Linus tech tips on dashcams.

[Dashmellow]

A 4k camera with with normal FoV could capture all those plates too.

Perhaps a 4K might have captured those plates but not with that angle of view or at the distance I was from the subjects, nor without having to zoom in and crop from a larger image in post.

There's been no evidence you have any personal experience with telephoto dash cams, so how can you even make such comments when you don't know what it's like to use one? You're comparing apples to oranges here.

What do you consider to be a "standard wide angle dash cam"?

Any typical commercial dash cam as opposed to a custom telephoto camera.

 

[Nigel]

Perhaps a 4K might have captured those plates but not with that angle of view

If we are comparing a 4K "normal" sensor/lens with an FHD x2 telephoto sensor/lens, then you should be able to use the digital zoom function of your video player to zoom in to the 4K video and get exactly the same field of view with exactly the same detail.

Our 4K lenses tend to be a little wider than normal, so generally the 4K dashcam image has a little less detail, but you don't appear to be recommending a long telephoto like DAP's anyway, so there is not going to be much difference.

How much telephoto are you recommending - x2, x3 x4?

 

[Dashmellow]

If we are comparing a 4K "normal" sensor/lens with an FHD x2 telephoto sensor/lens, then you should be able to use the digital zoom function of your video player to zoom in to the 4K video and get exactly the same field of view with exactly the same detail.

Our 4K lenses tend to be a little wider than normal, so generally the 4K dashcam image has a little less detail, but you don't appear to be recommending a long telephoto like DAP's anyway, so there is not going to be much difference.

How much telephoto are you recommending - x2, x3 x4?

You obviously don't understand what using a telephoto camera is all about. Recording to a telephoto camera full time provides unique, very useful and often fascinating footage you would never capture or see even if you can zoom in to an individual frame of interest on 4K. Like DAP you are making personal assumptions, expressing opinions and reaching conclusions based on speculation, without any hands-on experience with these lenses or footage. Plus as you know, 4K has many drawbacks regarding low light capture, heat and memory requirements.

As for "zooming" in to a 4K video, I can see from many of your comments that you've never had to submit raw, unedited footage to law enforcement, a court of law or an insurance company. Once you hand off your video to the authorities nobody is going to do any "zooming in" on a frame in live footage you've submitted. And as I've often pointed out, many law offices, insurance companies and law enforcement agencies do not yet have computers, graphics cards or monitors that can properly handle 4K video or imagery.

Another thing to add is that with a full frame video or screen grab from a telephoto dash cam, you get the time and date stamp that you would not get by zooming into or cropping from a 4K image, so it make for more defintive evidence.

As for DAP, he may capture a limited number of plates if they happen to fall within the tiny over-magnified angle-of-view he created but he will miss far more plate numbers than he captures, including likely key evidence when the critical moment arises if the plate he needs to capture is not dead center in front of him.

As to how much telephoto magnification I prefer to use, these screen grabs offer a good illustration. Of course, this is why @Vortex Radar selected these examples for his video. As I've mentioned several times already, the consensus among the growing core group of DCT members who've adopted using telephoto lens cameras, an 8mm matched to a camera with a 1/3" sensor seems to be the sweet spot for telephoto magnification. Keep in mind that over the last 5 years of using various telephoto lenses and configurations I do periodically experiment with focal lengths and alternative lenses. These days I opt for a slightly wider view than I began with 5 years ago.

One of the whole points of using a telephoto is to have an ancillary AOV perspective to your main camera that also acts as a back-up to the main camera. Both cameras working in concert tell the story.

 

[Dashmellow]

I like to capture at least two lanes of traffic. I sometimes point my telephoto slightly to the left to better capture oncoming traffic. That effect is slightly exaggerated here due to the angle my vehicle is facing as I entered the lane.

(Note that again the camera captured a license plate through the glass of the vehicle in front of me. )

 

[Nigel]

As to how much telephoto magnification I prefer to use, these screen grabs offer a good illustration.

That shows x4, so I assume an 8mm coupled with a small sensor...

DAP's videos show that he has x4.17, so pretty much the same magnification...

And yet you write:

As for DAP, he may capture a limited number of plates if they happen to fall within the tiny over-magnified angle-of-view he created but he will miss far more plate numbers than he captures, including likely key evidence when the critical moment arises if the plate he needs to capture is not dead center in front of him.

