thanks hoping to have a play around with them tomorrow if what i am thinking is right if my shutter speed is 1000 and i put on a nd2 filter correctly that should come down to around 500 and a nd4 filter would come down to 250
and if i am looking to get a cinematic shot at 24 fps i would want the shutter speed to come down to around 50
That is correct. Another way to see it is that dividing your shutter speed by the target frame rate (50 in your example) will give you the ideal ND filter grade to achieve that.
So, for instance a shutter speeed of 1600/s divided by 50 will give you 32, so spot on.
An exposure time of 1000/s divided by your target frame rate will give you 20.
Therefore you will have a choice between using a 16 grade filter and a 32,, given that is all you have.
With the 16 filter on, setting the exposure time to 50/s will give you a brighter image that 1000/s with no filter.
So you would want to look at your histogram and see if that causes any highlights clipping to an extent which bothers you. If it does, you can either try to film your scene keeping particularly objectionable highlights (for instance very bright portions of the sky) out of the frame, do so in post processing by cropping highlights out and consider a compromise by setting 60/s as shutter speed which will reduce the effect you seek but also cut brightness down a bit.
Ideally, you would want to film in pLog, which should give you more ability in postprocessing to bring down the scene to whatever luminosity you were looking for and recovering highlights details to an extent.
Using a 32 instead would work just the other way around, by producing a darker exposure than 1000/s. You would need to watch out for clipping in shadows and brightening up the scene in post processing would cause noise to show up. Given our ideal ND filter is 20 in this case, 16 would be a closer, easier choice.
The final effect is to blur details in every single frame of the clip. The remark that
this will only affect moving objects in the scene is
only correct if you are keeping the drone still while filming. If you are moving the drone about, blur will be visible on the whole scene because the whole scene is moving. The faster you move or rotate, the more blur you will see.
However, if you are reviewing your 4k footage on a lower resolution screen, this will be less evident to your eyes, because resizing causes sharpening. In any case, it is supposed to be a subtle effect which mimic the way we naturally see movement. If you set your shutter speed to 25/s, instead of 50/s, you will see an overdone version of it.
To be clear, the reliable way to do this is to set your drone to manual exposure, locking ISO to the minimum number (the Anafi sensor is quite noisy) and setting exposure so to expose your scene like you want. If the result is for example 800, divide by 50 and you will get 16. Put you 16 on and manually set exposure to 50.
Now, at midday in an open field, or from a certain height, your exposure result will be the same wherever your camera is pointing. In other times of the day and if large features are about, you might find out that your 50/s with a certain filter will produce nice results only pointing in certain directions. Your evening beach scene might look just fine, but the mainland might be reduced to shadows against the backdrop of the sky. It is up to you whether this is a problem. You might film short sections with different exposures and/or filters. You might use HDR, but I think that doing so will force you out of manual exposure.
Do ND filters (e.g. setting your shutter speed to 50/s) influence still images?
Most definitely yes!
The reason why the Anafi sensor needs to be 21 megapixels, which is way larger than 4K (12mp), is that there is no mechanical stabilization for the vertical axis. When filming the sensor stabilizes the image digitally, by relying on a much larger frame.
When you take photos, you are using the full sensor resolutions, so there is no stabilization of the vertical axis.
If you use a shutter speed of 50/s with no digital stabilization from a flying drone, you most likely will see some details blurring in your still images. How much will depend on air conditions.
So, the cinematic effect is cool but it does require some work and thinking and it has some drawbacks:
- hard to get decent results in scenes with changing luminosity (morning and evenings, fast moving clouds etc..)
- still images and frame captures will show blur
- if planning to slow down your footage with Premiere (which interpolates frames to make new frames in between, turning a 24fps to 48fps, for instance) you should refrain from slow shutter speed, because the software needs sharp details to do that.
However, having a filter on will protect your lense. When flying on the coast with lots of salty and sandy wind, I would keep at least a clear polarizer on most of the time.
Polarizers cut on scattered light.
This only works at certain reflection angles.
Make an imaginary gun with your hand, like children do, by extending your index finger and pointing your thumb up, froming a 90 degree angle with your index finger.
Keep pointing your gun at the sun (or any light source). Your thumb will be pointing in a direction where the polariing effect is maximised. if you rotate your hand left or right, every direction the thumb is pointing at is one filming angle for which polarizing will work very well.
For instane, if you are facing the sun, which is 45 degree up in the sky, the polarizing effect will be very strong with your camera:
pointing in the direction of the sun but 45 degrees down,
pointing to the right or the left and levelled to the horizon
pointing opposite to the direction of the sun, but 45 degrees up
And anything in between.
You can use that to choose filming angles which will work..
For instance, imagine that your girlfriend is floating with her inflatable on very clear water, and you want to do a reveal shot pointing down at the water. The "pistol trick" will tell you what angle your camera should be pointing at to keep the water as transparent as possible when coming from certain directions (and with your circular polarizer rotated so to maximise the effect).
Incidentally, by exclusion, it will also tell you which directions will increase reflections.. If you want to film clouds reflecting mirror-like on water or glass.
However, reflections and specular highlights can be good.
When showing to my mum some footage of her favourite beach, her first comment was "how beautiful, that sprinkles of light in the water". And it's true, the moving speckles of light made for a very peaceful view, there are plenty of times when reflections will work just fine. People like wonderful expanses of unbelievably transparent water because they are such a rare sight. But plenty of views benefit from highlights in the right places.
