Mamiya RB67 6x8 Power Drive to Produce 6x7 or 6x4.5

[tkamiya]

No, it doesn't apply to RB-SD. I called Mamiya and asked. Since all RB-SD are designed from start to use 6x8, none of its baffles are labeled with "8" but all are capable of 6x8.

[al5256]

Hi

Do you see the symptom I described about top edge not being crisp on vertical and vignetted corners on horizontal but long end actually a bit longer with crisp edges? I've been wondering if this is common on ProSD with 6x8 back. I can scan my film and post it if my description is confusing.

The ProSD gives crisp, well defined and sharp edges and corners on vertical orientation to form a 56x76mm negative. On horizontal (Landscape) orientation bottom corners (really the upper since it is upside down) are vignetted to give 72mm long bottom side. Other than this all sides are crisp and sharp also on horizontal orientation.

[tkamiya]

That's probably not a good thing....

Here's what my neg looks like.

Frame49 was shot in vertical orientation. As you can see, top edge isn't clean. Vertically, it measures 74.5mm
Frame51 was shot in horizontal orientation. Vegnetting is uneven and horizontally, it measures 74mm.

[grantlyd]

Thanks for posting those images tkamiya! I was patient and found a 6x7 motorized back! For some reason I would rather have the crisp edges!

[voceumana]

There are a couple of Pro-SD backs 6x7 on ebay right now in the UK. I've had no trouble with international purchases from the UK. Buy it now for about $88 each. It I already didn't have 5 backs, I'd go for them.

[tkamiya]

I found something interesting while playing with my setup.

With 6x8 back, there is a little bit of play when it's set on the revolving adapter. (when it is unsecured) It will slide just a little, about 1mm, along the track. I rotated the back to vertical position and released the back, then pushed the back UP, then secured. Because the top edge wasn't sharply defined, I knew the bottom was the problem. I then took some test shots.

With this, in vertical orientation, all edges are sharply defined. In horizontal position, just a very little on both bottom corners are vignetted. Just VERY VERY little.

So there is some manufacturing tolerance in play here.

I actually ordered a second body to compare and keep as a second body. Unfortunately, this body came damaged so I neither could use it or test with it. (it went back). As far as dimension goes, it was identical to mine, except the "play" was even bigger. This confirms manufacturing tolerances is part of the issue.

I'm not sure if this helps anyone.

I heard from a third party, with some lens and distances, more or less vignetting can be experienced. I'm trying to get a documentation on this.