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swing lens cameras and focussing distance



 
 
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  #1  
Old May 1st 04, 05:46 PM
RolandRB
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Default swing lens cameras and focussing distance

I would have posted this in the original thread but it has got long
now and fragmented as to topic. I posted some detailed calculations in
the thread with the subject line "The opposite of a close-up lens?" on
April 6th 2004 two times and April 7th 2004 once and in addition on
April 14th 2004 showing an important link for people interested in
swing lens cameras, namely
http://www.funsci.com/fun3_en/panoram2/pan2_en.htm

I have posted a lot of technical stuff and maths backing it up. I use
swing lens cameras for maybe 10% of all my photography so maybe that
is a high proportion. I have a college degree (BSc) in Physics for
what it is worth and of course I studied Optics as part of that. I am
not claiming to be an expert on Optics, especially since I have earned
my living developing software for many years, but at least I can claim
to have some sort of awareness of the subject and a rudimentary
grounding. These cameras are important to me so I thought that anybody
who followed my calculations might be interested in what I have to say
next.

Here goes...

Now this is theorising and speculation but I personally do not believe
that anybody can make a lens with an accurate focal length. I assume a
0.5% error at least. So taking the Noblex 150, assumed fixed-focussed
at 10.4m, then this has a 50.93 millimeter drum radius according to
the film width and angle specs and there won't be much variation in
the examples they make. Fair enough! They say their lens is a 50.75mm
focal lens lens. You what?!? It could be anything from 51mm to 50.5mm.
There is nothing they can do to stop that unless they adjust the gap
between the front converging lens and the diverging lens behind it to
correct it. Do they do that? Do they do any adjustment at all? I
suspect that the manufacturers of these cameras do make some
adjustment but the most important adjustment, if you have followed my
calculations, is to make sure the secondary principal point of the
lens is exactly on the axis so that the magnification is correct and
so that as the lens swings round then parts of an image will always
stay on the same place on the film surface. Now I challenge anybody
here to find out from manufacturer-published specifications where the
lens is fixed-focussed to on any swing lens camera except the Noblex
range. I doubt you wil find it. And why? It could be that the only
adjustment they are making to the camera is to make sure the secondary
principal point is on the axis so that the image doesn't move on the
film as the lens swings round. But then the focussing distance will be
thrown out when they adjust this. So they will not be able to publish
any figures. So you don't know what distance your camera is
fixed-focussed to and you have got to take pot luck in getting one
that focusses at the distance you have a preference for. In my case I
will not pick bones and will say outright that I want my swing lens
camera to be focussed at infinity because I use it most at that
distance. But secondary principal point on the axis is the most
important thing otherwise you lose horizontal resolution in a big way.
The two are opposites. For me, at least, anybody claiming a distance
focussed to is setting the lens to focus at that distance rather than
doing the far more important thing of getting the secondary principal
point sited exactly on the axis. If Noblex are claiming figures for
focussing distance then they will be adjusting the lens to achieve
that figure and not adjusting the lens to make sure the secondary
principal point lies exactly on the axis which I feel they should be
doing instead.

It is possible to have the best of both worlds but it takes a lot of
adjustment. If you want a lens in a swing lens camera fixed-focussed
at infinity then you have got to make sure that the secondary
principal point stays on the axis at all time but you can adjust the
gap between the converging lens and the diverging lens behind it (for
as Tessar design) to focus it. This will shift the secondary principal
point again off the axis but by a process of adjusting them both you
will finally arrive at the optimum setting. But it seems to me that
the emphasis for the Noblex focussing models has shifted entirely away
from the position of the secondary principal point being on the axis
which to me (with calculations to back it up) is the most important
thing.
  #2  
Old May 3rd 04, 08:36 AM
Bob Monaghan
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Default swing lens cameras and focussing distance


Hi Roland,

Sorry, but the Horizon 202 cameras are not focused at infinity, as I have
shown in a related posting, citing the Noblex 135 series (same format)
models, but more like focused at a mid-distance of 7m or so. The noblex
135 models are focused at an even farther mid-distance point (7.5m), as
shown by the comparison of focusing tables for the two cameras in my
posting. For both the horizon 202 and Noblex 135 (and 150 series) cameras,
infinity is on one edge of the hyperfocal setting, rather than at the
precise focusing point. So any calculations assuming an infinity focus are
simply in error, yes?

Second, the critical value is not focal length variations of the lens etc.
but whether the (curved) plane of focus is placed on the (curved)
emulsion. See critical focusing at http://medfmt.8k.com/mf/critical.html

regards bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************
  #3  
Old May 3rd 04, 06:15 PM
RolandRB
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Default swing lens cameras and focussing distance

(Bob Monaghan) wrote in message ...
Hi Roland,

Sorry, but the Horizon 202 cameras are not focused at infinity, as I have
shown in a related posting, citing the Noblex 135 series (same format)
models, but more like focused at a mid-distance of 7m or so. The noblex


I missed that. What is your evidence that the Horizon 202 is not
focussed at infinity? What posting? I'll look but might not be able to
find it.

