Cokin and Hitech ND filter test

I have started using Cokin P size filter system for landscape shots. I like it because it is simple, light, and compact. A good set up to go on trails and fishing expeditions, I think.

Anyway, I did some testings to compare a few different ND filters today.

Here is a list of ND filters that I used for my test.

Graduated ND filters:

Cokin 121M  ND 4.  It is hard edged apparently, but it looks more like soft edged to me.

Cokin 121S  ND 6, 3 stop soft edged graduated filter. 

HITECH ND4 (0.6) Graduated.  2 stop soft edged filter. 

Solid ND filters:

Cokin 154.  A solid ND8 filter made of resin.

Kenko PRO ND8.  A circular screw in filter. 3 stop.

HOYA PRO1 Digital Filter ND64.  6 stop circular screw in filter.

First, I took shots using each individual graduated ND filters. You can see that both Cokin filters have changed the colour of the sky noticeably, whereas HITECH filter is quite neutral in terms of colour cast. 

Also, it looks to me that the HITECH filter has a smoother graduation than the Cokin filters do.  For example, my copy of Cokin 121s has some areas of inconsistent transition of shading around the top 1/3 of the filter. The filter appears to get darker much more evenly on the copy of HITECH filter that I have.

Here is a shot w/o filter as my control

Cokin 121M  ND4 Graduated

Cokin 121S  ND8 Graduated

HITECH ND4 (0.6) Graduated

The next testing that I did was a stacking test.  I stacked each graduated filter on top of Cokin ND8 filter (solid ND resin filter) to see what kind of colour cast that each filter combinations will cause.

As you can see, colour change is quite strong, and it is not so simple to fix on Lightroom. Well, this particular colouring may appeal to some people, but It is something I would rather avoid for landscape shots.

Cokin 154  ND8 + Cokin 121M  ND4 Grad

Cokin 154  ND8 + Cokin 121S ND8 Grad

Cokin 154  ND8 + HITECH ND4 (0.6) Grad

Here, I replaced Cokin 154 ND8 resin filter with a screw-in ND filter made by Kenko (Pro ND8).  Interestingly, a strange colour shifting was gone.

I must admit that screw-in filters are fiddly to use. Not like sliding a square filter into a filter holder. However, it has become clear to me that the screw-in glass ND filter has less problem of colour change than the combination of two square resin filters that I tested earlier.

shot with Kenko Pro ND8 only

Kenko Pro ND8 + Cokin 121M  ND4 Grad

Kenko Pro ND8 + Cokin 121M  ND4 Grad

Kenko Pro ND8 + HITECH ND4 (0.6) Grad

This time, I tried a different screw-in ND filter, HOYA ND64 (6 stop).

The results were similar to ones with Kenko screw-in ND8 filter.  Just each exposure time was longer (6 stop as opposed to 3 stop).

HOYA PRO1 ND64

HOYA PRO1 ND64 + Cokin 121M ND4 Grad

HOYA PRO1 ND64 + Cokin 121S ND8 Grad

HOYA PRO1 ND64 + HITECH ND4 (0.6) Grad

Finally, I screwed Kenko ND8 (3 stop) and Hoya ND64 (6 stop) together to make 9 stop ND filter.

On top of this combo, I put grad ND filters to see if everything would go wild.  Well, it didn't.  There wasn't any colour change I could notice.

The problem was that the two filters started causing vignetting on 24mm lens that I was using for the test.

So, I took off one screw-in filter, and slotted the Cokin ND8 square filter instead. The vignetting was gone, but the extra resin filter had created a new problem of colour casting.

Kenko Pro ND8 + HOYA PRO1 ND64

Kenko Pro ND8 + HOYA PRO1 ND64 + Cokin 121M ND4 Grad

Kenko Pro ND8 + HOYA PRO1 ND64 + HITECH ND4 (0.6) Grad

Cokin ND8 resin + HOYA PRO1 ND64 + HITECH ND4 (0.6) Grad

After these tests, here is my conclusion.

First, stacking resin filters will be more likely to cause a colouring problem, which is not so easy to fix on post processing, I thought. Adjusting WB didn't fix it, and it required too much fiddling and tweaking on Lightroom.

Second, stacking two glass screw-in filters doesn't seem to create a colouring issue.

Third, stacking two glass screw-in filters, however, does creates a problem of vignetting on a wide angle lens. One solution would be to get a single screw-in 10 stop filter.  A screw-in 10 stop filter is a half cost of a square filter like LEE Big Stopper.

Fourth, once a screw-in ND filter is in place, an optical view finder becomes so dark, and it becomes impossible to use it for composing.  The live view mode however works fine even the view finder becomes as dark as a blackhole. I actually find that adjusting a graduated ND filter is easier on the live view.