evaluated string for filter doesn't work

[Sivakatirswami]

Field "extension" contains ".jpg"

script has

   put ("*" & fld "extension") into tFilter
   filter tFiles with (quote &tFilter & quote)
   put tFiles into fld "Listing"

result "nada!"

Why?

filter tFiles with "*.jpg" works

and

put tFilter

returns 

*.jpg

I tried this too:

   put (quote & "*" & fld "extension" & quote) into tFilter
filter tFiles with tFilter
   put tFiles into fld "Listing"

still "nada"

??