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I'd like to challenge the view that 6x9 folders give soft pictures



 
 
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  #1  
Old July 8th 09, 10:18 PM posted to rec.photo.equipment.medium-format
Alan Browne
external usenet poster
 
Posts: 12,640
Default I'd like to challenge the view that 6x9 folders give soft pictures

RolandRB wrote:
I'd like to challenge the view that 6x9 folders give soft pictures.
I've heard this opinion oft repeated on websites that discuss medium
format. The view is that "the film is not flat" and so gives poor
results. I challenge that. I've just got the results back from a 1931
6x9 Zeiss Ikonta and there is no evidence of lack of film flatness
leading to poor focus. Because the camera is old, I tightened the
springs on the pressure plate before taking any photos and I always
wind on just before taking the shot, because it is only natural for
the film to warp over the plate in the heat over time, so I avoid
that. If I delay taking a photo after winding on - maybe waiting for
better light or sky - then I start to wind on to tighten the film and
then I get no problem.


If it were just the 'wind on' need, that would be of little concern.

From the various replies to my enquiry some time ago, I think there is
also the issue of RF focus errors to take into account. This is what
scared me off buying a used one a few months ago.
  #2  
Old July 8th 09, 10:45 PM posted to rec.photo.equipment.medium-format
Richard Knoppow
external usenet poster
 
Posts: 751
Default I'd like to challenge the view that 6x9 folders give soft pictures


"Alan Browne" wrote in
message
...
RolandRB wrote:
I'd like to challenge the view that 6x9 folders give soft
pictures.
I've heard this opinion oft repeated on websites that
discuss medium
format. The view is that "the film is not flat" and so
gives poor
results. I challenge that. I've just got the results back
from a 1931
6x9 Zeiss Ikonta and there is no evidence of lack of film
flatness
leading to poor focus. Because the camera is old, I
tightened the
springs on the pressure plate before taking any photos
and I always
wind on just before taking the shot, because it is only
natural for
the film to warp over the plate in the heat over time, so
I avoid
that. If I delay taking a photo after winding on - maybe
waiting for
better light or sky - then I start to wind on to tighten
the film and
then I get no problem.


If it were just the 'wind on' need, that would be of
little concern.

From the various replies to my enquiry some time ago, I
think there is
also the issue of RF focus errors to take into account.
This is what
scared me off buying a used one a few months ago.


The Super Ikonta has a very good rangefinder. Probably,
in a camera this old, it may need some adjustment, mostly to
make sure the infinity point is set properly.
It is an error to think that flare exists only for
back lighted scenes the flare in uncoated lenses is there
all the time. The amount depends on the number of air-glass
surfaces and goes up exponentially as the number of surfaces
increases. For a relatively simple lens like a Tessar the
flare is not bad. Backlighting can bring out other sources
of flare such as reflections from the lens mount and from
the insides of the camera. Those are also always present but
strong light within the image area can make them more of a
problem. In general a good uncoated Tessar has pretty good
contrast.
The Tessar in the Ikonta series is a front element
focusing lens. This is a very elementary zoom lens whose
focal length is changed to change focus. The problem is that
the corrections for aberrations change with the change in
focus and there is nothing in these simple lenses to
compensate for it. In general front element focusers are
designed to have the best correction at distant focus
because the assumption is that one will want the best
rendition of detail there.
Nonetheless, the Super-Ikonta series has an excellent
reputation for sharpness.
BTW, since the focal length of the lens is changed to
effect focus the viewing angle remains constant with
distance. For that reason a fixed finder such as used on the
Super-Ikonta is accurate at all distances (other than for
parallax).



--
Richard Knoppow
Los Angeles, CA, USA



  #3  
Old July 8th 09, 10:51 PM posted to rec.photo.equipment.medium-format
Richard Knoppow
external usenet poster
 
Posts: 751
Default I'd like to challenge the view that 6x9 folders give soft pictures


"Richard Knoppow" wrote in message
m...

"Alan Browne" wrote in
message
...
RolandRB wrote:
I'd like to challenge the view that 6x9 folders give
soft pictures.
I've heard this opinion oft repeated on websites that
discuss medium
format. The view is that "the film is not flat" and so
gives poor
results. I challenge that. I've just got the results
back from a 1931
6x9 Zeiss Ikonta and there is no evidence of lack of
film flatness
leading to poor focus. Because the camera is old, I
tightened the
springs on the pressure plate before taking any photos
and I always
wind on just before taking the shot, because it is only
natural for
the film to warp over the plate in the heat over time,
so I avoid
that. If I delay taking a photo after winding on - maybe
waiting for
better light or sky - then I start to wind on to tighten
the film and
then I get no problem.


If it were just the 'wind on' need, that would be of
little concern.

From the various replies to my enquiry some time ago, I
think there is
also the issue of RF focus errors to take into account.
This is what
scared me off buying a used one a few months ago.


The Super Ikonta has a very good rangefinder.
Probably, in a camera this old, it may need some
adjustment, mostly to make sure the infinity point is set
properly.
It is an error to think that flare exists only for
back lighted scenes the flare in uncoated lenses is there
all the time. The amount depends on the number of
air-glass surfaces and goes up exponentially as the number
of surfaces increases. For a relatively simple lens like a
Tessar the flare is not bad. Backlighting can bring out
other sources of flare such as reflections from the lens
mount and from the insides of the camera. Those are also
always present but strong light within the image area can
make them more of a problem. In general a good uncoated
Tessar has pretty good contrast.
The Tessar in the Ikonta series is a front element
focusing lens. This is a very elementary zoom lens whose
focal length is changed to change focus. The problem is
that the corrections for aberrations change with the
change in focus and there is nothing in these simple
lenses to compensate for it. In general front element
focusers are designed to have the best correction at
distant focus because the assumption is that one will want
the best rendition of detail there.
Nonetheless, the Super-Ikonta series has an excellent
reputation for sharpness.
BTW, since the focal length of the lens is changed to
effect focus the viewing angle remains constant with
distance. For that reason a fixed finder such as used on
the Super-Ikonta is accurate at all distances (other than
for parallax).



--
Richard Knoppow
Los Angeles, CA, USA


Another BTW, I rather think that focus problems
attributed to film flatness are often actually due to focus
shift. I've found that even some very good lenses (Zeiss
Tessar, Kodak Ektar) have enough shift to affect the
accuracy of focus on a Speed Graphic using a rangefinder.
This would also apply to other types of cameras that do not
show focus directly at the f/stop used. Focus shift comes
from residual spherical aberration which is affected by the
stop. Usually, when stopped down perhaps two stops from
maximum, most of the spherical is gone. If a lens is focused
as best as possible when wide open and then stopped down a
couple of stops one finds that the point of best focus may
have changed. This effect is relatively large for lenses
like the Goerz Dagor, which as a large residual of
spherical, is less for Tessars, depending on the exact
design, and is minimal for the six element lenses of the
Biotar type and more complex lenses based on it commonly
used in 35mm cameras.

--
Richard Knoppow
Los Angeles, CA, USA



 




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