swing lens cameras and focussing distance

quoting roland again ;-) :

The only adjustment you have to make between a 35mm fixed lens camera and
the Horizon 202 is to allow a larger CoC because the photograph has a
wider horizontal size and so is unlikely to be enlarged by the same extent
as would a 24x36mm shot. If the CoC is 0.03mm for the 24x36m frame then it
will higher for the wider frame of the swing lens frame.
end-quote

this is my point, namely that image size and magnification required for a
given size of enlargement, which in turn is dependent on the negative
format, is really what DOF is about. The COC is different between the
28mm lens on 35mm format because the horizon/noblex format is more like a
cropped 6x6cm or 6x7cm shot, viz., 24x56mm IIRC for horizon 202s.

Consider a 50mm lens with extended coverage. If you take a 110 film
format sized image out of the center of coverage, you have a telephoto
shot; take a 35mm shot, and it is a normal lens; take a 6x6cm shot, and it
is a wide angle, and take a 4x5" panoramic shot and it is an ultrawide.
The perspective, the lens, the f/stop, the focus point, nothing has
changed, we are just changing the format. Yet the magnification and
enlargement factors have changed considerably, as has angles of coverage
from telephoto to ultrawide (and corresponding effective DOF limits).

The swing lens camera is taking in 110 degrees (in Horizon 202 case) on
24x56mm cropped film format. You would get a similar image with an 18mm
lens (non-fisheye) covering 6x6cm, if one existed. That is the lens whose
equivalent DOF is controlling the swing lens case, not the lens used to
make the photo.

Finally, suppose I replace the 28mm lens in the horizon 202 with a 50mm
lens. I still swing it thru 110 degrees. The major change will be the
coverage on the vertical axis (24mm) will be diminished against the 28mm
coverage. Right? But the swing lens is still showing an ultrawide 110
degree image, as that's the swinging angle. I could use a 300mm lens, or a
14mm (if I could make them fit ;-).

My point is that the enlargeability of the swing lens is determined by the
equivalent coverage (here, 110 degrees horizontally), not by the coverage
of the fixed lens DOF that we happen to use in the camera. As a result,
you can't use a DOF calculator for the fixed lens being used on a lesser
format size to provide enlargement factors (cf. DOF/COC) for a swing lens
image of different format (24x56mm) and different coverage (110 degrees
vs. 65 degrees for 28mm on 35mm format).

The "math" converges largely, I suspect, because we are near the
hyperfocal points, fiddling with the COC to make them match, and a 28mm
lens (65 deg.) crop of 24x36mm (to match DOF standard calculator model) is
a close enough match for a 24x36mm crop out of a 24x56mm image taken with
a 110 degree coverage (circa 18mm) lens on that larger format. If you try
the same calculations with a 50mm lens rotated 110 degrees, you won't be
close, yes? ;-) Or 300mm lens being rotated? ;-) or a 12mm lens being
rotated?

grins bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************

(Bob Monaghan) wrote in message ...
quoting roland again ;-) :

The only adjustment you have to make between a 35mm fixed lens camera and
the Horizon 202 is to allow a larger CoC because the photograph has a
wider horizontal size and so is unlikely to be enlarged by the same extent
as would a 24x36mm shot. If the CoC is 0.03mm for the 24x36m frame then it
will higher for the wider frame of the swing lens frame.
end-quote

this is my point, namely that image size and magnification required for a
given size of enlargement, which in turn is dependent on the negative
format, is really what DOF is about. The COC is different between the
28mm lens on 35mm format because the horizon/noblex format is more like a
cropped 6x6cm or 6x7cm shot, viz., 24x56mm IIRC for horizon 202s.

Consider a 50mm lens with extended coverage. If you take a 110 film
format sized image out of the center of coverage, you have a telephoto
shot; take a 35mm shot, and it is a normal lens; take a 6x6cm shot, and it
is a wide angle, and take a 4x5" panoramic shot and it is an ultrawide.
The perspective, the lens, the f/stop, the focus point, nothing has
changed, we are just changing the format. Yet the magnification and
enlargement factors have changed considerably, as has angles of coverage
from telephoto to ultrawide (and corresponding effective DOF limits).

