Extension Tubes for RB67...

ChristopherCoy · May 24, 2021

Thinking about getting a set. I've been using my 105 macro on my F2's a lot lately and I've enjoyed shooting macro-esque stuff. I've read that some of the Mamiya lenses don't perform optimally, and will vignette a little. This seems to be supported by the attached literature that was printed.

I'm just a little confused as to how they work exactly. My only experience with extensions is with a Nikon TC, which effectively doubled my 70-200, to a 140-400. But as I understand it, that's not what extension tubes do. All they do is allow you to focus closer to the subject correct? So where I might have been 3ft away with the 180mm, I can now get to 1ft away and focus correctly? You're not really getting a 1:1 magnification right?

wiltw · May 24, 2021

Watch what happens when you focus your SLR to some relatively close distance (5') from Infinity...the lens optics moves away from the body travelling within the barrel of the lens exterior
An extension tube is simply a tubular 'extension' with no optics, and it effectively moves the lens even farther from the body than the lens tube can extend!...it is that simple for 'getting closer' and even to 'getting to macro distance'.from the subject.

When the travel distance of the lens optics gets far enough away from the body (distance of lens node to focal plane = 2*FL) iit will present a 1:1 reproduction (lifesize on film)

The same thing applies to RB67...the lens optics move outwared on the bellows...and when the bellows cannot extend the lens outward any farther, extension tubes take on the role of moving the lens optics even farther outward.

MattKing · May 24, 2021

The 65mm RB67 lens will allow you to obtain the highest magnification, both without extension tubes, and with them.
The calculations respecting magnification reference the lens nodal points - and different lens designs result in lens nodal points being in a lot of different places. Telephoto lenses put them in front of the lens itself, while retro-focus lenses (primarily wide angle lenses) put them behind the lens itself.
While a 65mm lens allows for the highest magnification with an RB67, its close focus performance isn't the highest - primarily due to poor flatness of field.
If you look at the magnification numbers for the 140mm macro lens, they are less than for many others.
However, the flat field performance of the 140mm lens is much better than the other lenses that give higher magnification.
That 140mm lens was part of my favorite two lens kit, along with the 65mm.
Even though I didn't use it for close focus/high magnification work all that frequently.
Orchids, with the 140mm macro and an extension tube:

narsuitus · May 25, 2021

The 140mm Mamiya Sekor f/4.5 macro lens with the #1 and #2 extension tubes allow enough extension to obtain a 1:1 magnification.

RB67 macro by Narsuitus, on Flickr

1:1 Macro by Narsuitus, on Flickr

ChristopherCoy · May 25, 2021

MattKing said:
The 65mm RB67 lens will allow you to obtain the highest magnification, both without extension tubes, and with them.

If the 65, 127, and 180 lenses that I have, the 127 is what I use most, and the 67 is what use the least. In fact I'm not even sure I've used the 65 yet.

Why does the 65 allow the highest magnification? That seems backwards to me.

Donald Qualls · May 25, 2021

The bellows and macro tube will move the lens a fixed maximum distance from the film plane -- and the ratio of that distance to the focal length of the lens sets the focus distance to the object. The ratio of object distance to film plane distance, in turn, determines image size ratio; if the two distances are the same, you get 1:1, if the lens is further from the film than its focal length (with macro tubes, possible with 127 and shorter, maybe barely with the 140) your image on the film will be larger than the object. Overall, for given maximum extension, the shorter the focal length of the lens, the larger the image because the closer the lens can be to the subject and still focus.

For a 50mm lens, you'd need 100 mm flange to film to get 1:1, and your object would be 100 mm ahead of the lens node. If you have 200 mm of flange to film, you can get closer -- IIRC, with that same 50 mm lens you'd get around 67 mm front focus, to give a 3:1 larger image on the film vs. the object size (this is just an example -- Mamiya doesn't recommend using their 50 mm lens on more than the single shortest tube, probably for the same reasons given above for the 65 mm).

ChristopherCoy · May 25, 2021

Hunh... I just found a video where someone put the 82mm tube on the 180mm lens, then taped a reversed 127mm lens to the front of that. Interesting.

Donald Qualls · May 25, 2021

ChristopherCoy said:
Hunh... I just found a video where someone put the 82mm tube on the 180mm lens, then taped a reversed 127mm lens to the front of that. Interesting.

Hope they used good tape. I'd hate to drop the 127 on whatever I was trying to photograph...

ChristopherCoy · May 25, 2021

Donald Qualls said:
Hope they used good tape. I'd hate to drop the 127 on whatever I was trying to photograph...

Right. I wouldn't be worried about what I was photographing though, I'd be more worried about the lens.

