Floating element(s)?

[Donald Qualls]

I recently learned that the Sekor 50mm f/4.5 that I got for my RB67 has a "floating element" -- a user-adjustable internal element or group with a calibrated ring to allow the user to optimize the lens performance for different focus distances.

Then, when the metered chimney finder arrived yesterday, I was testing it with the 250mm f/4.5 and noticed that that lens, also, has a distance calibrated front ring -- is this a floating element control also, or just an unusually sophisticated DOF scale (much easier to read and harder to misread than the one on the side of the bellows)? Even my 90mm f/3.8 has such a scale (though it's operated by a tab, rather than a ring), suggesting it isn't just something brought in with the retrofocus or telefocus designs of the long and wide lenses.

I've heard of floating element lenses -- I just hadn't realized that seemingly all the Sekor lenses for the RB67 have them. Seems like a nice way to get the last little bit of image quality for a primarily studio oriented camera system, or when working on tripod in the field, but much less handy when shooting off tripod (which, admittedly, I don't do much due to the weight of the camera and lenses).

In a lens in helicoid, it would seem obvious to use internal gearing to link these floating elements to the focus, but that's not available for a lens that focuses on a bellows -- is this common with lens designs post-1970, and I just never knew it (because I don't use many newer cameras or lenses)? And how much have I been giving up by not even knowing the setting was there to check when I've shot with my 250mm in the field?

 

[ic-racer]

It is better to have the floating elements on a separate ring if you are the one repairing the lens Doing repairs on lenses with coupled second helicoid for the floating element is like doing repairs on zoom lenses.

Speaking of floating elements, I noticed my 'state of the art' 50mm/2.8 Super Angulon Autofocus lens uses the floating element to focus. I don't think there is even a helicoid in there, more of a pin-and-slot mechanism. So, its mechanism seems even simpler than any of the other 50mm wide-angle Rolleiflex lenses (except the SL66 lenses with no focus mechanism).

 

[osella]

I’m not entirely sure about the RB, but in the case of the RZ all the lenses have a DOF scale on the front of the lens that has a tab.

There are only a few lenses that have the floating element and are adjusted with a ring. So I would think any ring with a tab is just a DOF scale. On the RZ lenses the rings had no stops and could be rotated 360 degress freely. The floating elements did have limits to their travel.

 

[Alan Edward Klein]

The scale you're referring is for determining DOF for all aperture settings. Only the 50mm has a floating element.

 

[Alan Edward Klein]

Note that the scale on the side of the camera is for determining additional stops of exposure required when extending the bellows to shoot close-ups. It's not a DOF scale.

There's also another scale on all the lenses that show what the aperture should be would be if you changed the shutter speed from the present setting. That scale is along the shutter and aperture rings.

Mamiya has a breakdown of DOF for different focus points and apertures for all their lenses in their manual. They explain their operation as well including how to set the floating ring. The manuals on the camera are also available. This site provides those manuals for a small fee which is recommended.
https://www.butkus.org/chinon/

 

[Donald Qualls]

The scale you're referring is for determining DOF for all aperture settings. Only the 50mm has a floating element.

Okay. Makes it a little confusing -- "Oh, this isn't something mandatory, unless you have the 50mm mounted, then it's mandatory." But I guess it's good that there wasn't a need for this except in the very wide lens. I need to get out with the 50mm soon, the widest I've shot on 35mm is a 35mm lens, and this is about equivalent to a 25-28mm.

 

[138S]

or just an unusually sophisticated DOF scale (much easier to read and harder to misread than the one on the side of the bellows)?

In my 140mm Macro C it is only a DOF scale...



Those Sekors are quite fine lenses !!!

I have the 50, 65, 90, 127, 140 macro, 180, 250, 360 and 500, plus the teleconverter... all are superb.

 

[Alan Edward Klein]

Donald, the 50mm is a wonderful lens. Here's are some of my shots with it. I think you're really going to enjoy it. Good luck.
https://www.flickr.com/search/?sort...h=1&tags=50mm&user_id=55760757@N05&view_all=1

 

[Donald Qualls]

Those Sekors are quite fine lenses !!!

