I've rebuilt, and now use, two 5x7 Rittreck cameras, along with the 4x5 reducing backs for each. No question, it's heavy at 9 pounds, 6 ounces, but stable.
Offhand, like Tin Can, I cannot see where making any holes would effectively lighten the camera except in the shell, which is essentially the entire structural support system and which provides protection against dirt, weather, and damage when folded.
Where one could save a great deal of weight on this camera without sacrificing rigidity, structural integrity, or protective sealing of the folded camera would be to make the body shell and bed out of magnesium alloy, which is 33% lighter than the structurally equivalent aluminum and to honeycomb the thicker top and bottom plates of the apparently one-piece cast shell. Reesigning the front and back focus rail mechanisms on the bed would also help reduce weight as would shifting to a Toyo 45A-style compendium.
However, using more modern materials like Magnesium alloy would go a very long way in lightening the camera without a major retooling or redesign, probably reducing the weight of the 5x7 unit by at least two pounds, down to about 7.25 pounds, which would be much more manageable.
Any re-design would likely be expensive as the parts are largely die-cast, and making precision dies is costly, not something reasonably undertaken by a poorly-funded casual operation.
Wista, as corporate successor to Rittreck, might still have the dies, though. Rittreck 5x7 models stopped appearing in Wista's View Camera Magazine ads at the beginning of 1990, so the dies might still be around somewhere in Wista's back rooms.
Bookmarks