Viofo VS1 (Novatek NT96565, unboxing & first impressions) (Sony IMX675, HDR, GPS, 5Ghz WiFi, 2.5K video quality)

[Nigel]

What level of reduction of incoming available light, how many 'stops' is expected from using a CPL, if any, and especially at night?

I have not tested this particular CPL, but in general you will reduce the light by 1 stop, and that is likely to increase the exposure time by x2, resulting in 2x the motion blur and no other changes. There will be times when the camera changes the ISO instead, but it is fixed aperture and a dashcam should use the highest ISO possible with reasonable quality, so normally the effect is extra motion blur. The HDR fast frame will likely stay the same speed, so for the highlights, such as reflective plates at night, this may reduce over exposure a little rather than increase motion blur, and at night there will probably be some plates, not quite in the headlamp beam, that the HDR decides not to process so become totally blurred instead of sharp, or maybe they slip out of HDR a couple of frames earlier than they would otherwise do.

Some people will say that it must be more than 1 stop, but some of that more is reflections that we don't want. Out of the light that we do want, it will be very close to 1 stop.

Removing reflections generally makes the job of the video codec a lot easier, since then the whole scene is moving consistently rather than the main image moving but overlayed by non-moving reflections, so then the bitrate can be used more effectively and the image quality and detail will increase. Since the VS1 is not particularly high on bitrate, this may make a significant improvement to image quality, depending on how bad the reflections are in your car, having a ventilation grill reflection particularly prominent can use up a lot of bitrate.

Overall, CPLs are normally worth having, day and night.

 

[kamkar]

For sure, i would not run ANY dashcam without CPL, it is a absolute MUST HAVE in most cars.

Granted reflections dont block much evidence you might record, but the presence of it i think make the camera have to work harder.

 

[Agie]

For sure, i would not run ANY dashcam without CPL, it is a absolute MUST HAVE in most cars.

Granted reflections dont block much evidence you might record, but the presence of it i think make the camera have to work harder.

This. It's my go-to now if there is an option for CPL for a dashcam

 

[Paul Iddon]

In photography circles a CPL loses generally between 1.5 and 2 stops of light.

 

[Nigel]

In photography circles a CPL loses generally between 1.5 and 2 stops of light.

I've never worked out why they make most photograph CPLs quite dark? They are not all dark, some are quite close to 1 stop, but most are closer to 2, and some are 3 stops.

 

[cozzykim]

I've never worked out why they make most photograph CPLs quite dark? They are not all dark, some are quite close to 1 stop, but most are closer to 2, and some are 3 stops.

I was thinking that that would reduce the shutter speed in the VS1, and reduce the reported over sharpening.

 

[Nigel]

I was thinking that that would reduce the shutter speed in the VS1, and reduce the reported over sharpening.

It will reduce the shutter speed to approximately half, not so good around dusk, but most of the time it results in little difference.

I don't think it will have much effect on the sharpening, in most situations. The sharpening is a digital filter that only effects fairly high contrast edges, and since a CPL tends to increase contrast, the CPL may actually increase the sharpening. I wouldn't worry about it though. The sharpening on the VS1 isn't too bad, it could be better, but I think the reason it is worse than, for example the A119 Mini 2, is the use of an older and cheaper processor for the cheaper dashcam. Compare it to last generation dashcams, and it is fairly normal. Most of the time it makes plates more readable rather than less, it tends to only be a noticable issue on high contrast road signs and overhead power cables, which are never very important for evidence purposes. It was also improved in a firmware update.

I've never worked out why they make most photograph CPLs quite dark?

For those that are technically minded, and somewhat knowledgable about the physics of polarised light, the top answer is an interesting read:

Why don't circular polarizers reduce light transmission by just one stop?

I assume that an ideal circular polarizing filter should cut light transmission by exactly half – i.e., 1 stop – because every photon has (on average, with respect to a filter) either one of two ci...

photo.stackexchange.com

In summary, I think the answer is, because photographers tend to use CPLs in bright sunshine, when having a neutral density filter built into your CPL may be an advantage, at least for analogue film cameras!

Viofo do normally make a good effort to source filters that are high transmission and have reasonable anti-reflection coatings, they will be reasonably close to 1 stop.

 

[Dashmellow]

I've never worked out why they make most photograph CPLs quite dark? They are not all dark, some are quite close to 1 stop, but most are closer to 2, and some are 3 stops.

The quality and light transmission of a polarizer depends very much on cost, design, type of glass, thickness and coating technologies employed in their manufacture.

HOYA is known as the manufacturer of the finest CPLs in the world, especially their HD line of polarizers, which is now in their 3rd generation (HD3). It loses only 1 stop compared to their other offerings. Notice how much lighter it is than the others in the collection below. Check the specs on each of the models to see the transmission differences on each of those. I happen to own an original 1st generation HD1 version and it is quite impressive. They are rather pricey, however.

Circular Polarizer

Top 5 Reasons To Own a Circular Polarizer Controls reflections on glass, water, leaves, and sky. Improves contrast Increases color saturation Removes atmospheric haze Provides 1-2 stops of Neutral Density for longer exposures

hoyafilterusa.com