I assembled my Sinar f and when I try to get focus to my subject I can't, I have to stay way far and the rail (I guess that what's called) is short! You can see it in this picture

Sinar F parts by Mohammed Basamh, on Flickr

My nikkor 210mm f5.6 will only focus really far....would 18" rail extension do the job or should I look for longer rail? The bellow seems good enough (if not I'll look for longer bellow)

Regards,
Mohammed