12-24mm DX now in my lens table

Started Sep 7, 2003 | Discussions
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Joseph S Wisniewski Forum Pro • Posts: 34,130
12-24mm DX now in my lens table

For all you panorama shooters, I've added the entrance pupil measurements for the 12-24mm DX (for 7 different focal lengths) to my lens measurement table.

http://www.swissarmyfork.com/photo_resources.html

The "entrance pupil" is the point you rotate about when shooting panoramas. It's often referred to as the "nodal point". (I've also measured the "real" nodal points, as well as the exit pupil. It's all in the table).

It's a "pano friendly" lens, the entrance pupil is within a couple of mm of the line engraved right before the zoom collar, for all focal lengths. If you're doing your panoramas with the "PhiloPod" plumb bob method, just tie your strign around that line, and you're good to go.

Also added a golden oldie, the measurements for the 105mm f4.0 Nikkor-P bellows lens.

And, just for grins, the rare and obscure Leica 24mm Macro-Summar.

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Bradford Bohonus Forum Member • Posts: 61
Re: 12-24mm DX now in my lens table

Can be a little more specific in your description of this, or include a picture of what you are talking about?

As my Nikon 12-24mm lens has no such lines "engraved" in the manner you speak of.

Joseph S Wisniewski OP Forum Pro • Posts: 34,130
Sorry. This line....

Bradford Bohonus wrote:

Can be a little more specific in your description of this, or
include a picture of what you are talking about?

As my Nikon 12-24mm lens has no such lines "engraved" in the manner
you speak of.

Sorry if I wasn't clear enough. Maybe yours is tooled a bit different, but on mine, Nikon put a healthy bevel on the front edge of the zoom collar, and a similar bevel on the back of the barrel where it mates, so the appearance is that of an engraved line.

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Pete Biro Veteran Member • Posts: 3,798
Which means what? (nt)

Joseph S. Wisniewski wrote:

Bradford Bohonus wrote:

Can be a little more specific in your description of this, or
include a picture of what you are talking about?

As my Nikon 12-24mm lens has no such lines "engraved" in the manner
you speak of.

Sorry if I wasn't clear enough. Maybe yours is tooled a bit
different, but on mine, Nikon put a healthy bevel on the front edge
of the zoom collar, and a similar bevel on the back of the barrel
where it mates, so the appearance is that of an engraved line.

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Pete Biro

Joseph S Wisniewski OP Forum Pro • Posts: 34,130
Re: Which means what? (nt)

Pete,

If you're stitching panoramas, the stitching process works best if all the pictures are taken with an identical perspective. Every lens has a "center of perspective" called the entrance pupil (some incorrectly call it the "nodal point"). You have to rotate the lens and camera around the entrance pupil. This can be done using an expensive QT-VR head like the Bogen or Kaiden heads, or it can be done using home made brackets, or it can be done using a string tied around the lens dangling down to a plumb bob.

If you are going to use this last approach, simply tie the string about the line I've illustrated, and you will be correct within 2 or 3mm, no matter what the zoom setting of your 12-24mm DX.

Not as easy as using your widelux

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motofoto Contributing Member • Posts: 544
Re: Which means what? (nt)

Joseph S. Wisniewski wrote:

Every
lens has a "center of perspective" called the entrance pupil (some
incorrectly call it the "nodal point").

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motofoto Contributing Member • Posts: 544
Re: Which means what? (nt)

Joseph S. Wisniewski wrote:

Every
lens has a "center of perspective" called the entrance pupil (some
incorrectly call it the "nodal point").

Well, you’ve got a new one on me … I’ve heard of nodal points, ( sometimes called principal points), and have experience with both homemade and manufactured pano head brackets but I’ve yet to hear the term “ center of perspective “

Aside from your own, is there another reference or usage for “center of perspective” ??

the concept of nodal point is well explained by Leslie Strobel and the effect can be determined by following the Kaidan guide found on their website … neither of these two well accepted sources of information on lenses and panoramas makes any mention of “ center of perspective “ that I’m aware of … could you point us to this please ??

And the commonly accepted definition of an entrance pupil is the effective aperture ( the entering beam of light that just fills the diaphragm opening ) used in caculating the F number.

