RB 6x8 Back on RZ67 ProII

kauffman v36 · Jan 7, 2010

ok, well i accomplished my first goal of finding a place to get the inafmaous "g" adapter that allows rb backs on the rz series. i somehow found a thread on apug from 2007 talking about doing what i am trying to do and it said its impossible to mount a 6x8 back from the rb on the rzproii and it work. my question is why?

the measurement posted in that thread show the rb pro-s having a rear opening of 69x68mm and the rz having one 68x67mm. the 6x8 back is like 74x58 or something along those lines. i dont understand why 74mm works on 69 but it does on the pro-s, so ill accept it. my quesiton is why wouldnt it work the same on the RZ with a g-adapter. it seemed in the other thread that the adapter was the weak link and it was too small, could it not be machined to match the film back or rear camera opening?

is there anything that can be done to outfit an rb 6x8 back to an rz67proii???

kauffman v36 · Jan 7, 2010

also, the opening on the RZ is big enough to fit 72mm x 72mm quaddra images so im about 99.9% sure that the limiting factor in making the 6x8 back work on the RZ67 is the size of the opening on the G-Adapter. if that is the case, and i have pictures of the adapter and why can it not be machined bigger? or even better, leave it how it is, and stack in order from the body of the RZ- G adapter- pro-sd revolving adapter- 6x8 back. im goin crazy trying to find a way for this to work.

nick mulder · Jan 7, 2010

Just a guess but what if the wide lenses don't cover ? (at infinity at least)

kauffman v36 · Jan 7, 2010

the lenses def. cover. there are people who use rb and rz lenses for 4x5 cameras with little or no light falloff. thanks for the suggestion tho, one more thing to check off the list. once i find the nasty dirty culprit, hes/shes going down. lol

nick mulder · Jan 7, 2010

kauffman v36 said:
the lenses def. cover. there are people who use rb and rz lenses for 4x5 cameras with little or no light falloff. thanks for the suggestion tho, one more thing to check off the list. once i find the nasty dirty culprit, hes/shes going down. lol

Sure the longer focal lengths, stopped down and close focused ...

But the 50mm rectilinear fully open at infinity ? (worst case I guess)

Not to dissuade you though, good luck

kauffman v36 · Jan 7, 2010

maybe, havent thought about that certian situation, thank u for pointing it out nick

John Koehrer · Jan 7, 2010

Never having seen a G adapter I wonder if there's enough material to remove & still have rigidity enough.
I suspect there is.
Since I have more time than $$$ I'd attack it with files.

thisismyname09 · Jan 8, 2010

It's most likely because the opening on the G adapter is only 6x7. If you managed to file that adapter to the correct size, I guess nothing else would prevent you from using the 6x8 back.

Also, I think it's doubtful that the RZ/RB lenses cover 4x5 at infinity. Some might come close, but 6x7 to 4x5 is a pretty big increase. I don't see why mamiya would design lenses with such large image circles, save the RZ's short barrel 75mm and 180mm for use with the tilt/shift adapter.

kauffman v36 · Jan 8, 2010

yea, i think thats what it it. i will be filiing down, or dremeling down, the opening to bigger. but my question is why doesnt the light baffle have to have an opening 6x8. neither the rz, rb pro-s, or rb pro-sd have a rear opening 70mm or above on either side.

MattKing · Jan 8, 2010

kauffman v36 said:
yea, i think thats what it it. i will be filiing down, or dremeling down, the opening to bigger. but my question is why doesnt the light baffle have to have an opening 6x8. neither the rz, rb pro-s, or rb pro-sd have a rear opening 70mm or above on either side.

The instructions for the 6x8 back say:

Following two steps should be taken before using 6 x 8 roll film holder:

1) Replacement of the light baffle frame on camera body back with a new light baffle frame for 6x8 format (*Mamiya service centre will do this improvement for you)
2) 6x8 revolving adapter should be used.

Matt

kauffman v36 · Jan 8, 2010

matt,

thank you for pointing that out. i already have in way the 6x8 back and the G adapter that fits rb backs on the rz. judging from your post it seems like i will need more than just making the adapter opening larger. what do you propose i do? monday i will try and call mamiya and see if i can find out the dimensions of the light baffle they offer for the RB series and see if they offer a similar situation for the RZ series, if not, i will see what can be done myself.

second, it says the 6x8 adapter should be used, but isnt that only for the non pro-sd cameras? the pro-sd camera does not need the revolving back as far as i know. and i know the dimensions of the rear which are not too different from my rz proii rear.

im really looking for someone who has considered doing this or has some input on how it shall be achieved. i also wouldnt mind seeing pictures of the regular light baffle compared to the "6x8" one mamiya offers.

last question, as you guys can tell, i am probably way in over my head but am determined to try this and while i am no expert on the RB or RZ cameras since ive only had mine 2 months i am very handy, but exactly how does the g-adapter with the rb backs work. i know i know, why in the hell did i get all this stuff without knowing exactly it works, idk why, but ill figure it out. do the RB bodies and backs have the same physical dimensions to the film plane as the RZ backs to cameras? essentially, stacking g-adapter + pro-sd revolving back + 6x8 back would make the film farther away and cause OOF images correct?

thank you,
and please anyone who has thought of this id love to hear your input

MattKing · Jan 8, 2010

Hi kauffman:

I'm afraid that my contribution above is the full extent of my ability to help you on this.

