Soft edges on C330 shots

Attempt at on topic post...


This shot, from my C330f got accused of being from a Holga:

http://www.petezilla.co.uk/gallery/m...geViewsIndex=1

Now the edge burning was one aspect of this acusation, but I suspect that
the forground in the corners being closer than the point of focus meant
that the corners were soft. Lens was fairly wide open, probally f2.8 - f4,
80mm lens.

Do you think it is lens softness wide open or solely focus? I don't think
I'd expect enough softness to be seen on a lowish res scan with a MF lens.
Am I thinking along the right lines?

Pete


--
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"Peter Chant" wrote in
message ...
Attempt at on topic post...


This shot, from my C330f got accused of being from a
Holga:

http://www.petezilla.co.uk/gallery/m...geViewsIndex=1

Now the edge burning was one aspect of this acusation, but
I suspect that
the forground in the corners being closer than the point
of focus meant
that the corners were soft. Lens was fairly wide open,
probally f2.8 - f4,
80mm lens.

Do you think it is lens softness wide open or solely
focus? I don't think
I'd expect enough softness to be seen on a lowish res scan
with a MF lens.
Am I thinking along the right lines?

Pete


--
http://www.petezilla.co.uk

Its hard to tell from a web image, actually, it looks
pretty sharp to me, not at all like a Holga image.
Are you saying that the stop could have been anywhere
from f/2.8 to f/4 or that its an f/2.8 lens used at f/4? In
any case I think depth of field may be one of the troubles.
You can get some idea of what the lens is doing by
fitting a piece of ground glass into the film gate. Then
examine the image using a fairly powerful magnifier. Its
typical of most lenses to loose sharpness away from the
corners. Tessars, for instance, suffer from an inherent
aberration known as oblique spherical. It looks much like
coma although it comes from a different mechanism in the
lens. The result is smeared highlights away from the center.
The smear is radial along the line from the optical center
to the margin. A good Tessar type lens will be pretty much
free of this if stopped down about two stops from maximum
aperture. Other types of lenses have less of this and less
coma. I am not sure what generic type of lens is used in the
Mamiya C330, perhaps a Heliar type since Tessars do not do
well above about f/3.5.
In any case, get a small, bright highlight near the
corner of the ground glass and see how far you have to stop
down to get rid of the smearing. It should be no more than
two stops.
If the lens is smeary or generally blurry look for a
loose element. Usually you can hear them rattle. While the
retainers in lenses are generally quite tight and often
sealed with paint they can work loose and, in a good lens,
the spacing is very critical. If you have a loose element it
should be easy to fix.
Since the C330 is a twin lens reflex also check to see
that the finder and tanking lenses are adjusted properly for
co-incidence. From the photo posted I don't think this is
the problem.
Of course, a photographic test, using a flat surface
with lots of fine detail like a brick wall, will tell you a
lot. Make sure the camera is exactly parallel with the
surface and shoot a series of exposures at different stops.
That will prove the lens performance.
In general Mamiya lenses have an excellent reputation
for sharpness.


--
--
Richard Knoppow
Los Angeles, CA, USA

Peter Chant wrote,on my timestamp of 27/01/2009 11:51 AM:

Now the edge burning was one aspect of this acusation, but I suspect that
the forground in the corners being closer than the point of focus meant
that the corners were soft. Lens was fairly wide open, probally f2.8 - f4,
80mm lens.

Do you think it is lens softness wide open or solely focus? I don't think
I'd expect enough softness to be seen on a lowish res scan with a MF lens.
Am I thinking along the right lines?

At such a low rez and size, it is DOF-related. No way
a C330 will be that soft even wide open.

Peter Chant wrote:
Attempt at on topic post...


This shot, from my C330f got accused of being from a Holga:

http://www.petezilla.co.uk/gallery/m...geViewsIndex=1

Now the edge burning was one aspect of this acusation, but I suspect that
the forground in the corners being closer than the point of focus meant
that the corners were soft. Lens was fairly wide open, probally f2.8 - f4,
80mm lens.

Do you think it is lens softness wide open or solely focus? I don't think
I'd expect enough softness to be seen on a lowish res scan with a MF lens.
Am I thinking along the right lines?

Could be softness from being wide open.

Tripod? Shutter speed? Release cable? Bad scan?

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"Peter Chant" wrote:
This shot, from my C330f got accused of being from a Holga:

http://www.petezilla.co.uk/gallery/m...geViewsIndex=1

Now the edge burning was one aspect of this acusation, but I suspect that
the forground in the corners being closer than the point of focus meant
that the corners were soft. Lens was fairly wide open, probally f2.8 -
f4,
80mm lens.

The foreground will be way out of focus, and the corners darker, with those
wide f stops. For critical sharpness with an 80mm lens, shoot at f/16
focused to 50 feet or so, or f/22 focused to 30 feet or so, and everything
from 25 or 15 feet, respectively, to infinity will be sharp, even on high
res scans.

DoF gets shallower with the square of the focal length, and by 80mm, you are
already in a range where DoF is quite limited whatever the f stop. (Don't be
afraid to shoot at f/22 with medium format; images will be plenty sharp if
your tripod is adequate.)

--
David J. Littleboy
Tokyo, Japan

Richard Knoppow wrote:


Its hard to tell from a web image, actually, it looks
pretty sharp to me, not at all like a Holga image.
Are you saying that the stop could have been anywhere
from f/2.8 to f/4 or that its an f/2.8 lens used at f/4? In
any case I think depth of field may be one of the troubles.

