Mamiya RB lens adapter for LF

pdccamerqs

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Hi all,

I am working on building an Actus type camera on a 6x9 view camera platform. My plan is to use a Mamiya RB lens (eg. 90m f/3.8) for the objective and mount my Sony A7RIV as the digital back. The front standard would be from a Toyo 23G which uses the 110mm (11 cm) square boards also used on the Toyo 45A type field cameras. I saw the add below on Ebay for a lens board that may work - it says the board is 11.8 cm x 11.8 cm and I am wondering if this would mount on a Toyo 45A type board.

Thoughts?

Thanks for the help,

Paul

 

choiliefan

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I'd contact the seller for more details.
Otherwise it seems this new board is 1/3" over-size.
 
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pdccamerqs

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choiliefan said:
I'd contact the seller for more details.
Otherwise it seems this new board is 1/3" over-size.
Click to expand...

Good advice. Thank you for your reply. I have been waiting for a reply to my inquiry from the seller. I wasn't sure if "about 11.8 cm" meant on the high side or the low side. Also, I don't have the front standard of the 23G to measure, so I am not sure if the 110mm x 110mm Toyo standard is a nominal dimension or an actual dimension and what the tolerance is on Toyo lens boards.However, as you state 110mm +/- 8mm sounds like a lot.

Regards,

Paul
 

Donald Qualls

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I have one of these -- I can report that they do correctly operate the RB67 lenses I have. The board doesn't fit anything I own, but I keep thinking I can remount the ring with its operating parts on a different size board.
 

Alan Edward Klein

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ags2mikon

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I have 2 of the adapters. I have mounted 1 to a Cambo SC 4x5 and another to a Rittreck 5x7 view. They do work.
 
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pdccamerqs

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Thanks for the all the help and the pointer to the existing thread!

Best,

Paul
 
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pdccamerqs

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Donald Qualls said:
I have one of these -- I can report that they do correctly operate the RB67 lenses I have. The board doesn't fit anything I own, but I keep thinking I can remount the ring with its operating parts on a different size board.
Click to expand...

Thanks, Donald. Do you think a Copal #3 bore size (65mm) would work?

Best,

Paul
 

Donald Qualls

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I'd have to measure the ring parts. It's front surface mounted to the board, as I recall.

Worth noting that with RB67 lenses, you'll have a fixed 112 mm flange to film distance, regardless of the focal length mounted, so you won't need much bellows (an RB67 has roundly three inches of travel).
 
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pdccamerqs

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Thanks!

The mount definitely attaches to the front of the board, and it appears to fit on the 118mm x 118mm board with some clearance to spare, so it should fit on the 110 x 110mm board standard for the Toyo. I guess the real question is if a 65mm OD hole in the lens board would be big enough, and while I don't currently have a Mamiya RB lens to measure, I think 65mm would be ok, as the published data for Mamiya RB-SD type lenses is 61mm. The problem than becomes that the 65mm bore may be too large not allowing enough meat to drill and tap holes for the mounting screws. The rear of an RB lens looks like the actual rear lens group is considerably smaller than the lens mount diameter, so perhaps, even a Copal #1 bore (41mm) might be adequate.

Paul






 

ags2mikon

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I mounted mine on a Cambo SC board with a copal 3 hole. I centered it, drilled 4 holes and used 4 #8 x 32 bolts and nuts to secure it. I used black polyurethane sealer in the light trap groove on the adapter board and married them. They have lived happily ever after. If I get any free time today I will make images of them and post them.
 

Donald Qualls

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Measure the opening in the adapter; any board opening that large or larger will be fine. Smaller may still work, too.
 
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pdccamerqs

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Thanks AGS and Donald! Sounds like Copal #3 is a good choice.

All the best,

Paul
 

ags2mikon

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Here is my Cambo adaption.
 

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ags2mikon

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If I change to another view camera like a Toyo or Horseman I could just unbolt it and move it to the other system.
 

ags2mikon

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Here is the one I did for the Rittreck 5x7 view. I had to machine it down on the edges to match the Rittreck boards and machine it on a lathe on the back side to match the light trap of the camera and set the right thickness for the camera.
 

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pdccamerqs

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ags2mikon said:
Here is the one I did for the Rittreck 5x7 view. I had to machine it down on the edges to match the Rittreck boards and machine it on a lathe on the back side to match the light trap of the camera and set the right thickness for the camera.
Click to expand...

