RB67 50mm Lens Floating Element Test

[Andrew O'Neill]

No disrespect Andy, but this isn't a well controlled test. To do a well controlled test you should take pictures of a relatively flat subject, and refocus after adjusting the floating element ring (which you may have done but it wasn't clear in the video).

I believe a major point of a floating element adjustment is to compensate for field curvature. Field curvature can change significantly as a function of focus distance, that is a lens with a fairly flat field at infinity might have a fairly curved field at 1 meter. This is one reason that normal fast lenses often make poor macro lenses. However, it also means that to see the effect of the floating element it would be clearer to take pictures of a flat subject as Matt pointed out.

Field curvature is not really improved by stopping down, because it has to do with the position of the focused image, not with the size of the focused spot. That is, the central zone of the lens and the outer zone are focusing the image at more or less the same place, so stopping down to eliminate the outer zone doesn't undo the field curvature. Stopping down at best encompasses the curvature with the depth of field. This is one reason a lens designer would try to address curvature with a floating element.

Distortion is also not addressed by stopping down, because again it is caused by the position of the focused image. Front element converters and closeup lenses can have a lot of distortion, so that's probably what Donald saw.

Yes, I realise that now. I'm learning as I go. And yes, I do adjust the ring in the video. But in reality, who photographs a flat field one metre away from the film plane?? The dial only shows corrections from one metre to infinity...

 

[Andrew O'Neill]

And with the floating element, it can be set before or after focusing, according to Mamiya...

 

[mshchem]

Nikon referred to this as close range correction, fast wide angle lenses has floating elements, but these would adjust automatically

 

[MattKing]

In an effort to make a useful contribution, the RB lenses are summarized here quite usefully. It says that both early and late versions of the 50mm had floating elements, and you can find which others had them as well--the easiest place to check is on the right of the page for each lens, under Pros and Cons, where it will indicate (in green) "Floating Element System" if the lens has it.

Interestingly, the "Floating Element System" link appears as blue-cyan on my screen
And by the ay, it is the 65mm lens that changed through its production history. The initial version and the "NB" version do not offer a floating element, but the final "C" version does.

 

[MattKing]

And with the floating element, it can be set before or after focusing, according to Mamiya...

It is most accurate if you first focus, then read the distance from the side of the camera, then set the ring, and then, if necessary, adjust the focus to its final position.
You would be most likely to notice the benefit of this if it was one of those photos where the primary point of interest was near the edge of the frame.
Something like the chain in this one

(and yes, I'm posting images I have from Andrew's portfolio)

 

[RalphLambrecht]

No disrespect Andy, but this isn't a well controlled test. To do a well controlled test you should take pictures of a relatively flat subject, and refocus after adjusting the floating element ring (which you may have done but it wasn't clear in the video).

I believe a major point of a floating element adjustment is to compensate for field curvature. Field curvature can change significantly as a function of focus distance, that is a lens with a fairly flat field at infinity might have a fairly curved field at 1 meter. This is one reason that normal fast lenses often make poor macro lenses. However, it also means that to see the effect of the floating element it would be clearer to take pictures of a flat subject as Matt pointed out.

Field curvature is not really improved by stopping down, because it has to do with the position of the focused image, not with the size of the focused spot. That is, the central zone of the lens and the outer zone are focusing the image at more or less the same place, so stopping down to eliminate the outer zone doesn't undo the field curvature. Stopping down at best encompasses the curvature with the depth of field. This is one reason a lens designer would try to address curvature with a floating element.

Distortion is also not addressed by stopping down, because again it is caused by the position of the focused image. Front element converters and closeup lenses can have a lot of distortion, so that's probably what Donald saw.

Andy performed a real-world test and that is good. The real world doesn't behave like flat test charts!

 

[Andrew O'Neill]

It is most accurate if you first focus, then read the distance from the side of the camera, then set the ring, and then, if necessary, adjust the focus to its final position.
You would be most likely to notice the benefit of this if it was one of those photos where the primary point of interest was near the edge of the frame.
Something like the chain in this one
View attachment 341338
(and yes, I'm posting images I have from Andrew's portfolio)

I was outside just now photographing a wall. I placed the camera one metre from the wall, levelled the camera, focused then set the distance on the floating ring. Did one at infinity, and another at the actual subject distance. I made the exposure with the aperture at its largest setting. I had to use an ND8 filter to accomplish this. Just developed the film. I'll scan 'em when they're dry.

 

[Andrew O'Neill]

Andy performed a real-world test and that is good. The real world doesn't behave like flat test charts!

I photographed a scene that I am more likely to photograph. Doing that made more sense to me.

 

[Andrew O'Neill]

I just finished the addendum video... will be uploading it tomorrow, June 15th, 1500 PST.

 

[John Earley]

I recently had my 50mm RB67 lens (C version) apart due to the floating ring being stuck. There is a small ball bearing and leaf spring that provides tension on it. When I took it apart I couldn't determine how it could possibly be adjusting anything. It's back together and works smoothly but again I just didn't see it adjusting anything.

I'm no mechanical genius so I may be completely wrong.

