Questions about RV Daheng low distortion lens for David SLS-2 projector K132

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mdesign
Posts: 37
Joined: 03 Jan 2022, 14:51

Questions about RV Daheng low distortion lens for David SLS-2 projector K132

Post by mdesign »

Hi, I`m David SLS-2 user (David 4 with single cam 3.1MP - I used that for many years with success) and a RangeVision user (fresh user). I`ve bought RangeVision software and 2 Daheng MER2-630-60U3M.

I would like to buy lenses for Range Vision (Daheng camera) and I`ve thought about a couple ZLKC (I may buy something different but I don`t want to go much more expensive).

I know that I should think about pixel size value (aka pixel pitch) what is in the Daheng cameras about 2.4uM.

I scan often 1-4 meter objects and I have a problem with deviation along with scans so I`ve thought to buy a low distortion lens for the bigger sensor.
Using a bigger sensor lens on a smaller sensor camera will give you smaller errors near frame edges of the lens view (IMO).
I think I should buy 10MP ZLKC camera for that Daheng MER2-630-60U3M.

8mm ZLKC: https://www.aliexpress.com/item/3295953 ... 7514sodTcc
12mm ZLKC: https://www.aliexpress.com/item/3296590 ... 7514sodTcc
16mm ZLKC: https://www.aliexpress.com/item/3296967 ... 7514sodTcc
25mm ZLKC: https://www.aliexpress.com/item/3296022 ... 7514sodTcc

1) What lens could you recommend me for using with RangeVision and Daheng MER2-630-60U3M and ACER K132 (original David SLS-2 projector with projector lens modified for shorter throw projection)?
2) What lens could you recommend to me for the same setup as above if important would be to have low distortions with long 2-4m scans which would contain many patches in one line?
3) What lens focal length do you use with the SLS-2 projector and Range Vision? (I know that focal length fitment depends on lens size too)

I have used David on small and big objects. I`ve scanned with it jewellery and big cars but I can`t update to David 5 anymore and I would like to evolve. Another thing I`m tired of with "banana-like" scans on long objects and I think that with a better lens my scans should be more straight because it`s the fault of lens distortion.

This is my sample use of SLS-2 David 3.1MP camera with a 12MP lens: https://skfb.ly/ootwu
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OBNRacerMan
Posts: 372
Joined: 12 Aug 2019, 09:46
Location: Obninsk, Russia

Re: Questions about RV Daheng low distortion lens for David SLS-2 projector K132

Post by OBNRacerMan »

Unfortunately, I didn’t have any experience with a projector like yours. But for large scanning areas, the most versatile (for many scanner models) is a 12mm focal length lens. 16mm is needed for scanning small objects, and 25mm for very small objects. I am starting from the basic scope of delivery of the Rangevision Pro scanner, whose kit includes three sets of lenses - 12.5mm, 16mm and 25mm
I myself use 16mm ZLKC 10MP lenses because my main interest is in scanning small things.
Also, I did not notice any difference in image quality between the ZLKC 5MP and 10MP lenses. Recently I tried to install the Fujinon HF12.5HA-1B lenses (12.5mm with 1.5MP resolution) purchased for my second scanner - and still the scan quality was very good.

The best option for choosing a lens for a specific projector is to measure the size of the light projection at a certain distance and, then, using an optical calculator, select the most appropriate focal length value.
guide_01.jpg
Unfortunately, I do not know any English-language counterparts of such calculators.
Soft: RangeVision DIY, Calibration panel/Rotary tables - RangeVision, Prj: LG PF1500G, Cam: Daheng Mercury MER2-630-60U3M-L (USB3.0, monochrome) x2, Obj: ZLKC FM12036MP5 (F2.8/5Mp/12-36mm) x2. And a handheld scanner Creality Ferret
mdesign
Posts: 37
Joined: 03 Jan 2022, 14:51

Re: Questions about RV Daheng low distortion lens for David SLS-2 projector K132

Post by mdesign »

Thanks for your answer. Cyrillic is not a problem (google translator ;) ). Where can I find that calculator?

The first thing is a theory (I can be wrong).
lens distortion.jpg
IMHO a bigger sensor lens for a smaller sensor camera should have more straight lens area (in a narrower view) what should cause less distortion near frame edges. This will be visibly noticeable IMO on closeups (smallest possible area of scanning) and on thin long objects: like straight wooden plank 3m x 15cm. After scanning that kind of plank with 15cm patches you will have a banana shape instead of straight lines. It`s because the curvature of the lens causes that kind of barrel distortion.

Second thing is that 12mm will be something different for a couple of Daheng 6MP + 6MP lens and Daheng 6MP and 12MP lens. Both 12mm will coverage dramatically different areas (different angles of viewing). As I`ve drawn above, the real view of the 12MP lens on the 6MP camera will be much more narrow than the 12mm 6MP lens on the same camera.

Maybe it`s only theory and it`s too small a difference to be noticed. Maybe it would be more visible on a 1GP lens covering a 6MP camera.

This is table from aliexpress of ZLKC 12MP. You can see how the angle of view changes with decreasing sensor size. A more narrow look means more flat lens surface what should mean less barrel distortion and more flat lens area (what should cause better scans in the final).
angles of views.jpg
angles of views.jpg (11.28 KiB) Viewed 8898 times
Maybe ZLKC has not so good quality to be seen. Maybe it could be visible on high-quality Tamron or other more expensive brands with low distortion lenses which are many times more expensive than ZLKC.