Haven't had any complaints yet with the 90mm and 250mm -- slowly building up the set.

 

[Alan Edward Klein]

Here are the instructions for the 50mm lens floating element and the DOF chart, both from the Mamiya lens manual.

 

[Alan Edward Klein]

Here' the DOF chart in Feet. The last one was in meters.

 

[Donald Qualls]

Wow -- hyperfocal from half a meter at f/32?! I guess it makes sense; you've got roughly double the negative diagonal of a 35mm, so you get more DOF at the same focal length (less enlargement for a given viewing scale means larger circle of confusion is acceptable).

 

[woodlandSerenade]

Only the 50mm has a floating element.

I'm relatively certain that the 65mm and 140mm lenses also have floating elements; at least my Sekor C copies do.

 

[Louis J. P II]

The scale you're referring is for determining DOF for all aperture settings. Only the 50mm has a floating element.

Not true Alan. The RB SD lens set straight from a RB SD brochure 2005 The RB SD lenses in FL of 50mm 65mm 75 f3.5 mm 90mm & 140mm macro have a front floating element. I have all but the 75mm ( so 50/65/90/140macro) and all are the newer KL design all but the 50mm(never available in newer style), I can confirm all have a floating front element with near focus to infinity focus limits.

 

[138S]

Haven't had any complaints yet with the 90mm and 250mm -- slowly building up the set.

This is an amazing system to enjoy... very studio oriented as it is massive, but if hauled around one saves gym sessions

Let me tell my "review".

Personally, I finally could get used to its ergonomy: lelft hand handling !!! IMO best solution is having the strap tensioned in the neck and firing with left index or middle finger, with the camera in the left hand, helped with right hand in the right focus knob... with the chimney finder.... this places the camera at a good height to photograph kids. Also it is a good camera height for full body shots, but I find that with the chimney the camera stays a bit too low for head+shoulders, in that case the (metered) prism finder is better, bbut it weights a lot. Sadly the RZ pentamirror cannot fit. To nail precise focus often I move forward/back to refine, instead turning the know, useful for moving kids.

I've the grip, but I never felt confortable with it.

A bit difficult to explain it... but I always feel happy when I've the RB67 mistress in the hands... you get instantly inspired.

Also it is always a pleasure to operate it, it sports a very high quality construction, precision in a solid block. Weight is painful... but it also helps stability. Sometimes I've used a monopod, the poorman's VR.

Also see bokeh nature... I find it rocks...

https://www.flickr.com/photos/125592977@N05/14563773497/

 

[Alan Edward Klein]

I'm relatively certain that the 65mm and 140mm lenses also have floating elements; at least my Sekor C copies do.

It could be. I don't have those lenses. But the Mamiya lens manual only mentions the 50mm. If you have one of those two lenses, just check if there's that extra focusing ring and act accordingly.

 

[Alan Edward Klein]

Not true Alan. The RB SD lens set straight from a RB SD brochure 2005 The RB SD lenses in FL of 50mm 65mm 75 f3.5 mm 90mm & 140mm macro have a front floating element. I have all but the 75mm ( so 50/65/90/140macro) and all are the newer KL design all but the 50mm(never available in newer style), I can confirm all have a floating front element with near focus to infinity focus limits.

I stand corrected. I was going by the original RB67 instruction manual and my lenses which are the C type or the pre-C type. If later lenses like the KL or SD have this ring, then of course use it.

 

[Alan Edward Klein]

This is an amazing system to enjoy... very studio oriented as it is massive, but if hauled around one saves gym sessions
...this places the camera at a good height to photograph kids. Also it is a good camera height for full body shots, but I find that with the chimney the camera stays a bit too low for head+shoulders, in that case the (metered) prism finder is better, bbut it weights a lot. Sadly the RZ pentamirror cannot fit. To nail precise focus often I move forward/back to refine, instead turning the know, useful for moving kids.
...
https://www.flickr.com/photos/125592977@N05/14563773497/

I use the eye-level viewfinder as well. I also have a magnifier that fits over the finder for more precise focusing. It has a diptor focuing ring. It flips out of the way when you want the full view and is removeable when you don't need it.