(Note that again the camera captured a license plate through the glass of the vehicle in front of me. )

My 4K dashcam can also see through glass, nothing special about that, they all have to look through our own windscreens! Although with this example it would be at the limit of resolution, so maybe wouldn't actually read the plate, wouldn't quite read the "Vermont" at the top of the plate on the previous image either.

Realistically, you are achieving 2x more resolution than a 4K dashcam with a normal FoV would, the same as an 8K dashcam would produce across 4x the field of view.

For plate reading, probably better off investing in a Starvis-2 4K dashcam, once they are available, unless your roads are a lot smoother and straighter and better illuminated than my roads.

 

[Dashmellow]

That shows x4, so I assume an 8mm coupled with a small sensor...

DAP's videos show that he has x4.17, so pretty much the same magnification...

And yet you write:



My 4K dashcam can also see through glass, nothing special about that, they all have to look through our own windscreens! Although with this example it would be at the limit of resolution, so maybe wouldn't actually read the plate, wouldn't quite read the "Vermont" at the top of the plate on the previous image either.

Realistically, you are achieving 2x more resolution than a 4K dashcam with a normal FoV would, the same as an 8K dashcam would produce across 4x the field of view.

For plate reading, probably better off investing in a Starvis-2 4K dashcam, once they are available, unless your roads are a lot smoother and straighter and better illuminated than my roads.

True, other cameras can see through windshields, but not quite as consistently or as well as my telephoto. It's not really an important aspect of why one would want a telephoto though. It was just an interesting anecdotal thing I tacked on the end of my post. It seems typical of you to repeatedly dwell on something like this as a way of sidestepping everything else I've said. As always Nigel, you elide practically everything I say in my posts because you haven't really much of anything worthwhile to offer other than what you've done here today in what amounts to a daylong, gratuitous, petty argument caviling against the concept of telephoto lens dash cams.

I often wonder why you so often initiate spats like this and demand that anyone and everyone adhere to your personal preferences about how to use dash cams or what kind of camera or lens is best. (If it's not a Viofo you often act with disdain apparently because you are one of their loyal forum operatives.)

I recall recently when you insisted that EVERYONE should use 2560x1080 resolution because that is YOUR preference, stating that "you do not need the sky, because you are not recording meteors, and do not need the front of your car and part of your dash in the image, because they never change and there is nothing interesting there anyway", BUT that's been demonstrated not to be true at all and many here do not agree with you, preferring instead 2560 x 1440 resolution to capture things like overhead traffic lights or side impacts to your fenders. You engaged in a very similar argument not long ago as well about whether to include your car's hood when you aim the camera, which you seem to think is completely unnecessary but many others find important to include. The fact is Nigel, that people should do what they find works best for them based on their own personal experience and preferences rather than what some overweening guy who spends most of his waking hours on a web forum proclaims is best for them.

And now, here you are insisting in post after post that a 4K camera is superior and preferable to a separate telephoto regardless of the fact that you've never pesonally experienced using one. And speaking of ignoring what I say in my posts you completely disregard the concerns I've raised about the impracticality of 4K cameras in regard to heat, memory requirements, the prospect of handing off video to parties who don't have 4K monitors or graphics cards, etc. etc.

Personally, I have ZERO interest in owning a 4K camera as my preference is 2K cameras which I consider the perfect "sweet spot" for dash cam resolution. And I much prefer the telephoto cams I've built as a secondary angle of view camera rather than having a single unit to rely upon. I find telephoto cams to be practical, extremely useful, fun and interesting. I capture all kinds of interesting and unexpected things typical dash cams miss and that I wouldn't go hunting for by zoom in or cropping indivdual 4K frames. Telephoto cams have opened up a world that previously never existed in dash cams and that is the reason so many have expressed an interest in them. Indeed, I think you'd be quite surprised by just how many DCT members have adopted them. Some remain quiet once they are up and running, or maybe they check in with a question now and again but I hear from them all the time. None of them would likely trade in their telephoto for a single camera. Then again, they've experienced them first hand rather than making opinionated assumptions.

If you don't like the concept and don't wish to use a telephoto lens, then fine, but who the hell are you to dictate what others should or shouldn't do?

