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This may be a dumb question, but I haven't borked around with the Pi Camera at all yet.... Why does the lens have a megapixel rating? I'd assume that there's no

This may be a dumb question, but I haven't borked around with the Pi Camera at all yet.... Why does the lens have a megapixel rating? I'd assume that there's no imaging sensor in it, right?

deleted 6y ago
[deleted]
throwanem 6y ago
It doesn't make sense, no. The whole article seems very barebones - I'd have expected to see discussion of how the sensor-lens system needs to work for proper focus, at least. Granted they link the STL for their case, which will be designed for correct alignment, but some discussion would still be useful to those wanting to mod for different lenses or sensors.
- commonvision 6y ago
  Correct, the MTF of a lens is meaningless unless the lens and sensor are aligned (aka focused) correctly. Contrast in the image is directly related to the square-wave geometrical MTF. Once you factor in focus/alignment error, it can be difficult to tell the difference between a "3MP" and "12MP" rated lens. We're talking about <10 micron accuracy. This is why companies like Apple use 6-axis active alignment machines to manufacture every camera module. The "Megapixel" rating of a lens is based on the nominal as-designed MTF and image sensor Format. There's a lot of manufacturer fudging that goes on with these ratings. And some in China literally print whatever they want on the side of a lens. I've seen the same lens with both "3MP" and "5MP" printed on it. Here are a few tips on how to focus a camera. Regardless, it'll be hard to get within 2-5 microns with a CS Mount 1"-32TPI thread. https://commonlands.com/blogs/technical/how-to-focus-a-camera https://commonlands.com/blogs/technical/how-to-focus-a-camer...
dheera 6y ago
The lens having an MP rating is likely just saying that the optics is good enough to resolve an image to the detail that a 10MP sensor would capture. I know it's a shitty way to specify lens resolution, but that's likely what the manufacturer called it, not the fault of the article's author.
- daveslash 6y ago
  Thank you. That makes sense. Yes - that's the description from the manufacturer, not the post author. Lens may be found here. https://www.adafruit.com/product/4562 https://www.adafruit.com/product/4562
playpause 6y ago
Good question. It looks like the Raspberry Pi HQ camera module (the bit with the sensor) is rated at 12MP. My guess is that the angle of this lens means you can only make use of the middle portion of the sensor, in this case 10MP’s worth of it. And as there’s only one sensor module on the market that this lens can screw onto, they can tell you the effective megapixel rating of the lens. There’s also a ‘wide angle’ 6mm lens [1] available for the same camera module, rated at 3MP, which I assume casts the image on a even smaller portion of the sensor. I could be completely wrong though, not an expert. [1] https://thepihut.com/products/raspberry-pi-high-quality-camera-lens https://thepihut.com/products/raspberry-pi-high-quality-came...
- JKCalhoun 6y ago
  I don't think you are correct. For this reason only: I have played with the Raspberry Pi HQ camera module and a pair of lenses for it and the frame-grab software never returned an image with a black (or otherwise) border. From your description I would instead expect a thick black border around the image where no photon data was captured. To be sure the frame-grab tool could be sensing the lightless border from the image and cropping, but I doubt it's that clever.
  - brudgers 6y ago
    Your description of the frame grab software output is consistent with the proposed degree of cleverness.
PragmaticPulp 6y ago
> Why does the lens have a megapixel rating? I'd assume that there's no imaging sensor in it, right? The megapixel rating is an indicator for sharpness. There are more technical ways to rate sharpness, but listing the megapixel rating and sensor size is a quick way to suggest that the lens is sharp enough to resolve pixels that small.
brudgers 6y ago
The rPi camera accepts c-mount lenses. C-mount is a mechanic standard for the connecting threaded couple of lens and camera. It is not an optical standard. C-mount lenses project image circles of different sizes depending on their intended use. The initial use was 8mm film cameras. But it was also used by lenses designed to cover the larger super8 film image standard. And today there is at least one c-mount lens that can nominally cover APS-C though with noticeable vignette...anyway... The rPi camera sensor has a diagonal of 7.9mm. This is about 20% larger area than super8 film. For a photographer whose opinions of image quality revolve around technical details, such a super8 format intended lens might produce about 10 “acceptable” megapixels on a 12mp sensor. Most photographers tend to think about image quality in those terms. Limiting the specifications that way heads off complaints about unfulfilled expectations. It is easier to hold strong opinions about technical measures than to consider aesthetic possibility created by a lens’ optical limitations.
jrockway 6y ago
They are using megapixel to mean "modulation transfer function": https://en.wikipedia.org/wiki/Optical_transfer_function https://en.wikipedia.org/wiki/Optical_transfer_function As many of the replies state, it doesn't make sense. I think the original author knew of the idea, but not the word. Now you can know the word :)

