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61Dynamic

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« Reply #40 on: March 29, 2006, 09:15:13 PM »

Thanks for posting the images and info.

Another question: Are the images able to be calibrated in any version of the C1 software or only in the DB specific version?
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Anon E. Mouse

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« Reply #41 on: March 29, 2006, 09:15:56 PM »

The problem is called "vigneting" and is a product of the cosine 4th law. Certainly not new and it does happen with film. Has anyone tried a center filter?
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mtomalty

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« Reply #42 on: March 29, 2006, 09:50:43 PM »

Daniel

As far as I know the LCC calibration option is available  in all versions of C1 pro
I don't have C1 lite so someone else will have to confirm that it is available.

That having been said any purchased back will come with the appropriate software.

Mark

P.S. Anon E.  ,the color cast does not manifest itself in a geometric fashion (i.e. it doesn't appear
       equidistant from the center) so a center filter should not be effective.
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BernardLanguillier

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« Reply #43 on: March 29, 2006, 11:18:13 PM »

Quote
The problem is called "vigneting" and is a product of the cosine 4th law. Certainly not new and it does happen with film. Has anyone tried a center filter?
[a href=\"index.php?act=findpost&pid=61327\"][{POST_SNAPBACK}][/a]

As far as I know light fall off doesn't introduce any color casts on film, it results in a mere darkening of the frame as one comes closer to the corners.

On view cameras I typically don't bother using a center filter for lenses 110 mm or longer.

Vignetting is different from light fall off in that it is provoked by a mechanical obstruction preventing the entry of the light (possible causes being a filter that is too thick or a lens shade for instance).

Regards,
Bernard
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Anon E. Mouse

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« Reply #44 on: March 30, 2006, 12:32:57 AM »

Quote
As far as I know light fall off doesn't introduce any color casts on film, it results in a mere darkening of the frame as one comes closer to the corners.

On view cameras I typically don't bother using a center filter for lenses 110 mm or longer.

Vignetting is different from light fall off in that it is provoked by a mechanical obstruction preventing the entry of the light (possible causes being a filter that is too thick or a lens shade for instance).

Regards,
Bernard
[a href=\"index.php?act=findpost&pid=61332\"][{POST_SNAPBACK}][/a]

Vignetting and light fall off are one and the same thing. Vignetting can be a natual condition of light as in the case of the cosine 4th law or it can be caused by a menchanical obstruction of the lens barrel. And this does shift color. I would try a 55mm lens with 4x5 film if you want to see the effect clearly.

Digital camera can be programmed to a certain degree to counter this effect as it is predictable. Or, as others have done, it can be fixed later.
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Anon E. Mouse

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« Reply #45 on: March 30, 2006, 12:53:41 AM »

Quote
P.S. Anon E.  ,the color cast does not manifest itself in a geometric fashion (i.e. it doesn't appear
       equidistant from the center) so a center filter should not be effective.
[a href=\"index.php?act=findpost&pid=61330\"][{POST_SNAPBACK}][/a]

The examples you give show a classic case of vignetting so I don't see why a center filter will not help. Have you tried a center filter?
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mtomalty

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« Reply #46 on: March 30, 2006, 01:01:38 AM »

Quote
The examples you give show a classic case of vignetting so I don't see why a center filter will not help. Have you tried a center filter?

Both examples were shot with the Hasselblad ArcBody using the Apo Grandagon 45mm
There is a dedicated center filter for this lens and it was used in both cases.
Sorry.  Theory and practice don't always intersect

Mark
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Anon E. Mouse

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« Reply #47 on: March 30, 2006, 01:58:12 AM »

Quote
Both examples were shot with the Hasselblad ArcBody using the Apo Grandagon 45mm
There is a dedicated center filter for this lens and it was used in both cases.
Sorry.  Theory and practice don't always intersect

Mark
[a href=\"index.php?act=findpost&pid=61343\"][{POST_SNAPBACK}][/a]

What does it look like without the center filter?
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BernardLanguillier

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« Reply #48 on: March 30, 2006, 03:25:11 AM »

Quote
Vignetting and light fall off are one and the same thing. Vignetting can be a natual condition of light as in the case of the cosine 4th law or it can be caused by a menchanical obstruction of the lens barrel. And this does shift color. I would try a 55mm lens with 4x5 film if you want to see the effect clearly.
[a href=\"index.php?act=findpost&pid=61340\"][{POST_SNAPBACK}][/a]

Interesting, I haven't noticed any color shift when using my Schneider 58 mm XL on 4*5. But I do indeed typically use a dedicated center filter with that lens.

Would mind sharing with us the physics underlying the appearance of a color shift?

Regards,
Bernard
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Anon E. Mouse

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« Reply #49 on: March 30, 2006, 05:09:07 AM »

Quote
Interesting, I haven't noticed any color shift when using my Schneider 58 mm XL on 4*5. But I do indeed typically use a dedicated center filter with that lens.

Would mind sharing with us the physics underlying the appearance of a color shift?

Regards,
Bernard
[a href=\"index.php?act=findpost&pid=61349\"][{POST_SNAPBACK}][/a]

I use a 55m Grandagon on a 6x12 camera and when I don't use a center filter there is a color shift - usually to blue. I am not sure there is a whole lot of research on this, but my educated guess says it seems to be because of underexposure - variations in exposure cause color shifts. There is most likey a transmission problem with the film because the incoming light is at such an oblique angle and the blue layer for color film is at the top.  Film is also most sensitive to blue. The underexposure emphasizes this problem. (I use a 1.5 stop neutral density center filter and it almost completely eliminates the problem.)

