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one unsharp corner on prints? Help!



 
 
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  #1  
Old January 31st 04, 08:04 PM
Ed Margiewicz
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Default one unsharp corner on prints? Help!

Hello,
I need some help. I have been making some 8x10 prints from 4x5 slides using
my 150mm rodenstock rodagon lens.
For the most part my prints are full frame. I am getting one corner that is
not sharp and in fact it looks like movement. It always happens in the same
corner. I re-aligned my enlarger and assured my paper is laying flat. My
easel is totally flat. When I change to my 135mm Nikon lens problem goes
away. Prints made with my 80mm rodenstock lens from 6x6... no problem.
That I know of I haven't noticed this problem before with the 150mm lens.

Am I doing something wrong? Could it be the lens? Has anyone experienced
this before?

Thanks
Ed Margiewicz


  #2  
Old February 1st 04, 05:45 PM
CWal871581
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Default one unsharp corner on prints? Help!

I'd say it's the lens. But just to be sure set up a negative and do a print
that shows the problem. Don't touch the negative and rotate the lens 90 deg in
its mount. If the unsharp area moves to follow the lens rotation you've proven
it's the lens (but could also be the lens mount board if you're using something
like a Beseler.

Curtis
  #3  
Old February 2nd 04, 02:30 PM
Ed Margiewicz
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Default one unsharp corner on prints? Help!

Thanks Curtis and Robert I am going to try both.
Ed
"Ed Margiewicz" wrote in message
...
Hello,
I need some help. I have been making some 8x10 prints from 4x5 slides

using
my 150mm rodenstock rodagon lens.
For the most part my prints are full frame. I am getting one corner that

is
not sharp and in fact it looks like movement. It always happens in the

same
corner. I re-aligned my enlarger and assured my paper is laying flat. My
easel is totally flat. When I change to my 135mm Nikon lens problem goes
away. Prints made with my 80mm rodenstock lens from 6x6... no problem.
That I know of I haven't noticed this problem before with the 150mm lens.

Am I doing something wrong? Could it be the lens? Has anyone experienced
this before?

Thanks
Ed Margiewicz




  #5  
Old February 4th 04, 01:54 AM
Gary Beasley
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Posts: n/a
Default one unsharp corner on prints? Help!

On Sat, 31 Jan 2004 11:04:07 -0800, "Ed Margiewicz"
wrote:

Hello,
I need some help. I have been making some 8x10 prints from 4x5 slides using
my 150mm rodenstock rodagon lens.
For the most part my prints are full frame. I am getting one corner that is
not sharp and in fact it looks like movement. It always happens in the same
corner. I re-aligned my enlarger and assured my paper is laying flat. My
easel is totally flat. When I change to my 135mm Nikon lens problem goes
away. Prints made with my 80mm rodenstock lens from 6x6... no problem.
That I know of I haven't noticed this problem before with the 150mm lens.

Am I doing something wrong? Could it be the lens? Has anyone experienced
this before?

Thanks
Ed Margiewicz


Quite likely the carrier is not centered with the lens and you are
running the image outside the circle of sharpness of the lens.
Remember the circle of illumination and the circle of sharpness is not
the same. Most lenses lose definition when approaching the limits of
thier circle of illumination.
Does the corner sharpen up by much when the lens is stopped down to
f/22?
Possibly the lensboard has an off center lens hole in it.
  #6  
Old February 4th 04, 06:10 AM
Ed Margiewicz
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Posts: n/a
Default one unsharp corner on prints? Help!

I never thought the the center of the lens and slide could be out of line.
But I took my lens and lens board in hand an managed to move the lens around
in the lens board hole. I found there is alot of play there. The lens
thread is 50mm and the lens board hole is 52mm in diameter. This is a new
beseler lens board and is supposed to be 50mm. I must have moved it around
while putting it in and out of the enlarger. Thanks for your help. I am
going to try your method of alignment.
Ed Margiewicz
"Dr. Dagor" wrote in message
om...
For the most part my prints are full frame. I am getting one corner

that is
not sharp and in fact it looks like movement. It always happens in the

same
corner.


The importance of lens alignment dawned on me about thirty years after
I started printing. The center of the neg and the center of the lens
need to be aligned. They need to be on center and they need to be
parallel.

There are lots of methods to doing this. Among the current popular
methods is to use a laser. You can make a suitable laser out of one
of the cheap, small laser levels from the hardware store and a penta
prism or right angle prism.

Here's the method I use.

1. Level the easel and place the laser on it so the beam is straight
up. (That's the hard part.)

2. Put a good, first surface mirror in the negative stage, and make
sure it is parallel to the easel (no lens installed). Repeat this for
the lens stage.

3. Install the lens and position the laser so the light is aimed near
the center of the lens. Adjust the horizontal position of the
negative stage and lens to make sure the center of the negative stage
opening lines up with the center of the lens. (Laser, lens, and
negative stage are co-linear.)

4. Put the mirror back in the negative stage. If everything is in
alignment, the laser light should go to the negative stage and back
along the same path -- even if the lens is slightly off center. It
took me a while to realize this, but if the laser light hits the lens
straight on, it should leave the lens straight (at least close to the
center of the lens). If the laser beam hits the mirror straight, it
should be returned along the same path.

Hope this helps.



  #7  
Old February 4th 04, 10:11 PM
Dr. Dagor
external usenet poster
 
Posts: n/a
Default one unsharp corner on prints? Help!

For the most part my prints are full frame. I am getting one corner that is
not sharp and in fact it looks like movement. It always happens in the same
corner.


The importance of lens alignment dawned on me about thirty years after
I started printing. The center of the neg and the center of the lens
need to be aligned. They need to be on center and they need to be
parallel.

There are lots of methods to doing this. Among the current popular
methods is to use a laser. You can make a suitable laser out of one
of the cheap, small laser levels from the hardware store and a penta
prism or right angle prism.

Here's the method I use.

1. Level the easel and place the laser on it so the beam is straight
up. (That's the hard part.)

2. Put a good, first surface mirror in the negative stage, and make
sure it is parallel to the easel (no lens installed). Repeat this for
the lens stage.

3. Install the lens and position the laser so the light is aimed near
the center of the lens. Adjust the horizontal position of the
negative stage and lens to make sure the center of the negative stage
opening lines up with the center of the lens. (Laser, lens, and
negative stage are co-linear.)

4. Put the mirror back in the negative stage. If everything is in
alignment, the laser light should go to the negative stage and back
along the same path -- even if the lens is slightly off center. It
took me a while to realize this, but if the laser light hits the lens
straight on, it should leave the lens straight (at least close to the
center of the lens). If the laser beam hits the mirror straight, it
should be returned along the same path.

Hope this helps.
 




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