Regards,
Mike

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Pete Biro Veteran Member • Posts: 3,798
OK, didn't know that stuff, thanks (nt)

Joseph S. Wisniewski wrote:

Pete,

If you're stitching panoramas, the stitching process works best if
all the pictures are taken with an identical perspective. Every
lens has a "center of perspective" called the entrance pupil (some
incorrectly call it the "nodal point"). You have to rotate the lens
and camera around the entrance pupil. This can be done using an
expensive QT-VR head like the Bogen or Kaiden heads, or it can be
done using home made brackets, or it can be done using a string
tied around the lens dangling down to a plumb bob.

If you are going to use this last approach, simply tie the string
about the line I've illustrated, and you will be correct within 2
or 3mm, no matter what the zoom setting of your 12-24mm DX.

Not as easy as using your widelux

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Pete Biro

Joseph S Wisniewski OP Forum Pro • Posts: 34,130
About entrance pupils...

motofoto wrote:

Joseph S. Wisniewski wrote:

Every
lens has a "center of perspective" called the entrance pupil (some
incorrectly call it the "nodal point").

Well, you’ve got a new one on me … I’ve heard of
nodal points, ( sometimes called principal points), and have
experience with both homemade and manufactured pano head brackets
but I’ve yet to hear the term “ center of perspective

It really exists.

Nodal points also really exist, but you've never actually used them in your panoramic photography. A lens has two nodal points. Those are the mathematical points from which the lens "appears" to have its front and back focus.

For example, if your subject is infinitely far away from a 50mm lens, the image will come to focus 50mm behind the "rear nodal point" or "rear node" of the lens. If you turn the lens around, the image will come to focus 50mm from the front nodal point.

These points are meaningless to stitched panorama work. They have meaning to people using the old "swing lens" style panorama cameras, such as a WideLux. (Ahhhh, the WideLux....)

Aside from your own, is there another reference or usage for
“center of perspective” ??

R. Kingslake, Optics in Photography, SPIE Optical Engineering Press, 1992

He explains it very well, starting with a pinhole camera, and working up to lens systems. Kingslake is a smart fellow, was the director of optical research at Kodak for quite some time.

The pinhole camera is a good example, because the entrance pupil, exit pupil, front node, and rear node are all the same point.

If you want a few online references, here's a lovely photo.net thread discussing the "center of perspective", the "extrance pupil", and the misuse of the term "nodal point" by panorama photographers. It even references Kingslake

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=003bju

And a couple of other online references...

http://medfmt.8k.com/mf/nodal.html

http://www.spie.org/web/abstracts/3200/3295.html

the concept of nodal point is well explained by Leslie Strobel and
the effect can be determined by following the Kaidan guide found
on their website … neither of these two well accepted sources
of information on lenses and panoramas makes any mention of
“ center of perspective “ that I’m aware of
… could you point us to this please ??

Many "well accepted sources" get this totally wrong. It's a common misconception: years ago panoramic cameras had rotating lenses. These cameras, such as the WideLux, the Kodak Panoram and Cirkut (Curcuit) Camera, the Horizon, or the Noblex would rotate the lens around the rear nodal point of the lens. This is necessary, because the lens is moving relative to the film, rotating about any point other than the rear node would result in image smear. This usage kind of "stuck". Among people who have no idea what a nodal point really is, a nodal point became "the point that any type of panoramic camera, no matter how it works, rotates about".

And the commonly accepted definition of an entrance pupil is the
effective aperture ( the entering beam of light that just fills the
diaphragm opening ) used in caculating the F number.

That's not a "commonly accepted definition" in any optical literature that I have ever read. It would be difficult to measure, requiring a variable diameter columnated light source (or a y axis slider on the laser on my optical bench).

The "effective aperture" can be calculated fairly easily by walking the image of the aperture through the lens, one element at a time. This really is "commonly accepted". Chapter 6 "Stops and Apertures" of Warren Smith's "Modern Optical Engineering" has a good discussion (and nice illustrations) of this. Or try using a lens design program like OSLO (the academic version is a free download). It will show you the entrance pupil, exit pupil, etc. for any lens design.

p.s. Kaidan's site search turns up 68 hits for "nodal" and zero hits for "pupil". That pretty much puts Kaidan to bed.

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Joseph S Wisniewski OP Forum Pro • Posts: 34,130
Question for you...

Pete,

Do you scan those WideLux negatives?

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brian Senior Member • Posts: 1,157
Coolpix??

