Dear all, I work in the Croatian Forest Institute, and I have learned a lot just by monitoring posts on this listserv during the past 1,5 years. However, time has come to post a question of my own. I hope you will find it interesting enough to provide me with some info. I would appreciate it much! PROBLEM: I intend to utilize hemispherical photography for my PhD research concerning oak decline in mixed deciduous forests in Croatia to describe canopy features of stands of different age, stocking, species composition, decline history. After review of the literature on hemispherical photography, I have browsed the equipment manufacturers just to find out that, for example, WinSCANOPY full system (camera, lens, tripod, self- leveling mount and software) lies well outside my budget constraints (as usual). Since I have an excellent digital camera Canon Rebel XTi with 10.1 Mpix (EOS 400D in Europe) I have tried to find hemispherical lens I could mount on my camera and calibrate it myself, just to find out that with existing 180°view circular hemi-lenses you can get full circle only on digital cameras that have sensor equivalent to 35 mm analog cameras, and that such camera lies, of course, well outside my budget constraints. I have also heard that hemispherical lens converters are designed only for low-cost digital cameras with fixed lenses. I gave up my quest for a while, and resumed yesterday, when I found out that Sigma (the producer of the most popular 8 mm circular fisheye lens) has produced a new circular hemi-lens designed for the Digital cameras just like my Canon (cameras with APS-C digital sensor that is smaller than equivalent of 35 mm film). This time, the price is within my budget boundaries :). So I intend to buy this lens, sturdy tripod and a leveling mount, but I have some questions since this lens is 4.5 mm versus previous Sigma with 8 mm (focal lenght?). QUESTION(S): 1) pro's and con's concerning the utilization of configuration I mentioned above against some professional system fully calibrated (e.g. WinSCanopy) with first pro being the price. 2) are there any calibration problems I should consider given the difference in 4.5 mm and 8 mm. I intend to calibrate the lens sensu Frazer, G.W. et al. 1997: A method for estimating canopy openness, effective leaf area index, and photosynthetically active photon flux density using hemispherical photography and computerized image analysis techniques. Pacific Forestry Centre, Information Report BC-X-373, Canada. There is also a calibration procedure in free software GLA (Gap Light Analyzer). All I need is some date on calibration from the manufacturer, and I hope they will provide the data given the special purpose of this lens.
At the end, I would like to apologize for the lenght of this post, and express my gratitude up in front to all those who can find some time and willingnes to share some of your experience with me and the rest of the ECOLOG listserv. If you reply directly to my e-mail, I will make a summary of responses and post it on listserv. Thank you very much in advance! Stjepan Dekanic