135 models are focused at an even farther mid-distance point (7.5m), as
shown by the comparison of focusing tables for the two cameras in my
posting. For both the horizon 202 and Noblex 135 (and 150 series) cameras,
infinity is on one edge of the hyperfocal setting, rather than at the
precise focusing point. So any calculations assuming an infinity focus are
simply in error, yes?


No, you just didn't follow what I wrote. I assumed a 10.4m focussing
distance for the Noblex 150. The comparison I did was between a
Horizon 202 (which I assumed to be fixed-focussed at infinity) and the
Noblex 150 (which I assumed to be fix-focussed at 10.4m) both
photographing a scene at effective infinity. In which case the Noblex
150 would be slightly out of focus and the resolution would be limited
by the circles of confusion due to the scene at infinity being
slightly out of focus. I'll probably have to stress this again.

Second, the critical value is not focal length variations of the lens etc.
but whether the (curved) plane of focus is placed on the (curved)
emulsion. See critical focusing at
http://medfmt.8k.com/mf/critical.html

No, the lens used in most swing-lens cameras is a Tessar type. This
has a flat field (or aims to have). This is because the upright needs
to be flat so that the top and bottom of the image are also in focus.
The width of the slit matters very little. Yes, it is curved, but
curved over a very narrow width. The out of focus effect of the curved
film over the slit width is negligible. It is important to use a flat
focus field for these cameras. I'll let you do the calculations
yourself to convinve yourself that the curvature of the film over the
slit width hardly affects focus across the slit.

regards bobm

  #5  
Old May 6th 04, 04:05 AM
Bob Monaghan
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Default swing lens cameras and focussing distance


the evidence that the horizon 202 is focused at 7 meters is very simple;
it is virtually identical to the noblex 135 series in format/coverage,
which we know per mfger's specs is focused at 7.5 meters. If you compare
the noblex 135 DOF for various f/stops against matching horizon 202 DOF,
you get nearly identical values - if anything, the horizon is slightly
closer, meaning its focusing point is less than 7.5m at same stops etc.

so if the noblex 135 is focused at 7.5m, the horizon 202 has to be focused
at about 7.5m as well, given similar DOF values, lenses, and film formats.

Again, you can't use the fixed lens DOF calculator with the fixed 28mm
lens and apply it to the swing lens case with a different film format and
much wider coverage on the larger film format etc., even if you do modify
CoC. That's why your answer for fixed 28mm lens doesn't match case of
noblex 135, which has similar specs, swinging lens, and format and
coverage. It is just a happy coincidence (or more russian copying?) that
the horizon 202 matches the Noblex 135 so closely...

in short, the horizon 202 is nearly identical to the Noblex 135 in DOF vs.
f/stop charts, format, swing lens type, etc., so it must be focused at the
same point, viz., 7.5 meters or so, not infinity.

bobm


--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************
  #6  
Old May 6th 04, 05:34 PM
RolandRB
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Default swing lens cameras and focussing distance

(Bob Monaghan) wrote in message ...
the evidence that the horizon 202 is focused at 7 meters is very simple;
it is virtually identical to the noblex 135 series in format/coverage,


That tells you nothing about the distance it is focussed to. It has
the same format, yes, and it might have the same coverage, but there
is nothing to stop one manufacturer choosing one focal distance and
another manufacturer choosing a different focal distance.

which we know per mfger's specs is focused at 7.5 meters. If you compare
the noblex 135 DOF for various f/stops against matching horizon 202 DOF,
you get nearly identical values - if anything, the horizon is slightly
closer, meaning its focusing point is less than 7.5m at same stops etc.


Then show me your calculations as I have shown you mine. Let's see the
maths. I have predicted the depth of field list from my values for
focal distance and CoC size for both the Noblex 135U and the Horizon
202 and have virtually proved that I am correct. Let me see your
calculations and your assumptions that predict the published depth of
field values for the Horizon 202.

so if the noblex 135 is focused at 7.5m, the horizon 202 has to be focused
at about 7.5m as well, given similar DOF values, lenses, and film formats.


Let's see the maths.

Again, you can't use the fixed lens DOF calculator with the fixed 28mm
lens and apply it to the swing lens case with a different film format and
much wider coverage on the larger film format etc., even if you do modify


So the fact that the lens swings or the camera has a wider film
distance then the laws of physics no longer apply? I'm all eyes and
ears. Tell me about this new physics.