Hi Joe:

I know your main interest is in SLR lenses, but I'm working on an optical adapter to mount a Coolpix 990/4500 to a fast Schmidt camera, and I'm only able to make educated guesses about the entrance pupil position based on some old patent data for the Coolpix 900 lens. Any chance you'll ever measure the entrance pupil positions for consumer digicams, esp. the Coolpixes? I would think that digiscopers would also be very interested in such measurements.

What sort of bench setup do you use to do the measurements?

Thanks,
Brian

Joseph S. Wisniewski wrote:

For all you panorama shooters, I've added the entrance pupil
measurements for the 12-24mm DX (for 7 different focal lengths) to
my lens measurement table.

http://www.swissarmyfork.com/photo_resources.html

The "entrance pupil" is the point you rotate about when shooting
panoramas. It's often referred to as the "nodal point". (I've also
measured the "real" nodal points, as well as the exit pupil. It's
all in the table).

It's a "pano friendly" lens, the entrance pupil is within a couple
of mm of the line engraved right before the zoom collar, for all
focal lengths. If you're doing your panoramas with the "PhiloPod"
plumb bob method, just tie your strign around that line, and you're
good to go.

Also added a golden oldie, the measurements for the 105mm f4.0
Nikkor-P bellows lens.

And, just for grins, the rare and obscure Leica 24mm Macro-Summar.

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motofoto Contributing Member • Posts: 544
Re: About entrance pupils...

Joseph S. Wisniewski wrote:

If you want a few online references, here's a lovely photo.net
thread discussing the "center of perspective", the "extrance
pupil", and the misuse of the term "nodal point" by panorama
photographers. It even references Kingslake

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=003bju

sorry Joe, I've scanned the thread and can not see the words "center of perspective" anywhere ... lots of "nodal points", some "entrance pupil" but no "center of perspective" .... maybe I'm not looking hard enough.

but I noticed a couple of names from the old Quang-Tuan Luong large format forum ... I stopped participating in that forum shortly after it migrated to Photo.net.

that was one of the most imformative forums I'd ever participated in.

That's not a "commonly accepted definition" in any optical
literature that I have ever read. It would be difficult to measure,
requiring a variable diameter columnated light source (or a y axis
slider on the laser on my optical bench).

check page 67 of the 6th edition of "View Camera Technique" by Leslie Strobel for the definition of entrance pupil.

Strobel is a professor at the Rochester Institute of Technology, where he has taught photography for the past forty-four years.

he is also chairman of the Professional Photography Department and the Department of Imaging and Photographic Technology.

his numerous books have become standards.

p.s. Kaidan's site search turns up 68 hits for "nodal" and zero
hits for "pupil". That pretty much puts Kaidan to bed.

as can be expected ... Kaidan is concerned with panorama photography and the correct position of the nodal point is an essential part of setting up the equipment properly.

entrance pupils have no value in panoramas, but nodal points do ... and if you put Kaidan to bed you will put to bed the #1 supplier of manufactured panorama equipment and support.

also a quick search of panoguide.com turned up no reference to "center of perspective" ... you sure you didn't make this up yourself ??

Regards,
Mike

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Joseph S Wisniewski OP Forum Pro • Posts: 34,130
Re: About entrance pupils...

motofoto wrote:

Joseph S. Wisniewski wrote:

If you want a few online references, here's a lovely photo.net
thread discussing the "center of perspective", the "extrance
pupil", and the misuse of the term "nodal point" by panorama
photographers. It even references Kingslake

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=003bju

sorry Joe, I've scanned the thread and can not see the words
"center of perspective" anywhere ... lots of "nodal points", some
"entrance pupil" but no "center of perspective" .... maybe I'm not
looking hard enough.

"second - your French is perfect! Kingslake and Ray merely state that the entrance pupil is the center of perspective of the picture (regarding the object space; the center of perspective for the image space is the center of the exit pupil), without thrusting into a more detailed study."

If you google "center of perspective" you'll find a considerable number of hits.

The Photonics Dictionary defines it as

center of perspective - That viewpoint at which the angular subtenses of points in the picture are identical to angular subtenses of the original points in the scene, at the camera lens.

That's a bit obscure, even to me. I'll stick with Kingslake.

but I noticed a couple of names from the old Quang-Tuan Luong large
format forum ... I stopped participating in that forum shortly
after it migrated to Photo.net.

that was one of the most imformative forums I'd ever participated in.

The old forums were always the best.

