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Author Topic: Counting Ants  (Read 20031 times)
bjornaagedk
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« on: March 27, 2006, 11:55:53 AM »
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Michael,
very interesting article. I have an equipment ”almost” like yours, - P45 back, Cambo Ultima 23 and Schneider Apo-Digitars. The Cambo Wide DS 35mm also.
I was expecting to read about you having problems with lens cast, because that’s what I have, shooting with P45 both in studio and on location.

As soon as I use tilt/shift functions with Cambo Ultima I see magenta/green colors, making the picture almost unusable without being corrected i C1 Pro with the LCC function.
When I use ´my Cambo Wide DS the I see lens cast even with the lens centered.

It seems like I am not the only P45 owner who has problems with LC, according to several threads about this subject.

How about you? No problem??
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michael
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« Reply #1 on: March 27, 2006, 01:00:58 PM »
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Not sure what you mean by "problem". It's the nature of the beast. With very wide lenses and when using movements a lens cast frame needs to be shot.

I use an Expodisk rather than the plastic card provided by Phase. Works much better and more quickly.

Michael
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bjornaagedk
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« Reply #2 on: March 27, 2006, 01:54:35 PM »
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Not sure what you mean by "problem". It's the nature of the beast. With very wide lenses and when using movements a lens cast frame needs to be shot.

I use an Expodisk rather than the plastic card provided by Phase. Works much better and more quickly.

Michael
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OK. Maybe it is me, but I don't like that I have to shoot an extra image every time I change camera movements. I do this 15-20 times every day in the studio, and is takes me a lot of time.

B
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collum
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« Reply #3 on: March 27, 2006, 02:28:31 PM »
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OK. Maybe it is me, but I don't like that I have to shoot an extra image every time I change camera movements. I do this 15-20 times every day in the studio, and is takes me a lot of time.

B
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are there examples of the level of cast?

i do a lot of shift stitches. if you shift left, expose (once with the expo), middle then shift left, expose (once with the expo).. are the color cast between the three and exposures identical after the software gets through with them? or do you need curves to match them

      jim
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michael
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« Reply #4 on: March 27, 2006, 03:09:49 PM »
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What you can do is spend a couple of hours building a library of cast files. Just shoot a series with increments of about 3 degress of rise or shift on each axis, for each lens, and label them appropriately.

A lot of work, I know, but then you never have to do them again.

Michae
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alainbriot
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« Reply #5 on: March 27, 2006, 03:13:57 PM »
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i do a lot of shift stitches. if you shift left, expose (once with the expo), middle then shift left, expose (once with the expo).. are the color cast between the three and exposures identical after the software gets through with them? or do you need curves to match them

 jim
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Do you have to use masks when you shift stitch with the Canon 1DsMk2 and the Canon Tilt-shift lenses ?

Alain
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Alain Briot
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« Reply #6 on: March 27, 2006, 03:17:18 PM »
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Do you have to use masks when you shift stitch with the Canon 1DsMk2 and the Canon Tilt-shift lenses ?

Alain
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no.. they pretty much match exactly, exposure and cast (ensuring you use manual exposure)
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alainbriot
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« Reply #7 on: March 27, 2006, 03:27:39 PM »
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no.. they pretty much match exactly, exposure and cast (ensuring you use manual exposure)
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That's nice.  I have to try it since I have the 1DsMk2 and the 24TS.  I need to get the 45TS or 90TS as well.  Do you use all 3 lenses or have a favorite?

Alain
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Alain Briot
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« Reply #8 on: March 27, 2006, 03:38:30 PM »
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That's nice.  I have to try it since I have the 1DsMk2 and the 24TS.  I need to get the 45TS or 90TS as well.  Do you use all 3 lenses or have a favorite?

Alain
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i do 90% of my work with the 90T/S. it's the sharpest as well. I used to use the 45 as well, but picked up a mamiya 50mm shift lens, which is much sharper than the Canon 45 T/S (also cheaper.. you can find them for $4-500)
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Jack Flesher
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« Reply #9 on: March 27, 2006, 03:58:35 PM »
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What you can do is spend a couple of hours building a library of cast files. Just shoot a series with increments of about 3 degress of rise or shift on each axis, for each lens, and label them appropriately.

A lot of work, I know, but then you never have to do them again.

Michae
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Michael:  What about lens tilts -- do they impart a color-cast, or is it only lens shifts that cause it?
« Last Edit: March 27, 2006, 04:00:31 PM by Jack Flesher » Logged

michael
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« Reply #10 on: March 27, 2006, 05:23:49 PM »
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Only shifts, unless the tilts are significant.

Michael
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Boghb
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« Reply #11 on: March 28, 2006, 12:43:21 PM »
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The "problem" is that you just bought a camera that unpredictably casts unwanted color in different parts of your images.  You then have to figure out a way to take this color out, either in C1, or Photoshop, or both.  This does not only happen with wide angles or movement, but in my experience, it happens with all lenses and in all conditions.

