Mount Adapter EF-EOS R questions about drop-in filters

[DJ_aa7]

A) Do the drop in filters made for telephoto lenses work with the ef eos r drop in filter adapter? 

B) is clear glass required in the ef to r adapter? Does it affect focus/image quality if using a drop in filter body with no glass? Would the camera still properly focus or would the images be soft, like YouTubers are claiming.

[NatalyaP]

Greetings DJ_aa7,

The Drop-In Filter Mount Adapter EF-EOS R is not compatible with the 52mm drop-in filters found in Canon's super telephoto lenses. The filters that can be used are the ones that are designed and offered for this type of an adapter.

A filter or glass is recommended when using the adapter since leaving the filter holder out of the adapter will leave the adapter prone to dust and debris entering the slot. Image quality will not be reduced.

[DJ_aa7]

I'm not leaving the filter bay empty for light & dust to spill onto my sensor. I'm talking about inserting a filter without the glass in. A blank. So the filter entrance will be closed, but there will be no glass. 

Everyone on YouTube is claiming this affects focus and the images will be soft when pixel peeping. This doesn't add up to me, but i don't know for sure.