The swing lens camera is taking in 110 degrees (in Horizon 202 case) on
24x56mm cropped film format. You would get a similar image with an 18mm
lens (non-fisheye) covering 6x6cm, if one existed. That is the lens whose
equivalent DOF is controlling the swing lens case, not the lens used to
make the photo.

You say an 18mm lens on 6x6 is equivalent to a 28mm lens on 24x56. I
would say it is 28mm in both cases except you are not going to get a
fixed 28mm lens on 6x6 with that sort of edge coverage since the extra
angle on 24x56 is got by swinging the lens. But concentrate on this
and try to come up with a convincing argument that the 18mm lens is
the same. Can you come up with ANY maths to back this up? If it is OK
with you, then for this thought experiment, the 6x6 film plane has a
mask in it that cuts out the top and bottom of the film area and
leaves it as 24x60mm (actually 24x57mm since the 6cm is really 2 1/4
inches). If that is OK with you then you now have an 18mm lens
covering 24x57mm and a 28mm lens covering 24x56m. Do you still think
they would be equivalent? If so in what sense? Do you consider that
very roughly they both give the same image (consider the
magnification)?

Finally, suppose I replace the 28mm lens in the horizon 202 with a 50mm
lens. I still swing it thru 110 degrees. The major change will be the
coverage on the vertical axis (24mm) will be diminished against the 28mm
coverage. Right? But the swing lens is still showing an ultrawide 110
degree image, as that's the swinging angle. I could use a 300mm lens, or a
14mm (if I could make them fit ;-).

My point is that the enlargeability of the swing lens is determined by the
equivalent coverage (here, 110 degrees horizontally), not by the coverage
of the fixed lens DOF that we happen to use in the camera. As a result,
you can't use a DOF calculator for the fixed lens being used on a lesser
format size to provide enlargement factors (cf. DOF/COC) for a swing lens
image of different format (24x56mm) and different coverage (110 degrees
vs. 65 degrees for 28mm on 35mm format).

The "math" converges largely, I suspect, because we are near the
hyperfocal points, fiddling with the COC to make them match, and a 28mm
lens (65 deg.) crop of 24x36mm (to match DOF standard calculator model) is

I look forward to your mathematics published here to back this up.

a close enough match for a 24x36mm crop out of a 24x56mm image taken with
a 110 degree coverage (circa 18mm) lens on that larger format. If you try
the same calculations with a 50mm lens rotated 110 degrees, you won't be
close, yes? ;-) Or 300mm lens being rotated? ;-) or a 12mm lens being
rotated?


grins bobm

quoting roland:
inches). If that is OK with you then you now have an 18mm lens
covering 24x57mm and a 28mm lens covering 24x56m. Do you still think
they would be equivalent? If so in what sense? Do you consider that
very roughly they both give the same image (consider the
magnification)?
endquote

The Horizon 202 covers a horizontal angle of 110 degrees on 24x56mm film.
To get that same 110+ degrees of horizontal subject matter with a
rectilinear ultra wide angle lens on a 6x6cm camera (from which we can
crop a 24x56mm panoramic shot) requires an 18+mm rectilinear lens on 6x6cm
(see http://www.mat.uc.pt/~rps/photos/angles.html) which covers 110+
degrees horizontally. That's the math that counts here, IMHO ;-)

with a swing lens camera, you can use any lens you want, as long as you
swing it thru 110 degrees. The difference between swinging a 28mm (as in
horizon 202) and a 50mm normal lens will simply be that the vertical scale
will cover much more with the 28mm than with the 50mm. The horizontal
coverage is determined mainly by the swing angle with an open shutter,
yes? ;-)

the cropped 6x6cm 18mm rectilinear lens shot, if such a lens existed (and
AFAIK, it doesn't) would cover the same horizontal angle (110+ degrees) as
the swinging lens horizon 202 shot, and it would include the same amount
of horizontal subject, but there would be differences dues to swinging
lens design (and related "cigar" distortions etc.) and to how much
vertical subject would be on the frame (image height or magnification
etc..) - probably lots more with the 18mm than the 28mm as you would
expect ;-) - and so on.

