choosing the right ND filter value

[canonuser78]

Hello there,
I am about to search and buy one or two screw on ND filters and I plan to use it specially in video mode. I have some difficulties in choosing the right ND filter values in order to be able to shoot in daylight with wide open aperture (f2.8-4), ISO 100-160, shutter speed 1/50 at 24fps.

According to this chart considering 1/4000 shutter speed in daylingt at ISO 100-160, f2.8-4, 24fps, I wonder which one between these filters ND 1.8(1/60) and ND 2.1(1/30) will fit my needs better (?)
I just need a confirmation .
thanks,

[hsbn]

Exposure value is never a fix number, so any given ND can give you different value from situation to situation and it also depend on other setting too. Either one of them will work just fine.
For me, i'll get the ND2.1. Since it is darker, if the shutter speed is too slow for a certain situation, i can just bump up the ISO or open the aperture. But with ND1.8, if it's a stop brighter and i am at my lowest ISO and smallest intended aperture, I cannot do anything about (assuming I only have one filter).
If you plan to use 2 filters, it's better to buy Vari-ND where you can adjust exposure from 2 to 8 stops.

[canonuser78]

For video at least , as far as I've read the Vari ND looks like is a good option BUT...

in my case, (wide lens 16-35 82mm thread on FF) vari ND can produce the uneven polarization when it's turned all the way to maximum .

Anyway , I am waiting for this one FOTGA Slim Fader Variable ND Filter Adjustable ND2 to ND400 82mm , hope will be usable at least at 3/4 from his minimum - maximum range.

cheers

[hsbn]

You don't want to use Vari-ND at max anyway. It will give a weird color cast that hard to get rid even for still shooting. For 2-8 stop VariND, most people stop around 5.

Most good vari-ND goes for around $200 or more. The link you gave is just $17 for the filter, so don't expect much. But do let me know how it turns out.

[canonuser78]

Hi again,

I received yesterday the FOTGA Slim Fader Variable ND Filter Adjustable ND2 to ND400 82mm

Overall it looks like a good solution on 16-35 USM II  (at maximum 3/4 by his range no distinguishable color cast ,no uneven polarization and no distinguishable vignetting at 16mm )  .

Anyway, after ~ 3/4 the things going wild : black cross (uneven polarization) appear .

regards,

[hsbn]

That's great, even expensive filter like has this issue. So I say it's a money well-spent for you. Have fun shooting.

[TCampbell]

A variable ND is really a couple of polarizers that you twist to decide how much light is blocked.  There are some issues...

If you use a polarizer with a particularly "wide" lens you get a wonky pattern of light reduction.  Thats because the amount of light blocked depends on the angle of the light to the polarizer and since a wide angle lens gathers light from such a wide area the amount of light blocked is not even.  This results in banding -- where a section of the image is particularly dark as compared to others.

I prefer a true ND -- not a variable ND based on polarization.