Bill,
I'm not sure what your application is for a helical. Are you just looking for s omething that moves a lens backwards and forwards to focus it on a ground glass. If that's the case, things like depth of field and distance scales aren't requ ired. Or, are you looking to make a point-n-shoot camera that you will focus ba sed on guestimated distance (like the Linhof 6x17). In this case you will need a helical with the proper distance and depth of field scales to match your lens focal length, as well as the proper mechanical size to match the shutter. You w ill also need to calibrate the "zero" distance (infinity focus) from the film pl ane.
On the other hand, if you will have a gound glass to check focus, any helical of the proper mechanical size will do. How close you can focus will depend on the fore/aft travel of the helical. By all means, if you can afford one of the nic e helicals from Schneider or Rodenstock get one. They are well made and worth t he price (check places like Robert White and Badger Graphics for the most reason able prices - you should be able to get one in the $200 range). If this is a lo w budget "experiment", there are cheaper (although less elegant) solutions. In addition to the Mamiya helicals, you might want to watch eBay and the used deale rs for a Pentax helical extension tube. This may require a little hacking and w ill only work with lenses with a small rear diameter, but you might be able to f ind one for less than $100. Also, the guy who makes the Granview makes helicals to adapt a variety of lenses to his cameras. I have no idea how much they cost , but you might check his web site (I think it's www.granview.com).
Good luck, Kerry
Reply With Quote
Bookmarks