This may be a dumb question, but I haven't borked around with the Pi Camera at all yet.... Why does the lens have a megapixel rating? I'd assume that there's no imaging sensor in it, right?

deleted 6y ago

[deleted]

throwanem 6y ago

It doesn't make sense, no. The whole article seems very barebones - I'd have expected to see discussion of how the sensor-lens system needs to work for proper focus, at least. Granted they link the STL for their case, which will be designed for correct alignment, but some discussion would still be useful to those wanting to mod for different lenses or sensors.

commonvision 6y ago
Correct, the MTF of a lens is meaningless unless the lens and sensor are aligned (aka focused) correctly. Contrast in the image is directly related to the square-wave geometrical MTF. Once you factor in focus/alignment error, it can be difficult to tell the difference between a "3MP" and "12MP" rated lens. We're talking about <10 micron accuracy. This is why companies like Apple use 6-axis active alignment machines to manufacture every camera module. The "Megapixel" rating of a lens is based on the nominal as-designed MTF and image sensor Format. There's a lot of manufacturer fudging that goes on with these ratings. And some in China literally print whatever they want on the side of a lens. I've seen the same lens with both "3MP" and "5MP" printed on it. Here are a few tips on how to focus a camera. Regardless, it'll be hard to get within 2-5 microns with a CS Mount 1"-32TPI thread. https://commonlands.com/blogs/technical/how-to-focus-a-camera https://commonlands.com/blogs/technical/how-to-focus-a-camer...

dheera 6y ago

The lens having an MP rating is likely just saying that the optics is good enough to resolve an image to the detail that a 10MP sensor would capture. I know it's a shitty way to specify lens resolution, but that's likely what the manufacturer called it, not the fault of the article's author.

daveslash 6y ago
Thank you. That makes sense. Yes - that's the description from the manufacturer, not the post author. Lens may be found here. https://www.adafruit.com/product/4562 https://www.adafruit.com/product/4562

playpause 6y ago

Good question. It looks like the Raspberry Pi HQ camera module (the bit with the sensor) is rated at 12MP. My guess is that the angle of this lens means you can only make use of the middle portion of the sensor, in this case 10MP’s worth of it. And as there’s only one sensor module on the market that this lens can screw onto, they can tell you the effective megapixel rating of the lens. There’s also a ‘wide angle’ 6mm lens [1] available for the same camera module, rated at 3MP, which I assume casts the image on a even smaller portion of the sensor. I could be completely wrong though, not an expert. [1] https://thepihut.com/products/raspberry-pi-high-quality-camera-lens https://thepihut.com/products/raspberry-pi-high-quality-came...

JKCalhoun 6y ago
I don't think you are correct. For this reason only: I have played with the Raspberry Pi HQ camera module and a pair of lenses for it and the frame-grab software never returned an image with a black (or otherwise) border. From your description I would instead expect a thick black border around the image where no photon data was captured. To be sure the frame-grab tool could be sensing the lightless border from the image and cropping, but I doubt it's that clever.
- brudgers 6y ago
  Your description of the frame grab software output is consistent with the proposed degree of cleverness.

PragmaticPulp 6y ago

> Why does the lens have a megapixel rating? I'd assume that there's no imaging sensor in it, right? The megapixel rating is an indicator for sharpness. There are more technical ways to rate sharpness, but listing the megapixel rating and sensor size is a quick way to suggest that the lens is sharp enough to resolve pixels that small.

brudgers 6y ago

The rPi camera accepts c-mount lenses. C-mount is a mechanic standard for the connecting threaded couple of lens and camera. It is not an optical standard. C-mount lenses project image circles of different sizes depending on their intended use. The initial use was 8mm film cameras. But it was also used by lenses designed to cover the larger super8 film image standard. And today there is at least one c-mount lens that can nominally cover APS-C though with noticeable vignette...anyway... The rPi camera sensor has a diagonal of 7.9mm. This is about 20% larger area than super8 film. For a photographer whose opinions of image quality revolve around technical details, such a super8 format intended lens might produce about 10 “acceptable” megapixels on a 12mp sensor. Most photographers tend to think about image quality in those terms. Limiting the specifications that way heads off complaints about unfulfilled expectations. It is easier to hold strong opinions about technical measures than to consider aesthetic possibility created by a lens’ optical limitations.

jrockway 6y ago

They are using megapixel to mean "modulation transfer function": https://en.wikipedia.org/wiki/Optical_transfer_function https://en.wikipedia.org/wiki/Optical_transfer_function As many of the replies state, it doesn't make sense. I think the original author knew of the idea, but not the word. Now you can know the word :)