I just got some strobes and started playing with them. When I bought them there was a choice between 250 and 500 Ws, and because they were not that much more expensive I opted for the more powerful ones. They will be more versatile in portrait shoots and the like but in the first projects I tried with them, some table top photography, they turned out to be too powerful. Easy solution was to get some ND filters which would also be handy for other projects. I was tempted by the variable ND filters but opted for a cheaper solution by getting a set of Stealth Gear ND filters and holders. I had never heard of the company and could find little about them on the ‘net but they are compatible with Cokin’s P-Series filters so I can also get those in the future. And really, how bad could a set of ND filters be?
To answer that question I made some test shots. My intention was to determine how close the filters come to the rated density and how much color cast they have. I set up my test with the strobe at the lowest setting while taking shots of the neutral card in my ColorChecker Passport. I then developed all the photos in Lightroom with the same settings I got from a shot that I calibrated and color corrected. To compensate the density of the filters used I adjusted the aperture on the camera. So, the density determination is dependent on the accuracy of the aperture in my Sigma 50mm f/1.4. Later tests might show this to be incorrect but for now I just believe it is perfect.
Because a picture’s worth a thousand words and I am lazy:
Two things jump out: first the color cast when the ND4 and ND8 are used together and secondly the darkness of the ND8. In numbers:
The values under R, G and B give the rounded values I got from using the eye dropper in Lightroom on the middle of the gray area. Yes, I missed the ND8 + ND2 combination. The numbers confirm what the photos show.
The filters work as advertised as far as blocking light, the ND8 even stronger than advertised. But, as far as being grey, two of the three leave something to be desired. Especially when these two filters are used together the red cast is major. But nothing that cannot be solved in post processing. I now know, whenever I use the ND4 or ND8, I need to make sure to get a shot to calibrate this post processing with.