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2x3 polaroid backs

 
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hseaver



Joined: 16 Mar 2006
Posts: 6

PostPosted: Wed Mar 22, 2006 6:06 pm    Post subject: Reply with quote

Somewhere here I read that the Mamiya RB67 polaroid backs wouldn't work with the 2x3 Century with the Graflok back. Perhaps someone can clarify this for me -- I can't understand why they wouldn't since the Mamiya RB67 roll film backs certainly work with this camera.
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disemjg



Joined: 10 Jan 2002
Posts: 469
Location: Washington, DC

PostPosted: Wed Mar 22, 2006 11:48 pm    Post subject: Reply with quote

My RB polaroid back replaces the entire revolving back on the camera; it does not fit the camera the same way as a RF back. And I do not think removing the mounting plate from the back will do you any good, either. Maybe someone out there has modified one to work, and can say how they did it.
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hseaver



Joined: 16 Mar 2006
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PostPosted: Thu Mar 23, 2006 11:38 pm    Post subject: Reply with quote

So what type of RB polaroid back do you have, or do you think it doesn't matter, do they all work the same way? Seems strange they just wouldn't connect the same way as the roll film holders.
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disemjg



Joined: 10 Jan 2002
Posts: 469
Location: Washington, DC

PostPosted: Fri Mar 24, 2006 1:46 am    Post subject: Reply with quote

Its the only one I have recently handled, and while there may be other types I doubt it. It is bulky, at least compared to the normal back end of the camera, and the only way you could get the film plane in the right positon would be to remove the rotating back and integrate the hardware into the Polaroid back. Which is what they did. I'll send a photo via Les so you can see what it looks like; once you see it you'll understand.

The only Polaroid back that I've seen that would fit a normal Graflok 2X3 is the Horseman. At least the older one I have will (I think). I'll have to pull it out and check, but they're hard to come by and pricy.

[ This Message was edited by: disemjg on 2006-03-23 17:49 ]
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Les



Joined: 09 May 2001
Posts: 2682
Location: Detroit, MI

PostPosted: Sat Mar 25, 2006 3:53 am    Post subject: Reply with quote

For illustration purposes:


[ This Message was edited by: Les on 2006-03-24 19:54 ]
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disemjg



Joined: 10 Jan 2002
Posts: 469
Location: Washington, DC

PostPosted: Sat Mar 25, 2006 9:49 pm    Post subject: Reply with quote

Thanks, Les.

The Mamiya back is in the rear, and you can see the plate that mounts to the rear of the camera after the rotating back has been removed.

The Horseman back is in the front, and you can see the raised area that fits into the normal camera back where the film holder normally goes. It even looks like a sheet film holder, mounted on the Polaroid back. Since the Horseman back changes the film plane, a spacer is used to reposition the front lens standard to compensate.

I suppose that you could use a 2X3 film holder to modify the Mamiya back, but you'll need to make a spacer like the Horseman to compensate for the change in the film plane. I'd only try that if I could get the Polaroid back really cheap, so that it would not matter if the idea did not work out.

[ This Message was edited by: disemjg on 2006-03-25 14:09 ]
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hseaver



Joined: 16 Mar 2006
Posts: 6

PostPosted: Sun Apr 02, 2006 6:00 pm    Post subject: Reply with quote

Thank you -- that helps a lot. I bought a Lane (BSI LB-77) polaroid back for the RB67 on ebay for only $30 including shipping, so I guess I'll try to cut off the adapter part and glue on a 2x3 film holder. One thing I do notice with this tho is that the opening is surprisingly large -- almost exactly 3"x3 3/16", which seems rather large for the 6x7 format.
Are you saying that if I put a spacer behind the lens standard, the ground glass focus will be right on, but then I'd have to remove that before shooting? Or I could put another ground glass on a different film holder, correctly spaced for the film plane in the polaroid back?
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disemjg



Joined: 10 Jan 2002
Posts: 469
Location: Washington, DC

PostPosted: Sun Apr 02, 2006 11:29 pm    Post subject: Reply with quote

The spacer goes between the front standard's base and the infinity stops on the yoke. So the spacer is in FRONT of the lens.

The Polaroid back has a film plane that is further to the rear than a normal back. The spacer has the effect of keeping the lens the correct distance from the adjusted film plane, by pushing the lens plane to the rear. The spacer is of course supposed to be equal to the setback of the Polaroid holder compared to a normal holder.

Once you lock the front standard in place using the spacer, remove the spacer as typically they just sit there and you would lose it.
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hseaver



Joined: 16 Mar 2006
Posts: 6

PostPosted: Mon Apr 03, 2006 4:08 pm    Post subject: Reply with quote

But that doesn't help with focusing with the ground glass. Don't you also need an equal size spacer between the body and the groundglass?
To add further to my confusion, I noticed on ebay people selling a "P adapter" to use with polaroid backs on the RB67. A lot of googling and asking questions of Mamiya people didn't clarify things a whole lot (in fact some of them seemed more confused about it then me, including the people selling them) -- but what it seems to be is that some RB67s and some polaroid backs need this P adapter to fit together, and as far as I can see from the pictures of that adapter, it looks like what is glued on my Lane back, and what your pictures show on the Mamiya polaroid back.
At any rate, as soon as I can find the time, I'll try to do the surgery on the Lane back. I was hoping it screwed together, but no such luck, it seems to be firmly glued on, so I'll try an exacto knife first, then a cutoff wheel on the dremel if need be.
Both of the 2x3 film holders I have seem to be made of wood -- are there plastic ones available?
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disemjg



Joined: 10 Jan 2002
Posts: 469
Location: Washington, DC

PostPosted: Mon Apr 03, 2006 11:27 pm    Post subject: Reply with quote

The spacer will work with GG focusing; all you do is focus on the GG with the front standard up against the infinity stops, as though you were not even using the Polaroid back. Then, with the yoke locked, back off the front standard, insert the spacer, swap the GG insert with the Polaroid back, and shoot.

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hseaver



Joined: 16 Mar 2006
Posts: 6

PostPosted: Tue Apr 04, 2006 1:59 am    Post subject: Reply with quote

Oh duh! yeah, that would work okay. thanks. Now I'm really wondering about the old roll-film polaroid adapter I bought for my 4x5 -- that had a GG adapter, but obviously the smaller cheaper front spacer would have worked as well or better. I wonder if that was hand-made. I know the Lane back I bought on ebay looks like the coversion was home done. Actually, the polaroid back itself looks a lot like the horseman one you pictured, only the adapter part looks different, and that looks like the picture of the mamiya, as I said before.
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