Dual camera decision
Ned Horning
I think it's time for me to get a dual vis/nir camera setup and I could
use some input from PLOTS folks using or interested in using dual
cameras. I'm looking at this as an entry into dual cameras with an
interest in developing or experimenting with software, mounts, triggers,
and applications.
I'm torn between getting something similar to the PLOTS kit (
http://publiclaboratory.org/wiki/dual-camera-kit-guide) and getting
something different. An advantage of duplicating the PLOTS rig is that I
would have the same setup as lots of other people which has advantages
especially if PLOTS is going to make more or promote the use those
specific cameras - any word on that? Getting a different setup would
allow me to possibly improve upon the existing setup and test and report
on another system. If I got another type of camera it would still have
to be inexpensive but it could probably be slightly more than a
used/rebuilt A490. Any thoughts?
On a related note are there any plans for a NIR camera conversion party
in the New England area?
Ned
Chris Fastie
Ned,
The A495 cameras in the PLOTS IR kit seem to be performing really well. It is hard to beat the $70 price and 175 gram weight. If I were starting from scratch, I might opt for a bigger sensor just to get better image quality, although I would not opt for more pixels – 10MP is about all the lens can exploit especially while flying. The one feature to add to the A495 for better aerial photos is manual focus. In some situations (poor light, homogeneous scene, swaying camera) automatic focus will struggle to lock in before the camera shoots, resulting in out of focus shots. If you are interested in precise records of NDVI, then avoiding lossy JPG compression could help. Although CHDK allows non-lossy RAW or DNG capture on any Powershot, it is extremely nice to produce a RAW format that most programs can read without conversion, and native RAW will include EXIF data which CHDK RAW does not (CHDK DNG apparently does include EXIF). Another nice camera feature is shutter priority mode to lock in a fast shutter speed while the camera adjusts aperture to get a good exposure. CHDK offers this on any Powershot, but it is easier just to turn the dial on the camera. A great camera to have for an NIR/visible pair would be the S90/S95/S100 which have all of the above. They weigh 195 grams, and even the three year old S90 will cost about $200 apiece (ebay). So it is a big commitment over the A495, but you get a bigger sensor, manual focus, shutter priority, and RAW capture.
The much bigger decision to make if you are hacking your own NIR camera is what to use for the visible light block filter that replaces the IR block filter during the modification. The PLOTS IR camera uses exposed developed color print film which works incredibly well and is the ultimate hack. An alternative might be photographic gel filters. These are thin sheets which might be closer to the thickness and flatness of the removed IR filter and replicate the optical system more closely. They also have precise spectral qualities – the Wratten 87 filter blocks all visible light and passes almost all NIR light above 750 nm. Color print or slide film leaks a little visible light at 500 and 600 nm and apparently does not pass as much NIR light as the W87. A 3 inch by 3 inch square of Wratten 87 gel filter is about $80 but will modify dozens of cameras. I might chip in if anyone is buying. Conversion party time?
Jeffrey Warren
The one feature to add to the A495 for better aerial photos is manual focus. In some situations (poor light, homogeneous scene, swaying camera) automatic focus will struggle to lock in before the camera shoots, resulting in out of focus shots.