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Sunday, March 3, 2013

Cokin P Series filters tests

9:54 PM By Franz , , ,

I recently bought a set of Cokin filters.

ND .3 - 1 stop
ND .6 - 2 stops
ND .9 - 3 stops

Or as they label them here: http://www.cokin.co.uk/pages/colour5.htm


ND2 Ref. 152 - 1 stop
ND4 Ref. 153 - 2 stops
ND8 Ref. 154 - 3 stops



I learned about ND in the point measurements so I chose to call them that way instead.

They are the cheapest I could find and the filters themselves are plastic. Unwrapping them from their bags though, you can tell that they are quality plastic and have some kind of coating over. I decided to run them through some tests for sharpness and color quality.

Below are my results. I compensated the stops by ISO adjustments and exposed for the flower's inner petals.

Clean

.3 ND

.6 ND

.9 ND








The first observation is the obvious loss of contrast. The biggest and most important aspect is that the area exposed for is indeed exposed properly in all of the pictures. So they all work well enough for their intended purpose.

Ideally, a small contrast adjustment should fix the washed out look however it wasn't that simple. This is how the histogram reads for the respective images both raw and processed.

Clean



ND .3



ND .6




ND.9




I did all the corrections to the best of my ability and odd temperature changes throughout. The ND.3 changes one stop and all I had to do to make it match the look of the clean shot is to add contrast and reduce brightness. It looks perfect.

ND .6 was a bit trickier. I noticed a blue tint to the image after my contrast adjustments. So rather than having the image at 5200 K for Daylight, I warmed it up to 5400 K. After this, I noticed a slight green hue to the highlights so I added a -1 tint. It works well enough.

ND .9 was of course just a bit more problematic. It seemed to have even more of a blue tint and I had to bump up the temperature to 5800 K to get the correct look. It does appear to have a green tint but doing -1 tint on it makes it just look too pink 

All of these images seem to get more and more "contrasty" as the ND thickens. I was using both the flower versus the grass, the highlights and the shadows of the building in the background to try to reach a happy medium. You can see that the ND .9 image has darker grass but lighter shadows in the background. The only explanation for this kind of behavior is that the blue tint the filters seem to have is blocking some wavelengths more than others.

Sharpness

To test sharpness and image quality in general, I cropped ND .3, .6 and .9 respectively below:


There seems to be some sharpness lost as the ND thickness goes up. Or at least it's more apparent. I would say it's still acceptable. Not much more I can say about that.