I have one 16mm 12MP Tamron c-mount with very good parameters (cost of 6 x ZLKC10MP 12mm). I have a fight in my head. Should I risk and buy a second Tamron for my setup or better to buy two ZLKC 10MP what should be a lot cheaper. I`m not sure If I will see any differences in the final scans. as you said because it`s only theory.

Second thing is that David projector (Acer K132) is only 1280x720 so it will be a bottleneck for sure (I can change it in future).

The bad quality of scans is not the worst thing for me on the David SLS-2 bundle. The worst thing is the banana shape on long thin objects with many patches. Because each patch is representing a real shape only near the centre of the frame. I know that I could stay with David and bigger lens but I would like to evolve. That`s why I`ve chosen RV (I`ve thought also about FlexScan- maybe in future).
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OBNRacerMan
Posts: 372
Joined: 12 Aug 2019, 09:46
Location: Obninsk, Russia

Re: Questions about RV Daheng low distortion lens for David SLS-2 projector K132

Post by OBNRacerMan »

The initial curvature of a 12mm / 10MP objective lens does not differ from a 12mm / 5MP objective - this value is only an indicator of the quality of the lenses and their maximum resolution according to a special measuring world.
The very distortions introduced by the lenses are compensated (to some extent) in the scanning program itself, based on the analysis of the reference points of the calibration table.
But the size of the camera matrix, and the one for which the lens is designed - plays a role. And a lens for a 2/3 "sensor on a 1 / 1.8" camera will actually "crop" edge distortion. It should also be taken into account that when cropping onto a smaller sensor, the focal length of the lens will be slightly larger than what is written on it (for example, 12mm for 2/3 "on a 1 / 1.8" sensor will be about 13.5mm (unfortunately, I don't know how to calculate the real focal length for such a situation)).

Optical calculator address
Soft: RangeVision DIY, Calibration panel/Rotary tables - RangeVision, Prj: LG PF1500G, Cam: Daheng Mercury MER2-630-60U3M-L (USB3.0, monochrome) x2, Obj: ZLKC FM12036MP5 (F2.8/5Mp/12-36mm) x2. And a handheld scanner Creality Ferret
mdesign
Posts: 37
Joined: 03 Jan 2022, 14:51

Re: Questions about RV Daheng low distortion lens for David SLS-2 projector K132

Post by mdesign »

Thanks a lot. Maybe you are right. It`s more the matter of cutting distorted areas than what I`ve written above about the curvature of the lens itself.

So probably I should wait for Daheng Cameras and use one of them with my High-quality 12MP Tamron to see how it works in David and long thin objects. If it will work well then I will decide about buying a second one for RV. I`ve tried that 12MP lens with a 3.1MP David camera but the distortions were bigger than earlier. I think it`s a matter of lens weight and it was pulled the whole camera too much down with gravity force. I don`t have any different explanation why that 12MP high-quality lens on 3.1MP gave me so bad results( not only distortions but also size mismatch (not linear changes - like working In many directions).

I will test it further.

Cheers!!!
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Micr0
Posts: 586
Joined: 15 Nov 2016, 15:20
Location: New York City

Re: Questions about RV Daheng low distortion lens for David SLS-2 projector K132

Post by Micr0 »

mdesign wrote: 03 Jan 2022, 22:23 Thanks a lot. Maybe you are right. It`s more the matter of cutting distorted areas than what I`ve written above about the curvature of the lens itself.

So probably I should wait for Daheng Cameras and use one of them with my High-quality 12MP Tamron to see how it works in David and long thin objects. If it will work well then I will decide about buying a second one for RV. I`ve tried that 12MP lens with a 3.1MP David camera but the distortions were bigger than earlier. I think it`s a matter of lens weight and it was pulled the whole camera too much down with gravity force. I don`t have any different explanation why that 12MP high-quality lens on 3.1MP gave me so bad results( not only distortions but also size mismatch (not linear changes - like working In many directions).

I will test it further.

Cheers!!!
The distortion of a lens as you move further away from the center should be mapped and published by the manufacturer. the better the lens the less this will be an issue. when you are scanning you are rarely sampling from the extreme of the image anyway. Hi rendering index (Noted as megapixels) is always good. IIRC in lower quality lenses you can get band shifting or refractory error at the edges which will be noise/distortion in 3D scanning.
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mdesign
Posts: 37
Joined: 03 Jan 2022, 14:51

Re: Questions about RV Daheng low distortion lens for David SLS-2 projector K132

Post by mdesign »

Thanks, Micr0. I think I remember you from the David forum.

What do you think about those ZLKC "low distortion" lenses? Do you think it`s worth paying much more for high-quality Tamron like this:
https://www.rmaelectronics.com/tamron-m23fm16/

vs

https://www.aliexpress.com/item/3296590 ... 7514sodTcc

Will I notice any difference in the scanning of 3-4m thin objects (on 6MP Daheng cameras)? I would like to get lower distortion but I don`t know how good a lens should I buy for this camera to feel the difference.
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