CoC. That's why your answer for fixed 28mm lens doesn't match case of
noblex 135, which has similar specs, swinging lens, and format and
coverage. It is just a happy coincidence (or more russian copying?) that
the horizon 202 matches the Noblex 135 so closely...


Not close enough. If it helps, then the origins of the Horizon 202 was
military use. The original cameras were made for the military so that
their mathematicians and statisticians could work out the
effectiveness of munitions based on the holes they made in the ground,
as photographed by a 360 degree camera. Far distance damage would be
clearer if the lens were focussed at infinity.

in short, the horizon 202 is nearly identical to the Noblex 135 in DOF vs.
f/stop charts, format, swing lens type, etc., so it must be focused at the
same point, viz., 7.5 meters or so, not infinity.

bobm


I have posted my calculations here. There is no point my repeating it
for your benefit unless you request it. I now look forward to your
maths that can match the depth of field values for these two cameras,
at least get as close as I got, with your plugged in values,
assumptions and calculations. I won't hold my breath.
  #7  
Old May 6th 04, 07:05 PM
Ralf R. Radermacher
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Default swing lens cameras and focussing distance

Bob Monaghan wrote:

It is just a happy coincidence (or more russian copying?) that
the horizon 202 matches the Noblex 135 so closely...


Are you suggesting the Russians had a time machine?

From Marco Pauck's excellent web site:

| The Horizon 202 is in production since ca. 1989. It is a successor of
| the Horizont (note the 't') which was produced from ca. 1967-1973.

The first Noblex, the model 150 medium format camera, was made in 1992,
the first 35 mm model appeared in 1994.

Ralf

--
Ralf R. Radermacher - DL9KCG - Köln/Cologne, Germany
private homepage: http://www.fotoralf.de
manual cameras and photo galleries - updated April 29, 2004
Contarex - Kiev 60 - Horizon 202 - P6 mount lenses
  #8  
Old May 7th 04, 04:39 AM
Bob Monaghan
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Default swing lens cameras and focussing distance


no, but good points dates; however, there are lots of models of both
noblex 135/150, some of which are adjustable focus, others fixed focus,
and as others have pointed out in this thread, they evidently come in
various focusing distance flavors ;-) Ditto, there are models of the
Horizon 202 series, such as my horizon 202S, which were aimed at the
post-soviet market, vs. the military Horizon/Horizont/Horizon series.
Certainly, a lot of changes have been made by various parties in some
post-soviet camera models (cf. Kiev88CB/CM series) to appeal to the world
market more, adapted other back styles (e.g., hasselblad compatible backs)
and so on.

Moving the focusing distance between two models is simple in comparison
;-)

grins bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************
  #9  
Old May 7th 04, 05:18 AM
Bob Monaghan
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Default swing lens cameras and focussing distance


Your calculations say the horizon is focused at 280 meters, while the
specs of the similar lens/format noblex 135 swing lens camera are 7.5m,
yet the DOF between the two are remarkably similar ;-), viz.:

horizon 202 noblex 135
5.6 2.9m to inf 2.3m to inf
8 2 m to inf 1.8m to inf


DOF
DOF deals with image size and image magnification to allowable printing
sizes for a given quality level (viz., CoC). There is no underlying
physics, it is purely a darkroom print quality range based on assumptions
of film format and enlargement factors.

why swing lens is not same as fixed lens
The swing lens camera produces an image that is equivalent in coverage and
magnification to one which would be produced by a much wider lens on a
much larger format (e.g., 18mm on a 6x6cm which would be cropped to 24x56
or 24x65mm yielding 110 degrees horizontal coverage, as with the Horizon
202s etc.).

You aren't enlarging the image produced by the 28 or 29mm lens on a
24x36mm film slice, you are enlarging the equivalent of an 18mm lens used
with a cropped MF negative size of 24x56mm etc.

This is why using a DOF calculator designed for fixed lenses doesn't do
justice to the swing lens case.

They happen to be close, if you fiddle with them and vary CoC etc.,
because the 28mm lens is close to its hyperfocal distance at any distance
past 3.3m (at f/8 on 35mm format per http://medfmt.8k.com/brondof.html).

In short, DOF is about image magnification, and the limits for a cropped
image covering 110 degrees on 24x56mm (equiv. to 18mm on a cropped 6x6cm
format) from a Horizon 202 is going to be different than a fixed 28mm lens
on some lesser format.

