CPL filter? Would you recommend?

[Vioq]

Do you take it off at night? Is it easy to take off and put back on?
Did you find it necessary ?

 

[kamkar]

I have always used CPL filters if i can, even on the rear facing cameras in my car.
And of course i do not remove them at night, not even now where newer better sensors might even give a tiny boost if the CPL was not there.

I wholeheartedly think no dashcam should be sould without a CPL filter.

 

[DT MI]

Do you take it off at night? Is it easy to take off and put back on?
Did you find it necessary ?

Use them on front and rear cameras, if possible, and never take them off. Front camera to reduce reflections and rear to reduce reflections as well as glare from the windshield (windscreen) of the vehicle behind me making it easier to see the actions of that driver.

A229 Pro, when?

Wow rear Starvis 2 sounds great.

dashcamtalk.com

 

[AS87]

Do you take it off at night? Is it easy to take off and put back on?
Did you find it necessary ?

Given an option I'd love to have the CPL filter for both the front and rear dashcam's. The A229 Duo or for that matter, the A139 Pro 2Ch versions do NOT support CPL for the rear camera which makes the video quality not so good thanks to the glare arising from street lights falling on the rear windscreen and panels surrounding it.

Removing the CPL is easy but being able to refit it 'correctly' isn't that easy on-the-go. Every CPL filter requires a minor adjustment to be done to help obtain an almost minimal glare from the front dashboard.

 

[DT MI]

...the A139 Pro 2Ch versions do NOT support CPL for the rear camera...

Look through the DIY forum, there a some threads for putting together polarizing filters that you might be able to use.

DIY Projects

Discuss & share different DIY dash camera related projects

dashcamtalk.com

 

[Nigel]

The A229 Duo or for that matter, the A139 Pro 2Ch versions do NOT support CPL for the rear camera

Image from Viofo of a CPL on the rear camera:

 

[kamkar]

You can be without CPL on the rear camera, but it is a must in my book for the front camera.
I have never seen any brand / model that come with a CPL for the rear camera, not even as a option.
But at least with the wedge shaped remote cameras of old, you was able to put on a CPL filter like you would use on the front camera.

Also us addicts, well we have old CPL filters lying around so we can play with these things for a direct " boldt " on fit, or if not take the DIY route and whip something up.

The later cameras i have tested, well no CPL in the back as like pictured above you dont have a direct fit and so will have to DIY something.

 

[Cyker]

A polarizing filter cuts down maybe 50% of the light because of the way they work - Does this have much of an effect on the image? I imagine during a bright day it wouldn't make any difference, but in low light and night I imagine it would force the dashcam to increase the exposure time significantly, adding to the blur...? Have there been any clear comparisons of CPL vs non-CPL for low-light high-speed motion blur?

Also, I've always wondered - Are the CPLs actually circular polarizers, or are they just linear polarizers that happen to be circle-shaped?
I ask because I've noticed a lot of posts where people have had to rotate them to make them work better, which you shouldn't need to do with an actual circular polarizer... (unless it's on the wrong way round maybe...!)

 

[Landbo]

Do you take it off at night? Is it easy to take off and put back on?
Did you find it necessary ?

If you have no reflections from the window in your camera without a CPL filter, you can do without.

A correctly mounted CPL filter only removes reflections in the image, which means you get a "cleaner" image to look at. The light loss through a CPL filter is negligible. Then just keep your CPL filter on the camera when it's dark, because it also works against reflections from the window there.

 

[Nigel]

A polarizing filter cuts down maybe 50% of the light because of the way they work - Does this have much of an effect on the image? I imagine during a bright day it wouldn't make any difference, but in low light and night I imagine it would force the dashcam to increase the exposure time significantly, adding to the blur...? Have there been any clear comparisons of CPL vs non-CPL for low-light high-speed motion blur?

Also, I've always wondered - Are the CPLs actually circular polarizers, or are they just linear polarizers that happen to be circle-shaped?
I ask because I've noticed a lot of posts where people have had to rotate them to make them work better, which you shouldn't need to do with an actual circular polarizer... (unless it's on the wrong way round maybe...!)

Most of them are circularly polarised, but linear polarisers will work fine. Both need identical correct alignment, your statement is incorrect.

 

[Dashmellow]

The light loss through a CPL filter is negligible.

I'm afraid this statement is not true. The average CPL has an exposure factor (otherwise known as "filter factor" of 3-4 depending on the particular CPL filter used. This means that the CPL will block enough light entering the lens to create an exposure penalty of as much as 1.3 to 2 full ƒ stops. Each smaller ƒ stop aperture (increased filter factor) has half the light-gathering area of the previous one, so 2 full ƒ stops would increase the amount of light required to achieve the same exposure by 4 times.

Even on a sunny day there will be a measurable difference in how sharp an image of a moving object can be captured. While this may seem negligible in brighter light, under low light or cloudy conditions there will be a pronounced increase in motion blur with a CPL compared to the same image captured without a CPL. Of course, this works in concert with the shutter speeds and so results will vary according to the conditions.

A CPL will darken your image by 1.3 to 2 ƒ stops thus causing your camera to compensate by using a longer shutter speed.