How effective is C1 in dealing with this?  Reasonably, but only if you take a LCC shot for every set of captures with a particular lens and in a particular setting.  Changes in lighting conditions or elevation in my experience will lead to partial removal of the cast by C1.  A standardized library of LCC shots will not, in my view, satisfy a stickler for image quality.

I ran the following test with my 250SA CFE: I took a shot of snow at 1000m.  I then went down to 450m and took another shot of snow in the same lighting conditions and an LCC reference shot.  When I applied the reading to the shot taken at 1000m, it only partially removed the cast.  And this is a telephoto lens on a Hassy 503 -- no wide anlge on an LF camera!

The "problem" is that Phase One does not prepare you for this.  The issue of lens cast is treated under the heading "large format photography" in their manual.  It is given thin treatment.  The manual states that lens cast is "very rare" in lenses longer than 60mm.  It also does not state with any clarity at all that lens cast correction would require an LCC reading for every set of captures.

Would you buy a camera knowing in advance that it degrades your images, no matter how well you could reverse the degradation through added workflow steps?  The answer would perhaps differ for every customer, but the manufacturer needs to acknowledge that this is a problem and be completely forthright with its customers about it.
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Jack Flesher
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« Reply #12 on: March 28, 2006, 01:09:55 PM »
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What specifically is causing the color shift?  

I was under the impression it was the aperture-grille IR filter (pinkish metallic looking that rainbows as you turn it at an angle).  I also understand the color IR filter (blue-cyan) does not cause this?  

IF my assumption above is correct, then it would seem a relatively simple fix for Phase to deal with...  So I suppose there is more to it?
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bjornaagedk
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« Reply #13 on: March 28, 2006, 01:27:58 PM »
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The "problem" is that you just bought a camera that unpredictably casts unwanted color in different parts of your images.  You then have to figure out a way to take this color out, either in C1, or Photoshop, or both.  This does not only happen with wide angles or movement, but in my experience, it happens with all lenses and in all conditions.

How effective is C1 in dealing with this?  Reasonably, but only if you take a LCC shot for every set of captures with a particular lens and in a particular setting.  Changes in lighting conditions or elevation in my experience will lead to partial removal of the cast by C1.  A standardized library of LCC shots will not, in my view, satisfy a stickler for image quality.

I ran the following test with my 250SA CFE: I took a shot of snow at 1000m.  I then went down to 450m and took another shot of snow in the same lighting conditions and an LCC reference shot.  When I applied the reading to the shot taken at 1000m, it only partially removed the cast.  And this is a telephoto lens on a Hassy 503 -- no wide anlge on an LF camera!

The "problem" is that Phase One does not prepare you for this.  The issue of lens cast is treated under the heading "large format photography" in their manual.  It is given thin treatment.  The manual states that lens cast is "very rare" in lenses longer than 60mm.  It also does not state with any clarity at all that lens cast correction would require an LCC reading for every set of captures.

Would you buy a camera knowing in advance that it degrades your images, no matter how well you could reverse the degradation through added workflow steps?  The answer would perhaps differ for every customer, but the manufacturer needs to acknowledge that this is a problem and be completely forthright with its customers about it.
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Just my words. I think it is a big problem. If it is the "nature of the beast" I think it is a very bad nature of a 30.000$ back.
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collum
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« Reply #14 on: March 28, 2006, 04:44:38 PM »
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Just my words. I think it is a big problem. If it is the "nature of the beast" I think it is a very bad nature of a 30.000$ back.
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any chance someone can post a full jpg of one of the discolored shots from off axis?

      jim
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Jack Flesher
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« Reply #15 on: March 28, 2006, 05:19:54 PM »
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any chance someone can post a full jpg of one of the discolored shots from off axis?

      jim
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And while we're at it, how about the corresponding white frame image? ...
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bobtowery
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« Reply #16 on: March 28, 2006, 05:34:28 PM »
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I for one would just like to see more shots from the trip! Especially the forest shots...
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61Dynamic
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« Reply #17 on: March 29, 2006, 12:02:25 AM »
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Having never heard of lens cast before coming across this thread, I find the subject quite fascinating. I too would like to see examples of the phenomena and learn more about it.

If anyone could elaborate on the cause of lens cast and the process of dealing with it or point me to more information on it I'd be appreciative.
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mtomalty
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« Reply #18 on: March 29, 2006, 10:23:39 AM »
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A pretty comprehensive overview can be found at:

http://support.phaseone.com/KBFiles/1557/1/LCCMac.pdf

Mark
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mtomalty
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« Reply #19 on: March 29, 2006, 10:28:01 AM »
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Here is a typical example using a Hasselblad ArcBody with Rodenstock Apo-Grandagon 45mm
The degree and position of the green/magenta shift varies from lens to lens
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