With the added thickness of this converter on a full frame, is, for instance, a 50mm lens still a 50mm lens or more like a 60mm?

OK, you need some knowledge, let me help. The basic answer is that it is still a 50mm lens, or whatever the lens is it is not effected in this way. For more info, read on. To start, you have adapting confused with crop factor, and crop factor only applies to sensor size, not the distance the lens is to the sensor. And to make it even more muddy, crop factor doesn't change the focal length of the lens, it changes the field of view. I'll try to explain each thing.. Adapting - So, this adapter makes it so older EF lenses can work on the new RF system. The new cameras do not have the mirror the older cameras do, and thus allow the new lenses to be placed much closer to the sensor. This is called "flange distance". Lenses are designed to focus based on this lens distance. So the older lenses require a much longer flange distance, and the adapter creates that space, otherwise the lenses wouldn't be able to focus (or fit, they are engineered to make it so you can put them on the wrong camera). It makes no changes to the function or properties of the lens, and no crop factor applies. Crop Factor - This can get complicated, I will try to stick to the basics. Crop factor only applies if the sensor size is different, usually in this case it means the sensor is smaller, but some sensors can use a "crop mode" which uses a smaller version of the sensor. The physical properties of the lens are the same; a 50mm lens is still 50mm, but it's overall angle of view is reduced (on Canon it's reduced by 60%). So it frames more like what an 80mm lens would on a full frame camera. Really, crop factor only exist because at one point there were 35mm film camera users that were coming into the digital world, and the most affordable cameras were these APS-C "crop" cameras. So they would put an 85mm lens on to take a portrait, only to find the angle of view was now much less, that what they really needed was a 50mm lens for the same use. So crop factor was made as a way for them to know what lenses were for what functions. Now, it's still a useful thing to know, but only if you know all the old tropes, to make it easier to select the proper lenses. When Crop Factor Applies - In any case, the lens or adapter is not relevant to when it applies, it only matters if using a smaller sensor size. Any crop camera will need it's crop factor applied to all lenses that are on it, even ones made only for crop cameras. This is because the standard for measuring lenses was created for 35mm format cameras, and that standard still applies, even to the smaller format lenses, because it is an industry standard. Some feel like crop only lenses should be labeled with their crop factor applied, but the thing is, that is I think a more muddy river than it currently is. People will want to know "why is it when I use this 24mm lens (crop) it is not the same as this other 24mm lens (full frame)?" And then they now have to learn to look out for lenses that can serve a completely different function on their camera than one that they think is the same. This way, a 24mm lens works the same no matter if for crop cameras or not. Probably a lot more info than you needed LOL.

What does the control ring get you that the basic adapter doesn't do?

They both adapt the lens to the RF mount, both use the same method to do so. Both have the same performance. The only difference is the control ring adds an additional control in the form of a dial that can be programmed to do several different things. This can be anything from changing the aperture, the shutter speed, ISO, exposure compensation (what I use it for), white balance, AF mode, and so on. It can only be one at any time, and you would set it up in the menu in the same way you would customize any other control. I would say if you have the R5, R6, or R3 then it is mostly not needed, mostly just a luxury that cost an additional 100 bucks. This is because those cameras have additional controls on them that can take the place of the ring. If you have the R or RP, then it might be a good idea to get the ring since they lack in the controls the other cameras have. Or, if you just want it, that is fine too. Otherwise, your lenses will behave exactly the same. If you would like more info about the adapter, you should check out the review I have on my profile. Here is a link. https://www.amazon.com/gp/customer-reviews/R27553TB7FWPCN?ref=pf_ov_at_pdctrvw_srp

Does it work with ef-s 24mm f/2.8 stm lens?

It actually does, yes. The adapter allows the use of all EF and EF-S lenses. However, as that is a crop lens, it will place the camera into what is called "crop mode" to mimic the smaller sensor size the lens was made for. This means that only 40% of the sensor will be used, and that certain video modes will no longer be accessible. So this is more or less just a way to help users coming from the older crop systems (like the Rebel line) to the new full frame models, where unlike the EF full frame cameras you can actually use your crop lenses on them via this adapter. Older DSLR full frame cameras had a mirror that could impact the rear of the smaller lenses, and that is why they could not be used on them. The new RF models no longer have the drawback, but the lenses still have too small of a projection to fill a full frame sensor, and thus the sensor "crops" down the images to make it so it works normally. You do lose some of your resolution, 60% roughly. So 20mp becomes 8mp, 30mp becomes 12mp, and so on. While it will work, I wouldn't suggest it as a long term solution, but at some point Canon is going to release RF crop series cameras, and this lens will be just fine on those. Maybe sometime late in 2022, or early 2023. In the meantime, as long as you don't mind the crop mode, this lens will work, but if you want something that works fine without the crop mode, gives the same general framing, look at the following... EF 40mm F2.8 STM - also a pancake lens, its basically the full frame version of the 24mm, and is also pretty affordable. RF 35mm F2.8 IS STM Macro - Probably the best "cheap" 35mm lens for the RF system. Usually 500 USD new, but sometimes reduced to 400. Surprisingly good lens, and does not need the adapter to use on an RF camera, but will not work on EF cameras.

If i buy the ef eos r adapter, do i need this control ring? tia

Technically no. They are both adapters for EF lenses to the RF mount, both perform the same function and they do it the exact same. However, this adapter cost twice as much, but adds an additional adjustment dial that can be set to change an individual setting. If you have and R3, R5, or R6, it really isn't much help, since they have three control dials. If you have the R, RP, R10, or R7, then it might be worth the extra 100 USD. For more info about the control ring adapter, check out the review on my profile. Here is a link. https://www.amazon.com/gp/customer-reviews/R27553TB7FWPCN?ref=pf_ov_at_pdctrvw_srp

Brand	Canon
Manufacturer	Canon, ‎Canon
Model	2972C001
Model Year	2018
Product Dimensions	7.37 x 7.37 x 2.29 cm; 130.41 g
Item model number	2972C001
Mounting Hardware	Mount Adapter
Number of items	1
Minimum diaphragm opening	1 f
Min Focal Length	1 Millimeters
Batteries Included	No
Batteries Required	No
Lens type	Standard
Actual viewing angle	1 arcmin
Does it contain liquid?	No
Has audio recording capabilities	No
Has Auto Focus	No
Manufacturer	Canon
Item Weight	130 g

Canon Control Ring Mount Adapter EF-EOS R

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