And why do you keep using the term FOV? The appropriate term here is AOV.

And just what they hell is this "unless your roads are a lot smoother and straighter and better illuminated than my roads" business all about? This comes across as more of your habitual UK vs USA nation bashing? Explain yourself please!

 

[Kremmen]

Those images above are very sharp and almost unbelievable from any dashcam. I can see a lot wanting and striving to get that quality.

For me though, I look at what my V3 is returning and compared to my old Nextbase models it's superior in so many ways that I'm happy the footage would be ample if needed in earnest.

As it is I just use it to identify speed cameras type and exact location for another website I frequent as a 'verifier'.

 

[Dashmellow]

Those images above are very sharp and almost unbelievable from any dashcam. I can see a lot wanting and striving to get that quality.

For me though, I look at what my V3 is returning and compared to my old Nextbase models it's superior in so many ways that I'm happy the footage would be ample if needed in earnest.

As it is I just use it to identify speed cameras type and exact location for another website I frequent as a 'verifier'.

As I've tried to explain, I use the telephoto Mobius along with an A119 V3 and it is both cameras working in concert with one another that makes for such a winning combination. The telephoto alone would not make for a fully effective dash cam despite how well it can perform.

 

[TonyM]

Currently the 2K cameras tend to give the best results on motion blur, not always, depends on lighting, speed, distances, etc., but on average it is the 2K camera that wins, not the 4K that can see further.

I've been wondering what the ideal base (camera & sensor) would be for a telephoto dashcam. Is low light capability important? How about motion blur, given the higher magnification? For capturing licence plates, maybe an HDR telephoto makes sense?

A number of us started out with a 1080p Mobius because it was easy to work with. The video quality is very good in daylight, but drops off in low light. The physical format allows users to be creative in how they mount the telephoto camera.

Currently I am experimenting with a telephoto lens on a 4K Mobius. In good light the detail is fantastic, but again the performance drops in low light.

I wonder if a telephoto dashcam based on the A119V3, or another camera with the IMX335 sensor, would be better? Could be interesting with the HDR.

Some members have tried using the remote rear camera from a 2ch system. It's a lower cost than experimenting with a primary camera, however these rear cameras are often lower resolution and/or have a lower bitrate than front facing cameras.

 

[Nigel]

I've been wondering what the ideal base (camera & sensor) would be for a telephoto dashcam. Is low light capability important? How about motion blur, given the higher magnification? For capturing licence plates, maybe an HDR telephoto makes sense?

If you are sitting still at the lights in bright lighting, as in Dashmellow's images, then motion blur isn't much of an issue. If you are driving on bendy UK winter roads, with trees alongside the road and roundabouts instead of lights, so instead of stopping you sweep your telephoto around an arc, with it pointing at the wrong lane, then motion blur is definitely an issue. For my driving, I find that motion blur is most often the limiting factor, for me it is the most important thing to improve. I rarely want more magnification than I can get by zooming into a A129 Pro 4K video.

Currently I am experimenting with a telephoto lens on a 4K Mobius. In good light the detail is fantastic, but again the performance drops in low light.

So an IMX317?

I wonder if a telephoto dashcam based on the A119V3, or another camera with the IMX335 sensor, would be better? Could be interesting with the HDR.

Yes, I think so, but it won't be a big difference, not really enough to bother trying, especially as you will lose some control over exposure settings.

I think it is best to think of increased sensor resolution as giving you a wider FoV rather than allowing more magnification. Having chosen a resolution, you can easily get to the magnification limit by choice of lenses, and it occurs at about the same detail whichever resolution you choose. The IMX335 has a small sensitivity improvement over the IMX317, the IMX291 has a small sensitivity improvement over the IMX335. So I think DAP probably has the best implementation of a telephoto, if he is happy with the small FoV (it is a bit too small for my liking, I would prefer a 2K sensor at that magnification). Of course some lenses are better than others, and better matched to the sensor than others, and that can have an effect, I don't know how good DAP's lens is.

The FHD Mobius sensor was a good sensor last decade, but it is not as good as any of those newer Sony sensors.

Some members have tried using the remote rear camera from a 2ch system. It's a lower cost than experimenting with a primary camera, however these rear cameras are often lower resolution and/or have a lower bitrate than front facing cameras.

