Laser Rangefinder + Telephoto Dash Cam = Need Help

[Chuck McCoy]

Whenever I get a new dash cam for testing one of the first things I do is check focus.
In the past I’ve been able to do this in my garage, and confirm with driving footage.
But this time I don’t think I’ll be able to that with the A229 Pro & A229 Plus remote telephoto cameras because my garage is too small, so I plan film across the street.
I tried to pace off the distance but I want an exact measurement.
So I ordered yet another piece of test equipment solely for testing dash cams I never thought I would own.
I’m obsessed with being a “finder of fact” given the advertised claims across all brands in the dash cam industry.
First it was a Variable DC power supply for parking mode power consumption.
Then a Thermal Imaging Camera to measure heat signature.
And now a Laser Rangefinder.
I’m feeling in over my head, and this is where you guys come in if you have actual hands on experience, (not just theory) I’m looking at you Nigel. lol

I would first like to know if the Laser Rangefinder I ordered is junk, and should consider a different model.
I spent 24 hours of exhaustive research looking for the best “bang for your buck” option.
I remember seeing these decades ago in my hunter safety course, and they were $500.
I settled on the CIGMAN CT-1000 ($53);
https://www.amazon.com/gp/B0CQ891725

CIGMAN | Professional Laser Level Manufacturer

CIGMAN is committed to manufacturing high-precision laser levels, laser measure, golf rangefinders and other precision instruments to help professionals solve multi-scenario tasks.

cigman.com

I preferred the CT-1000 Pro but, it was ($98), double the cost for OLED Red & Green reticle display, (non-Pro is black).
I can’t wait to tell Ariel I got my first “radar gun” it apparently has a Speed Test Mode. lol
Second I would like to know if there are any special considerations taken into account when testing telephoto dash cams, as opposed to traditional wide angle.
1.) Mounting Location Front Windshield: Center of windshield, or off center closer to oncoming traffic).
2.) Mounting Location Rear window: Center, or off center closer to passing traffic.
3.) Horizon Line Adjustment: Viofo have instructed me to adjust the telephoto cameras with “more road than sky”.
Without a numerical specification, and HLA in the live view of the APP I’m not sure how I can achieve repeatable results.
I’ll start out with my tried & true 50/50 Road & Sky to film baseline test footage so I can confirm & verify “more road than sky” makes an improvement.
4.) Test Mule Ride Height: Car, SUV, 4x4 Truck all have different overall heights that may affect telephoto aiming, and POV.
My test mule is a 2004 Ford Crown Victoria (civilian model).
Front Windshield Mounting Height: 52” inches (132cm)
Rear Window Mounting Height: 55” inches (140cm)
The rear is higher because I installed heavy duty shocks meant for 1997-2003 F-150.

@TonyM
@Mtz
@Nigel
@pinoyplaya4life
@rcg530
@safedrivesolutions
@Vortex Radar
@evad
@kamkar
@viofo
@Karagandinez
@MarcoM
@evmedievalol
@LeadMonkey
@Oban
@Zackw419
@SafetyStealth
@Harsh
@Voldur
@JardaB
@black9white
@Search&Rescue
@Agie
@DoubleDawg
@ogzogz
@DAP
@VIOFO-Support
@Julian23

 

[Vortex Radar]

Has Viofo provided the focal length and aperture of their telephoto lens? If so you can punch those details into a hyperfocal calculator. When a lens is focused at its hyperfocal distance, all objects half the distance to that point all the way to infinity will be in focus.

Also congrats on your first lidar gun! lol. I love the ones with a 7x scope like that. I keep an LTI TruSpeed S in my car (easily one of my fav police lidar guns), because of its compact size and the scope.

 

[Chuck McCoy]

You lost me at hyperfocal. lol
I requested these specs in the same email as the minimum distance to check focus;
Image Sensor
Processor / Chipset
Focal Length
Total Length
F/NO
Mechanical BFL
Optical FOV (D)
Optical FOV (H)
Optical FOV (V)
TV Distortion
Relative Illumination
Chief Ray Angle
Construction (6 Glass + 1 IR-CUT)?
Mount (M12)?
Any other specs we need?

