My 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