Need help with M42 to RF adapter (vintage Helios-44-2)


Apr 23, 2020
I've decided to jump into the world of vintage lenses and recently purchased a Helios-44-2 2/58 Jupiter M42 lens on eBay.

Now I need to find an adapter to make it fit my Canon EOS R6. As far as I understand, the adapter doesn't do anything except convert one mount to another, so a cheap adapter should work just as well as a more expensive one, right?

Looking at Amazon, I've found a few different M42 adapters. What confuses me is that some of them seem to be thicker than others. Ideally, I would like to go with the smallest adapter I can find.

I hope it's OK to link to Amazon. Here are two examples:

M42 Screw Mount Lens Adapter Manual To Canon RF Lens for Canon EOS RP, EOS R Camera (£8)

K&F Concept M42 to EOS R Lens Mount Adapter for M42 Mount Lens and Compatible with Canon EOS R Cameras (£43)

Why wouldn't I go with the cheaper and smaller option?

EDIT: I found another small/cheap adapter and noticed one of the reviews stating that it didn't work with the Helios due to flange distance:
I used this to connect a Helios 44-2 lens to the can eos r. Wouldn’t allow me to focus at all. I think it leaves the lens too close to the sensor to focus properly. Not sure what this is actually useful for.
These thinner ones is definetly a EF-M42 adapter, not RF. The marking "M42-EOS.R" on this thinner adapter is a lie. The flange distance in RF mount is 20mm, EF is 44mm, so RF-M42 adapter should be 24mm thicker than EF-M42.
However, you are still able to use M42 lenses with this thinner adapter on EOS-R Cameras, but you need to use an additional RF-EF adapter.
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