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Author Topic: Lens cast calibration - opal white plate  (Read 14487 times)

eiaa

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Lens cast calibration - opal white plate
« on: September 17, 2008, 09:24:08 pm »

– The opal white plate has a glossy and a matte side. I would assume that the matte side should face to lens and the glossy to the sky. Is this assumption correct?

– Do I have to leave the center filter mounted for doing a white calibration?

Thank you for your help and time.
« Last Edit: September 17, 2008, 10:26:53 pm by eiaa »
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rainer_v

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Lens cast calibration - opal white plate
« Reply #1 on: September 18, 2008, 06:02:14 am »

Quote
– The opal white plate has a glossy and a matte side. I would assume that the matte side should face to lens and the glossy to the sky. Is this assumption correct?

– Do I have to leave the center filter mounted for doing a white calibration?

Thank you for your help and time.
[a href=\"index.php?act=findpost&pid=222213\"][{POST_SNAPBACK}][/a]


what back, what software, what lenses ?
« Last Edit: September 18, 2008, 06:02:32 am by rainer_v »
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rainer viertlböck
architecture photograp

eiaa

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Lens cast calibration - opal white plate
« Reply #2 on: September 18, 2008, 08:51:56 am »

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what back, what software, what lenses ?
[a href=\"index.php?act=findpost&pid=222292\"][{POST_SNAPBACK}][/a]
I use a Phase back with a Digitar. The software that will be used is CaptureOne.
 
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Doug Peterson

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Lens cast calibration - opal white plate
« Reply #3 on: September 18, 2008, 10:12:16 am »

– The opal white plate has a glossy and a matte side. I would assume that the matte side should face to lens and the glossy to the sky. Is this assumption correct?

In my experience it doesn't make a difference and the current generation of documentation doesn't indicate either direction as correct.

– Do I have to leave the center filter mounted for doing a white calibration?

I would suggest shooting the LCC with the same set of optical filters as the shot you want to correct.

Some other quick points:
> LCC is aperture and shutter speed independent
> LCC depends only on the combination of the lens & back and the rise/shift/tilt of the lens.
> In a crunch the "easy gray" ICC profile can be used to supplement an imperfect LCC or even replace the LCC procedure. It's not going to give the same perfect result as a well done LCC, but it's a useful trick to know.

When you do an LCC imperfectly the result is not bad, it's just no perfect. For instance, if you took an LCC and then (without noticing) changed your amount of tilt slightly you would end up with a very good final image with just the slightest hint of color cast.

Doug Peterson
Capture Integration, Phase One Dealer
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tho_mas

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Lens cast calibration - opal white plate
« Reply #4 on: September 18, 2008, 04:09:10 pm »

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> LCC depends only on the combination of the lens & back and the rise/shift/tilt of the lens.[a href=\"index.php?act=findpost&pid=222349\"][{POST_SNAPBACK}][/a]
I'd like to add focal distance. It's a difference whether the lens is set to close distance or infinity. But as you mentioned with regard to the other points: this is quite minor.
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Jost von Allmen

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Lens cast calibration - opal white plate
« Reply #5 on: September 20, 2008, 04:39:23 am »

If you want perfect LCC, it's not that simple!
I shoot a lot in high altitudes (swiss mountains) with high contrast situations: Dark blue sky (with a LOT of UV) and bright snow scenes, or overcast scenes with a lot of mist, where lens cast can easily been seen.
Using an ALPA SWA (with shift), the Rodenstock HR series lenses (35mm, 60mm, 100mm) and a Phase One P45+, I have found differences in LCC not only concerning every lens and shifting, but also distance setting, aperture (although minor) and (especially important to me) depending on the sun hitting (or not) the lens (and the opal white plate accordingly).
In addition, after shooting series of LCC files to find about about the impact of exposure, I now make shure the histogram of the LCC file is not in the left or right quarter (on the screen of the P45+). This means I opt for an average exposure of the LCC file, but always without changing the aperture.
For general use however I can take one of the LCC files of a library I have built for my lenses and the most common situations. It works but in critical situations lens cast can still be seen sometimes.
So therefore I generally shoot an LCC file with EVERY scene I take!
Of course that slows down the process of shooting and developping the files (in C1), but it's worth the effort. There's no way to achieve the same quality of correction with either CS3 or LR 2.

IF you are happy with the results you get, you might as well ignore all these details concerning LCC.
All my findings come from practical experience (outdoors in very changing situations) and so I think the manuals you generally find about LCC (by any brand) don't tell you the whole story.

Interestingly enough, shooting with the same back on my Phase One camera (Mamiya 645 AFD III; 2,8/45mm as the widest) there's hardly ever any LCC needed, as the lenses have a totally different construction and are placed further away from the back (due to the distance required by the whole mirror mechanism).
« Last Edit: September 20, 2008, 04:51:57 am by Jost von Allmen »
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Jost von Allmen
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rainer_v

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Lens cast calibration - opal white plate
« Reply #6 on: September 20, 2008, 05:11:10 am »

i do exactly the same than jost. reg. sunlight hitting the plexi:
i try to shade allways with my hands or with something the plexi during the white- referenze shot.
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rainer viertlböck
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macz5024

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Lens cast calibration - opal white plate
« Reply #7 on: September 20, 2008, 05:25:22 am »

... and another experience from Switzerland

Just to reply to the side to take: gloss side in front, matte side towards the lens.

In my experience using the P45+ on the Alpa and the H1 I have a lens cast library for my H-lenses at different f-stops and ISO settings - there I have the EXIF data... In critical situations, I always shoot an LCC file.

Critical situations means bright sunlight coming in in delicate angles. But on the other hand critical also means captures in dark situations. You always have to overexpose LCC files by 2 f-stops. However make sure that you do not overexpose completely as you will then lose the information.
With very long exposures catching LCC files can be a problem!

With the Alpa you do not have the EXIF information. Therefore it will be difficult to know lateron what lens it was - and you will be very happy to have a LCC file for every situation!

On the Mac you have the LCC files in the Preferences for Capture One 4.1 - on the PC they are in the CaptureOne directory directly in the corresponding RAW file directory. For the moment I don't know what is better - I would be tempted to tell Phase One to store them in both locations - as you may easily lose them. When you move your images from one computer to another, you have the LCC files on the PC side. Otherwise you have to copy them from one Mac to the other Mac. As for backups, it makes sense to store both the RAW images as well as the LCC files!
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eiaa

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Lens cast calibration - opal white plate
« Reply #8 on: September 20, 2008, 12:53:16 pm »

I certainly appreciate all the personal knowledge shared in this thread. I will go ahead with some more testing and use the suggestions which you all kindly described very well.

BTW the air won't be anything like in Switzerland – so let's see what kind of effect that smog   will do to my LLC files...
« Last Edit: September 20, 2008, 01:12:14 pm by eiaa »
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