Hello,
I'm shooting landscapes on a Phase One system (P65+ digital back). I need a 10 stop neutral density filter. Lee seems to be reference. But there is a 3-6 month delivery delay... Is the Hightec Pro Stop a good alternative ? In case of yes, I suppose the 1.5mm version (compatible with lee holders) is the best solution ?
Hi,
I have tested the quality of another brand (
Haida, sold via Amazon amongst others) ND filter, that I saw rather neutral looking results from, and compared it to the Lee "Bigstopper". These Chinese filters look well made, from high quality optical (Schott) glass, and are much more affordable than the Lee filter although you need multiple filters (or step-up rings) if you need to use multiple lens diameters.
I compared the spectral transmission, and density, of both the Lee Big Stopper and the Haida Pro II version of these 10-stop (ND 3.0, 1000x) filters. Here are the results based on the absorption characteristics of Daylight (6568 k), as a Transmission plot and as a relative Density plot:
As can be seen, the Lee filter transmission is slightly smoother across the spectrum, but both have a similar profile which allows to correct the White balance with a simple Kelvin and Tint correction. Some spectrally very pure colors may be hard to get exactly right without targeted post-processing due to the more bumpy absorption spectrum in the yellow-orange region.
As always, shooting Raw-file data is preferable, also because these filters do introduce additional light fall-off towards the corners (especially on wide-angle lenses), because oblique corner rays travel further through the filter medium and coating efficiency changes, which can be compensated for by a Flat-field compensation or Lens Cast Calibration which is best done in Linear gamma Raw before demosaicing.
I also purchased an ND 0.9 (3-stop, 8x), Pro II coated version.
I've recorded it's spectral transmission characteristics by measuring the spectrum of daylight (6586 k) with and without filter (same procedure as above), and plotted the absorption of the filter expressed as Density (-Log10(transmission%) ), because I wanted to know how accurate it would match the intended 0.9 density. Here is the result:
It shows that there is a slightly warm response, a bit more UV and Blue density (less transmission), and a bit less Red density (more transmission), but overall it hits the 0.9 density pretty well across the visible spectrum. The slightly higher IR transmission will be compensated for by the IR-filter that covers the sensor (combined with the Optical Low-pass Filter, if present). The exact color response therefore depends on the particular camera it is used with, but it looks pretty neutral to me, and the smooth spectral transmission is easily tweaked with a simple Color temperature and tint control.
Cheers,
Bart