Le 08/06/2014 18:17, Leonard Evens a écrit :
My second question: My 70-300 mm lens works for FX format, so I can use
it on my D800, but the lensfun database for this lens refers to using
it in DX format. I presume that means that I can't just use the D7000
Lens Correction for this lens on a D800. Could I go far off if I did
that anyway?
First, as far as I know, the worse that could happen is that you'd have
to pretend those photographs were taken with a DX camera before applying
lens correction. But I think you shouldn't have (see below).
* Testing
You could test that taking a photograph with you D800 in conditions as
different as possible from a plain rectilinear projection (best would be
to use e.g. a fisheye).
Use darktable lens correction to reproject the photograph to
rectilinear, see if result is faithful (straight lines).
Now pretend it's taken with another camera with a different crop factor
(e.g. D90 or D7100) and same lens, and see if the result changes.
If the picture taken on the D800 was in DX mode, the result should not
change at all because darktable already figured out that the picture was
in DX mode anyway.
Is there any chance of an entry for my lens on a D800
appearing any time soon?
The database includes the crop factor for lenses, too, so I think it's
already ok.
From lensfun 0.2.8 again:
<lens>
<maker>Nikon</maker>
<model>Nikkor 70-300mm f/4-5.6D ED AF</model>
<mount>Nikon F AF</mount>
<cropfactor>1.5</cropfactor>
<calibration>
<distortion model="ptlens" focal="70" a="0" b="-0.001254" c="0" />
<distortion model="ptlens" focal="100" a="0" b="0.004173" c="0" />
<distortion model="ptlens" focal="135" a="0" b="0.006434" c="0" />
<distortion model="ptlens" focal="200" a="0" b="0.005485" c="0" />
<distortion model="ptlens" focal="300" a="0" b="0.004364" c="0" />
</calibration>
</lens>
As a result, I would expect that data to be correct for use on a DX
camera as well as on a FX camera, provided that darktable can figure out
from NEF or JPG file if file was taken in FX or DX mode.
Can darktable figure that out ? Well, exiftool can extracts the
information from some pictures I have taken with a D610, so I guess it's
already ok.
exiftool myfile.JPG | grep -i mm
Exif Byte Order : Big-endian (Motorola, MM)
Sensitivity Type : Recommended Exposure Index
*Focal Length : 85.0 mm*
Lens : 24-85mm f/3.5-4.5
Exit Pupil Position : 93.1 mm
Min Focal Length : 24.5 mm
Max Focal Length : 84.8 mm
User Comment :
*Focal Length In 35mm Format : 85 mm*
Lens ID : AF-S VR Zoom-Nikkor 24-85mm f/3.5-4.5G IF-ED
Lens : 24-85mm f/3.5-4.5 G VR
*Scale Factor To 35 mm Equivalent: 1.0*
Circle Of Confusion : 0.030 mm
Focal Length : 85.0 mm (35 mm equivalent: 85.0 mm)
I'm fairly confident that darktable does the right thing and the test
above would conclude "no difference".
Regards.
--
Stéphane Gourichon
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