for all of these reasons, I don't think DOF calculators for fixed lens
cases do a good job of dealing with swinging lens and similar panoramic
camera designs, unless you can use the equivalent fixed lens (e.g., 18mm
here) and appropriate enlargement factors (cf. CoC etc.)...

my $.02 ;-)

bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************

(Bob Monaghan) wrote in message ...
quoting roland:
inches). If that is OK with you then you now have an 18mm lens
covering 24x57mm and a 28mm lens covering 24x56m. Do you still think
they would be equivalent? If so in what sense? Do you consider that
very roughly they both give the same image (consider the
magnification)?
endquote

The Horizon 202 covers a horizontal angle of 110 degrees on 24x56mm film.
To get that same 110+ degrees of horizontal subject matter with a
rectilinear ultra wide angle lens on a 6x6cm camera (from which we can
crop a 24x56mm panoramic shot) requires an 18+mm rectilinear lens on 6x6cm
(see http://www.mat.uc.pt/~rps/photos/angles.html) which covers 110+
degrees horizontally. That's the math that counts here, IMHO ;-)

That calculator is only good for a flat film format.

with a swing lens camera, you can use any lens you want, as long as you
swing it thru 110 degrees. The difference between swinging a 28mm (as in
horizon 202) and a 50mm normal lens will simply be that the vertical scale
will cover much more with the 28mm than with the 50mm. The horizontal
coverage is determined mainly by the swing angle with an open shutter,
yes? ;-)

Yes of course. Your point is...?

the cropped 6x6cm 18mm rectilinear lens shot, if such a lens existed (and
AFAIK, it doesn't) would cover the same horizontal angle (110+ degrees) as
the swinging lens horizon 202 shot, and it would include the same amount
of horizontal subject, but there would be differences dues to swinging
lens design (and related "cigar" distortions etc.) and to how much
vertical subject would be on the frame (image height or magnification
etc..) - probably lots more with the 18mm than the 28mm as you would
expect ;-) - and so on.

In other words the pictures are not compatible so your comparison is
meaningless.

for all of these reasons, I don't think DOF calculators for fixed lens
cases do a good job of dealing with swinging lens and similar panoramic
camera designs, unless you can use the equivalent fixed lens (e.g., 18mm
here) and appropriate enlargement factors (cf. CoC etc.)...

my $.02 ;-)

bobm

You are not thinking this through. You are comparing two very
different images. The swing lens shot does not look like a flat film
shot. You recognise this and yet you are assuming that a comparison is
valid. That makes no sense to me. But if you insist in using this
logic then let's do it properly. Let's compare the image made in the
centre of the film because here the difference in the swing lens photo
and the flat film photo will be much less and the images will look
similar. Depth of field applies there, does it not? So keep to your
logic and tell me if the 18+mm lens will give the same image in the
centre of the film as would a 28mm swing lens. Again, consider the
magnification.

quoting Roland again ;-):
Depth of field applies there, does it not? So keep to your
logic and tell me if the 18+mm lens will give the same image in the
centre of the film as would a 28mm swing lens. Again, consider the
magnification. endquote:

No, it won't be the "same" image, as a swing lens had different
distortions than a fixed lens. The point about the 18mm on 24x36mm format
is that corresponds to a horiz. coverage around 110 degrees+, which is
what these swing lens cameras provide (on a 24x56mm format or larger,
depending on model, however), regardless of whether they use a 28mm or
50mm or 300mm whatever lens with the swinging slit mechanics...

again, this is why I don't feel a fixed lens DOF calculator used with the
particular swing lens focal length (here, 28mm or 29mm for the 35mm swing
lens models Noblex 135.. and Horizon 202 etc.) can be substituted for the
swing lens case. If I put a 300mm lens on a swing lens camera, and swung
it thru 110 degrees, would you still believe that the 300mm lens was a
good indicator of the DOF of the ultrawide 110 degree horiz. coverage
image? ;-)

grins bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************

(Bob Monaghan) wrote in message ...
quoting Roland again ;-):
Depth of field applies there, does it not? So keep to your
logic and tell me if the 18+mm lens will give the same image in the
centre of the film as would a 28mm swing lens. Again, consider the
magnification. endquote:

No, it won't be the "same" image, as a swing lens had different
distortions than a fixed lens. The point about the 18mm on 24x36mm format
is that corresponds to a horiz. coverage around 110 degrees+, which is
what these swing lens cameras provide (on a 24x56mm format or larger,
depending on model, however), regardless of whether they use a 28mm or
50mm or 300mm whatever lens with the swinging slit mechanics...

Consider the central 10mm wide image on the film. You would not be
able to tell if you were using a swing lens camera or a fixed camera.
Do you still think that for that narrow band of film in the center
then the 18+mm lens on medium format would give the same or very
similar results as the 28mm swing lens?

again, this is why I don't feel a fixed lens DOF calculator used with the
particular swing lens focal length (here, 28mm or 29mm for the 35mm swing
lens models Noblex 135.. and Horizon 202 etc.) can be substituted for the
swing lens case. If I put a 300mm lens on a swing lens camera, and swung
it thru 110 degrees, would you still believe that the 300mm lens was a
good indicator of the DOF of the ultrawide 110 degree horiz. coverage
image? ;-)

grins bobm

sure; for example, the subject could be a nearby park bench; the swing
lens "cigar-shaped" distortion could easily be present and observed to
depart from a straight line, which the rectilinear 28mm lens would NOT
project onto film in a fixed camera.

You might find that a fixed 18mm equiv. rectilinear lens (which doesn't
exist in MF, which is why swing lens cameras are used past 100 degrees or
so), if cropped for the central 24x36mm equiv. of 35mm, might be
reasonably close to the fixed 28mm image, except that the DOF would be for
the 18mm MF lens, and the image height would be for the 18mm MF lens, and
so on.

Again, I think the convergence between the DOF calculator for the 28mm
lens and the swing lens is simply a side-effect that all these lenses are
close to the "tipping" point of hyperfocal distances, and small shifts can
let you match the numbers and slopes up (as with picking a 0.04" CoC
etc.?). But the underlying fixed lens vs swing lens, and equiv. fixed lens
for a swing lens horiz. coverage (here, 18mm MF for 110 degrees+ coverage)
is what I understand to be the underlying case.

Switch to a 50mm lens on the same horizon 202 (hacked camera? ;-) and you
end up with a different DOF calculation from your DOF calculator, but the
50mm lens still ends up covering 110+ degrees horizontally in a swing lens
camera. In this case, the "cropped" 24x36mm out of the swing lens MF sized
24x56mm would not look like a normal lens shot; for one thing, it is
covering 36mm/56mm of 110 degrees (or 70 degrees). If the 28mm is a good
match, then the 50mm swing lens must be a bad match, and so on.

In short, you can't fully model a swing lens camera on the fixed lens used
to make it; coverage and distortion and DOF and other issues will vary,
which is why these cameras are built in the first place ;-)

my $.02 ;-)

bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************

"Bob Monaghan" wrote:

sure; for example, the subject could be a nearby park bench; the swing
lens "cigar-shaped" distortion could easily be present and observed to
depart from a straight line, which the rectilinear 28mm lens would NOT
project onto film in a fixed camera.

You might find that a fixed 18mm equiv. rectilinear lens (which doesn't
exist in MF, which is why swing lens cameras are used past 100 degrees or
so), if cropped for the central 24x36mm equiv. of 35mm, might be
reasonably close to the fixed 28mm image, except that the DOF would be for
the 18mm MF lens, and the image height would be for the 18mm MF lens, and
so on.

I think you are trying too hard and that this is a bad way to think about
it. You need to go back to basics.

DOF is a perceptual phenomenon that occurs in the viewers head due to the
CoC on the _print_ and the distance at which the print is viewed. (CoC on
the _film_ is based on an assumed enlargement and viewing distance.)

Without an assumed print size and viewing distance, DOF calculations and
agonizing are completely meaningless.