I too have been researching the Mamiya RB and RZ systems, and stumbled upon the link to the instruction manual for this back while wandering through the attachment to the links associated with the compatibility chart linked (Reznitsky) to another recent RB67 APUG thread.

Good luck, and be sure to report your results .

Matt

thisismyname09 · Jan 8, 2010

kauffman v36 said:
essentially, stacking g-adapter + pro-sd revolving back + 6x8 back would make the film farther away and cause OOF images correct?

You can't stack adapters, as far as I know. One side of the G adapter mounts to the camera, and the back fits on the other side. It *is* the rotating back adapter, essentially.

Are you sure you have the RZ67 G-adapter? There's also a G-adapter for the old mamiya press cameras.

kauffman v36 · Jan 9, 2010

yes im aware mamiya made two g adapters, one for the rb/rz, and one for the press. the one i have in transit is the right one, i double checked. i was pretty sure you cannot stack adapters, im just wondering how it all worked. essentially, does the adapter work as the "rear mount" of the camera? im assuming thats how it is.

thisismyname09 · Jan 9, 2010

Normally, with the RZ67, it's simply [camera body - rz67] attached to [RZ67 film back]. The rotating back is built into the body and/or film back.
With the RB67, it goes [camera body - rb67] : [rotating back adapter] : [RB67 film back]
The G adapter functions as the rotating back adapter, because they are not built into the RB67 film magazine as they are with the RZ's film backs.
So, [camera body - RZ67] : [G-adapter] : [RB67 film back]

unclemack · Jan 9, 2010

I use RB's & RZ's and I do have a couple of 6x8 electric backs that are fine with the Pro SD & 6x8 adapter - but cut off with Pro S bodies because I never got around to modifying them.
When I saw this post I checked to see what the possibilities might be and I don't think there is any way to get full coverage at infinity. The rear opening on the RZ is just 68mm. square. The gate on the 6x8 back is 74mm. wide and the film plane is roughly 5mm. behind the body.

Filing an RZ back might get you 3mm. extra width but why bother?

kauffman v36 · Jan 9, 2010

thanks everyone, it seems to be making progress in my head, lol. unclemack, im curious as to why you think the rear opening of the RZ would be the limiting factor? according to this thread, (there was a url link here which no longer exists) in post #4 the rear opening of the pro-sd is not much bigger (maybe 1mm), if at all than the rz rear opening.

unclemack · Jan 9, 2010

Because of the rotating adapter between the RB body and back.
The back fits to the RZ without adapter and is therefore closer to the limiting factor, ie. the 68mm. square rear opening.
Have fun.

kauffman v36 · Jan 9, 2010

ahh i see. very good poiint

kauffman v36 · Jan 14, 2010

ok people, the g adapter has been modified and it is more than big enough to allow the clearence for the 6x8 back on my RZ. now im shooting a roll of HP5 to see what the final negative size will be and i will post when done. maybe even make a new thread about finally succeeding on fitting a 6x8 back on the rz cameras.

thanks everybody for the help

nick mulder · Jan 14, 2010

Out of interest how do/did you frame for 6x8 on a RB anyway ? - on the RZ you wont see any vignette until you develop or I guess put a GG on the film plane to see

kauffman v36 · Jan 14, 2010

i have no idea, ive never own or used an RB with the 6x8 back. but there is an auction on ebay for it that says it comes with a focusing screen for the 6x8. i just dont know. and i wont know what the extra 1 cm will look like until i develop. ill get a hang for it after a couple rolls.

europanorama · Dec 4, 2010

image-sizes

nick mulder said:
Just a guess but what if the wide lenses don't cover ? (at infinity at least)

i have 6x8 motor-cassette data-sheet for rb67 pro-s(not rz of course)
there is a table about eff. image-sizes.
smaller side is always 56mm.
depending FL, fstop, distance and vertical or horizontal image-width vary from 70mm(500mm lens horizontal) to 74-76mm vertical for 50,65,90,127, 140 macro lenses. also data for other lenses are given.

homeiss · Jan 20, 2012

kauffman v36 said:
ok people, the g adapter has been modified and it is more than big enough to allow the clearence for the 6x8 back on my RZ. now im shooting a roll of HP5 to see what the final negative size will be and i will post when done. maybe even make a new thread about finally succeeding on fitting a 6x8 back on the rz cameras.

thanks everybody for the help

What was the result after filing the G adapter down. Were the negatives any larger?

Thanks,
Cory

RB 6x8 Back on RZ67 ProII

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