Nodal points of current Leica M lenses

[harry__florida_]

If this has been asked/answered somewhere I can't find it. Has anyone

published the location of the nodal points of the current M lenses? My

application is panoramic photography. I have the means accurately to

make the measurements (focus at infinity, from flange mounting surface

to nodal point within 0.5 mm) but would be glad to take advantage of

work already accomplished. If it has not been done, I will post my

numbers here for comment.

[Rob F.]

I can't recall it ever being mentioned here in 7 years of following this forum! Sounds like you're way ahead of us, Harry! I have no idea how to locate the nodal point. I know it's important to pivot the camera around the N.P. for panos. I've gotten away without doing so, but that was with distant mountains for the subject. I imagine that makes a difference. I'm not aware of Leica marking the N.P.

[jim_bennet]

Start with that science crap and you'll ruin a good bokeh argument.

[harry__florida_]

It's easy enough with a reflex system. The approach I would take with the M lenses is to use a specially machined fixture (on hand) onto which the lens is mounted at the front.

 

At the rear, with proper spacing from the flange, is a ground glass with some fine markings taken from the focoslide-like stage of the Reprovit IIa. Onto that can be attached either the old Leitz 4x chimney magnifier or their 30x magnifier for detailed work. The fixture is mounted onto the movable carrier of a Bellows I from which the bellows has been removed. It can be racked back and forth and position measured by a digital caliper to better than 0.1mm.

 

The bellows rack is mounted atop a pan head and the lens is moved fore and aft until there is no parallax shift noted when panning left to right about the vertical axis. The position of the center of the pan head supporting the bellows rack should then be that of the nodal point. In theory. Correct me if wrong!

[Craig_Cooper11664875449]

Basically, it needs to be at the plane where the aperture blades have been positioned in the lens...

[eliot_rosen1]

I could be wrong about this. I thought that the distance between the rear nodal point and the film plane (on axis) was equal to the focal length when the lens is focussed at infinity.

[Rob F.]

Harry: sounds reasonable.

 

Eliot: also sounds reasonable, but I wonder if this holds up with retrofocus lenses, since the retro design scoots the lens forward so that the rear element will not be inside the dark chamber. Wouldn't that scoot the nodal point forward along with it?

[Craig_Cooper11664875449]

<i>the distance between the rear nodal point and the film plane (on axis) was equal to the focal length when the lens is focussed at infinity</i>

<p>

Not necessarily so... <br>

but for the few times Ive played with this, it became obvious that by definition of what occurs at the rear nodal point, if the aperture blades arent positioned at this point within the lens (or at least very close to it) there would be a problem at very small apertures.

[stuart_richardson]

You might try asking Andrew Nemeth -- he just had a thread up here about doing a 360

degree quicktime panarama, so he might know what you need to do. He was using a 16mm

Elmarit R with an adapter though...

[mark cortella]

Harry,not to sound like a smart a**,but go over to the official Leica website,go to the forums,and there is a forum there to ask Leica questions like this. Or just email them and ask-they Will know the answer. And telling them which lenses,including the serial numbers would probably help. And Andrew Nemeth does this stuff-QTVR panoramics,so he should know. http://www.nemeng.com

[nemeng]

Harry - don't sweat it.

 

M lenses are so small that the nodal point is effectively in the middle of the lens. A couple of millimetres here or there won't matter.

 

With rectilinear lenses you don't have to be so precise with parallax. It only becomes an issue with fisheyes, although even there you can cut corners (been doing it for 9 years now!)

 

:?)

[miles_s.]

Harry, I am very interested in line of research. Please share your results.

 

It is good to know that one need not be exact when it comes to rectilinear wide angle lenses. This will me that there is no adjustment needed for close focusing.

 

I agree with Elliot's statement that the rear nodal point is located at forward of the film plane by the lenses effective focal length. For Leica lenses of FL > 50 mm the exact effective focal length is recorded on each lens to the tenth of milimetres. (See Andrew N.'s FAQ for explaination on how read format of the recording. I think the page is called "what are those white numbers for?") I am away from my optics books at the momement but I think I can confirm Elliot's statement in O'Shea _Elements of Modern Optical Design_. I think the assumption is the object is at infinity and the media infront of and behind the lens have the same refractive index (such that nodal and principal points coincide.

[helenbach]

The correct point of rotation for a stitched panorama is neither the front nor the rear nodal point, it is the entrance pupil, so there's not a lot of point in worrying about where the nodal points are. The entrance pupil is easy to locate: it is where the iris appears to be when you look into the front of the lens.

 

Best, Helen