The opposite of a close-up lens?

RolandRB wrote:

[... a lot...]

Just a few short notes as I'm almost out of the door for a week's
holiday:

Now I believe from reading some Internet sites that the Noblex 120
film models have a fixed slit at the back and different exposures are
achieved by using different rotational speeds. I have no confirmation
of this, though.

This is right. The slit (they call it the gap length) is 3 mm wide and,
unlike that of the Horizon, it is not variable.

http://www.kamera-werk-dresden.de/en...s/frameset.htm

If the lens is a Tessar type then they could adjust
the air gap between the front converging element and the strongly
diverging element behind it.

The lenses on early MF Noblex cameras were even labelled as Tessars.
They're calling them Noblar now that they have them manufactured by
Docter Optics. One may safely assume that it is in fact a Tessar clone.

Ralf

--
Ralf R. Radermacher - DL9KCG - Köln/Cologne, Germany
private homepage: http://www.fotoralf.de
manual cameras and photo galleries - updated March 30, 2004
Contarex - Kiev 60 - Horizon 202 - P6 mount lenses

(Ralf R. Radermacher) wrote in message ...
RolandRB wrote:

[... a lot...]

Just a few short notes as I'm almost out of the door for a week's
holiday:

Now I believe from reading some Internet sites that the Noblex 120
film models have a fixed slit at the back and different exposures are
achieved by using different rotational speeds. I have no confirmation
of this, though.

This is right. The slit (they call it the gap length) is 3 mm wide and,
unlike that of the Horizon, it is not variable.

http://www.kamera-werk-dresden.de/en...s/frameset.htm

If the lens is a Tessar type then they could adjust
the air gap between the front converging element and the strongly
diverging element behind it.

The lenses on early MF Noblex cameras were even labelled as Tessars.
They're calling them Noblar now that they have them manufactured by
Docter Optics. One may safely assume that it is in fact a Tessar clone.

Ralf


I have tried emailing the manufacturers to get information about what
mechanism is used to focus the lens in the focussing models 150U and
150UX. I have an answer but I feel there is a language problem. I
think it would be better if the question were both asked and answered
(and perhaps clarified) in German. I wonder if perhaps you could find
the time to do this? I feel it would be worthwhile to clarify this for
the newsgroup and hence to have it archived for the future. The
contact page I have is:
http://www.kamera-werk-dresden.de/de...ntaktframe.htm

Roland

(RolandRB) wrote in message . com...
(Ralf R. Radermacher) wrote in message ...
RolandRB wrote:

[... a lot...]

Just a few short notes as I'm almost out of the door for a week's
holiday:

Now I believe from reading some Internet sites that the Noblex 120
film models have a fixed slit at the back and different exposures are
achieved by using different rotational speeds. I have no confirmation
of this, though.

This is right. The slit (they call it the gap length) is 3 mm wide and,
unlike that of the Horizon, it is not variable.

http://www.kamera-werk-dresden.de/en...s/frameset.htm

If the lens is a Tessar type then they could adjust
the air gap between the front converging element and the strongly
diverging element behind it.

The lenses on early MF Noblex cameras were even labelled as Tessars.
They're calling them Noblar now that they have them manufactured by
Docter Optics. One may safely assume that it is in fact a Tessar clone.

Ralf


I have tried emailing the manufacturers to get information about what
mechanism is used to focus the lens in the focussing models 150U and
150UX. I have an answer but I feel there is a language problem. I
think it would be better if the question were both asked and answered
(and perhaps clarified) in German. I wonder if perhaps you could find
the time to do this? I feel it would be worthwhile to clarify this for
the newsgroup and hence to have it archived for the future. The
contact page I have is:
http://www.kamera-werk-dresden.de/de...ntaktframe.htm

Roland


I did get a response in clearer English (I'm not complaining because I
should be able to speak German) and the person from the company said
that they do indeed move the lens towards and away from the film
(moving the secondary principal point). I am very surprised about this
for the reasons I have stated. I would be interested in a focussing
model but not if it worked the way they said it did. I would want some
assurances as to horizontal resolution before I parted with the
considerable money for one of those focussing Noblexes.

(RolandRB) wrote in message . com...
(RolandRB) wrote in message . com...
(Ralf R. Radermacher) wrote in message ...
RolandRB wrote:

[... a lot...]

Just a few short notes as I'm almost out of the door for a week's
holiday:

Now I believe from reading some Internet sites that the Noblex 120
film models have a fixed slit at the back and different exposures are
achieved by using different rotational speeds. I have no confirmation
of this, though.

This is right. The slit (they call it the gap length) is 3 mm wide and,
unlike that of the Horizon, it is not variable.

http://www.kamera-werk-dresden.de/en...s/frameset.htm

If the lens is a Tessar type then they could adjust
the air gap between the front converging element and the strongly
diverging element behind it.

The lenses on early MF Noblex cameras were even labelled as Tessars.
They're calling them Noblar now that they have them manufactured by
Docter Optics. One may safely assume that it is in fact a Tessar clone.