 

[Andrew O'Neill]

I recently had my 50mm RB67 lens (C version) apart due to the floating ring being stuck. There is a small ball bearing and leaf spring that provides tension on it. When I took it apart I couldn't determine how it could possibly be adjusting anything. It's back together and works smoothly but again I just didn't see it adjusting anything.

I'm no mechanical genius so I may be completely wrong.

Can you take it apart again and show us? Just kidding!

 

[John Earley]

Can you take it apart again and show us? Just kidding!

I'll consider it.

 

[reddesert]

Yes, I realise that now. I'm learning as I go. And yes, I do adjust the ring in the video. But in reality, who photographs a flat field one metre away from the film plane?? The dial only shows corrections from one metre to infinity...

Well, I do agree with that, and it was left out of my original post. I rarely/never do controlled lens tests because it's always something like shoot a brick wall or a newspaper or a test chart, and doesn't have a lot to do with real world photo situations. If I were going to do something like that, I would try aiming the camera down obliquely at a field of grass (technique borrowed from Roger Cicala at lensrentals.com). To understand how the image detail changes center to edge and if the position of best focus changes - that is, it allows one to separate field curvature from image quality, and it is sort of like a real photo situation.

However, there's a difference between "floating element doesn't make a difference in this real situation" and "floating element doesn't make a visible difference at all." To assert the latter, we would have to do a controlled test like the flat-field subject. I expect that there must be a case where the floating element makes some difference or Mamiya wouldn't have bothered.

Once upon a time, people probably did use the RB67 and other cameras to shoot flat subjects, for reproduction purposes, like making photos of artwork/paintings. I made slides for a painter many years ago and IIRC used a macro lens (with floating element!) on 35mm, even though the subjects weren't particularly small, it seemed best suited to the job. Of course lighting them was a bigger PITA than choosing the lens.

 

[Andrew O'Neill]

Well, I do agree with that, and it was left out of my original post. I rarely/never do controlled lens tests because it's always something like shoot a brick wall or a newspaper or a test chart, and doesn't have a lot to do with real world photo situations. If I were going to do something like that, I would try aiming the camera down obliquely at a field of grass (technique borrowed from Roger Cicala at lensrentals.com). To understand how the image detail changes center to edge and if the position of best focus changes - that is, it allows one to separate field curvature from image quality, and it is sort of like a real photo situation.

However, there's a difference between "floating element doesn't make a difference in this real situation" and "floating element doesn't make a visible difference at all." To assert the latter, we would have to do a controlled test like the flat-field subject. I expect that there must be a case where the floating element makes some difference or Mamiya wouldn't have bothered.

Once upon a time, people probably did use the RB67 and other cameras to shoot flat subjects, for reproduction purposes, like making photos of artwork/paintings. I made slides for a painter many years ago and IIRC used a macro lens (with floating element!) on 35mm, even though the subjects weren't particularly small, it seemed best suited to the job. Of course lighting them was a bigger PITA than choosing the lens.

As stated a few posts up, I'm uploading an addendum video today at 1500, which addresses the flat field subject...

 

[John Earley]

I'm no mechanical genius so I may be completely wrong.

I am definitely not an optical technician either. I looked again and there is a lever pin I didn't see that likely goes to a mechanism to adjust the focus.

My bad.

 

[Andrew O'Neill]

aaaaaaaand..... here it is!

 

[juan]

This matter closed? Ha!
thanks for your research.

 

[Andrew O'Neill]

This matter closed? Ha!
thanks for your research.

HAHA I know, right? It is for me, at least!

 

[MattKing]

Outside of the world of walls, here is another example of where you might have seen a difference

 

[Andrew O'Neill]

Outside of the world of walls, here is another example of where you might have seen a difference
View attachment 341429

It's a good thing I didn't use the RB for that series

 

[Sharktooth]

Not so fast, young man.

Who's going to shoot walls wide open. What about normal apertures like f11 or f16. What's the difference then, huh?

No donuts for you!!

 

[Andrew O'Neill]

Not so fast, young man.

Who's going to shoot walls wide open. What about normal apertures like f11 or f16. What's the difference then, huh?

No donuts for you!!

An idea for another video! It never ends!!!!!

 

[Neil Grant]

Interestingly, the "Floating Element System" link appears as blue-cyan on my screen
And by the ay, it is the 65mm lens that changed through its production history. The initial version and the "NB" version do not offer a floating element, but the final "C" version does.

...the 'NB' 65mm had the same , new type barrel, as the 'C' 65mm that replaced it. The NB has the same floating elements as the C lens. Only the original 65mm was non-floating.

 

[MattKing]

...the 'NB' 65mm had the same , new type barrel, as the 'C' 65mm that replaced it. The NB has the same floating elements as the C lens. Only the original 65mm was non-floating.

That is interesting. The link shared above by rulnaco says that the NB and C versions have different optical constructions, and only the C is shown there as having the floating element.

 

[reddesert]

Thanks for making the follow up video!

It may not have the largest practical application (except for all the wall photographers out there), but good to know.