variable nd filter

[Tom Van den Berghe]

I have a genustech variable nd filter

I use this on my FS100 and ea50.

But something I don't understand.

I put my nd filter on the Fs100 that i just tested here in my garden with sun going under.

The camcorder is in full auto gain. So I rotate the ring of the ND till I have F3.5 and 0 db gain without zooming? Is this the basic to start? (I use the stocklens)

When start zooming to full tele the gain goes up to +12 db.

I tested the same scene side by side with my sony hxr-nx3 with 3 x 1/3" sensor.

With the nd filter on ND1 and auto gain it only gives -3db in the same telezoom range!??

I just saw my test footage of both and both look good.

is this normal?

[Mike Watson]

Turn the auto-gain off. In fact, turn everything off.

Manual gain to 0db in full sun.
Manual iris to f/3.5 (which is I think the best that lens can do).
Shutter speed 1/60 if you're shooting 30p.

Run everything manually. In full sun, leave everything set as it is. Then rotate the vari-ND.

[Tom Van den Berghe]

thx Mike for your quick answer.

So rotating the ND controls the rest?
So when start zooming I also have to start rotating the ND filter?

Sounds difficult to me. That's why I thought auto gain was best here.

For example shooting a soccer game outdoors....

[Noa Put]

A ND filter is used to have better control over your shutter, iso/gain and f-stop in very bright light, basically you first set your shutter which should be 1/50 if you are shooting at 25fps or 1/100 if you are shooting at 50fps. This is a general rule for having natural looking motion blur, for sports you could experiment with a higher shutter as it will decrease motion blur but a too high shutter might also give unwanted side effects.

Once your shutter is set you set your f-stop as that will determine your depth of field, this you normally do not change during a shot, lets say if you are at f1.4 and adjust your exposure to f8 your dof will change dramatically ad that is not what you want during a continuous recording.

If you are using a ND filter your iso should always be at it's lowest value as there is no need to have a higher iso since it will only introduce more grain.

Then you turn your variable ND filter to set your exposure, the advantage of this is that you can control your exposure during continuous recording using that vari ND without ever having to change your f-stop, iso and shutter.

If you have fixed nd, like on your nx3, it's more difficult to have a fixed f-stop or shutter because lets say you set your f-stop and shutter to a fixed value and then you select a ND1, 2 or 3 to get the exposure as close as you need to but you still need to finetune your exposure with your irisring which then affects your f-stop, so you might want to shoot at f4.5 but you might be ending up shooting at f5.2 for perfect exposure because you cannot finetune with your ND filter.

In any case, don't use autogain but set everything manually and use your variable ND to control exposure. Only watch out how far your turn the ND because if you go to far you get a black cross over your image.

[Noa Put]

When start zooming to full tele the gain goes up to +12 db.

That's normal because the lens ramps from f3.5 to f5.6 and your camera is compensating for that by raising the gain.

With the nd filter on ND1 and auto gain it only gives -3db in the same telezoom range!??

It's a different sensor with different sensitivity so it does not compare.

[Tom Van den Berghe]

Originally Posted by Noa Put

A ND filter is used to have better control over your shutter, iso/gain and f-stop in very bright light, basically you first set your shutter which should be 1/50 if you are shooting at 25fps or 1/100 if you are shooting at 50fps. This is a general rule for having natural looking motion blur, for sports you could experiment with a higher shutter as it will decrease motion blur but a too high shutter might also give unwanted side effects.

Once your shutter is set you set your f-stop as that will determine your depth of field, this you normally do not change during a shot, lets say if you are at f1.4 and adjust your exposure to f8 your dof will change dramatically ad that is not what you want during a continuous recording.

If you are using a ND filter your iso should always be at it's lowest value as there is no need to have a higher iso since it will only introduce more grain.

Then you turn your variable ND filter to set your exposure, the advantage of this is that you can control your exposure during continuous recording using that vari ND without ever having to change your f-stop, iso and shutter.

If you have fixed nd, like on your nx3, it's more difficult to have a fixed f-stop or shutter because lets say you set your f-stop and shutter to a fixed value and then you select a ND1, 2 or 3 to get the exposure as close as you need to but you still need to finetune your exposure with your irisring which then affects your f-stop, so you might want to shoot at f4.5 but you might be ending up shooting at f5.2 for perfect exposure because you cannot finetune with your ND filter.

In any case, don't use autogain but set everything manually and use your variable ND to control exposure. Only watch out how far your turn the ND because if you go to far you get a black cross over your image.

Noa, I had several times needed your to understand your answer. Ok, yesterday evening I had to shoot a outside theater. So mostly there were shadows but the heads were mostly in the evening sun.

I locked shutter at 1/100 because I always shoot 50p.Gain manually at 0db. I also used zebras and histogram. (never used this before)

This was difficult becaue when I rotated the nd filter too much (too dark) or less (too brighten)

Yes, I saw the zebras and I tried to avoid this but avoid all zebras returned otherwise in a dark picture.

There were 4 groups that permormed about 20 minutes each time. When the last group started the sun was gone and I had rotate the nd filter to the less dark stop. Then I switched to auto gain and auto iris.
At the end of the "show" the gain kicked till about 12-15 db. I knew this was no problem for the FS100.

Afterwards I could removed the ND filter before the last group started but didn't wanted to take that risk.

Or lowering the shutter speed from 1/100 to 1/50. I thought 2x your shutter was good for natural motion blur and slowmotions.

I watched the footage and mostly it's good. Only when zooming in and out you mostly see I turn the nd filter.

I attached 2 samples.

[Doug Jensen]

There are many things you can do to address the exposure issue you're having with the aperture of the lens ramping Here's my top four suggestions:

1) Invest in a better lens that has a faster max. aperture (such as f/2.8 or f/4) and that doesn't ramp when you zoom. The lens you are using is not a professional lens.

2) Set your iris to whatever the max. aperture of lens is when zoomed in, and treat that as the lens's max. aperture even when zoomed out. For example, if you've got a lens that is f/3.5 when zoomed out, but only f/6.4 when zoom in, then set your lens at f/6.4 and then the exposure will remain constant throughout the full zoom range.

3) Sell the FS100 and get yourself a camera, such as the Z150, that has a built-in 12x zoom lens, better recording format codecs, better servo zoom, better viewfinder, and that is better better suited for the type of work it appears you are doing. You'll even have 4K and 120 fps slow motion as added bonuses when you want them.

4) Turn off all automatic exposure settings because it's just going to make a big mess of your work -- as you have found.

That's my advice, anyway. As a former FS100 owner, and producer of a 3-hour in-depth training video on the camera, I know it is capable of great things, but if you hobble it with a crappy lens you'll never come out on top.

https://vimeo.com/ondemand/fs100