Once you determine print size and viewing distance, you can determine CoC on
the print and back calculate the required CoC on the film for that DOF.

I don't see how swing lens cameras would be any different from fixed lens
cameras. The only difference occurs if the swinging operation blurs the
image resulting in a larger CoC on the film than focal length/f stop
calculations imply.

I'd guess that for a given enlargement (magnification), viewing distances
would be larger. E.g. if you normally make A4 prints, you'd put roll paper
in your printer and make 8.25" x whatever panoramas. And since whatever
is a lot longer than 11.5", the viewer will be standing back further.


You might find that a fixed 18mm equiv. rectilinear lens (which doesn't
exist in MF, which is why swing lens cameras are used past 100 degrees or
so), if cropped for the central 24x36mm equiv. of 35mm, might be
reasonably close to the fixed 28mm image, except that the DOF would be for
the 18mm MF lens, and the image height would be for the 18mm MF lens, and
so on.


If you crop out a section of the image and print it at the same enlargement,
then the viewer will move in closer, and DOF goes down.

Switch to a 50mm lens on the same horizon 202 (hacked camera? ;-) and you
end up with a different DOF calculation from your DOF calculator, but the
50mm lens still ends up covering 110+ degrees horizontally in a swing lens
camera.

Uh, no. To switch focal lengths, you'd have to rebuild the camera with a
different radius of curvature at the film plane.

David J. Littleboy
Tokyo, Japan

yes, but once you "hacked" the camera, you could swing a 50mm lens thru
110+ degrees. It would look different from a similar 110+ degree sweep
with a 28mm lens for a variety of reasons. The image magnification would
be different, the image height on film would be different, and the amount
of enlargement needed would be different. So the CoC and the DOF would all
also be different, just as they are when you switch from a 28mm to a 50mm
lens.

However, in both 28mm and 50mm swing lens cases, you might end up with a
110+ degree angle of coverage on a 24x56mm piece of film. The horizontal
coverage is the same. The vertical coverage is obviously different. The
amount of "cigar shape" swing lens distortion is also quite different
(28mm wide is worse).

But the key point is that the you see 110+ degrees of subject horiz. on
film in each case. Therefore, the swing lens camera requires a different
analysis than simply using the fixed lens focal length in a standard DOF
calculator.

It can't be both a 28mm and a 50mm DOF case at the same time ;-) Nor can a
28mm or a 50mm fixed lens DOF calculation take the actual coverage (110
degrees+ here) into account. Nor will a 24x36mm crop of the uniquely
cigar-shaped distorted image of a swing lens shot be the same in
appearance or coverage to a rectilinear lens shot of the same subject.

You could build a lens which projects 110+ degrees rectilinearly (or with
cigar shaped distortion, for extra $$ ;-) onto 24x56mm slice of film. Such
an equiv. rectilinear lens is circa 18-19mm on MF (6x6cm). There is no
rectilinear 35mm lens which can cover 24x56mm; an 18mm ultrawide on 35mm
is covering only 24x36mm, not 24x56mm.

So I maintain that swing lens cameras are special cases, and that you
can't just take the DOF of the fixed lens (28mm in Horizon 202s, 50mm or
whatever in my hacked camera case), and say that the fixed DOF and
enlargement calculations all work the same.

For one thing, those DOF calculators are working with the 35mm equiv.
format, 24x36mm, while I am enlarging from a 24x56mm piece of film. It is
an MF sized film crop of an MF sized image from an equiv. swing lens, not
a 24x36mm sized crop as used in the DOF calculator, right? ;-)

my $.02

bobm

PS I suspect that you might be able to model the DOF factors, ignoring the
swing lens distortion, by creating an equiv. lens based on the film format
size (here 24x56mm) and equiv. wide angle rectilinear lens required to
capture the observed swing lens angle (here, 110+ degrees), say 18+mm for
6x6cm equiv. in this case. Now the problem is that the image height is not
that of an 18mm lens on 6x6cm, but rather, that of the underlying 28mm
lens being swung thru 110 degrees, yes?

