RB67 Help, please

[Ariston]

Well, I just bought a 50mm Sekor C for my RB, and it appears to have a focusing ring on it. Can someone tell me what that is for and how I use it?

 

[MattKing]

That lens and the 65mm lens both have a floating element. The adjustment of that floating element allows you to correct for a variety of distortions and aberrations that otherwise vary with subject distance.
Here is a link to a pdf copy of a version of the Mamiya RB67 lens manual that describes in detail (on page 7) how to use that adjustable floating element: http://www.cameramanuals.org/mamiya_pdf/mamiya_rb67_interchange_lenses.pdf
The link comes from Mike Butkus' excellent site. This page on his site lists a lot of the Mamiya resources: https://www.butkus.org/chinon/mamiya/mamiya_lenses_accessories/mamiya_lenses_accessories.htm
This page on his site lists several more: https://www.butkus.org/chinon/mamiya.htm
If you get benefit from the manuals he makes accessible, I highly recommend sending him his requested donation.

 

[MattKing]

In the interest of preventing anxiety D) the floating element is most effective at refining resolution in the corners of your image. If you set the indicator by the infinity mark, and then forget about it entirely, most of your photos will be optimized or close to it, and you will have trouble seeing any problem with anything other than a flat surface parallel with the film when you work at close distances.
I have been known to forget about setting the floating element ring and still end up with a photograph I am happy with.
The effect is advantageous, but subtle. You can see probably it in your prints if you take two identical shots of a suitable subject with the ring set to two different positions, but you won't be able to see the differences in the camera's finder.

 

[Ariston]

Thanks again, Matt!

 

[MattKing]

By the way, in the interest of improving the usability of this site for everyone,it is really helpful if thread titles are a bit more specific. Something like: "Extra ring on 50mm C lens for RB67?"

 

[Ariston]

Noted - I would change it if I could. Of course, the last specific title I used got changed to the much more generic "KEH Review" -

I have to send the lens back, anyway. The shutter stays open the whole time until the end. It arrived with the shutter already cocked, anyway, which bugs me. I should have know there might be problems.

 

[MattKing]

Noted - I would change it if I could. Of course, the last specific title I used got changed to the much more generic "KEH Review" -

I have to send the lens back, anyway. The shutter stays open the whole time until the end. It arrived with the shutter already cocked, anyway, which bugs me. I should have know there might be problems.

RB67 lenses are designed to be stored with the shutter cocked, because you cannot mount (or unmount) them unless both the body and the shutter are cocked. So it would be unusual to receive the lens with the shutter uncocked.
To request a thread title change, just "Report" your own post, and make the request to the moderators in that report.
Check to make sure that the "mirror up' function has not been switched to on on that lens.

 

[Ariston]

RB67 lenses are designed to be stored with the shutter cocked, because you cannot mount (or unmount) them unless both the body and the shutter are cocked. So it would be unusual to receive the lens with the shutter uncocked.
To request a thread title change, just "Report" your own post, and make the request to the moderators in that report.
Check to make sure that the "mirror up' function has not been switched to on on that lens.

Just so you know, the Mamiya manuals say to uncock the lenses if you are going to be storing them for any length of time. This relieves the pressure from the spring and, I assume, preserves the shutter speeds. Every RB body or lens manual I've seen says to uncock it if storing for several days.

See Page #4 in the manual you posted above. You have to re-cock them to mount them.

 

[David Brown]

In the interest of preventing anxiety D) the floating element is most effective at refining resolution in the corners of your image. If you set the indicator by the infinity mark, and then forget about it entirely, most of your photos will be optimized or close to it, and you will have trouble seeing any problem with anything other than a flat surface parallel with the film when you work at close distances.
I have been known to forget about setting the floating element ring and still end up with a photograph I am happy with.
The effect is advantageous, but subtle. You can see probably it in your prints if you take two identical shots of a suitable subject with the ring set to two different positions, but you won't be able to see the differences in the camera's finder.

Ditto.

 

[Alan Edward Klein]

Noted - I would change it if I could. Of course, the last specific title I used got changed to the much more generic "KEH Review" -

I have to send the lens back, anyway. The shutter stays open the whole time until the end. It arrived with the shutter already cocked, anyway, which bugs me. I should have know there might be problems.

If the lens is set to mirror lock, it has to be released manually by the mirror lock knob on the lens.

 

[MattKing]

Just so you know, the Mamiya manuals say to uncock the lenses if you are going to be storing them for any length of time. This relieves the pressure from the spring and, I assume, preserves the shutter speeds. Every RB body or lens manual I've seen says to uncock it if storing for several days.

See Page #4 in the manual you posted above. You have to re-cock them to mount them.

I am aware of that suggestion, just as I am aware of there being some controversy about it - my camera repair resource being one who disagrees with it.
I leave mine cocked, and try to exercise them reasonably regularly.