That's not a "commonly accepted definition" in any optical
literature that I have ever read. It would be difficult to measure,
requiring a variable diameter columnated light source (or a y axis
slider on the laser on my optical bench).

check page 67 of the 6th edition of "View Camera Technique" by
Leslie Strobel for the definition of entrance pupil.

Strobel is a professor at the Rochester Institute of Technology,
where he has taught photography for the past forty-four years.
he is also chairman of the Professional Photography Department and
the Department of Imaging and Photographic Technology.

his numerous books have become standards.

Dr. Rudolph Kingslake is professor of optics at the University of Rochester, also a department chairman, in addition to his duties as director of optical design at Kodak. His numerous books have become standards

His methodologies agree with what I have measured on my own optical bench.

p.s. Kaidan's site search turns up 68 hits for "nodal" and zero
hits for "pupil". That pretty much puts Kaidan to bed.

as can be expected ... Kaidan is concerned with panorama
photography and the correct position of the nodal point is an
essential part of setting up the equipment properly.

entrance pupils have no value in panoramas, but nodal points do ...

The only thing wrong with that statement is that it is 100% reversed. Again, unless you are using a WideLux or other swing camera, the nodal points have absolutly no impact on panoramic photography.

Give it a try, yourself. Take your favorite Nikkor, the one you use most for panoramas. Write to Nikon and tell them you are doing panorama and macro work, and would like to know the front and rear nodal points, the entrance pupil, and the exit pupil. Then sewe which of these points you have been rotating around.

and if you put Kaidan to bed you will put to bed the #1 supplier of
manufactured panorama equipment and support.

If you set up the equipment the way Kaidan says, you will end up rotating around the entrance pupil, not either of the nodal points.

And as far as putting Kaidan to bed, have you ever tried to change those silly "detent discs" in the field, without contaminating the whole head and jamming it up?

also a quick search of panoguide.com turned up no reference to
"center of perspective" ... you sure you didn't make this up
yourself ??

http://www.pauck.de/archive/mailinglist/tech-3d/mhonarc/msg00265.html
http://www.vanwalree.com/optics/misconceptions.html
http://home.vicnet.net.au/~vic3d/cop.html
http://www.computer.org/proceedings/icpr/0750/Volume%201/07501876abs.htm
http://www.angelfire.com/ca2/tech3d/images/persp.pdf
http://www.cs.unr.edu/~bebis/CS791E/Notes/CameraParameters.pdf
http://vision.ai.uiuc.edu/~manoj/aggarwal_center.pdf
http://www.swissarmyfork.com/lens_table_1.htm

I like the way Paul van Walree summed it up.

"Many sources that write this don't specify whether it is the front or rear nodal point, but either way it is incorrect. To preserve the perspective during rotation, which prevents a displacement of nearby objects relative to the background, the axis of rotation should pass through the entrance pupil, which is the center of perspective of a lens. No doubt instructions to find the position of the rotation axis will lead to the correct point, it's just that the designation nodal point is wrong. The good news is that, unlike a nodal point, the entrance pupil can be found by visual inspection. When you look into a lens from the front, the entrance pupil is the image of the diaphragm opening."

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Joseph S Wisniewski OP Forum Pro • Posts: 34,130
Re: Coolpix??

brian wrote:

Hi Joe:
I know your main interest is in SLR lenses, but I'm working on an
optical adapter to mount a Coolpix 990/4500 to a fast Schmidt
camera, and I'm only able to make educated guesses about the
entrance pupil position based on some old patent data for the
Coolpix 900 lens. Any chance you'll ever measure the entrance
pupil positions for consumer digicams, esp. the Coolpixes? I would
think that digiscopers would also be very interested in such
measurements.

You're in luck, I'm doing Bryce Dennison's CP990 in a couple of weeks. I'll let you know when I do.

What sort of bench setup do you use to do the measurements?

It's actually pretty simple. I have two setups, but they both work the same way. Mount the lens (or camera) on a rotating platform with a micrometer slide, stop the lens down as much as you can, hit the diaphragm with a laser, rotate the camera back and forth and adjust the micrometer slide until the spot the laser is fixed on does not move as you rotate the camera.

The big setup on my optical bench can hit the point to within 0.05mm. The portable setup uses a Bogen VR head instead of a "real" nodal slide, but can still end up within 0.25mm.

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Joseph S Wisniewski OP Forum Pro • Posts: 34,130
Found a cool drawing...