 

[Cyker]

Most of them are circularly polarised, but linear polarisers will work fine. Both need identical correct alignment, your statement is incorrect.

Oh, I thought that was the whole point of them! What's the advantage of a circular polarizer over a linear one then...?

 

[DT MI]

A polarizing filter cuts down maybe 50% of the light because of the way they work - Does this have much of an effect on the image? I imagine during a bright day it wouldn't make any difference, but in low light and night I imagine it would force the dashcam to increase the exposure time significantly, adding to the blur...? Have there been any clear comparisons of CPL vs non-CPL for low-light high-speed motion blur?...

In photography the 'average' CPL filter generally causes a 2-4 stop reduction of light. That's roughly 1/4 to 1/16 the amount of light versus no filter. Most(?) dash cams claim to be able to make up to 3 stop adjustments to exposure but this does come at the expense of increasing motion blur and noticeably affecting low light image quality.

In this thread (from long, long ago) I did a comparison of different cameras with and without a polarizing filter.

https://dashcamtalk.com/forum/threa...-sg9665xx-a118xx-and-b40xx.11698/#post-152074

...Also, I've always wondered - Are the CPLs actually circular polarizers, or are they just linear polarizers that happen to be circle-shaped?
I ask because I've noticed a lot of posts where people have had to rotate them to make them work better, which you shouldn't need to do with an actual circular polarizer... (unless it's on the wrong way round maybe...!)

There is a physical difference between circular and linear polarizing filters - the difference is explained in this article.

Linear Polarizer vs Circular Polarizer: What's the difference?

Difference between a linear polarizer and a circular polarizer

www.lindseyoptics.com

Edit: I see @Dashmellow and I were typing at the same time.

 

[Nigel]

Oh, I thought that was the whole point of them! What's the advantage of a circular polarizer over a linear one then...?

A CPL instead of a linear polariser is necessary for use with DSLR Autofocus systems.
For a fixed focus dashcam there is no advantage.

 

[Cyker]

Huh... in that case, why do people even buy these CPL filters?? They're over a tenner! You could just buy a small sheet of self-adhesive linear polarizing film for a few quid, cut it to size and stick it on the lens, no?

 

[DT MI]

...You could just buy a small sheet of self-adhesive linear polarizing film for a few quid, cut it to size and stick it on the lens, no?

Not quite that simple (adhesive directly on the lens is probably not a good idea) but linear material is what I used for DIY filters and it worked well.

 

[Cyker]

Do you have some links with more details of your DIY filters? I just feel the Viofo CPL is extremely expensive for what it is, and if a linear filter works just as well I don't see the point of going to that expense!

 

[DT MI]

Do you have some links with more details of your DIY filters? I just feel the Viofo CPL is extremely expensive for what it is, and if a linear filter works just as well I don't see the point of going to that expense!

For what it's worth this is what I did. There are other examples in the DIY forum. I've gotten lazier since then and am of the mind that a manufacturer provided quality filter is worth the cost if for no other reason than fit, finish and esthetics.

"Poor Man's" Polarizer for SG9665xx, A118xx, and B40xx

Inspired by Niko's DIY polarizer for the SG9665GC and the discussion that followed in this thread - https://dashcamtalk.com/forum/threads/magnetic-cpl-lens-filter-for-street-guardian-sg9665gc.10942/ - I decided to try doing something with items I had laying around the house and that would work...

dashcamtalk.com

This is what it looked like in use.

https://dashcamtalk.com/forum/attachments/sensormount-jpg.28309/

 

[Nigel]

Huh... in that case, why do people even buy these CPL filters?? They're over a tenner! You could just buy a small sheet of self-adhesive linear polarizing film for a few quid, cut it to size and stick it on the lens, no?

A professional filter may be a little better, it might have some anti-reflection coating and better light transmission than would not be found on a plastic sheet, but I have used a plastic sheet plenty of times and not noticed any issues. The Viofo CPLs are decently made, I think the cost is reasonable, but a DIY one will work fine. Decent linear polarising sheet does cost a bit, for most people I think the Viofo one is the better choice.

 

[Landbo]

I'm afraid this statement is not true. The average CPL has an exposure factor (otherwise known as "filter factor" of 3-4 depending on the particular CPL filter used. This means that the CPL will block enough light entering the lens to create an exposure penalty of as much as 1.3 to 2 full ƒ stops. Each smaller ƒ stop aperture (increased filter factor) has half the light-gathering area of the previous one, so 2 full ƒ stops would increase the amount of light required to achieve the same exposure by 4 times.

Even on a sunny day there will be a measurable difference in how sharp an image of a moving object can be captured. While this may seem negligible in brighter light, under low light or cloudy conditions there will be a pronounced increase in motion blur with a CPL compared to the same image captured without a CPL. Of course, this works in concert with the shutter speeds and so results will vary according to the conditions.

A CPL will darken your image by 1.3 to 2 ƒ stops thus causing your camera to compensate by using a longer shutter speed.
View attachment 66604

If that is correct then my statement is not true. LOL

Have a CPL filter sitting on my old DOD dash cam, which won't be coming home until late next week, but never observed any major light loss when I put it on. Maybe it should be peeled off now ?