Donald Qualls · May 25, 2021

I guess that depends on what you're photographing. That 127 isn't light. Well, by RB67 standards, it is, but...

ChristopherCoy · May 25, 2021

Ok. I just scored a set of tubes for $40 shipped. Looking forward to using them.

MattKing · May 25, 2021

ChristopherCoy said:
Why does the 65 allow the highest magnification? That seems backwards to me.

Donald Qualls said:
The bellows and macro tube will move the lens a fixed maximum distance from the film plane -- and the ratio of that distance to the focal length of the lens sets the focus distance to the object. The ratio of object distance to film plane distance, in turn, determines image size ratio; if the two distances are the same, you get 1:1, if the lens is further from the film than its focal length (with macro tubes, possible with 127 and shorter, maybe barely with the 140) your image on the film will be larger than the object. Overall, for given maximum extension, the shorter the focal length of the lens, the larger the image because the closer the lens can be to the subject and still focus.

In addition, the 65mm might be a retrofocus design, which means that the rear nodal point (the point where you need to measure from) is actually even closer to the film - possibly even closer than the back edge of the lens.

ChristopherCoy · May 25, 2021

My 65mm is the old design with the flared front element.

Donald Qualls · May 25, 2021

MattKing said:
In addition, the 65mm might be a retrofocus design, which means that the rear nodal point (the point where you need to measure from) is actually even closer to the film - possibly even closer than the back edge of the lens.

I'm pretty sure the only RB67 lenses that aren't either tele or retrofocus are the 90mm and 127mm. The flange to film is greater than 65mm, as I recall (not much greater, it might get away with a slight protrusion inward and still clear the mirror).

ChristopherCoy · May 25, 2021

What happens if you stack extension tubes. Like two 82mm under the 180mm lens?

Donald Qualls · May 25, 2021

Other factors equal, that stack should get you past 1:1 with a 180 mm lens (you have 164 mm of tubes, but the bellows can extend about 40+ mm beyond its fully retracted infinity position).

Of course, you'd better have your tripod mount on the front bumper of a loaded dump truck...

MattKing · May 25, 2021

Do you really need a full frame image of someone's eyeball?
And does depth of field matter so little to you?

ChristopherCoy · May 25, 2021

MattKing said:
Do you really need a full frame image of someone's eyeball?
And does depth of field matter so little to you?

LOL. No, I just don't have any experience with tubes so I'm just wondering what the possibilities are.

wiltw · May 25, 2021

ChristopherCoy said:
LOL. No, I just don't have any experience with tubes so I'm just wondering what the possibilities are.

What happens with tubes is exactly what happens without tubes, the only thing changing is how close (how high of magnification of scale of reproduction.

Get closer = less DOF
Higher magnification = apparent increased loss of intensity of light at focal plane

ChristopherCoy · May 28, 2021

My tubes got here today - surprisingly quickly. They appear to be absolutely mint. Not a single scratch or smudge on them. Can't wait to get them on the camera.

I'm assuming that they don't have any gears or mechanics in them, and the jiggle sound they make is normal?

abruzzi · May 28, 2021

don't know about the RB67 stuff, but usually extension tubes will have some kind of coupling to the camera, because they need to stop down the lens to the working aperture, and I'm guessing on the RB it will have something to trigger the shutter, and probably to recock the shutter.

wiltw · May 28, 2021

ChristopherCoy said:
My tubes got here today - surprisingly quickly. They appear to be absolutely mint. Not a single scratch or smudge on them. Can't wait to get them on the camera.

I'm assuming that they don't have any gears or mechanics in them, and the jiggle sound they make is normal?

Research the proper ORDER of ASSEMBLY...some equipment requires you to mount the extension tube to the lens, and THEN mount the combination to the body.

And then, conversely, there is an ORDER of DISASSEMBLY.

Some designs can jam up if you do things wrongly!

ChristopherCoy · May 28, 2021

Holy hella extension batman!!! Both tubes with the 180! That’s a 1’ ruler for scale.

I did already notice how much easier it was to use the 65mm instead of the 180. I also thought something was wrong until I put the 65mm about 1/2 an inch from my test subject.

MattKing · May 28, 2021

They do have some mechanics in them - otherwise pressing the shutter release on the camera body wouldn't cause the shutter to cycle, and pushing the cocking lever on the camera body wouldn't cock the shutter.
But there isn't anything in them that deals with exposure - aperture and shutter speed controls are all on the lens.
Page 26 of the instruction manual for the RB67 Pro-S has everything you need. And I know you have that.

abruzzi · May 29, 2021

MattKing said:
But there isn't anything in them that deals with exposure - aperture and shutter speed controls are all on the lens.

doesn’t the rb have some linkage to stop the aperture down when you Fire?

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