Yes. Multicoating is necessary for every air-glass interface if you want to maximize image quality. The purpose of multicoating is to minimize unwanted reflections and maximize light transmission.
ngc7789 wrote:
Yes. Multicoating is necessary for every air-glass interface if you want to maximize image quality. The purpose of multicoating is to minimize unwanted reflections and maximize light transmission.
should i be concerned that there aren't many (if any) multi-coated 10stop ND filters? (for 82mm size, which i also need)
or that I can't find a triple-coated filter.. certainly that would minimize reflections even more
Multicoating is useful for two reasons. One is to minimize loss of light transmitted through the filter, and obviously for a neutral density filter that reason is not important, because you are all ready getting rid of a lot of light in the ND, and a slight bit more will not matter.
The second and more important reason for multicoating is to minimize reflections. Stray reflections can lower overall contrast in any image, and for a flat filter with digital cameras they can also cause what I call "sensor flare". Adding a single inside surface with only single coating rather than multi coating will not make an observable difference to general contrast of the image, so that is not really an issue. The sensor flare issue depends on the particular image and if it has any high intensity areas, like from lights at night or strong local reflections or the sun. Any strong light sources can be reflected back from the sensor assembly, hit the inside of the less well coated flat filter, and then find their way back to the image sensor. Sensor flare is very real, but it is not too bad for most of what we shoot.
I would initially think that multicoating should be important. However, the fact that good filter companies like B+W mostly offer non-coated strong ND filters, and that I tend to get good results with my 6- and 10-stop B+W ND filters indicates that my own initial thoughts on this could be wrong. It's not as if B+W is usually averse to making their filters expensive
I suppose there are several mitigating factors that make non-MC strong ND filters not such a bad thing:
- they are typically used for slow, carefully set-up tripod shots, when you have time to fiddle with extra light baffles to shade the lens from bright light sources outside the picture
- only the lack of MC on the inner surface matters; reflections off the outer surface have to pass through the ND filter two extra times, suppressing them by 12-20 stops
- for the same reason, extra reflections off of stacked filters outside the ND aren't a problem (and an ND stacked outside a polarizer gets a 2+ stop reflection reduction).
so MC on a strong ND filter is definitely not "necessary" (plenty of people get good shots with the available non-MC ND filters), although there may be occasional rare cases where reflections are problematic.
A little off topic. But I have been using cheap filters and I have yet to find a difference in the image quality of a $40 filter and a $150 filter. Seems overkill and all hype. Is there really any proof?
cheap ND filters are not as color neutral. even high quality coatings flare in the right conditions. cheaper filters do it sooner because it is the coatings that cost the money.
ngc7789 wrote:
Yes. Multicoating is necessary for every air-glass interface if you want to maximize image quality. The purpose of multicoating is to minimize unwanted reflections and maximize light transmission.
Singh-Ray ignores some basic lens design stuff that has been understood for more than half a century. they decided that the gain wasn't worth it. for someone of their size, i would have to agree. coating polycarbonate filters is very expensive and not very useful since the coatings would flake off if the filter flexed.
HerbChong wrote:
cheap ND filters are not as color neutral. even high quality coatings flare in the right conditions. cheaper filters do it sooner because it is the coatings that cost the money.
Herb...
Based on the discussion on Naturescapes, the more expensive ND filters also suffer from colour casts.
Have to agree. I have yet to see an ND filter that is trully neutral. In the 10-stop variety there is ALWAYS a strong magenta cast since the filters do not block IR very well. Surprisingly, the best performance I have seen in that respect is from the Hoya 400ND, but since I have vowed to never give Hoya any business ever again this is not an option for me. I am not sure that this matters much in a digital world. You can always correct color cast easily after the fact, with perhaps the only exception being the 10-stop ND. There the cast is heavily concentrated in the red channel and somewhat difficult to correct.
except for not being coated, not really. they are lighter but the polycarbonates will scratch more easily. at some point, you need to refresh filters simply because of scratches.
Herb...
louis fusco wrote:
herb, i broke my lee 3 stop glass nd, are the acrylic noticeably different?
the cast is not too hard to deal with if your camera's IR cut is sufficient. many Canon's seem to be only adequate. for my D3 and D3X, i haven't found it harder to deal with than auto-WB. B+W's 10-stop filter does about 8 stops at 900nm, which is pretty good. you have to have a camera that's pretty lousy at IR blocking to see an actual magenta cast. a brown cast is more the actual color of the filter in the visible range. that's my experience on my D3 bodies and on film.
Herb...
GroovyGeek wrote:
Have to agree. I have yet to see an ND filter that is trully neutral. In the 10-stop variety there is ALWAYS a strong magenta cast since the filters do not block IR very well. Surprisingly, the best performance I have seen in that respect is from the Hoya 400ND, but since I have vowed to never give Hoya any business ever again this is not an option for me. I am not sure that this matters much in a digital world. You can always correct color cast easily after the fact, with perhaps the only exception being the 10-stop ND. There the cast is heavily concentrated in the red channel and somewhat difficult to correct....Show more →
