Rolleinars have parallex correction, so there is worry of cropping off the subject.
Ebay may not offer the Rolleinar at cleap price.
I still have the Rolleinar for 2.8F, but the ones for Rolleicord may be hard to find.
Seng Cheong used to sell the Bay I Hoya close up filter, at close up range of +1 +2 or +3.
The +1 is easier to use, +3 need to get really close, so its not too useful.
I bought the +1 Bay I X2 , for the top and bottom lenses.
But unlike Rolleinar, there is no correction for parallex error, so need to move the camera up by about 1 inch to correct for parallex error.
Otherwise the subject will be cut off.
Here is a Seagull with Hoya +2
A cheap alternative is to use a Bay I adapter to something like a 46mm or 34mm.
Then use a +1 close up 46mm or 34mm for close up.
Because this is bigger, you cannot mount TWO filters at the same time.
So mount the 46mm/34mm +X at the top lens to focus.
Then move the taking lens up by one inch as the viewing lens' view.
Swap the close up lens to the bottom lens then shoot.
This is how I shoot. Troublesome, but the results is great.
For the Rolleiflex, connect the bigger lens to the finder lens, the red point has to be on top.
the smaller lens is attached to the taking lens at the bottom. Parallax is corrected automatically.

(for illustration purpose dot not aligned. Fitted with +3, the +1 set lying in front)
