale ratio between front and background due to going nearer to the subject than with a standard lens, to keep scale of one of them.

A lens that projects more of a scene at a given distance is more wide angle.
A lens with a larger image circle is wider than it says on the rim of the lens (with poorer quality no doubt).
I don’t see how that can be contested.

It is possible to do perspective correction/shift with a pinhole too. And pinholes are perfectly rectilinear in their protection.
The curving lines only applies to badly corrected wides or fisheyes.

 

[brbo]

I am almost positive that you wouldn’t get The same result from a super high tripod or a ladder.

No, I wouldn't. I wrote that I would prefer infinite ladder, but I'm willing to live with second best.

 

[brbo]

A lens with a larger image circle is wider than it says on the rim of the lens (with poorer quality no doubt).
I don’t see how that can be contested.

No. A 50 is a 50. No matter where you use it. Coverage or what is considered wide on a certain format is something completely different. Two lenses of the same focal length can have different angle of coverage.

 

[warden]

This thread is an enjoyable mind bender for someone like me who has never tried a lens with movements. In my case I'm limited to correcting perspective by tilting the easel in the darkroom.

 

[AgX]

A lens that projects more of a scene at a given distance is more wide angle.
A lens with a larger image circle is wider than it says on the rim of the lens (with poorer quality no doubt).
I don’t see how that can be contested.

I contest this in your context.
You have it about raising the camera versus rise of front standard. It is fair to assume that both you are doing at the same format. Thus the viewing angle will be the same.

 

[Helge]

No. A 50 is a 50. No matter where you use it. Coverage or what is considered wide on a certain format is something completely different. Two lenses of the same focal length can have different angle of coverage.

Didn't mention FL on purpose. Only the angle of view implied by the FL, on a given format.
A 50mm on 4x5 is very wide. but if you cut out the middle of the circle you get a view like 50mm on 135 (lower resolution no doubt).

The reverse is true too. If you chose to used more of the image circle than what the manufacturer has chosen to rate the lens at (with the possible problems of that) you get a wider view.
Right?

 

[Helge]

I contest this in your context.
You have it about raising the camera versus rise of front standard. It is fair to assume that both you are doing at the same format. Thus the viewing angle will be the same.

Yes, if from the plate of films "point of view". But the lens can of course see considerably more. And distorts that, like any wider angle lens.
My OQ is, is it that distortion effect, that is used for, for example converging lines correction? Or is something else at play?

*Note, I'm not talking about tilt here, only straight shift.

 

[abruzzi]

I've always wondered if the term "wide angle" actually started as an indicator of the coverage/image circle. A Dagor has an agle of coverge of ~80 degrees when stopped to f45, but a "Wide Angle Dagor" has a wider angle of coverage for the same focal length. Today "wide angle" is generally used to indicate a lens that is wide for a particular format, i.e. 90mm on 4x5.

Some lens designs, the Super Angulon for instance, have a wide angle of coverage, so while most people throw a 90mm SA on their 4x5 and call it a wide angle, you could get a 165mm Super Angulon and use it as a "normal" on your 4x5. You would get more or less the same optical behavior, but over a larger image circle, most of which you aren't using becuase it has the same optical design and therefore the same angle of coverage.

 

[brbo]

Yes, if from the plate of films "point of view". But the lens can of course see considerably more. And distorts that, like any wider angle lens.
My OQ is, is it that distortion effect, that is used for, for example converging lines correction? Or is something else at play?

No!

Lens distortion (or wide(er) view) has absolutely nothing to with fixing converged lines. There are no converging lines to begin with, since you position both standards parallel to the subject. And then use the rise to crop from the upper part of the imaging circle to get the scene you want. If you didn't have the rise capability, you'd have to point the camera upwards which would introduce converging lines.

 

[Mr Bill]

Then it begins to exhibit the geometry correcting/distorting traits of a wide lens.
Am I totally wrong?

Yeah. If you are looking at the top of the building converging as the problem, this is brought about by the film plane not being parallel to the face of the building.

Regarding the "wide lens distortion," I think Kingslake explains well. If you see a print that seems to have this "distortion," it generally means you are viewing the print from the wrong distance (or position). Here's an example... if you have ever used a wide lens for groups you've probably observed that people near the sides or corners have gotten elongated heads. But... if you view, using only one eye, from the "correct" position, then the heads will have the correct shape again. (They appear elongated if you view the print from too far away.)

I think an evening with the Kingslake preview may give you a new perspective (pun intended) on this. Again, the key is the "center of perspective" thing.

 

[Mr Bill]

No!

Lens distortion (or wide(er) view) has absolutely nothing to with fixing converged lines. There are no converging lines to begin with, since you position both standards parallel to the subject. And then use the rise to crop from the upper part of the imaging circle to get the scene you want. If you didn't have the rise capability, you'd have to point the camera upwards which would introduce converging lines.

I concur 100%

 

[Alan Edward Klein]

What is the ratio from camera rise to moving the whole camera higher?

 

[Helge]

I concur 100%

If the camera is tilted up to capture the top of the building, the lines convergence.
The fix for such situations is usually just to get a wide lens and point it straight ahead. But you get too much of the ground that way.
Solution: Only use the mid and top of a wide lens.
Rectilinear correction would indeed seem to have something to do with it.

 

[Sirius Glass]

This thread is an enjoyable mind bender for someone like me who has never tried a lens with movements. In my case I'm limited to correcting perspective by tilting the easel in the darkroom.

Not exactly the same, but an option.

Back to the OP, if raising the camera a few inches or centimeters would correct the distortion, then cameras would not have raise, shift, and tilt movements, why bother. That of course could put APUG Photrio and Large Format Photography Forum out of business!