As I said above, DAP's IMX291 is probably the best choice at the moment if you are happy with the FoV, if not then the rear camera on an A229 with the IMX335 sensor would be a good choice. Bitrate is definitely an issue though, not too bad when you are moving slowly in good light, but these rear cameras all tend to be rather poor in low light, I think more because of how the codec responds to low light + low bitrate than anything else.

So my current choice of camera for mounting a telephoto lens, assuming the aim was to read license plates, would be an A119 V3 "front camera" with about 2x magnification compared to the standard A119 V3. (2x gives it more detail than a switch to 4K would, plus the A119 V3 already has a narrow FoV compared to an A129 Pro.)

 

[TonyM]

I wonder if a telephoto dashcam based on the A119V3, or another camera with the IMX335 sensor, would be better? Could be interesting with the HDR.

Yes, I think so, but it won't be a big difference, not really enough to bother trying, especially as you will lose some control over exposure settings.

I have an unused T130 sitting in a box. Might be worth trying a lens swap, even though I don't think HDR is available on that model.

 

[Nigel]

I have an unused T130 sitting in a box. Might be worth trying a lens swap, even though I don't think HDR is available on that model.

It would be interesting to turn the interior lens to face the front and use that as a wide angle. It is low bitrate, but you don't really need high bitrate for a wide angle view since you are not trying to read plates, then use the front lens for a modest telephoto to read the plates. Not sure why the interior lens can't currently be rotated to face the front, maybe there is a stop that can easily be removed.

 

[Dashmellow]

If you are sitting still at the lights in bright lighting, as in Dashmellow's images, then motion blur isn't much of an issue. If you are driving on bendy UK winter roads, with trees alongside the road and roundabouts instead of lights, so instead of stopping you sweep your telephoto around an arc, with it pointing at the wrong lane, then motion blur is definitely an issue

A year ago, you made the exact same assertion regarding "sweeping your telephoto around an arc, with it pointing at the wrong lane, then motion blur is definitely an issue" which i debunked with the following video, yet here you are repeating it. It is remarkable how you continually make definitive pronouncements about how telephoto lenses function on dash cams regardless of the fact that you have no personal experience using one. So much of what you've asserted in this thread is based entirely on speculation or assumption in lieu of actual experience.

Like any dash cam, telephoto dash cams are prone to motion blur in many situations but they can also be less prone to motion blur in other situations because they are capturing objects at a greater distance.

This footage was taken on an overcast day.

Here is another example of panning with a Mobius fitted with a telephoto on an overcast day, in the case making a 90º left hand turn - along with plate captures of vehicles approaching each other at speed.

NIgel: If you are sitting still at the lights in bright lighting, as in Dashmellow's images, then motion blur isn't much of an issue.

Also, FWIW, in the screen shot with the red VW GTI and Subaru Legacy, things are not quite so static as you may think and despite your claim about how bright the light is it is an overcast day.

This footage presents a very detailed story about what is happening out in front of you that a wide angle dash camera could never really tell you. It is the reason so many members (there are quite a few) have become interested in and have been experimenting with secondary telephoto dash cams.

 

[TonyM]

Comparing 100% crop from 3 cameras

A139 - 5MP (CPL)


Mobius 4K (same sensor(?) and similar AOV to A129 Pro) (no CPL)


Mobius 4K with varifocal lens at approx 2x zoom (CPL):


I can understand the opinion that 4K resolution with approx 130deg AOV is 'enough', to resolve licence plates or identify another driver at a reasonable distance - perhaps 15m to the white car in this example. Using a '2x zoom' on a 4K camera resolves a whole load of detail in the middle 1/4 of the frame, but do we need to read plates at 30m? As a second camera it's nice to have though, and makes it easier to identify the driver of the white car or see if they're holding a phone while driving.

 

[Lothar]

So I just finished up a second followup video taking a look at police ALPR systems, how they're designed, how they're different than dashcams, and what it would take for our consumer grade dashcam to do something similar.

It is possible to freeze plates better than our current dashcams are able to, but it would require a different camera design.

Also shoutouts to @Dashmellow and @TonyM in this video.

I wouldn't mind a proper re-do of the A139 from Viofo.
Instead of the interior camera, it can be an exterior camera with a 2K varifocal telephoto lens!