 

[Ariston]

Did you ask your repair guy what the benefit is of leaving a spring under tension for years? I would go with the designer's advice, personally, but to each his own. This shutter didn't even fire, unfortunately.

 

[MattKing]

From what I understand, there are springs under tension in both states.
But more importantly, If you attempt to mount an uncocked lens on a cocked body, or for that matter a cocked lens on an uncocked body, it is relatively easy to cause some damage - the sort of damage that the repairer has seen much more frequently than any problems with leaving shutters cocked.
Thus his advice to leave both lens and camera cocked, and just be sure to give them some exercise from time to time.

 

[Ariston]

That's crazy - I've forgotten to cock the shutter before, and it simply won't go on. What kind of force are these people using to actually try to mount that lens uncocked? At any rate, I am in no danger of doing that, so I will uncock the shutter like the engineers who designed the lenses suggest.

 

[AgX]

Typically floating elemens automatically are moved by a cam.

In this case was the omitting of such just a means to save costs, was there a technical reason, or is there a benefit by having control of that floating element as in bokeh?

 

[Neil Grant]

That's crazy - I've forgotten to cock the shutter before, and it simply won't go on. What kind of force are these people using to actually try to mount that lens uncocked? At any rate, I am in no danger of doing that, so I will uncock the shutter like the engineers who designed the lenses suggest.

... on mine the lens will go 'on' in any condition, cocked or not. Body cocked or not. It just doesn't matter. But to take photos the body and lens must be both cocked and this condition is easily arrived at (without removing the lens) by either firing the body or cocking it.
Probably a good idea to operate the camera and lens from time-to-time. I leave the body cocked these days as the foam mirror dampers are getting tacking and can hold the mirror up.

 

[Oren Grad]

Typically floating elemens automatically are moved by a cam.

In this case was the omitting of such just a means to save costs, was there a technical reason, or is there a benefit by having control of that floating element as in bokeh?

This is not just a Mamiya thing. The 40mm and 50mm Distagon CF FLE lenses for Hasselblad have a separate ring for manual control of the floating groups.

 

[AgX]

I know, and there was such at enlarging lenses too. But I do no know such manual control at taking lenses for 35mm film.

But let us assume omitting a cam-automation was done to reduce costs, is there still a benefit for the user in having control on the floating element?

 

[GarageBoy]

I'm guessing the helicoid would have been too complicated to have it cammed - the 50 2.8f/fe hasselblad has floating elements without a separate focus ring, but it doesn't have an internal shutter

 

[MattKing]

Typically floating elemens automatically are moved by a cam.

In this case was the omitting of such just a means to save costs, was there a technical reason, or is there a benefit by having control of that floating element as in bokeh?

Where would you put the cam?
The RB67 mounts the lens and shutter combination at the end of a bellows and focuses by moving the entire assembly.

 

[Ariston]

I stand corrected - Although I could not remove the lens without cocking it, I could mount it by finnicking around with it a little, and without much force. So I can see how people might mount it mistakenly; but it was hard enough for me that I won't forget, so I will keep mine uncocked.

I am the same way with my manual SLRs. I will not store them with the shutter cocked. I have seen too many cameras with fatigued shutters. I guess that Mamiya just assumed that the pros that used these cameras would use them properly. Whether or not that is a wise assumption is up for debate!

 

[Alan Edward Klein]

SLR shutters are different than those mounted in the lens as in the RB67. How that effects the springs, I don't know

 

[Grim Tuesday]

Floating elements make sense to me for the Mamiya because the lens unit focuses and there is no way to communicate from the bellows to the floating element via cam. But in the case of the Hasselblad 40 and 50 it doesn't make any sense. Unless there are some intellectual property issues at stake.

 

[narsuitus]

Why did the Mamiya medium format TLR lenses not need floating elements but the Mamiya RB67 medium format SLR lenses need floating elements?

 

[MattKing]

Why did the Mamiya medium format TLR lenses not need floating elements but the Mamiya RB67 medium format SLR lenses need floating elements?

There isn't anything as wide in the TLR line as the 50mm in the RB line.
And with no mirror clearance issues with the TLR, it may have been easier to obtain decent flat field performance with the 55mm lens for the TLRs than it was for the 65mm lens for the RB.
And as, among all the RB lenses, the 65mm lens permits the highest amount of subject magnification through close focus without an extension tube, the designers may have included the floating element to meet the needs of users who needed "quick" close focus capability.
There actually is another lens in the RB line that has a floating element - the Macro 140mm lens. For that lens, you adjust the floating element by checking the image magnification on the scale at the side of the camera, and then transferring that setting to the floating element ring.
If I am going out with a two lens setup, I often choose to put the 65mm and the 140mm in my bag. As a result, I'm used to dealing with it.