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I have a Raspberry Pi High Quality Camera (C/CS-mount), and would like to mount the Canon EF-M 28mm f/3.5 Macro IS STM to it (EF-M). I have been looking for adapters, but can't find any. This got me wondering, is it possible at all to mount this lens to this camera?

P.S. photography noob

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    \$\begingroup\$ Why that lens in particular? Because the EF-S 35mm macro is very similar and being an EF-S mount, can use an EF to C mount which seem fairly easy to find. \$\endgroup\$
    – xenoid
    Commented Feb 16, 2023 at 15:35
  • \$\begingroup\$ Just guessing but... That lens in particular because the OP probably has that lens in particular. It's not a great solution to suggest: Buy a different lens. (Though, admittedly, that may be the only solution.) \$\endgroup\$
    – osullic
    Commented Feb 17, 2023 at 9:46
  • \$\begingroup\$ @xenoid osullic is correct, we have this lens lying around, the camera that fit the lens is no more. My main goal is to take a time-lapse in macro. Price-wise, wouldn't it make more sense to find a camera that can do this that fits the lens, rather than buying a lens that fits my camera? \$\endgroup\$
    – Olaf
    Commented Feb 17, 2023 at 10:34
  • \$\begingroup\$ @Olaf which is why I asked... \$\endgroup\$
    – xenoid
    Commented Feb 17, 2023 at 10:39

3 Answers 3

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Probably not.

There are two considerations: sensor size (ie. the target) and the flange focal distance.

Flange focal distance is the distance the lens needs to be from the sensor for images to be in focus. Imagine using a pair of binoculars. If you hold them away from your face and look thru them, everything is blurry, no matter how you focus. But put them up to your eyes and suddenly everything is in focus. For the binoculars, the flange focal distance is the distance from the lens to your eyes (kinda).

The EOS-M has an 18mm flange focal distance, and the C/CS mount lenses have a 17.5 Flange focal distance. This means that you would need to mount the EOS-M 0.5mm further from the lens than where the C/CS mount provides. So basically, a 0.5mm adapter. Perhaps this is trivial and will make no difference in actual image quality, but for sure the EOS-M lens is far far bigger than the camera module opening itself.

Another consideration is the sensor size. An EOS-M is designed to illuminate a sensor that is 23 x 14mm, whereas the C/CS illuminate one that is 6.287mm x 4.712mm. So the circle of light exiting an EOS-M lens is going to be much, much bigger than required, and likely far bigger than the hole provided for the camera module. Not a big deal, but you are only going to use a tiny central portion of the EOS-M lens to illuminate the tiny sensor. It's a bit overkill IMHO.

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    \$\begingroup\$ IMO, binoculars isn't a good analogy, because binoculars are afocal — i.e., they aren't image-forming lenses. I understand what you're getting at, but it opens up a can of worms of misunderstanding if the comparison continues. \$\endgroup\$
    – scottbb
    Commented Feb 16, 2023 at 16:21
  • \$\begingroup\$ ^^^^T^H^I^S^^^^ \$\endgroup\$
    – Michael C
    Commented Feb 16, 2023 at 23:18
  • \$\begingroup\$ If you look through binoculars while holding them several inches from your eyes (assuming they were in focus when held at the proper eye relief) they should still be in focus, you just won't see very much of the field of view. Eye relief is a measure of how far behind the eyepiece one's eye's can be and still see the full FoV. It has nothing to do with focus. Binoculars project a light field that is (hopefully) focused by the observer's cornea. \$\endgroup\$
    – Michael C
    Commented Feb 16, 2023 at 23:23
  • \$\begingroup\$ This is a very good explanation, thank you very much! \$\endgroup\$
    – Olaf
    Commented Feb 17, 2023 at 10:37
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Is it possible?

I don't think so (without some specific construction work).

I guess your camera is this one or equivalent. It has a CS mount (shorter flange distance) and provides a CS-to-C adapter (just a screw ring increasing the flange distance).

There's no electronics to control an intelligent lens like your EF-M one. So, there's no way to control aperture, and focussing has to be done manually (if your lens even has a manual focus ring).

If you can live with that, it's a matter of mounting the lens in the correct location in front of your camera. As the CS mount has a flange distance of 12.5mm and EF-M has 18mm, there's a nominal gap of 5.5mm to work with.

But the EF-M flange distance isn't the whole truth, as the rearmost surface of the bayonet reaches about 5mm into the camera body, thus being located only 13mm in front of the sensor. And the bayonet diameter is much bigger than the free space inside the CS mount, and the bayonet thus sits in front of the CS mount, not inside. this leaves only 0.5mm of free space, making a mechanically sound adapter virtually impossible.

I doubt that there are CS-to-EF-M adapters available commercially.

Is it worth the pain?

Your lens surely isn't bad, but it's meant for a much bigger sensor area and a much bigger pixel size. It surely has been optimized, trying to achieve pixel-exact sharpness over an area of 22mm by 13mm. But here, "pixel-exact" means a circle of diffusion like 4µm, the typical EOS-M pixel size. Your sensor has 1.5µm pixels, meaning that a circle of diffusion considered perfect for an EOS-M, results in a 3-by-3-pixel blurriness.

And the field of view changes with your small sensor, making it a telephoto lens, equivalent to about 135mm on a full-frame body.

And, as I mentioned, you have no control over the aperture, and can only focus manually.

So, maybe the results will not be what you hoped for.

What do you need?

If you're still with me, the only plausible way I see, is to 3D-print an EF-M mount to replace the plastic CS mount on your camera PCB. That needs 3D modelling skills and access to a 3D printer.

I don't think you can download an appropriate model anywhere, so you have to design it yourself.

It's doable. I've done the opposite thing myself, design and print a telescope adapter fitting into the EF-M mount of my EOS-M body, and it works quite well.

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I own a mokose uc70 usb camera and have bought a foldio adapter ring to fit an old EF 28-70 from 1995 and it works. Aperture is manual on adapter and focus / zoom is manual on lens...

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