Warning.. this post is very geeky and only for photography nerds. If your not into techy geeky stuff, close the browser now!!! As for you techy geeks… you’ll probably get a kick out of this
OK, this is something I’ve been wanting to do for a while now. I’ve always wondered whether Singh Ray and Lee filters are truly Neutral or whether they have a colour cast in them. Some of you may have seen this interesting experiment with Cokin “Neutral Density” filters that displayed a terrible colour cast and forced me to take the filter back and replace it with Lee Filters. So anyway I wanted to do some controlled test to see if I could measure any colour casts that filters introduce. So here’s my geeky write-up of the experiment.
Aim: To determine whether Sing Ray and Lee filters introduce colour casts when used separately or together, and what sort of correction curves I need to apply in Photoshop to fix any colour casts.
Method: I photographed a Macbeth Colour checker under a controlled 5000K fluoro light with the following filter combinations
- No filters (control image)
- 3 stop Singh Ray GND filter
- 3 stop Lee GND filter
- 3 stop Singh Ray GND filter + 3 stop Lee ND filter
- 3 stop Lee GND filter + 3 stop Lee ND filter
I used the control image to set my white balance settings in Light room and then copied these settings to the other images and opened them in Photoshop.
In Photoshop I applied a curve adjustment layer and used the black, white and grey eye droppers to white balance the control image and then saved this curve adjustment and applied it to my other images to ensure consistency.
I then created a second curve adjustment on each image that was shot through ND filters and again created a curve that was auto-adjusted using black, white & grey eye droppers. It was the result of this adjustment that showed me whether there was any colour cast. These curves have been saved so that I can see the impact of applying them to real-world images.
Results: When only one GND filter was used, The Lee filters were very neutral, however the Singh Ray filter had a definite bue cast (which surprised me a bit because they are significantly more expensive than the Lee filters). However when I used a GND filter together with a straight ND filter I DID get some minor colour casts as shown below.
Lee 3 Stop GND filter on it’s own
This first adjustment layer is for the Lee 3 stop GND filter used by itself. You can see that the RGB channels are pretty much right on top of eachother which means that besides the tonal adjustments, the curve didn’t need to adjust the colour mix.
Singh Ray 3 Stop GND Filter
The curve below shows the correction required to fix the colour cast introduced by the Singh Ray filter. There seems to be a blue / cyan cast added with Photoshop having to add more red and a touch of green to make the image neutral.
You can see that there is a slight yellow cast here as Photoshop has had to add more blue in the mid-tones to correct it.
This shows a blue cast introduced by the two filters.