 

[Chuck McCoy]

Also congrats on your first lidar gun! lol. I love the ones with a 7x scope like that. I keep an LTI TruSpeed S in my car (easily one of my fav police lidar guns), because of its compact size and the scope.

What?!?
You mean that’s an actual thing?
I thought is was typical gimmick false & misleading advertising.
Maybe the RDFORUM will get a new member application.
Is it as welcoming, and drama free as DCT?

 

[Nigel]

I would expect the focus to be quite reasonable from 5m to infinity, with best focus at around 25m.

So I'm not entirely convinced that the lidar gun is necessary, I would use a tape for the minimum focus distance, and leave it at that...

Problem is that minimum focus distance is going to be subjective, so maybe the tape isn't useable?

 

[Nigel]

Gray Honda Accord, Blue BMW 3 Series, Black Ford F-250.

If you are doing a test for maximum plate reading distance, they are going to be too close...

 

[Vortex Radar]

Yeah diving into the tech specs may be fun, but I agree that it may not be totally necessary. In practice we should be able to drive around and grab plates farther away than what the wide angle can do, right? Playing around with laser range finders can be a lot of fun, but up to this point I haven't felt the need to use mine when doing any telephoto dashcam testing.

Looking at the sample images you posted above are helpful for seeing the differences in AOV between lens configurations, but even the telephoto one is already beyond the limits of where the dashcam can resolve plates.

Thinking aloud, I suppose when judging the benefits of the telephoto, the main thing to look for is what distance we lose the capability to capture a plate with the wide angle and only the telephoto can do it, as well as what the maximum distance(ish) is for the telephoto. That's gonna vary with movement and lightning of course, just like with a wide angle, but I wonder roughly eyeballing things in terms of car lengths might be more helpful than trying to gauge exact distances?

That said, you could always try doing some stationary tests with both cameras at different distances like 10', 20', 30', etc. and use your range finder for that.

 

[Chuck McCoy]

Yeah diving into the tech specs may be fun, but I agree that it may not be totally necessary.

Whenever I start a test & review I just try to gather all the specs I can for the reader / viewer.

Playing around with laser range finders can be a lot of fun, but up to this point I haven't felt the need to use mine when doing any telephoto dashcam testing.

I think I screwed up my original post in the way I’m describing things.
I ordered the range finder for one simple task.
I just need something to measure distance so I can say I checked initial focus at X distance, before I start driving around gathering test footage.
After that the range finder is not needed.
I usually check focus in my garage, but I thought it would be too small for the telephoto so I planned to film across the street.

Looking at the sample images you posted above are helpful for seeing the differences in AOV between lens configurations, but even the telephoto one is already beyond the limits of where the dashcam can resolve plates.

The two screenshots are from my home security camera just to provide an idea of my testing quarry, and my intended subjects.

So I'm not entirely convinced that the lidar gun is necessary, I would use a tape for the minimum focus distance, and leave it at that...

I think I screwed up my original post in the way I’m describing things.
I ordered the range finder for one simple task.
I just need something to measure distance so I can say I checked initial focus at X distance, before I start driving around gathering test footage.
After that the range finder is not needed.
I usually check focus in my garage, but I thought it would be too small for the telephoto so I planned to film across the street.

 

[Mtz]

I would expect the focus to be quite reasonable from 5m to infinity,

My reasonable distance is starting from 9 m, but I agree, the best focus should be at about 25 meters.

 

[Nigel]

I just need something to measure distance so I can say I checked initial focus at X distance, before I start driving around gathering test footage.

Your garage is probably a bit small, but I would hope to get acceptable focus at only half way across the street.

The important focus distance is the distance at which plates become difficult to read, at 5m a plate is going to be big enough on the image that it can be read even with poor focus, but at maximum plate reading distance, you will want perfect focus. The far distance could be out of focus without it mattering for plate reading, but I would expect that to be in focus anyway.

