Basic CPL Filter question

[Storyline]

Hello

I just can't get my head round cpl filters.

I am used to using these filters on my dSLR and I rotate them until the sun in the shot is at 90 degrees to the lens to get the sweet spot and full effect.

I am now faced with a dilemma because I want to get one for my Mini 2 as I do a lot of flying over water. At first I thought it would only be useful for still photos when I could set it up for a predetermined shot. I could not see how it would help for video as it would activate/deactivate as I flew around at differing angles to the sun. When I made this point on a youtube video someone replied that I was wrong because they work like sunglasses and polarise everything. When I actually looked at the types made for the Mini 2 it does indeed seem like there are two types. One has a rotating element but most are just a fixed piece of glass.

So could someone explain if that is correct (ie two types) please ? The answer has another relevance for me. I have little experience of video but do understand the need to keep some motion blur and quickly discovered that to achieve that in the Mini 2 means ND filters are virtually essential. I have found you can get ND filters which have the 'always on - sunglasses' type of polarisation so maybe they would be my best option ..... ? Then also get a single clear rotating cpl for still photos when I can set it up for the shot in advance and use a high shutter speed.

Does the above make sense ?

Many thanks
Paul

 

[slup]

cpl filters...for video as it would activate/deactivate as I flew around at differing angles to the sun.

That's correct ... the polarizing affect will change depending on which relative direction to the light source (sky, direct sun or a reflection) you point your lens & that you have to live with if using a polarizing filter on a drone & film in multiple directions.

When I made this point on a youtube video someone replied that I was wrong because they work like sunglasses and polarise everything.

Here they mix up the polarizing effect with the ND effect. A ordinary polarizing filter will usually cut down on the light entering your lens (usually corresponding to approx. ND2) ... & that ND effect will stay constant no matter in which relative direction to the light source you point your lens ... but the polarizing effect will change.

Compare this with 2 equally dark sunglasses ... one with & one without a polarizer. Both will be equally dark but the polarized pair will "punch through" reflections in certain directions.

When I actually looked at the types made for the Mini 2 it does indeed seem like there are two types. One has a rotating element but most are just a fixed piece of glass.

Either you have seen & comparing circular pol filters with ND filters here ... or you have seen linear polarizing filters & compare them with circular polarizing filters.

Plain ND's doesn't have a need of any rotational adjustment as they are equally dark no matter how you turn them.

Circular polarized filters versions on the other hand, have a additional element known as a "quarter wave plate" in front of a linear polarizer that allow you to do changes regarding what light from which direction you want to let in. The circular filter is best on cutting out light coming from reflections as that usually comes into your lens in a cork screw shape ... it also, to some degree, cuts out on light coming in a linear shape (such coming from a clear sky).

The linear polarizing filter in mainly the same as a Circular polarized filters ... but without the "quarter wave plate" in front. It mainly blocks linear incoming light waves but let light waves coming in a corkscrew shape go through ... they still enhance contrast & color but aren't as good to block glare coming from reflections.... & can mess up your cameras auto exposure.

...do understand the need to keep some motion blur and quickly discovered that to achieve that in the Mini 2 means ND filters...I have found you can get ND filters which have the 'always on - sunglasses' type of polarisation

Here you also are mixing this with ND's & polarizers ... even though it exists combination filters, see below.

You have a couple setups available ...

-Plain ND filters in several strengths ... only "sunglasses", no polarizing effect.

-Polarizing filters ... either Circular or Linear. Most common is the Circular.

-Polarizing filters which also add in different "higher common ND filter" strengths (called circ. pol. + ND), a combination filter.

-Variable ND filters that combines 2 linear polarizing filters that can be turned in relation to each other & create different ND strengths ... (usually also give a small amount of polarizing effect).


Use cases ...

If you will be using different ND filter strengths on a regular basis & can't stand the time it takes to change filters all the time but can live with a slightly changing polarizing effect in you videos ... you can go with a Variable ND filter.

If you either only occasionally use ND's (not necessary if flying on 30m or above, motion blur not visible there) or doesn't think changing ND's are a hazzle, & don't want the sky, for instance, to change color (gets differently affected by the polarizer) depending on how you turn ... go with plain ND filters.

If you occasionally see the use of a polarizer on your drone & can plan the filming/photo directions ... go with a single Circular polarizer.

If you nearly always want a stronger polarizing effect but want the freedom of changing the ND strengths ... go with a combination filter ND + circ.pol.

 

[vindibona1]

As pointed out, impact of circular polarizers is only apparent in certain directions. That's why they have rotating lens on the front, so you can adjust it for the specific situation. But your drone being able to point in all sorts of directions makes them cumbersome to use effectively. They are great on a DSLR where you are not only can look at the effect as you hold your camera, but can adjust them right there. Unless you have really long arms you will have to bring your drone back to you for every adjustment, hopefully nailing each direction on the first try... but I wouldn't count on it.

It kind of leaves me scratching my head why so many companies include PL filters in their ND kits, where a wider range of ND would be far more useful and the PL's, IMO, should be ala-carte add-ones instead of being part of a basic kit.

 

[offtheback]

Hello

I just can't get my head round cpl filters.

I am used to using these filters on my dSLR and I rotate them until the sun in the shot is at 90 degrees to the lens to get the sweet spot and full effect.

I am now faced with a dilemma because I want to get one for my Mini 2 as I do a lot of flying over water. At first I thought it would only be useful for still photos when I could set it up for a predetermined shot. I could not see how it would help for video as it would activate/deactivate as I flew around at differing angles to the sun. When I made this point on a youtube video someone replied that I was wrong because they work like sunglasses and polarise everything. When I actually looked at the types made for the Mini 2 it does indeed seem like there are two types. One has a rotating element but most are just a fixed piece of glass.

So could someone explain if that is correct (ie two types) please ? The answer has another relevance for me. I have little experience of video but do understand the need to keep some motion blur and quickly discovered that to achieve that in the Mini 2 means ND filters are virtually essential. I have found you can get ND filters which have the 'always on - sunglasses' type of polarisation so maybe they would be my best option ..... ? Then also get a single clear rotating cpl for still photos when I can set it up for the shot in advance and use a high shutter speed.

Does the above make sense ?

Many thanks
Paul

Another caveat for polarizers with wide angle lenses.They don't polarize the whole field of view.Especially noticeable if there is a lot of blue sky in the scen the polarizer efect may not cover the entire piece of sky leading to uneven results.