A few weeks back while I was running a workshop, we noticed as a group that my 3.0 (10 stop) ND filter from HiTech had a more blue cast to its physical appearance than another one brought along by a participant.
I did some quick tests and discovered that they did not render the same. I had been under the impression since buying my original filter back in 2018 that it was colour neutral, and if memory serves me right, Firecrest took great pride in promoting that their filters were neutral.
Firecrest 10 stop filters. Left one manufactured in 2022. Right side filter manufactured in 2018.
I came home with both filters, as both my participant and I could not remember which filter was who’s, and I wanted to contact HiTech to see if they would replace the filter that I think has a pronounced blue cast. Here is a sample photo taken that shows my old 2018 filter has a pronounced blue cast, and is also a stop or more darker than the new filter. I made both exposures at the same shutter speed and aperture:
Left side of composite image is the 2018 10 stop ND. Right side of composite is the new 2022 10 stop filter.
HiTech have chosen not to replace the filter, and claim that the 2018 filter is within tolerances. They have asked me to point out that my original filter is from 2018, and that they have offered a free of charge laboratory testing on the filter.
On the positive side, it is good to see that their filters are improving and they are more neutral than they were. On the downside, I am disappointed. It is clear that their original filters weren’t as neutral as I had hoped, and that their stop rating is not that tight either. I suppose one can say that not all filters will be equal, and that there must be a tolerance. It’s just to my eye: I think there is quite a blue cast to the original filter. As for offering to do a laboratory testing for me: this will prove nothing for me, except that I have a filter that I deem unusable but somehow is quite within the tolerances that HiTech have for their products.
Perhaps the give away from all of this, is that it’s always worth testing out your filters to find out how they perform, and to understand that there are certain tolerances in filter production. 10 stop does not mean 10 stop, and neutral does not guarantee neutral colours.
I have since had to do a filter refresh. I tend to kill filters / damage them from my intensive schedule. I have chosen to try out the Kase ND filters. I must stress that this is NOT in response to HiTech’s response, as I was pretty happy with their filters for all this time (my Velvia film of choice has a lot of blue in it), so I think this is why I did not notice the cast.
If you would like to do a review of ND filters, I would recommend going over to OnLandscape / Tim Parkin’s site as he has made some extremely detailed analysis of filter neutrality. Tim has kindly offered two links that are free of charge, as his online magazine is a subscription model.
onlandscape.co.uk/2018/11/graduated-filter-colour-accuracy-testing
onlandscape.co.uk/2019/05/graduated-filter-test-part-four
Tim says that these cover colour accuracy and an overall score part. The other parts
that are paid cover things like sharpnes, water shedding, etc