The interesting distances are the maximum plate reading distances for the main camera and for the telephoto camera. It would be nice to have a maximum plate reading distance for all the cameras, so that people can compare them. For the standard cameras, you can calculate those from your test rig images rather than measuring them. The telephoto will not focus at your test rig distance, but it would probably be easier to extend your test rig by a few meters and then calculate it, rather than use trial and error with a range finder until you find the limit. You may want to extend your test rig anyway, to find the horizontal FoV, since you have that for the main cameras.

Of course, you also want to make sure that the telephoto is sufficiently in focus that it can take over from the main camera at the main camera's maximum plate reading distance, but that is unlikely to be an issue.

In practice we should be able to drive around and grab plates farther away than what the wide angle can do, right?

Depends on what the telephoto camera is for?

I think the main purpose is to read the plates that the main camera fails to read at any distance.
For UK drivers, it is also to record people's bad driving as they disappear into the distance, for reporting them to the police.

 

[Mtz]

I don't think the distance is the problem but the display used for live video from the APP. The WiFi video stream is poor, something like 480p but maybe you can mirror the smartphone screen or use some other trick to get the live feed on a big screen.

By the way, I don't know what is using Viofo to fix the focused lens but people should not use superglue because of the vapors which can enter between lens and CMOS.

 

[DAP]

What are you using for your focus target? I like this test pattern:

That is a jpeg, and not very high resolution. The source is a svg file in the attached zip file.
The idea with this image is to use the camera to take a picture of a high resolution printout of this, and see where it degenerates to grey in the center of the pattern. If it goes to moire patterns, the lens is focusing better than the sensors resolution, if it goes to grey, the sensor has higher resolution than the lens is providing. This should be helpful in finding out the depth of field of the camera and lens. The thumbnail image does a good job of showing what the moire pattern degeneration of the image looks like.
edit: It looks like the thumbnail only shows up when I am editing the post.
Be aware that image compression can make it hard to determine the accuracy of the focus since it tends to delete details.

 

[Chuck McCoy]

What are you using for your focus target? I like this test pattern:

Thank you for stopping in, and the test pattern.
This answers another question I had.
Before checking the focus across the street I plan to measure the Horizontal FOV with my yardstick;
https://dashcamtalk.com/forum/threads/viofo-horizontal-fov-database.50161/
I never knew what background test pattern to use so I just printed sheets that say VIOFO.
My original plan is to film across the street because my neighbor has three cars with license plates that face my garage.
See attached screenshot from my home security camera.
As far as high resolution printout all I have is a Brother HL-L2360D Black & White Laser Printer from 15 years ago.
It won’t die so I just keep using it.
I’ll print that test pattern on the Brother.

 

[Chuck McCoy]

My reasonable distance is starting from 9 m, but I agree, the best focus should be at about 25 meters.

According to my inseam across the street is 25 Meters.
I’ll know for sure when the range finder gets delivered.

 

[ogzogz]

Sometimes technical equipment can be useful. However, in my opinion, primitive alternative solutions can also work.

To give an example, in the various focusing attempts I made, it was not possible to read license plates from long distances, especially at night, with standard cameras. However, I tried to focus as much as I could during the day.
My focus ritual for this is to spot a few lights around at night. One is as far away as a nearby vehicle and the other is a light in the distance. I check how small the farthest light appears by looking at the camera screen (app screen for models without a screen). I also check the nearby light when it seems the smallest. They look good in almost the same environment. I get very good results in subsequent attempts.

If you want to focus during the day, I determine the near and far lines. I create brightness by keeping the camera exposure high. Then I check the lines I determined in the bright areas close to white. Focus is achieved when the lines can be seen.
In fact, as it is known, there are cards used for focusing. The other one I applied also yields the same result. I'm just adapting it to real usage conditions.
There is no clear measurement or distance. However, the method I use may offer you an alternative.