So you are in effect working from a cropped and enlarged image on film. A
28mm lens for 35mm SLR covers 46 degrees vertically on the (same) 24mm
film width format in 24x36mm format. By comparison, the 18+mm on 6x6cm
covers about 114 degrees vertically. An 18mm lens on a 24x56mm format
would cover 67 degrees vertically, versus 46 degrees for the actual 28mm
lens (for a 35mm format) used. So perhaps this is equiv. to cropping the
18mm lens by 46/67 to 68%, and then enlarging back to 24x56mm size (1/.68
or 1.45X?). If you used a 50mm lens for 35mm format swung 110 degrees to
create a 24x56mm image, you would have to use an enlargement factor for
that lens, namely, 50mm covers 27 deg. vertically, so 27/67=.4 or 40% and
so 1/.4= 2.5X enlargement factor. And so on? ;-0)

In short, you can model a swing lens camera, but the horiz. coverage
(e.g., 110+ degrees) and film form (24x56mm) determines the equiv.
rectilinear lens. The actual lens focal length (28mm) and original format
(24x36mm) is used to determine the vertical coverage only. In most cases,
this would be in effect a center crop and enlargement by some factor onto
the swing lens film format. Further enlargements from the 24x56mm film
slice would represent additional equiv. enlargements, with impacts on DOF
based on the original swing lens equivalent (here, 18mm), taking into
account the degree of vertical cropping and enlargement from the smaller
format lens (i.e., 28mm here). Phew! ;-0)

This is all different from the DOF case of a fixed 28mm lens on a 24x36mm
film slice ;-)

grins bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************

(Bob Monaghan) wrote in message ...
sure; for example, the subject could be a nearby park bench; the swing
lens "cigar-shaped" distortion could easily be present and observed to
depart from a straight line, which the rectilinear 28mm lens would NOT
project onto film in a fixed camera.

You might find that a fixed 18mm equiv. rectilinear lens (which doesn't
exist in MF, which is why swing lens cameras are used past 100 degrees or
so), if cropped for the central 24x36mm equiv. of 35mm, might be
reasonably close to the fixed 28mm image, except that the DOF would be for
the 18mm MF lens, and the image height would be for the 18mm MF lens, and
so on.

In other words, in the centtral portion, the image would be much
smaller for the 18+mm lens and the DoF would correspond to that lens
and not be that for a 28mm lens.

Again, I think the convergence between the DOF calculator for the 28mm
lens and the swing lens is simply a side-effect that all these lenses are
close to the "tipping" point of hyperfocal distances, and small shifts can
let you match the numbers and slopes up (as with picking a 0.04" CoC
etc.?). But the underlying fixed lens vs swing lens, and equiv. fixed lens
for a swing lens horiz. coverage (here, 18mm MF for 110 degrees+ coverage)
is what I understand to be the underlying case.

Switch to a 50mm lens on the same horizon 202 (hacked camera? ;-) and you
end up with a different DOF calculation from your DOF calculator, but the
50mm lens still ends up covering 110+ degrees horizontally in a swing lens
camera. In this case, the "cropped" 24x36mm out of the swing lens MF sized
24x56mm would not look like a normal lens shot; for one thing, it is
covering 36mm/56mm of 110 degrees (or 70 degrees). If the 28mm is a good
match, then the 50mm swing lens must be a bad match, and so on.

If you used a 50mm lens on a horizon 202 then you would have to use
the setting with the narrowest slit as the secondary principal point
of the 50mm lens would be a long way off the axis resulting in side to
side motion of the image on the film as the slit passed over. You
would then end up with a reasonably sharp image but with everything
very tall, about twice the height compared to the width.

In short, you can't fully model a swing lens camera on the fixed lens used
to make it; coverage and distortion and DOF and other issues will vary,
which is why these cameras are built in the first place ;-)

In short, the 28mm lens in the swing lens camera is just a 28mm lens
taking a picture through a slit and so you *can* use a depth of field
calculator as if it were a fixed lens, but because of the wider film
then you would expect less enlargement of the image and so the CoC
size would be greater than for a smaller 35mm format.

my $.02 ;-)

bobm