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.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.Do you take it off at night? Is it easy to take off and put back on?
Did you find it necessary ?
Look through the DIY forum, there a some threads for putting together polarizing filters that you might be able to use....the A139 Pro 2Ch versions do NOT support CPL for the rear camera...
Image from Viofo of a CPL on the rear camera:The A229 Duo or for that matter, the A139 Pro 2Ch versions do NOT support CPL for the rear camera
Do you take it off at night? Is it easy to take off and put back on?
Did you find it necessary ?
Most of them are circularly polarised, but linear polarisers will work fine. Both need identical correct alignment, your statement is incorrect.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...!)
The light loss through a CPL filter is negligible.
Most of them are circularly polarised, but linear polarisers will work fine. Both need identical correct alignment, your statement is incorrect.
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?...
There is a physical difference between circular and linear polarizing filters - the difference is explained in this article....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...!)
A CPL instead of a linear polariser is necessary for use with DSLR Autofocus systems.Oh, I thought that was the whole point of them! What's the advantage of a circular polarizer over a linear one then...?
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....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?
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.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!
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.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?
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.
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