 

[Alan Edward Klein]

Here's the eye level magnifier.
https://www.google.com/search?q=rb6...SGFkFHa5xCK8Q_AUoAnoECAkQBA&biw=2133&bih=1174

 

[138S]

I use the eye-level viewfinder as well. I also have a magnifier that fits over the finder for more precise focusing. It has a diptor focuing ring. It flips out of the way when you want the full view and is removeable when you don't need it.

hmmm, it has to be quite interesting for critical focus.... now that you say it....

Sometimes, with the RB67 on tripod , I have used the x8 loupe for the view camera, after removing the chimney, but I had to also use a dark cloth to see...

 

[MattKing]

For clarity, the biggest role of the floating element is to improve corner and edge resolution, by adjusting the flat field performance.
Which is quite important when you are using the 140mm macro lens at close distances.
I tended to leave the setting on my 65mm lens at the infinity position, except when working quite close, because I rarely worried much about the flatness of field except when I was photographing something that was both close and flat.

 

[Lachlan Young]

Wow -- hyperfocal from half a meter at f/32?! I guess it makes sense; you've got roughly double the negative diagonal of a 35mm, so you get more DOF at the same focal length (less enlargement for a given viewing scale means larger circle of confusion is acceptable).

I think the CoC on the scale may be pretty relaxed - it looks like about a 2.4x enlargement or so, at the minimum paper resolution requirement. It's a bit like the seemingly perplexing max reproduction scale on the Pentax 6x7 135mm macro - till you realise that it's intended to intended to deliver a life-size image when enlarged to 8x10...

 

[138S]

For clarity, the biggest role of the floating element is to improve corner and edge resolution, by adjusting the flat field performance.
Which is quite important when you are using the 140mm macro lens at close distances.
I tended to leave the setting on my 65mm lens at the infinity position, except when working quite close, because I rarely worried much about the flatness of field except when I was photographing something that was both close and flat.

Matt, I cannot tell if the displacement of the floating element also optimizes the field focus flatness, but IMO the main reason to implement that refinement is to optimize resolution at different magnifications, by minimizing the Point Spread Function dispersion, beyond field flaness, specially as we go off-axis, of course, the ray on axis has null dispersion in theory.

______________


It is not a secret that it is a challenge to optimize a lens for very different magnifications as we get close... an expensive design helps, a floating element/group (or several) helps more. In an Internal Focus design an additional mechanism can be actioned by the focus ring, or the internal focus movement may account for some distance optimization, but the R67 is basicly a Unit Focus system, with the lens having a fixed arrangement, so obviously that ring is the direct solution.

Unit Focus way allow relatively simple (and cheaper) lenses to deliver an impressive yield, but variable distance optimization is not supported, still a more expensive design may allow a better close performance.

In the Nikon realm we had the 50mm 1.8 vs 1.4 example, contrary to the 1.4, the 1.8 is Unit Focus having less distortion and being slightly sharper than the 1.4, but sporting focus breath that is the main drawback of the Unit Focus-

The RB67 prime lenses (the 100-200 zoom is internal focus) benefit a lot from Unit Focus advantage, traded by the drawbacks of Focus Breath and having to compensate when not TTL metering, plus requiring an additional ring for Macro.

 

[AgX]

If operating that ring shows internal lens elements moving, the answer is given. If not, the question may arise if one not just overlooked such movement, such would not make one wiser than before.

 

[138S]

If operating that ring shows internal lens elements moving, the answer is given. If not, the question may arise if one not just overlooked such movement, such would not make one wiser than before.

The DOF scale ring is only a ring, with nothing moving inside as it is rotated..