Pros: awesome construction quality in a compact back. Great for the handheld user.
Cons: quirky, no place for darkslide, not of much use to a tripod user.
The Mamiya 6x8 powerdrive film back has got to be the oddest and most misunderstood accessory for the RB67. I hope to shed some light on this interesting item and give you some help in deciding if it is for you.
The Mamiya RB67 SD 120/220 6x8 power drive film back in the latest evolution of the power drive backs for the RB67. It is extremely different from the Pro-S power drive backs. The Pro-S power drive back was a two-part system. It required a separate battery pack that was mounted on the bottom of the camera like a power winder. An awkward cord attached to the overly large film back that contained a large motor to drive the film. Film was advanced by an odd mechanism that attached to the battery pack via the shutter-cocking arm. Once the shutter-cocking arm was activated the back would advance the film. When the film got to the end the back would run continuously until you pulled the cord out of the back.
The RB67 Pro SD 6x8 120/220 power drive back seeks to improve on the idea by consolidating the battery pack, the motor and the film back into one small part that is pretty much the same size as a traditional 120 or 220 6x7 film back. The back takes 4 AA batteries that fit in the very back of the film back and are replace via a door that opens with a coin (good idea vs. needing a screwdriver).
Use of the back is fairly straightforward. Load the film insert as normal. Make sure the back is "on". Insert the film insert as usual into the back and close the door. Then hit the "start" button on the top of the back. This advances the film to the number 1 frame. Set the back to one of 3 positions.... quick, slow or bulb. I will come back to those later. Then shoot as normal. The film will advance after a prescribed amount of time has passed...under 1 sec, except with the bulb mode, which requires you to hit the "start" button to advance the film after each shot. Once the film hits the end it winds the film and it stops by itself after a few seconds.
Now that's the idea.... but what's all the fuss?
Well for one thing this is a 6x8 back... no that's not a misprint. Most people don't realize this, but since the end of the Pro-S production run, all RB67 cameras have been capable of an 8x8 frame shot. Making a 6x8 back to allow it to compete with the Fuji 6x8 was a logical choice since it had the ability anyway. Now, you have to be the one to decide if 6x8 is a great format. If attached to an early Pro-S or a regular Pro series there is the possibility of vignetting.
That's the good part.... now about the bad. Remember I said the back had 3 settings. Well the first one advances the film pretty much as soon as you hit the shutter release. Notice I said shutter release and not mirror up shutter release. If you use this back in mirror up mode in the fast setting it will advance the film when you raise the mirror. If you use it in the slow mode it will wait a little more than a second after you raise the mirror to advance the film. If you use a proper mirror up cable release you can indeed use the power back in the slow mode even at the 1 sec shutter speed without fear of blurring the frame. In the bulb mode you must manually advance the film.
Sounds Ok on paper.... but if you think about it, its a real pain in the butt and it isn't very useful. If you use the camera handheld its a godsend. It will advance the film about as fast as you could manually do it yourself. Works great!. On a tripod its another story. You MUST use a dedicated mirror up cable release or you will have to advance the film manually. I used to just hit the mirror up and then use a regular cable release on the lens for most shots. Why buy a $65 release when a $20 one will do fine? Well without the dedicated mirror up cable you will ruin frame after frame as the back advances the film 1 millisecond before the shutter closes. Remember that the RB67 is a mechanical camera. The back doesn't know if the shutter is open or closed. Why wouldn't you use mirror up when the camera is on a tripod? The film advance then takes over a second PLUS the time it wakes to advance the film. You could easily do it faster yourself. In Bulb mode you advance the film manually. So basically if you use the camera handheld its great. If you use it on a tripod you could do a better job manually and save some money. The only saving grace is the 6x8 format, which is unavailable in a traditional manual back.
The back also operates with 220 or 120 film via a rotating pressure plate. I never understood why Mamiya didn't use rotating plates on it's traditional backs.... so at least you do get a little extra bang for the buck.
Construction quality is very high. This back is at least as well constructed as a standard SD back. It DOES NOT have any provision for a darkslide holder. I forgive them on this one because the back is amazingly compact considering everything that is packed into that back. A darkslide holder would interfere with the battery compartment.
To fully appreciate the expanded field of view you must buy a special 6x8 focus screen. To come even close to getting good results you need a proper mirror-up cable release. So take these 2 items into account if you plan on buying a power drive back.
Conclusions.... if you use the RB handheld then you'll love the 6x8 Powerdrive back. If you use mirror up on a regular basis you WILL get blank and ruined frames unless you have impeccable technique OR you will have to sacrifice speed for the sake of convenience. I think I feel that if you needed automation you should buy an RZ67 instead. You really don't need the aggravation of the power drive back. You really can advance the film faster yourself. The only good reason to buy the back is if you have to have the 6x8 format. I owned a 6x7 power drive back a couple years ago and I sold it right away. I kept the 6x8 only for the format. It makes nice half frame panoramics (3x8).