Nice machining job - thanks for sharing! I am going to try to disassemble the mount from the Zhuuming board and mount it to a Toyo board. I can do some minor machining at home, but I don't have a mill and my lathe is one of those Harbor Freight table top lathes with a pretty small swing.

All the best,

Paul
 

B.S.Kumar

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I'm a great fan of adapting lenses and have been thinking of buying one of these adapters for myself. But I'm not convinced of the use case. If one already has RB lenses and uses both systems, I understand. But otherwise?

In the RB lineup, the 37mm and 50mm lenses are the most interesting, though I'm not a fan of fisheye lenses. The 47mm Super-Angulon MC and Mamiya Press 50mm lenses are great and can be used without any rework.
There isn't much incentive for the remaining focal lengths, all of which have readily available alternatives:
65mm - the big four, Topcor
90mm - Congo 90mm f/3.5, Topcor 6x9 lenses, big four
100mm/105mm - big four, Mamiya Press 100mm f/2.8, Carl Zeiss 100mm f/3.5
127mm - 125mm Fujinon, 127mm
140mm Macro - 135mm from big four
150mm - big four
180mm - big four
210mm - big four
250mm - 240mm from big four
350mm, 360mm, 500mm - from big four RB lenses are probably too unwieldy

The RZ 110mm f/2.8 and the Pentax 67 105mm f/2.4 lenses are probably the most desirable lenses for 6x7, but the Mamiya Press 100mm f/2.8 comes close, I think.

Fun fact: Mamiya RB, Fuji GX680 and Bronica SQ lenses are all mounted in Seiko #1 size shutters internally. The cells can be removed and mounted in conventional Seiko #1 shutters.

Kumar
 
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pdccamerqs

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Great info, Kumar - especially regarding the interchangeability of cells of the Mamiya, Fuji and Bronica lenses. I have a number of lenses, both LF and MF, but no Mamiya RB's. I specifically chose the RB lens for this project for two main reasons:

1) The whole point of the exercise is to be able to utilize view camera movements with a digital platform that doesn't require the use of a Leaf back or similar - in this case I plan to use my Sony A7RIV. To maximize the camera movements, a lens with both a large image circle and long flange focus distance (FFD) would be required. At 112mm the RB lenses have one of the longest FFD of any MF lens system. Both Bronica SQ and Pentax 67 are at 85mm, for instance. The image circle of RB lenses is pretty decent from what I have read. Reportedly, on 4x5:

37mm Fisheye hits all edges but obviously misses the corners.
50mm just misses the corners.
127mm covers 4x5 easily.
360mm just misses the corners

Since I am only trying to cover the full frame (24mmx36mm - 43mm diagonal) digital sensor of a Sony A7RIV, this should be fine.

2) IN GENERAL, the center resolution of MF optics can be higher than LF lenses of the same focal length.

Lastly, for about $100 USD for the adapter and $100 USD for a used 90mm or 127mm Mamiya RB lens, it's an affordable experiment. Resale should also be possible if the whole thing doesn't work out.

Does this make sense?

Paul
 

B.S.Kumar

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The large image circle and long FFD of RB lenses are strong points in their favor. But, given the small size of the Sony sensor, image circle is less of an issue. I'd be interested in finding out what happens when an RB lens is tilted or swung. Shift of course is not a problem. Can members who have actually used these lenses on view cameras show us some examples with tilt and/or swing?

Kumar
 

Alan Edward Klein

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Check out Clyde Butchers technical information at bottom right of the link. Then go to his actual photos where he shows both digital and film-captured shots. I'm not sure how to tell which were taken digitally and which taken film cameras.
https://clydebutcher.com/about-the-artist/technical-information/ prints.
 

B.S.Kumar

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Thank you, Alan. I had already seen Clyde Buthcher's digital portfolio when you mentioned him earlier. Unfortunately there are no technical details, not even which camera system or lens. I also know of others who use various other lenses from the Pentax 645 and 6x7 lineup. Again, no photos. Some of my customers have used Pentax 645 lenses on Sony cameras, but they were using them for stitching, rather than with tilts and swings. I was hoping to see images and technical details if possible..

Kumar
 
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pdccamerqs

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HI Kumar,

This photographer has some on his site including digital examples with tilt/shift.

I Built a Digital Technical Camera, and Yes, It's Slightly Ridiculous

I'm not one to obsess over gear; I've never suffered from GAS. Frankly, the seemingly endless discussions around cameras, lenses, and various bits of kit that just keep multiplying year after year, couldn't interest me less. And now that I've said that, I'm going to write about gear. The Camera...
fstoppers.com


P.
 
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