It was the 80mm f2.8 at an aperatureo f around f2.8-f4 It was getting a bit
late inthe day for that time of year and the cloud and mist was not helping
at all.

You can get some idea of what the lens is doing by
fitting a piece of ground glass into the film gate. Then
examine the image using a fairly powerful magnifier. Its
typical of most lenses to loose sharpness away from the
corners. Tessars, for instance, suffer from an inherent
aberration known as oblique spherical. It looks much like
coma although it comes from a different mechanism in the
lens. The result is smeared highlights away from the center.
The smear is radial along the line from the optical center
to the margin. A good Tessar type lens will be pretty much
free of this if stopped down about two stops from maximum
aperture. Other types of lenses have less of this and less
coma. I am not sure what generic type of lens is used in the
Mamiya C330, perhaps a Heliar type since Tessars do not do
well above about f/3.5.

I'm not sure. I found a very good website once that showed cross sections
through the lens complete with a description for the whole range. Can't
find it by google at the moment unfortunately.

In any case, get a small, bright highlight near the
corner of the ground glass and see how far you have to stop
down to get rid of the smearing. It should be no more than
two stops.
If the lens is smeary or generally blurry look for a
loose element. Usually you can hear them rattle. While the
retainers in lenses are generally quite tight and often
sealed with paint they can work loose and, in a good lens,
the spacing is very critical. If you have a loose element it
should be easy to fix.
Since the C330 is a twin lens reflex also check to see
that the finder and tanking lenses are adjusted properly for
co-incidence. From the photo posted I don't think this is
the problem.

Well, I can also check by swapping lenses. I've got several, including for
various reasons two 80mm's! I did make up a bit of ground glass a couple
of years back and used that to check to adjust the focus of the viewing and
taking lenses by focusing on a flat sheet of newspaper at about four feet
distant with the 135mm lens. A re-check would not do any harm. I did need
to adjust the position of the viewing screen, I also changed the foam in
various light seals, including the foam that supported the viewing screen -
that may have been some cause of change.


Of course, a photographic test, using a flat surface
with lots of fine detail like a brick wall, will tell you a
lot. Make sure the camera is exactly parallel with the
surface and shoot a series of exposures at different stops.
That will prove the lens performance.
In general Mamiya lenses have an excellent reputation
for sharpness.



--
http://www.petezilla.co.uk

Noons wrote:


Do you think it is lens softness wide open or solely focus? I don't
think I'd expect enough softness to be seen on a lowish res scan with a
MF lens. Am I thinking along the right lines?

At such a low rez and size, it is DOF-related. No way
a C330 will be that soft even wide open.

I had a feeling, just that it is not nearly so obvious when shooting 35mm.


--
http://www.petezilla.co.uk

RolandRB wrote:


The whole image is blurred. I have come across a few Mamiya TLRs where
the focussing of the viewing lens and the taking lens do not coincide.

That was the odd thing, bottom left of building a bit blurred but not the
centre or top. PErhaps the scan was playing up after all!


If you take them apart you will find on many of these cameras that
spacers have been added underneath the ground glass screen to correct
this problem. These cameras get dropped, as they are so heavy, and
often hit the ground with the taking lens first which knocks it back a
bit so spacers are needed underneath the ground glass screen to
compensate for this. I would guess that if you took your camera in to
be serviced, when this camera was in popular use, then this adjustment
would be made by the service technician. Picking them up on ebay or
whereever, having been out of use for some time, then don't expect the
focussing to coincide. You may have used this camera and gotten good
result at higher f-stop numbers with the focus being out only to find
out the hard truth at wide apertures.

Mine's got three little adjusters. As I said in an earlier post, it needed
a little adjustment when I replaced some rotten light seals.

--
http://www.petezilla.co.uk

Alan Browne wrote:

Do you think it is lens softness wide open or solely focus? I don't
think I'd expect enough softness to be seen on a lowish res scan with a
MF lens. Am I thinking along the right lines?

Could be softness from being wide open.

Tripod? Shutter speed? Release cable? Bad scan?


Can't be the tripod, wasn't using one...

Shutter speed, probaly 1/60th, may have been chancing it at 1/30th...
Actually amazed that with the 55mm lens I have gotten away with 1/15th
on occation.

Release cable, bit silly if you are hand held...

I know - I'm going to get the tripod lecture - I really must take it out on
a tripod and see what happens some day!

I'm wondering about the scan. Would explain why the bottom left of the
building is unsharp when the top is.

Pete


--
http://www.petezilla.co.uk

Peter Chant wrote,on my timestamp of 31/01/2009 9:16 AM:
Noons wrote:


Do you think it is lens softness wide open or solely focus? I don't
think I'd expect enough softness to be seen on a lowish res scan with a
MF lens. Am I thinking along the right lines?
At such a low rez and size, it is DOF-related. No way
a C330 will be that soft even wide open.

I had a feeling, just that it is not nearly so obvious when shooting 35mm.




I think you'll find in general DOF is much reduced in larger formats. You need
to clamp down a lot more to get similar DOF. If nothing else because you'll be
using a much longer lens for the same angle of coverage. I use f22 and higher
regularly in my rb67 with the "normal" 80mm lens.