The close convergence between the two DOF for similar swing lens cameras
suggests to me that they must have similar fixed focusing distances, viz.,
circa 7.5m per Noblex camera specifications. Suggesting that one must have
a fixed focus distance of 7.5m and the other 280m (!), and that in the
process the mfgers have gotten their own camera specifications wrong,
isn't convincing to me.

sorry, but we just have to agree to disagree on this issue ;-) As I've
noted, I do agree with you on other issues/posts, just don't find this
convincing, rather, an artifact of hyperfocal convergence in calculator
;-)

bobm

--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************
  #10  
Old May 7th 04, 01:19 PM
RolandRB
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Default swing lens cameras and focussing distance

(Bob Monaghan) wrote in message ...
Your calculations say the horizon is focused at 280 meters, while the
specs of the similar lens/format noblex 135 swing lens camera are 7.5m,
yet the DOF between the two are remarkably similar ;-), viz.:

horizon 202 noblex 135
5.6 2.9m to inf 2.3m to inf
8 2 m to inf 1.8m to inf


Let's look at the "bigger picture" and avoid maths this time.

Horizon 202 Noblex 135U
f2.8 5.5m - inf
f4 3.9m - inf
f5.6 2.9m - inf 2.3m - inf
f8 2.0m - inf 1.8m - inf
f11 1.5m - inf 1.4m - inf
f16 1.0m - inf 1.0m - inf

You can see from the above figures that the Horizon 202 must be
focussed at a further distance than the Noblex 135U. As the stop opens
up then the values diverge more. At f5.6, for example, the closest
in-focus object is 2.9m for the Horizon and 2.3m for the Noblex. That
is obvious. And yet why, at f16, do they both have objects 1.0 in
focus? The answer must be that the Horizon is assuming a greater CoC
size than the Noblex. So if the Horizon were using the smaller CoC
size that the Noblex is using then all those minimum distances for the
Horizon would be higher, right? I could produce the figures, but as I
said, I am skipping the maths this time. It is there in another post
of mine if anybody is interested.

DOF
DOF deals with image size and image magnification to allowable printing
sizes for a given quality level (viz., CoC). There is no underlying
physics, it is purely a darkroom print quality range based on assumptions
of film format and enlargement factors.

why swing lens is not same as fixed lens
The swing lens camera produces an image that is equivalent in coverage and
magnification to one which would be produced by a much wider lens on a
much larger format (e.g., 18mm on a 6x6cm which would be cropped to 24x56
or 24x65mm yielding 110 degrees horizontal coverage, as with the Horizon
202s etc.).
You aren't enlarging the image produced by the 28 or 29mm lens on a
24x36mm film slice, you are enlarging the equivalent of an 18mm lens used
with a cropped MF negative size of 24x56mm etc.

This is why using a DOF calculator designed for fixed lenses doesn't do
justice to the swing lens case.


The Horizon 202 has a 28mm lens and is exposing film through a slit at
the back. That is the simple physics of the situation. It effectively
takes lots of these shots during a single operation of the camera so
you get lots of slits worth of photograph all joined together. It is a
28mm lens with a frame size of 24mmxslit width which varies. The depth
of field calculators still apply. 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.

They happen to be close, if you fiddle with them and vary CoC etc.,
because the 28mm lens is close to its hyperfocal distance at any distance
past 3.3m (at f/8 on 35mm format per
http://medfmt.8k.com/brondof.html).

Then please go ahead and fiddle with these figures and vary the CoC
size and show us what you come up with. Note that as the stop opens
then the figures between the two cameras diverge.

In short, DOF is about image magnification, and the limits for a cropped
image covering 110 degrees on 24x56mm (equiv. to 18mm on a cropped 6x6cm
format) from a Horizon 202 is going to be different than a fixed 28mm lens
on some lesser format.

The close convergence between the two DOF for similar swing lens cameras


The figures show a divergence as the aperture opens up.

suggests to me that they must have similar fixed focusing distances, viz.,
circa 7.5m per Noblex camera specifications. Suggesting that one must have
a fixed focus distance of 7.5m and the other 280m (!), and that in the
process the mfgers have gotten their own camera specifications wrong,
isn't convincing to me.


What I am saying is that although one manufacturer may aim for a
focussing distance of 7.5 meters, they may actually end up with one
focussed to 7m if they are forced to adjust the position of the lens
to make sure the secondary principal point sits bang on the axis, as
it should. In the case of the Noblex then I just do not trust their
figures in any case. If they make focussing models that move the
secondary principal point off the axis then they aren't much better
than a bunch of monkeys so I mistrust all their figures.

sorry, but we just have to agree to disagree on this issue ;-) As I've


I can agree with that, at least. )

noted, I do agree with you on other issues/posts, just don't find this


That we agree or disagree on certain things does not matter. Obviously
you have one view and I have mine. If people all held the same views
then the world would be a boring place and we wouldn't want that (or
would we?). )

convincing, rather, an artifact of hyperfocal convergence in calculator
;-)


For far distant scenes, give me a Horizon 202 over a Noblex 135U any
time. I would recommend the Horizon 202 for that purpose warmly, so
long as you don't mind the camera dropping to bits in your hands.
 




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