A telephoto lens would certainly be more useful for me than having an interior camera.

 

[Dashmellow]

I wouldn't mind a proper re-do of the A139 from Viofo.
Instead of the interior camera, it can be an exterior camera with a 2K varifocal telephoto lens!

A telephoto lens would certainly be more useful for me than having an interior camera.

The idea for this concept was proposed more than four years ago here on DCT as a result of what was then the recently introduced technology of dual channel dash cams. There was a lot of interest in the idea but the consensus was that a varifocal lens wouldn't be a good idea for a commercially produced dash cam due to the challenges of adjusting and properly focusing such a lens. It was agreed that a well chosen fixed focus telephoto lens on a cable would be the best option so that the average dash cam buyer could install one without having to hassle with it. When you allow the customer to adjust the focus it can lead to much frustration and product returns. (according to Mobius)

 

[Lothar]

The idea for this concept was proposed more than four years ago here on DCT as a result of what was then the recently introduced technology of dual channel dash cams. There was a lot of interest in the idea but the consensus was that a varifocal lens wouldn't be a good idea for a commercially produced dash cam due to the challenges of adjusting and properly focusing such a lens. It was agreed that a well chosen fixed focus telephoto lens on a cable would be the best option so that the average dash cam buyer could install one without having to hassle with it. When you allow the customer to adjust the focus it can lead to much frustration and product returns. (according to Mobius)

Then an exterior camera with 2K fixed 8mm telephoto lens should work?

 

[TonyM]

It was agreed that a well chosen fixed focus telephoto lens on a cable would be the best option so that the average dash cam buyer could install one without having to hassle with it.

Then an exterior camera with 2K fixed 8mm telephoto lens should work?

2-channel or 3-channel systems with remote cameras could in theory have modular options for buyers (2x interior cameras for an A139 anyone??). I believe SG have an optional external waterproof camera for their latest 2CH offering.

If it was commercially viable a manufacturer might go for it. Until then you're left with DIY and choosing a platform that's best or easiest to work on. The A229 with a remote 'rear' 2K camera might be a decent option.

 

[Dashmellow]

Then an exterior camera with 2K fixed 8mm telephoto lens should work?

The choice of focal length would ultimately depend on the size of the sensor in the camera. The 8mm consensus was based on the Mobius 1 camera that has a 1/3" sensor.

I'm not clear why you would want an exterior telephoto camera but it could certainly be an option. Exterior cameras can be problematic though due to road dirt, raindrops - even with a hydrophobic lens coating, or snow covering the lens, plus wind driven particles pitting the lens surface. Placement and mounting may also be issues. As I recall, the waterproof external SG cabled camera module is intended for rear mounting so wind driven particles that can damage the lens surface would not be as much of an issue, even if the other factors might be. My preference is to have the lens protected by the windshield with the wipers keeping the view clean and with the camera mounted as high as possible in my vehicle.

In our original discussions about the concept a typical wedge style wide angle dash cam was envisioned with a telephoto lens module on a short cable of several inches that could be mounted nearby on the windshield and individually aimed. As @TonyM suggested, a modular approach could offer any desired option.

 

[Lothar]

The choice of focal length would ultimately depend on the size of the sensor in the camera. The 8mm consensus was based on the Mobius 1 camera that has a 1/3" sensor.

I'm not clear why you would want an exterior telephoto camera but it could certainly be an option. Exterior cameras can be problematic though due to road dirt, raindrops - even with a hydrophobic lens coating, or snow covering the lens, plus wind driven particles pitting the lens surface. Placement and mounting may also be issues. As I recall, the waterproof external SG cabled camera module is intended for rear mounting so wind driven particles that can damage the lens surface would not be as much of an issue, even if the other factors might be. My preference is to have the lens protected by the windshield with the wipers keeping the view clean and with the camera mounted as high as possible in my vehicle.

In our original discussions about the concept a typical wedge style wide angle dash cam was envisioned with a telephoto lens module on a short cable of several inches that could be mounted nearby on the windshield and individually aimed. As @TonyM suggested, a modular approach could offer any desired option.

By exterior, I mean one facing the front...and not one facing the interior.
I did not mean to say a camera outside my car if that is what you're getting at.