Mamiya Universal/23 backs on an RB Body?

[alpenglow]

Greetings,

 

I would love to be able to shoot 6x9 images on my Mamiya RB. So I wonder if

the Mamiya Press 6x9 camera backs will fit the RB body. Anyone ever try this?

 

Many thanks,

Mike

[dan_fromm2]

Won't go.

[michael_gilday]

You can fit Graflex or Horseman 6x9 backs on the RB, but the interlocks won't work, and you'll still only get 6x7 images, albeit just eight per roll, and with quite large gaps in between...

 

If you were meant to shoot 6x9 on a RB, it's be an RB69, not an RB67. :)

[alpenglow]

Thank you Michael... I thought this was probably the case, but I was wishful thinking. If only there were an RB69 ;)

 

Mike

[Vlad Soare]

Well, there are 6x8 backs for the RB, but they don't call it RB68. :-)

[michael_gilday]

Yes, but don't you have to remove the rotating back (which has a 6x7 gate) to use the 6x8 back?

[mag_miksch]

There are 6x7 and 6x8 rotating backs, you allways need one of them to attach the rollfilmback<br>

you can use Graflex backs on a RB67 without problems, I did it with the 6x6 and the 6x9; like the nonS backs the Graflex backs just dont have the "double exposure lock" and the "dark slide in lock"<br>

You can mill out the rotating back for 6x9 use, search here for "mamiya RB +6x9", what I remember Troy Ammon was interested in doing this, write him a PN. <br>

Regards<br>Martin

[michael_gilday]

Ah, thanks; the rotating back I have in a pile of parts has a 6x7 gate, and I'd always wondered about the 6x8 back.

 

I guess the next question would be whether the various lenses actually cover 6x9 wide open...

[mag_miksch]

ask Troy, maybe he milled out his back, I didnt, but I am pretty shure the circle is big enough for 6x9, maybe not wide open. Martin

[ondebanks]

Mike,

 

Most respondents are focusing on the native Graflok/RB mount approach, but (a) this is not what you were asking, and (b) this is not the best option, IMO.

 

Here are the facts:

 

Late RB67 ProS bodies, and all RB67 Pro SD bodies, have an enlarged light baffle (what you see at the back when the revolving adapter is removed) for 6x8. It should be marked "8" in the late ProS bodies; I don't know if it is marked anything in the ProSD ones but they were all made for 6x8 anyway. If you don't have this bigger baffle, then you are limited to 6x7, nomatter what backs you use.

 

(1) This is one approach, but as I said, not the best one...As long as your camera has one of these 6x8 light baffles, AND a 6x8 revolving adapter, you can shoot 6x8 on Mamiya 6x8 Graflok-mount RB backs.

 

(2) Alternatively, you CAN use the Press backs (sorry Dan!). Mamiya made a "P" adapter for mounting their Press rollfilm and Polaroid backs directly onto the RB67, without its revolving adapter. From my measurements, the internal aperture of the P adapter is 80x76mm (H x W) - big enough for 6x8 (which is actually 76mm wide) but not big enough to fully illuminate 6x9. So a Press 6x9 back mounted on the later ProS or ProSD would really give 6x8 (56x76mm) instead of 6x9 (56x84mm); and Polaroid's 73x95mm would become 73x76mm. However, the light must also traverse a further depth of 1.5cm or so through the wide M adapter (61x90mm) and the front of the rollfilm holder (62x90mm) before arriving on the film gate (56x84mm). With this extra width and depth behind the P adapter, some of the light might "fan-out" and make it through to a greater width than 6x8. It is speculation on my part though, as I have all the Press bits but I don't have an RB67 to test them on!

 

You can pick up a P adapter for about $25 on its own; or they are often sold bundled with the Polaroid backs in the RB67 category, giving you the whole shebang for about $45.

 

Although options (1) and (2) both give you only a guaranteed 6x8, I would still recommend option (2) if you care about film flatness - which I presume you do, having seen your wonderful astrophotography, which of course uses wide apertures and therefore demands excellent film flatness. The Mamiya Press S-shaped backs have outstanding film flatness (take it from me, I'm an astrophotographer too). Mamiya claim great flatness for their RB backs, but the double-back path design (shared with Hassys, Bronicas, Rolleis and all other cuboid cameras) just cannot be as good as the straight-across path, oversized pressure plate (103.7mm long!), and S-shaped curl of their Press backs. The Press backs design didn't really catch on with other manufacturers (except Plaubel), not because they are lesser in performance, but only because they are bulky (and some would add, ugly, though I wouldn't!).

[alpenglow]

Thank you so much Ray for the insightful information. I will look for the Press S-shaped backs, if for no other reason, for the flatness issue that you mentioned.

 

Thank you!!

 

Mike

[jack_welsh]

The press back will fit on the RB. The P adapter is needed for the rollfilm backs and the Polaroid back. But, to use the rollfilm backs, you also need the vertcal (or horizontal) adapter. i have the Universal and the rb. The vertical and horizontal adapters, i have yet to see one for sell.

[ondebanks]

Jack is referring to the "M" adapters. The horizontal M adapters are actually plentiful - nearly all Mamiya Universals were sold with one, and they can also be found on their own. The vertical M adapters are indeed rare, since their only practical use is for portrait-format orientation of the Press backs on the RB67. As he says, you also need the P adapter, which basically converts the back of the RB67 into the same thing as the back of the Mamiya Universal.

[kevin_mcgovern]

So to use a Universal Press S-channel film back for absolute film flatness, and get 6x8 images at the very least, one must get a P-adapter to interface with the Pro SD body, to allow mounting an M-adapter, and then the Universal Press back?

 

Raises a second question: if all the above is true, would that affect the plane of focus on the film itself. My assumption is that when focusing through the mirror, the distance to the film is calibrated inherently by the depth of the camera body. If I add two adapters and a “foreign” film back, will my focal point on my screen remain the same for the film, or need a small correction for a slightly longer distance from the lens to the film plane?

 

On the face of it, it seems to be a lot of trouble for a small increase in negative size, unless one might obtain a decent 6 x 9 image this way OR obtain a noticeable improvement in image quality from the better film flatness provided by the Press back. In the abscence of one or both benefits, it’d be difficult to justify the weight gain, complexity, and expense of all the extra equipment. Any thoughts much appreciated!

[orsetto]

if all the above is true, would that affect the plane of focus on the film itself.

 

You would think so, but apparently it does not. The two camera systems share a design philosophy of multi-part modular back panels. The rotating Graflok-type rear mount on the RB67 is completely removed before attaching the Press mount P and M plates. So, when attached to the bare RB67 body, the two Press plates + press film back bring the film plane to the same point as the native RB rotating mount + film back.

 

In theory, anyway. Slight discrepancies that "passed" in the all-analog MF film era might not fly today if the negatives made with such a contraption were scanned in high resolution and pixel-peeped. I sometimes miss the old days when you could use the bottom of a Coke bottle as a makeshift enlarging lens. And get away with it, because we didn't examine the resulting prints with anywhere near the OCD avidity people do today on a screen. Imagine the shrieks of disdain Edward Steichen's iconic "The Pond- Moonrise" would be greeted with today.