# Crazy question about RF TC's



## JPAZ (Nov 24, 2020)

Hi all,

Still converting my kit towards RF lenses and I have a question regarding Teleconverters. I understand how to use (and the issues with) the EF-RF converter with my EF TC 1.4x and an EF "big white" lens. But, as I move from EF to RF over time, I am thinking about RF TC's. Has anyone tried to stack as follows:
- EOS R5 (or any RF camera) with an RF TC followed by an RF to EF adapter then an EF lens?

I think a limitation of the RF TC's is that the glass extends so one cannot use it with all the RF lenses. But, if I someday have almost all RF glass, my EF TC's become useless and I would sell them to get RF TC's. Hope this makes sense. I am certainly no optics wizard and there might be an issue I am not aware of.

Thanks.


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## bhf3737 (Nov 24, 2020)

RF TC cannot be followed by an RF to EF adapter. As you mentioned, in RF TC the glass extends and adapter does not physically fit to it.
But RF to EF adapter can be followed by EF TC and EF lenses. 
Therefore, current EF lenses with EF TC can be connected to any R camera via the adapter and you can enjoy all EF glass on R. 
But only a few of current RF lenses (RF100-500mm, RF800mm, RF600mm) can connect to R cameras via RF TC. In this sense, RF TCs are of rather limited use.


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## koenkooi (Nov 24, 2020)

bhf3737 said:


> RF TC cannot be followed by an RF to EF adapter. As you mentioned, in RF TC the glass extends and adapter does not physically fit to it.
> [..]


Bryan at TDP showed that you can file down the baffles in an EF-RF adapter to make it work. So if you are motivated and have a steady hand...


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## koenkooi (Nov 25, 2020)

This one: https://www.the-digital-picture.com/News/News-Post.aspx?News=35054


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## JPAZ (Nov 25, 2020)

koenkooi said:


> This one: https://www.the-digital-picture.com/News/News-Post.aspx?News=35054



Now that is interesting. Wonder why Canon built in this incompatibility? If it is just the plastic and not the optics (any TC can reduce IQ a bit) than why?


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