In mark's case, he seems to be getting a green/magenta shift. The bayer pattern is mostly green. If the pixels are not physically flat, this may be giving the green shift toward the edge. The white balance may be trying to compensate so there is a magenta shift toward the center. The reason his dedicated center filter may not be working is the surface of the CCD causes a greater fall-off effect (this is why I asked him the difference with the filter off). Phase One in their instruction recognize the problems of the cosine 4th law (that is the reason for natural vignetting), but have decided to invent a new term called "lens cast."

But why not the Canon DSLR? Short focal length lenses are a reverse telephoto design so they can be far enough away from the CCD to allow the mirror to rise. So at a comparable angle of view, you are not actually getting light hitting the CCD at a similar angle of incidence as you would from a veiw camera. Also since the effect is predictable, DSLR manufacturers can compensate electronically to a certain degree - most DSLRs know what lens is attached. In fact lens data is stored in the exif file. Not something that can be done with the view cameras or Hasselblad Arc Bodies.

So it appears the cosine 4th law works. When using wide angle lenses, the term "vignetting" is applied. So far in this thread I have not seen anything new that would suggest another cause, but I am game if someone can come up with another explination.
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bjornaagedk

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« Reply #50 on: March 30, 2006, 06:11:56 AM »

Have a look:

Image Data:
Phase One P45 back on a Cambo Ultima 23 with slide back
Lens: Schneider ApoDigitar 120mm/5,6 Macro
Light: 1 Lightbox placed apx. 1m above object.
Images taken at 1/125 sec. f/11

JPG's: (4 posts)
Straight: All camera levels in center position / no shift/tilt.
Shift20mm: Lens shifted 20mm down
Tilt10: Lens tilted 10 dgr.
Lcc: Lens Cast Correction added, based on Shift20

This is what I call "the problem".
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bjornaagedk

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« Reply #51 on: March 30, 2006, 06:12:48 AM »

Shift 20mm
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bjornaagedk

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« Reply #52 on: March 30, 2006, 06:15:51 AM »

Tilt10
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bjornaagedk

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« Reply #53 on: March 30, 2006, 06:19:05 AM »

Shift20 w. LCC added in Capture1 Pro
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mtomalty

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« Reply #54 on: March 30, 2006, 11:32:33 AM »

Never shot the ArcBody and 45mm combo WITHOUT the center filter so I can't offer
any images under that scenario to act as a sort of 'control'.

Mark
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61Dynamic

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« Reply #55 on: March 30, 2006, 12:51:22 PM »

Quote
Daniel

As far as I know the LCC calibration option is available  in all versions of C1 pro
I don't have C1 lite so someone else will have to confirm that it is available.

That having been said any purchased back will come with the appropriate software.

Mark
[a href=\"index.php?act=findpost&pid=61330\"][{POST_SNAPBACK}][/a]
True, but I do post production work and I was just curious if the correction was available to standard versions of C1 in case I ever get a client sending me color-casted images. It wouldn't be very cost-effective to buy a P25 just to process a few raw files!
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mtomalty

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« Reply #56 on: March 30, 2006, 03:22:31 PM »

Daniel

I've had C1 pro for Mac installed for close to two years now and have installed the
incremental upgrades along the way at no cost. I've been using it for an assortment of
Canon digital cameras

Without owning a Phase back I am able to process P25 and P45 files and apply LCC
corrections where needed so it seems pretty clear that one doesn't have to buy  a back
to access the proper C1 software.

Assuming you have a version of C1 go to the White/Color Balance tab and in the upper
left hand corner under ICC profile info you will see the  Lens CC window.
It will be greyed out for files other than Phase files but at least you can see if you have
access to it should you need it.When C1 detects a phase file there will be,in this window,a
list of any LCC calibration files you have saved and can apply where neccessary

Mark
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dazzajl

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« Reply #57 on: March 31, 2006, 08:42:13 AM »

I've used various Leaf Valeo backs for the last few years on a Cambo 5x4 with Digitar lenses out to 28mm and I've never seen anything like that either.

I know you're all saying it's easy enough to correct but it would still really anoy me. Explaining to clients on location or art directors in the studio why the images they are seeing raw out of the camera look so lousey is not something I would expect from kit of this sort of cost.
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bjornaagedk

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« Reply #58 on: March 31, 2006, 09:52:38 AM »

Quote
I've used various Leaf Valeo backs for the last few years on a Cambo 5x4 with Digitar lenses out to 28mm and I've never seen anything like that either.

I know you're all saying it's easy enough to correct but it would still really anoy me. Explaining to clients on location or art directors in the studio why the images they are seeing raw out of the camera look so lousey is not something I would expect from kit of this sort of cost.
[a href=\"index.php?act=findpost&pid=61419\"][{POST_SNAPBACK}][/a]


I have now a Leaf Aptus 75 here in my studio for testing, comparing to my PhaseOne P45 back.
These images  are exactly the same camera position, just switched from P45 back to Leaf back.
The P45 image is in a version with LCC applied also.

What do you say?
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BernardLanguillier

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« Reply #59 on: March 31, 2006, 10:28:34 AM »

Bjorn,

Being on a slow connection now I couldn't get the samples.

What do you see?

Cheers,
Bernard
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