Filters for Seascape Photography (Part 3 of 3) Which Filters Create Colour Casts?

20 06 2009

colourchecker2Warning.. 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

  1. No filters (control image)
  2. 3 stop Singh Ray GND filter
  3. 3 stop Lee GND filter
  4. 3 stop Singh Ray GND filter + 3 stop Lee ND filter
  5. 3 stop Lee GND filter + 3 stop Lee ND filter

colourchecker

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.

Lee 3 stop GND

Lee 3 stop GND filter - You can see that the RGB channels were all pretty much on top of eachother. No colour cast.

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.

SR 3 stop GND
Lee 3 stop GND coupled with the Lee 3 Stop ND filter
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.
Lee3 plus Lee ND
Singh Ray 3 Stop GND coupled with Lee 3 Stop ND Filter
This shows a blue cast introduced by the two filters.
SR3 plus Lee3ND
If anybody would like copies of these adjustment curves, just drop me an email stating which filter combination you shoot with and I’ll send you back the saved curves file that you can apply in Photoshop.  I hope this gives the techy geeks their fix for the week.
Enjoy
Brent

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12 responses

20 06 2009
mattlauder

Great post Brent… go the Lee Filters !! Would be interesting to see the curve for the P series Cokin.

21 06 2009
David Richter

Interesting read, Brent! I always thought the Singh-Ray filters had a slight purple cast but yours seem without any red tint in there… anyway, thanks for sharing your effort. Much appreciated!

22 06 2009
Lee Duguid

Nice work Brent, you confirmed my suspicions. I’ll be investing in some Lee filters to replace my HiTech grads so I’ll let you know what combo I decide to go with.

Now all we need is a post for determining where the grad was placed at the time of capture and how to automate a corresponding graduated layer mask!

22 06 2009
Kajo

Great post Brent, I have not tested mine but certainly will give it a go.
Thanks

23 06 2009
mervfrench

interesting.

So what happens when 2 or 3 Lee grads are stacked together……….nothing?

23 06 2009
Brent Pearson

Hey Merv

If you check out the second last curve box, thats what you get when you stack two Lee filters together. In the case of the experiment it was a 3 stop GND stacked with a 3 stop ND.

It created a slight yellow cast.

BP

23 06 2009
mervfrench

Thanks Brent. I should have studied it more closely, Imissed that.

3 07 2009
Lee Duguid

Hey Brent,
I had a thought…if you are profiling the grad filters how did you shoot the colour chart? Did you shoot it with the black, white and grey at the very top of the frame? I only ask as the colour cast will graduate to nothing near the bottom (and will be inconsistent across the colour chart). Shooting it as you did in the picture will give varying results depending on where the graduation is placed.

Thanks

3 07 2009
Lee Duguid Photography Blog » Filters, Filter holders, and Vignetting…

[…] Ray filters I’ll let my fellow photographer Brent explain this one. For the tech heads click here. It would seem that regardless of the cost no filter is truly neutral (does that constitute as […]

3 07 2009
brentbat

Hey Lee

While I was testing a graduated ND filter, I slid it all the way down in the holder so that I was only shooting through the ND part of the filter.. essentially turning it into an ND rather than a GND.

BP

10 07 2009
Tim Parkin

Hi Brent.. I would be interested in playing with your shots if possible? I’m going to have to get a colour chart so I can test some film so while I’m at it I’ll check my singh ray 1.2H and 0.9Reverse against my Lee filters.. I’m 100% certain that Lee are more neutral than Singh Ray (which surprised me as well)..

11 07 2009
Brent Pearson

Hey Tim

Just so I’m clear, are you interested in getting the original shots or the curve correction files?

BP

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