This shows you where the pupils and nodal points fall, and what the "center of perspective" actually is.

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brian Senior Member • Posts: 1,157
Re: Coolpix??

Joseph S. Wisniewski wrote:

brian wrote:

Hi Joe:
I know your main interest is in SLR lenses, but I'm working on an
optical adapter to mount a Coolpix 990/4500 to a fast Schmidt
camera, and I'm only able to make educated guesses about the
entrance pupil position based on some old patent data for the
Coolpix 900 lens. Any chance you'll ever measure the entrance
pupil positions for consumer digicams, esp. the Coolpixes? I would
think that digiscopers would also be very interested in such
measurements.

You're in luck, I'm doing Bryce Dennison's CP990 in a couple of
weeks. I'll let you know when I do.

Thanks, I'll be interested in the results.

What sort of bench setup do you use to do the measurements?

It's actually pretty simple. I have two setups, but they both work
the same way. Mount the lens (or camera) on a rotating platform
with a micrometer slide, stop the lens down as much as you can, hit
the diaphragm with a laser, rotate the camera back and forth and
adjust the micrometer slide until the spot the laser is fixed on
does not move as you rotate the camera.

The big setup on my optical bench can hit the point to within
0.05mm. The portable setup uses a Bogen VR head instead of a "real"
nodal slide, but can still end up within 0.25mm.

How do you determine whether the laser beam is at the center of the aperture stop? Direct observation, or some sort of light throughput method?

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Joseph S Wisniewski OP Forum Pro • Posts: 34,130
Re: Coolpix??

brian wrote:

Joseph S. Wisniewski wrote:

It's actually pretty simple. I have two setups, but they both work
the same way. Mount the lens (or camera) on a rotating platform
with a micrometer slide, stop the lens down as much as you can, hit
the diaphragm with a laser, rotate the camera back and forth and
adjust the micrometer slide until the spot the laser is fixed on
does not move as you rotate the camera.

How do you determine whether the laser beam is at the center of the
aperture stop? Direct observation, or some sort of light
throughput method?

Direct observation. On the portable setup, the beam is "as is" from the laser, maybe 0.5mm round. I focus it on the top edge of the aperture. Since we're rotating horizontally, the fact that we're not vertically centered is negligable.

On the big setup, there's a nice telescope that knocks the beam down to an offensivley small, bright dot, and a cylindrical lens that turns it into a vertical line. Center that on the aperture, and it's remarkably easy to see weather or not it's staying centered, especially through the bench telescope.

It would be interesting to do a throughput system, vibrate the beam, and look for equal timing as it hits the left and right aperture edge. (Actually, that's a side effect of wanting to use a system like that to maintain centration when I asselble the UV Wisniewskinar lens. Wizonar? Wizogon?)

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Pete Biro Veteran Member • Posts: 3,798
Re: Answer for you...

Joseph S. Wisniewski wrote:

Pete,

Do you scan those WideLux negatives?

No, I have not... actually I have not used the camera for a loooooong time. Maybe time to put on ebay?

Thanks for reminding me I have one! (Cabinet is full of obsolete stuff)!

Joseph S Wisniewski OP Forum Pro • Posts: 34,130
Re: Answer for you...

Pete Biro wrote:

Joseph S. Wisniewski wrote:

Pete,

Do you scan those WideLux negatives?

No, I have not... actually I have not used the camera for a
loooooong time. Maybe time to put on ebay?

Probably the right time. I think that the people who actually use them for senic work are dumping them in favor of stitching, so the glut is jost going to get worse. Eventually, the collectors will catch up...

Thanks for reminding me I have one! (Cabinet is full of obsolete
stuff)!

I know the feeling. At least some of my "obsolete things" are fairly collectable and holding value (A nice Rolleiflex is definitely something to hang onto).

I'm waiting, I forecast a Hassleblad glut of epic proportions in about 3 years. 10 cents on the dollar kind of thing, as they transition from "meerly obsolete" to "obsolete junk 10 cents on the dollar". That's when I'll grab one. I think they will hit a "highly collectable" phase in about 10 years, though.

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brian Senior Member • Posts: 1,157
Re: Coolpix??

Joseph S. Wisniewski wrote:

.. . . . . the UV Wisniewskinar lens
--

There are times when I could really use a completely unfiltered camera to get really good UV/IR sensitivity. What are you planning to do with your UV lens, and are you doing your own CaF2 work?

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