 

[Augustus]

What are you using for your focus target? I like this test pattern:

View attachment 72385

That is a jpeg, and not very high resolution. The source is a svg file in the attached zip file.
The idea with this image is to use the camera to take a picture of a high resolution printout of this, and see where it degenerates to grey in the center of the pattern. If it goes to moire patterns, the lens is focusing better than the sensors resolution, if it goes to grey, the sensor has higher resolution than the lens is providing. This should be helpful in finding out the depth of field of the camera and lens. The thumbnail image does a good job of showing what the moire pattern degeneration of the image looks like.
edit: It looks like the thumbnail only shows up when I am editing the post.
Be aware that image compression can make it hard to determine the accuracy of the focus since it tends to delete details.

My eyes burn from that test pattern ..

 

[TonyM]

I've never measured an actual distance when setting up a telephoto lens. Similar to the comments above, I probably focus on a point around 20-25m away, usually the wall or roof texture on a nearby house.

The aperture of the lens will affect how much in front or behind the focus point will be acceptably sharp. A fast lens (large aperture) will have a shallower depth of field than a slower lens (small aperture).

Your static parked tests will be of some use, but bear in mind that telephoto cameras are more sensitive to movement than wide angle cameras:
1) Moving subjects pass across the sensor at a faster rate than on a wide angle camera, so motion blur is more noticeable, especially in low light conditions. DOL-HDR blur will be more pronounced too.
2) Mount vibration and the general movement of your car will be amplified by the longer focal length.
Due to both of the above, you will often find that you cannot resolve number plates at the same distance as when both camera and subject are stationary.

On a side note, it will be interesting to see how the telephoto compares to the wide angle in terms of metering and HDR. I've found that a telephoto is often less affected by the variable brightness of the sky, usually maintains more consistent metering on the cars ahead, but can be tricked by white or black cars into under- or over-exposing the video.

 

[Chuck McCoy]

Your static parked tests will be of some use

Right on Tony, so glad you showed up.
Yes, I simply want to confirm & verify the test units are in focus before I begin testing with moving targets.

On a side note, it will be interesting to see how the telephoto compares to the wide angle in terms of metering and HDR. I've found that a telephoto is often less affected by the variable brightness of the sky, usually maintains more consistent metering on the cars ahead, but can be tricked by white or black cars into under- or over-exposing the video.

You, and Mtz have solidified my plan to align the telephoto cameras with identical 50/50 Road & Sky along with the A229 Pro Front / Main unit so we can compare the differences, and get baseline test results.
As far as Viofo instructions for “more road than sky” I’ll do that later as part of fine tuning.

My side note:
The telephoto cameras (2) were delivered 15 hours ago, and were sitting on my doorstep unbeknownst to me.
I just discovered the box 30 minutes ago.
It looks like Viofo is using a new delivery service called UNIUNI.
Usually it takes 14 days from Hong Kong to California, (4PX to DHL to USPS to my locked mailbox).
This time delivery was only 7 days (4PX to UNIUNI to Doorstep), my home security camera captured a plain clothes contractor placing the package directly on my doorstep.
Heading out to the garage now to measure the Horizontal FOV.

 

[Nigel]

As far as Viofo instructions for “more road than sky” I’ll do that later as part of fine tuning.

I suspect that is going to be the same as "putting the horizon in the centre", and "aligning the lens horizontal".
Because of the amount of zoom, there will not be a lot of sky, so more road, cars and buildings than sky, is horizontal.
Maybe the 50-50 rule is actually wrong for all cameras, and the rule should be horizontal - horizon in the centre.

 

[Karagandinez]

I suspect that is going to be the same as "putting the horizon in the centre", and "aligning the lens horizontal".
Because of the amount of zoom, there will not be a lot of sky, so more road, cars and buildings than sky, is horizontal.
Maybe the 50-50 rule is actually wrong for all cameras, and the rule should be horizontal - horizon in the centre.

Maybe I understand something wrong, but for me 50/50 means the horizon in the center... 🤔