TITLE: Hemispherical photography - should the focus be set to infinity?
DATE: 2018-10-02
AUTHOR: John L. Godlee
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y assumption has always been that when taking hemispherical photos
of forest canopies, the focus of the lens should always be set to
infinity. However, I’m not sure where I got this assumption from, or
whether it’s even true, I’ve just always believed it. So to set my
mind at ease and back up my reasons for telling others to set the
focus to infinity I trawled through a few papers. This is just a
rundown of what those papers were with quotes of what they sai
regarding the issue.
This first paper only says that non-DSLR cameras should have the
focus set to infinity, either that or it’s confusingly written.
All camera internalsoftware filters (e.g. sharpen the picture)
need to be turned off. For non-DSLR cameras the “Fish-Eye setting”
means that the zoom is fixed at the widest angle and focus is set
to infinity.
– Melrose et al. 2012
These next few simply say that they did set it to infinity, but
don’t say why..
We used a Nikon MF-16 camera and a Nikkor 8-mm fish-eye lens with
TriX ASA 400 film, a red filter to increase sharpness of leaf
edges, and the focus set to infinity.
– Englund et al. 2000
The lens was set to a small aperture and focused on infinity
(Frazer et al. 2001; Zhu et al. 2003)
– Hu et al. 2009
Exposure settings were selected to obtain the best contrast
between foliage and sky and making the last one appear white
(cloudy sky offers the best condition in this context). The camera
was used in automatic mode using the parameters fixed in FISHEYE1
lens mode (focus set to infinity, widest zoom, metering
center-weighted), and the shutter speed was varied automatically
by the camera.
– Paletto & Tosi 2009
This next quote comes from a paper which many others reference when
describing proper protocol for taking hemispherical photos:
Unlike the Nikon F, the digital camera did not allow full manual
control of both the shutter speed and lens aperture. We therefore
set the autofocus, exposure mode, and f-stop of the digital camera
to infinity, aperture priority (shutter speed is set automatically
by the camera), and f/2.6, respectively.
– Frazer et al. 2001
This one references a really dodgy looking old downloadable tutorial
series on taking good digital photos, called 123di. Most of it is
behind a paywall though, so I can’t read the applicable bit. But at
least it sort of says why they set the focus to infinity, because
the depth of field is practically infinite under these conditions.
Photographic images were recorded using a Sigma 8 mm f/4 ‘fisheye’
lens (Sigma Corporation, Tokyo, Japan) at the highest possible
resolution (3040 × 2008 pixels) with highest ISO setting (ISO
200). Moreover, the focus ring was set to infinity when using the
fisheye lens, as depth of field is practically infinite and
focusing was not required (Bockaert, 2004).
– Jonckheere et al. 2005
References
elrose et al. 2012 - Manual on methods and criteria for harmonized
sampling, assessment, monitoring and analysis of the effects of air
pollution on forests - Part XVII Leaf Area Measurements
Englund et al. 2000 - Evaluation of digital and film hemispherical
photography and spherical densiometry for measuring forest light
environments
Hu et al. 2009 - Estimation of canopy gap size and gap shape using a
hemispherical photograph
Frazer et al. 2001 - A comparison of digital and film fisheye
photography for analysis of forest canopy structure and gap light
transmission
Jonckheere et al. 2005 - Assessment of automatic gap fraction
estimation of forests from digital hemispherical photography
Paletto & Tosi 2009 - Forest cnaopy cover and canopy closure:
comparison of assessment techniques
