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Sigma 8- 16 mm lens correction / metadata in PS & LR - especially at 8 mm
Posted By: beholder3, 02-21-2012, 06:07 AM

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Last edited by beholder3; 08-11-2013 at 06:39 AM. Reason: [deleted]
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02-21-2012, 02:57 PM   #2
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Cheers.. I'll give that a go.
02-28-2012, 01:24 PM   #3
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An interesting observation: The K-5 doesn't even display the focal lenght when below 10mm.

How to check that for yourself:

Take a picture with the Sigma 8-16 at for instance 10mm focal length or more.

Press the blue button once to display the image just taken.

Press the "Info" button repeatedly until the image is displayed rather smallish with lots of other information.

Slightly above the middle of the display, you'll find the focal length in mm.

When you repeat the procedure with a focal length below 10mm, the camera displays three dashes instead.

That at least is the state of affairs on firmware version 1.03 - I did not find any hints that Pentax has repaired that in 1.10 or 1.11.
02-29-2012, 10:32 AM   #4
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Last edited by beholder3; 08-12-2013 at 01:44 AM. Reason: [deleted]
02-29-2012, 11:08 AM   #5
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QuoteQuote:
There is some communication issue between the lens and the camera.
That's improbable.

QuoteQuote:
Nevertheless it always does write the correct info into the makernotes, as I described in the article.
When the camera does correctly write the data into the makernotes, it is quite obviously capable of obtaining the data from the lens. Hence it can't be a communication issue.

I'd rather say that this is a Pentax firmware bug. The firmware does read the lens data, because it writes it into the makernotes, but it does not process it correctly, neither for embedding in the more standard-ish EXIF data fields nor for it's own display info functionality.
02-29-2012, 11:59 AM   #6
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Last edited by beholder3; 08-12-2013 at 01:44 AM. Reason: [deleted]
02-29-2012, 12:24 PM   #7
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That would be the case, if the "makernotes" were merely a binary dump of lens-supplied data. But the "makernotes" are Pentax-specific, and created by actively processing the lens-supplied data and various other data created by the camera itself.

Here's a table of what appears in the standard field and in the maker notes, for various increasing focal lenght, first the standard EXIF field value and then the maker notes value:

Code:
Focal Length                    : 0.0 mm
Focal Length : 8.1 mm

Focal Length : 0.0 mm
Focal Length : 9.4 mm

Focal Length : 10.0 mm
Focal Length : 10.0 mm

Focal Length : 12.0 mm
Focal Length : 11.9 mm

Focal Length : 16.0 mm
Focal Length : 16.2 mm
(created by using "exiftool -FocalLength -copy2:FocalLength *.DNG", file names omitted for sake of brevity)

Since the firmware's inability to insert the focal length into EXIF data depends on the actual focal length used, this is definitively a firmware bug, and not a lens-camera communications issue.

Sorry for being so stubborn on that issue, but I'm a senior software engineer and part of my job is to locate and analyze errors in various types of communicating processes and machines, thus I'm quite sure about what I insist upon here.
02-29-2012, 12:42 PM   #8
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Last edited by beholder3; 08-12-2013 at 01:44 AM. Reason: [deleted]
02-29-2012, 12:46 PM   #9
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That is very much appreciated, and I've learned a lot by what you've posted about the usage of exiftool. Please don't misunderstand my point of view as criticism on what you do; it's directed towards Pentax, and hopefully someone there might stumble across my ramblings here.

Until Pentax fixes that bug, the workaround you describe here is worth it's weight in gold - or even more, given that data is weightless ...
02-29-2012, 02:23 PM   #10
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I mentioned this issue with the local Pentax distributor (who also distributes Sigma) and was laughed at and asked "you don't seriously expect Pentax to help out a competitor do you?"... he told me that they'd never fix that 'below 10mm thing' unless they made their own lens in that focal length.
02-29-2012, 03:14 PM   #11
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I'd consider that the kind of arrogance normally associated with dealers of the high-gloss advertising big-mouth "brand" type.

Anyway, thanks to the good work of beholder3, it is possible for us lowly Pentax-with-3rd-party-lens-users to fix the symptom.
04-02-2012, 07:50 PM   #12
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So I have begun using my Sigma 8-16mm. I would like LR to correct distortion at 8mm.
However, I am code illiterate. I have no idea how to get the above programs to work. Is there a step by step guide for dummies like me?
04-21-2012, 09:08 AM   #13
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It appears that I am close to getting this to work right, but I am not quite there.

Here is some background if anyone is interested:
.ExifTool_config for Dummies

I created the .ExifTool_config file by copying and pasting Beholder3's code shown above.

I run this command line:

exiftool "-exif:FocalLength<copy2:FocalLength" "-exif:FocalLengthIn35mmFormat<Calc35mm" MYIMAGEFILE.DNG

And I get confirmation that 1 file was updated, I check the Exif data and focal length = 8.1mm and 35mm equivalent = 12.1mm, so it looks ok.
However, when I enable profile correction in LR3 Develop, nothing happens.
Any idea why? Is my syntax on the command line correct? Do i need to modify the .ExifTool_config file in anyway?

I have tried a bunch of things and I just cant get it to work
This is so frustrating for me...why couldnt Pentax fix this for us


Thanks in advance
04-21-2012, 09:30 AM   #14
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Last edited by beholder3; 08-11-2013 at 07:34 AM. Reason: [deleted]
04-21-2012, 10:47 AM   #15
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QuoteOriginally posted by beholder3 Quote
Are you aware that LR holds the metadata in an internal database?
Just updating the picture file itself is not going to directly fix LR's behaviour. You need to right click the picture and then choose something like "metadata - update from file" or similar. Only then LR reads the newly corrected exif data into its database.
Then you need to enable lens corrections in develop mode, select the correct make, model and profile and all should be fine.
I finally got it!

My command line should've looked like this:

exiftool '-exif:FocalLength<copy2:FocalLength' '-exif:FocalLengthIn35mmFormat<Calc35mm' MYIMAGEFILE.DNG

Instead of the full quotation marks " i was using previously...works great now. Thanks for putting this together Beholder3 The world would be a better place if people offered up their knowledge to the community like you do, instead of wanting things in return.

Thanks
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