ND filter questions

W

willgote

Member
I'm new to the digital film world, and I have some questions about the ND filter. First, I'm wondering how the ND filter works. Obviously it cuts out light in bright situations, but how does it do this? Does it do it digitally? Is there an actual filter that moves across the iris? Also, does using the ND filter cut down on picture quality?

Lastly, and what I'm most curious about, is how can I calculate equivalent exposures when using the ND filter and and external light meter. For example, if I externally meter a scene, and my meter tells me f16 at 24fps, how can I calculate what the exposure will be if I use a ND 1/8 or ND 1/64 filter?

Thanks for your help!
 
Re: ND filter questions

An ND filter is a gray piece of glass (like sunglasses for your camera).

I don't know if the ND filters in the DVX are electronic or optical, I'm guessing they're optical (i.e., a piece of glass that gets physically moved into position) but I don't know.

Shouldn't affect picture quality to any visible degree, other than to make it darker (which is what you want).

As for equivalent exposure, that's tricky. Nominally each filter should represent 3 stops, but in some informal testing I found that ND 1/8 is actually about 3.5 stops, and ND 1/64 is another 4.5 stops.
 
Re: ND filter questions

The photographic standard is that each ND value equals a 1/3 stop loss. Thus, an ND.1 would be 1/3 stop down. The common ND filters are ND .3, ND .6 and ND .9 comprising light reduction equivilant to 1, 2, and 3 stops accordingly.

As the DVX's ND's are marked 1/8 and 1/64...it would make sense that the stop loss is non-standard.
 
Re: ND filter questions

Yeah, but the 1/8 and 1/64 nomenclature sure seems to imply 3 stops (1/8 the light) and six stops (1/64 the light), so it's a little confusing.

When I tested, I didn't fully understand the DVX's iris ring... I thought it was calibrated to the half-stops the viewfinder shows, but it's actually in 1/6 stop increments. So I could re-test and find out exactly how strong the filters are, but for ballpark it's 3.5 and 4.5 stops (or, cumulatively, 3.5 and 8 stops).
 
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