wavy color shift in first P25 experience

Questions, comments and suggestions regarding Phase One P+ series and P series digital camera backs.

wavy color shift in first P25 experience

Postby mtomalty » Mon Jul 18, 2005 4:58 am

Hi

In anticipation of a possible P25(or greater!) purchase in the near
future I was able to get hold of a 'blad mount demo P25 unit for testing
this past weekend.
By and large a very impressive experience coming from a Canon 1DsMkll
background.
The system that I would ultimately be using it with would be Contax645.
As such,I was only able to rent a few blad lenses for the weekend among
them was a SWC equipped with a Biogon 38mm.
As landscape photography makes up a significant portion of my shooting
an extreme wide is imperative.
The 38 with the P25 had very pronounced wavy bands of magenta
and green (equivalent to about CC015 units from old filter days)
in large continuous toned areas like a sky.
Can anyone comment on the prevalence of this 'effect' with other
lenses in the 35mm-45mm area.
Hopefully there is something in the optical design of the Biogon that
exaggerates this color shift.
Thanks in advance,
Mark
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Postby damienlovegrove » Mon Jul 18, 2005 10:21 am

Hi Mark,

I currently use an H1 with a 35mm lens as my 'superwide'. I used to own an SWCM with it's 38mm Biogon. The rear of the Biogon as you know is very close to the film / CCD plane. The trouble with this is the light from the lens has to first go through the glass infra red blocking filter and then to the sensor elements. The angle of optical path changes dramatically from centre to edge and this causes your problems. With the H1 35mm being a retrofocus design these issues are not a problem as the angle of light variation at CCD surface is minimal by comparison. I also find the new H1 35mm lens sharper edge to edge than my old SWCM. Modern glass and computer design I suppose.
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Postby mtomalty » Mon Jul 18, 2005 4:42 pm

Thanks Damien

I was hoping someone with firsthand experience would confirm
my suspicions.
Giving the weekends,and todays,announcement I itching to commit to
a back but was a little nervous given what i had been seeing concerning
wideangle performance with the SWC.
FWIW when the sky was not included in the frame with the SWC images
were stunning.

Mark
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Postby Dillon » Tue Jul 19, 2005 3:30 am

mtomalty, Several of my comments are seen in the thread \"lens cast calibration for each shot\". I've yet to resolve the problem after hundreds of photos. All of my work is architecture involving extreme shifts and stitches with 28mm and 45mm lenses. The problem is most noticeable, as you've stated in the sky. My 65mm and 90mm lenses show minimal magenta to green blotches.

Given my abnormally busy work volume of late, I have not had time to fix the problem entirely. Latest tests indicate the left sides need little, if no correction, and the right sides full correction. Residual color shifts are corrected in photoshop.

I believe you will see this with all lens manufacturers.

Good luck.
Dillon
 
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