Ralf


I have tried emailing the manufacturers to get information about what
mechanism is used to focus the lens in the focussing models 150U and
150UX. I have an answer but I feel there is a language problem. I
think it would be better if the question were both asked and answered
(and perhaps clarified) in German. I wonder if perhaps you could find
the time to do this? I feel it would be worthwhile to clarify this for
the newsgroup and hence to have it archived for the future. The
contact page I have is:
http://www.kamera-werk-dresden.de/de...ntaktframe.htm

Roland


I did get a response in clearer English (I'm not complaining because I
should be able to speak German) and the person from the company said
that they do indeed move the lens towards and away from the film
(moving the secondary principal point). I am very surprised about this
for the reasons I have stated. I would be interested in a focussing
model but not if it worked the way they said it did. I would want some
assurances as to horizontal resolution before I parted with the
considerable money for one of those focussing Noblexes.

I found just what I was hoping for. This is the web page of people who
built a swing-lens camera. Note how they say the rear (posterior)
optical node (second[ary] principal point is the same thing) must stay
exactly on the axis and how they had to adjust it using a microscope
and said that it could take a week to do this.
http://www.funsci.com/fun3_en/panoram2/pan2_en.htm

Now, if I am to believe it, the focussing Noblex 150U and 150UX moves
the lens back and forth when it is focussing and the information sent
to me clearly indicates that it is the secondary principal point that
is changing the distance to the film surface -- I quote (note that the
point 2 referred to was me listing possibilities of how the focussing
was achieved which was "2) by changing the distance of the lens to the
film surface").

"The outlook of the removal (focus) results through an axial
displacement of
the entire lens. In your second inquiry this would become the point 2)
correspond to. For the three areas following the image distance a' are
discontinued (removal secondary principal point in the lens to the
film):
Outlook "infinite" á = 50,9 mm
Outlook "m" á = 51,15 mm
Outlook "n" á = 51,7 mm"

So you have an amateur site where they have made their own swing-lens
cameras and they stress that the rear (posterior) optical node (same
as secondary principal point) must stay exactly on the axis and might
take a week to adjust using a microscope to get it right and a
manufacturer of professional expensive swing-lens cameras who are
moving the secondary principal point back and forth in the direction
of the film surface to achieve focussing.

What I thought they would be doing, when focussing at the different
distances, was using a combination of moving the lens back and forth
but altering the spacing of the front element such that the secondary
principal point always stayed exactly on the axis. That way the
magnification stays constant even though the lens is focussed at
different distances (or so it would seem from the equations I have
looked at).

Now somebody, somewhere has got it wrong. Maybe the information I
received wasn't official and was just a personal interpretation of a
technical issue they were not fully conversant with. Is there anybody
out there with a 150U or a 150UX who can do resolution tests for the
lens at the three focussing positions (without using the close-up
diopters) for both horizontal and vertical resolution? If the
horizontal resolution goes to hell when focussed at the closer
distances and there is horizontal movement of the image obvious from
an enlargement, then that would support the theory that they are
moving the secondary principal point. But then, who would buy a camera
designed that way?

Roland

"David J. Littleboy" wrote in message ...
"Roland" wrote:
"MikeWhy" wrote in message
"brian" wrote in message
(Ralf R. Radermacher) wrote in message
brian wrote:

I assume that you've got a "normalish" lens such as a Tessar with
a
modest field of view.

It is in fact a Tessar type but at a focal length of 50 mm for a
medium-format camera it isn't exactly what one would call
"normalish".

Ralf

Since the lens only has to cover the short side of the format it is
optically "normal" even though it produces an ultrawide panorama. The
vertical coverage would be about 54 degrees. If, as is discussed
below, the hyperfocal distance is set to about 30 feet, then you would
only need -1/10 diopter of correction to focus at true infinity. The
resulting astigmatism introduced by such a weak plano-concave negative
lens would be negligible compared to the inherent zonal astigmatism of
a Tessar. Alternatively, you could attempt to move the lens back by
about 0.25mm. Do you know where the focal distance is set?

1/100 of an inch is about two layers of bond paper. A layer of duct tape
on
the pressure plate ought to do it. I think Littleboy suggested that some
fifty posts ago.

That seems the best idea. Pad up the back that the film runs over so the
film is further away from the lens.

Oops. Wrong direction: you need to get the film closer to the lens.

Oh yes, silly me!

Perhaps some strips of Dynotape label
without any writing on. Could be called something different wherever you
are
but the plastic tape you press characters into so they turn white and are
raised and then you stick them on things.

FWIW, this is NOT what I suggested (which was to get a repair person to
adjust the lens position); this sounds like a screamingly bad idea. Getting
tape adhesive anywhere near a camera's internals is not something I'd even
think about doing. (Other than Holgas, where it's necessaryg.)

David J. Littleboy
Tokyo, Japan

Padding the cylinder out with Dyno tape might be a way to get a
Horizon 202 to focus closer, but a close-up lens might be better. But
then the close-up lens might shift the secondary principal point off
the axis whereas the tape will not. If close-up work is being done in
poorer light then the slit at the back might be wider and any movement
of the secondary principal point off the axis might show up as
unacceptable blur. Since the Horizon 202 won't last long in any case
then you might like to see it out in style by liberal use of Dyno
tape. You might get the frames overlapping slightly, though. See if
you can break it with less than 10 rolls through it.

Roland