TonyM
Well-Known Member
- Joined
- Jul 30, 2013
- Messages
- 5,446
- Reaction score
- 5,121
- Country
- United Kingdom
- Dash Cam
- Mobius 1S Telephoto, A139, B1W
For a number of years I have experimented with the use of third-party fixed telephoto and varifocal M12 lenses on a dashcam, the intention being to complement a primary wide-angle dashcam by capturing information that the primary camera might not record. A telephoto lens can do this by recording a narrower angle of view (AOV), thereby increasing the pixels-per-degree across the middle of the scene ahead, and therefore the possibility of higher detail on features such as number plates or the actions of other road users. A telephoto lens can also benefit from metering only the narrower AOV, perhaps ignoring a bright sky or dark dashboard, and can give better results on reflective number plates for example.
For this project I decided to repurpose the interior remote camera of the A139 3CH dashcam and fit a fixed focus 6mm F1.2 starlight lens. Experience has shown that telephoto lenses in the order of 6mm to 8mm focal length have sufficient magnification to make a worthwhile difference over a primary camera (which are approx 2 or 3mm focal length), whilst not over-magnifying the central portion of the scene and suffering too much from vibration, motion blur and depth of field issues.
https://www.aliexpress.com/item/32663560773.html
![1667220750911.png 1667220750911.png](https://dashcamtalk.com/forum/data/attachments/61/61984-aeb1ead3dbe6e3837b2574f6ee568078.jpg?hash=rrHq09vm44)
The remote camera is fairly easy to open, the lens mount is easily accessible, and the lens focus can be achieved without first reassembling the housing.
![1667221010893.png 1667221010893.png](https://dashcamtalk.com/forum/data/attachments/61/61985-0b92e595d5b0f3c48d6715c7966a9483.jpg?hash=C5LlldWw88)
The remote camera is also easy to position on the windscreen, and has a constant-friction stepless up/down angle adjustment.
![1667221041332.png 1667221041332.png](https://dashcamtalk.com/forum/data/attachments/61/61986-077ee6eeaae8f37ac78291071fa0692b.jpg?hash=B37m7qro83)
Note: I started with the interior camera because I am still using the rear remote camera for its intended purpose. However I may in future try the same lens swap with the rear camera to see if it works just the same.
For this project I decided to repurpose the interior remote camera of the A139 3CH dashcam and fit a fixed focus 6mm F1.2 starlight lens. Experience has shown that telephoto lenses in the order of 6mm to 8mm focal length have sufficient magnification to make a worthwhile difference over a primary camera (which are approx 2 or 3mm focal length), whilst not over-magnifying the central portion of the scene and suffering too much from vibration, motion blur and depth of field issues.
https://www.aliexpress.com/item/32663560773.html
![1667220750911.png 1667220750911.png](https://dashcamtalk.com/forum/data/attachments/61/61984-aeb1ead3dbe6e3837b2574f6ee568078.jpg?hash=rrHq09vm44)
The remote camera is fairly easy to open, the lens mount is easily accessible, and the lens focus can be achieved without first reassembling the housing.
![1667221010893.png 1667221010893.png](https://dashcamtalk.com/forum/data/attachments/61/61985-0b92e595d5b0f3c48d6715c7966a9483.jpg?hash=C5LlldWw88)
The remote camera is also easy to position on the windscreen, and has a constant-friction stepless up/down angle adjustment.
![1667221041332.png 1667221041332.png](https://dashcamtalk.com/forum/data/attachments/61/61986-077ee6eeaae8f37ac78291071fa0692b.jpg?hash=B37m7qro83)
Note: I started with the interior camera because I am still using the rear remote camera for its intended purpose. However I may in future try the same lens swap with the rear camera to see if it works just the same.