Where is the lens plane?

[Mike Anderson]

I have a basic understanding of Scheimpflug and the effect of camera movements, but where exactly is the lens plane? Is it the front of the lens board? The plane of the diaphragm? Always, usually, sometimes?

Just curious, at this point.

...Mike

[Larry H-L]

If you are just trying to estimate your camera movements, I think either that you mention will do.

If you want to be more precise, I think you might have to locate the nodal point(s) of each lens.

[Mike Anderson]

If you are just trying to estimate your camera movements, I think either that you mention will do.

If you want to be more precise, I think you might have to locate the nodal point(s) of each lens.

I'm just curious. On many cameras the film plane is precisely marked, even though I don't have much use for that precision. I thought modern view camera lenses would have some kind of precise indication, for the precision minded.

...Mike

[Oren Grad]

It depends on the optical design. In extreme cases - telephoto lenses, or especially in the case of small SLR cameras, retrofocus wide angle designs - the nodal point is actually out in space, in front of or behind the lens. That's what makes telephotos tricky to work with when you need movements.

[Mike Anderson]

It depends on the optical design. In extreme cases - telephoto lenses, or especially in the case of small SLR cameras, retrofocus wide angle designs - the nodal point is actually out in space, in front of or behind the lens. That's what makes telephotos tricky to work with when you need movements.

Is the nodal point on the lens plane? More precisely: is the lens plane between the front and rear nodal points?

...Mike

[Larry H-L]

I am not an optical engineer, but my lay-person's understanding of the nodal point is where the image converges, and then flips over inverted. If this is the case, then I would guess that the lens plane surrounds the nodal point at a 90-degree angle to the lens axis.

I'm sure some others with more optical knowledge can jump in and enlighten us.

But, just what are you trying to do with your camera?

[Jerry Bodine]

I pondered the same question many years ago. So I got out my Sinar Norma and all my lenses (in Compur shutters), and one-by-one focused each lens at infinity and measured (with a metric tape measure for finely spaced gradations) from the film plane (indicated on the back) to find the location near the lens where its focal length fell. I found that each of my three Symmars was located at the front surface of the lens board, and each of my three Super Angulons was located at the aperture control ring. So yes the lens design is certainly a factor. From a practical standpoint this has worked OK for me, but I'm open to opinions of course. BTW, I have no telephotos so can't comment on that.

[Emmanuel BIGLER]

Hello all
The question deals with the application of Scheimpfug's rule to a thick compound lens where the principal (H, H') or nodal (N, N', they are the same as H, H') are separated by a certain distance.

First plot the well-know diagram with a single thin lens element.
Here, no problem, the lens plane is... the single lens element plane.

Now plot on a piece of paper several entering rays of your choice, coming from different points of the slanted object plane and continue behind the lens to form the image of a slanted image plane. According to good old rules of geometical optics.

Ready ?

Now take a pair of scissors and cut your drawing in the middle of the single lens element.
Separate both sides of the drawing by a certain distance, slide both sides along the optical axis.
Glue both drawings on a second piece of paper underneath
On the left-side drawing, the object side, call H=N the "ex-center" of the lens element.
Same on the right side, image side, call the "ex-centre" of the lens H'=N'.
You are all set. You do not have to change anything in your ray tracing and you have now handy the graphical rule for Scheimpflug.

The original 'lens plane' is now split in to two separate planes with a "no man's land" in between but on the left side of H and on the right side of H' nothing has changed.
This is your Scheimpflug drawing for a thick compound lens.

Another issue is the front hinge for depth of field in the well-know wedge-shaped protion of object space.
No problem, the front hinge for depth of field is located in the front focale plane, one focal length ahead of the principal point H.

[jose angel]

Maybe you`ll find interesting "How to Find the Nodal Point" at the RRS site (http://reallyrightstuff.com/pano/05.html).
There are some links to Alain Hamblenne`s useful info about this topic after the paragraph #3.

[Mike Anderson]

...
The original 'lens plane' is now split in to two separate planes with a "no man's land" in between but on the left side of H and on the right side of H' nothing has changed.
This is your Scheimpflug drawing for a thick compound lens.
...

I appreciate the illustration you've provided but I still don't get it. In my mind I see 2 parallel planes. Which one is the lens plane? I'm guessing neither, that the lens plane is somewhere in between (in "the no man's land").

...Mike

[Mike Anderson]

...
But, just what are you trying to do with your camera?

It's really academic. As I read up on view cameras, there's many mentions of the "lens plane" and diagrams showing lens planes film planes and so on. I can see exactly where the film plane is, and I have an intuitive idea of where the lens plane exists (my intuition tells me it coincides with the diaphragm). I want to be sure my intuition isn't too far off.

...Mike

[Jack Dahlgren]

Set your camera back perpendicular to a flat surface.
Drop a plumb line from the front of the ground glass to the flat surface.
Mark that point.
Tilt the front standard until the flat surface is in uniform focus.
Extend a line from the point you have marked and make it parallel to the front standard.
By definition it will be the lens plane.

[Mike Anderson]

Set your camera back perpendicular to a flat surface.
Drop a plumb line from the front of the ground glass to the flat surface.
Mark that point.
Tilt the front standard until the flat surface is in uniform focus.
Extend a line from the point you have marked and make it parallel to the front standard.
By definition it will be the lens plane.

Well that's a clever trick.:) I'll have to try it sometime.

Thanks,

...Mike

[Emmanuel BIGLER]

I have attached a diagram to show what happens including Jack's plane which is located somewhere between the two principal planes and can be defined as the lens plane if you wish.

The important point is that the setting angles are exactly the same for any thick compound lens as for a single lens element of the same focal length ; or better, as for a dialyte lens like an apo ronar, apo artar, fuji-C etc.. where the principal planes H and H' are never separated by more than a few percent (not more than 3% for the apo ronar) of the focal length.

Hence all you can derive, plot, adjust, based on a single lens element is valid in practice; actually you'll slightly translate your rear standard until the image is sharp.
The fact that the angles are the same is important since even for a telephoto, you can easily compute mentally the tilt angle required to bring the plane of sharpness on ground in a classical setup for landscape with a foreground.
If the lens is located at 1.5m (5 feet) above ground and if you have a 150mm focal length (6 inches, 1/2 foot) then the tilt angle corresponds to a slope of 1/2 for 5, one for ten, i.e. about 6 degrees.
With a 360 apo ronar or a 360 tele arton, although those lenses are of very different designs, the angles in the same conditions with the lens at 1.5m above ground will be given by 6° x 36/15 ~= 14°

[Mike Anderson]

I have attached a diagram...

Finally it makes sense! That second (bottom) diagram is exactly what I was looking for.

I appreciate your help.

...Mike