Nigel, you're making an assumption that the window glass in my ex-police car is bulletproof glass. While it is an ex-police car (former Unit 41 of the San Joaquin County Sheriff's Department in California), it was never fitted with bulletproof glass or door panels. Some police upfitting companies may make such changes, but it's extremely expensive and many departments don't want the spend that kind of money on their patrol vehicles.
My car is a 2014 Chevrolet Caprice PPV (Police Patrol Vehicle). It was manufactured by the former GM Holden division in Australia (before they closed their doors in 2017). The base vehicle is a Holden Statesman and/or Caprice. Holden also manufactured the Holden Commodore VF and VF2 which is what the 2014-2017 Chevrolet SS Sedan was based on.
In the past, I owned a Chevrolet SS Sedan as well and installed dash cams to use and test. The 14-17 Chevy SS Sedan and 14-17 Chevy Caprice PPV are extremely similar in design with a few tweaks to the Caprice PPV for police service. It has a higher capacity alternator to allow it to charge the primary battery and an optional auxiliary battery. The interior of the 14-17 Caprice PPV has many low end plastics used and most of them came with a rubberized floor instead of carpet.
My point being that my 2014 Caprice PPV is for the most part a regular passenger vehicle with subtle tweaks to make it better for police service.
I wonder if it is the bulletproof glass of the police car?
The rear window glass in my car is rated as AS2 glass. AS2 is tempered with at least 70% light transmissions, and can be used anywhere except the windshield.
The windshield is rated as AS1 glass. AS1 is the clearest glass (at least 70% light transmission), is laminated, and can be used anywhere in a motor vehicle (typically just the windshield),
I checked my other two vehicles and their rear window glass are rated as AS3 glass. AS3 can be used in certain locations in certain vehicles (and can be laminated or tempered, and has less than 70% light transmission).
Of the three vehicles I own, my 2014 Chevy Caprice PPV has rear window glass that allows the most amount of light and it has no protection films installed nor any additional window tint installed.
I would be interested to see some raw footage from one of your rear cameras without the rear window glass in the way... see if the softness disappears.
I am doubtful that it is a focus problem given that the furthest point from the lens that is still inside looks perfectly in focus.
There are reflections on the rear glass that don't help, but there are also artifacts that really look like grease/polish or some sort of film that is reducing the clarity of the image.
The only things "on the inside of the rear window glass" are the heat element lines (rear window defroster) and FOB antenna line.
As far as the reflection on the inside of the rear window glass, that comes from the rear deck area behind the rear passenger seat. Most any car that is a sedan, will likely have the same type of rear deck area behind the rear seat. Not everybody drives a SUV (yet).
VIOFO and BlackVue do not offer CPLs for the rear cameras, otherwise I would use one. When I owned my former Chevy SS Sedan (same basic vehicle), I had my Thinkware F800 Pro dash cam installed. When Thinkware started selling their stick on CPL filters, I purchased them for both the front and rear cameras. I don't have that option for the dash cams I'm testing.
I have two screen shots from video I captured today with the A229 Duo rear camera. The first one is when I was backing out of my garage but just before the point when sunlight would hit the deck area behind the rear seat. I wanted to show an example with no reflections in the rear window glass. The clarity/focus of the image is quite good (I had to scale down the image size to allow them to be uploaded to this site).
Now look at the same camera after the camera has been powered up for about 38 minutes. I picked an example with no sunlight reflecting off of the rear deck area. Notice how horrible the focus is now. The speed info shows 17 MPH, but I had just come to a full stop and the GPS speed updated downward a second or so later as I started moving again.
This is the first time I've observed a focus issue get worse the longer the camera is running, but here's one example of that.
I also changed the settings of the T130 and the A229 Duo to turn off the WDR feature. I had to move back to my DR900X-2CH DMS Plus dash cam for my third powered dash cam in the car today (more firmware testing). I installed a CPL I purchased for the T130 front camera and I installed a CPL on the DR900X Plus front camera. As we all expected the windshield reflections were greatly reduced for those two cameras. I don't have an extra CPL that will fit the A229 Duo, so it was run without a CPL today (I ordered one and I hope to get it tomorrow).
The T130 front camera video looks much better with the CPL on during the daytime. The A229 front camera video looks good as well except for the windshield reflections.
The DR900X Plus front camera video has better colors as well, but there appears to be a focus issue with that camera. The left side is in focus, but gets worse if as you go the right in the image.
