Help required!

Hi all!
New here and hoping for a little help.
I have recently purchased a K-r and was told that any K mount lenses etc would work with it to some degree.
I have purchased a fixed zoom lens and more recently a doubler, both which say they are K mounts. Both fit the camera but when I focus with them the appateur range (F number) just flashes and will not allow me to take any pictures!
I have looked in the settings but there doesn't seem to be anything there to help.
Any help would be greatly appreciated.
Thanks in advance,
Ian

Someone will dive you better details. But off the top of my head. You need to go into your menu and set the aperture ring. (option 2 from memory)

Stub is correct, you need to set 'use aperture ring' to 'permitted' in order to use manual lenses. This will be the cause of the flashing 'f' box.

Press the menu button.
Press the left button on the four-way controller once to get to the Custom Settings menu
Press the down button on the four-way controller and select Using Aperture Ring
Press the down button on the four-way controller, select Permitted and press the OK button.
Press the Menu button to exit the Custom Settings menu

yes i get the same with my Vivitar mc tele convertor but not with my takumar-a tele convertor on closer inspection the contacts on the Vivitar do not press out far enough
to make contact with the K-5 when attached, so it could be this,
my K5 + takumar-a tele convertor + 100mm wr works fine,
but the Vivitar mc tele convertor does not work.

what make is the doubler? you use

If your doubler has anodized black mount you need to scrap the finish off to ground
the mount.

And I suggest setting the focus mode selector to 'm'.