I am in the process of setting up a Sony A6000 that I have had converted to full spectrum and have fitted with a Nikkor el 80mm lens. I now need to map the spectral sensitivity. It seems the way to go for me would be to use the pastel method to create standards that will work into the UV range.
I have a couple of queries that I would love some help with.
- Has anyone mapped the spectral sensitivities of the A6000 full spectrum?
- Should I be making a separate measurements for every filter arrangement I will be using? I will be using Baader UV pass and UV/IR cut filters.
Any guidance would be greatly appreciated
Conveniently/frustratingly I have also just invested in a bunch of A6000s for my lab, which I’m converting to full spectrum myself.
I will at some point need to do the full (monochromator-based) spectral sensitivity mapping. But the equipment I need (and fieldwork which requires the cameras) are all on hold for now due to COVID. So at some point I might have the ideal calibration done for you, but I can’t give you a timeframe I’m afraid (likely next spring).
So in the meantime the chart-based option is probably the best. In fact, I do have everything I need at home to do a chart-based calibration for you (assuming you’re using natural sunlight for your photography?) I have a set of 100 pastels with reflectance profiles measured under direct sunlight.
In answer to your second question, you need to photograph the chart using both filters and make a multispectral image which uses both channels (standard method for making a linear normalised vis-uv calibrated image).
Yes, there’s a brief description of the process in the user guide. Due to fluorescence I’d recommend you measure the pastel reflectance using the same light source as you’ll be using for the photography (ideally natural sunlight). So disable the spec’s own light source, have the pastels illuminated from one angle (e.g. 45 degrees) and measure from e.g. 90 degrees, then do exactly the same with the camera.
Thanks for that Jolyon. I have finally gotten around to measuring a pastel set and am just getting the measurements into the same format as the xrite chart excel sheet (but with 300 to 700nm range) provided in the MICA toolbox. However, I have noticed that some of reflectance (%) measurements have negative values,these are in the UV end of the specturm. Is it ok to leave these values as negative or can I make them zero? Or, do I need to convert the data somehow.
Would my best option will be to make my own set of pastel standards so I can measure the spectral response for each filter configuration I will use? I am pretty sure I can get access to the equipment necessary.