How to use K/L floating lens for RB67

[peterB1966]

I have a 90mm K/L floating lens for RB67, and while the fora on the RZ67 seems to indicate the DOF calculator at the front of the RZ67 lenses is just that, a calculator, the K/L actually tells the floating element where to sit based on the distance to your focal point, which would help with edge sharpness.

Can anyone confirm that this is correct (i.e. an additional step when shooting, if one wants the best results)?

 

[AgX]

Typically a "floating" group is displaced automatically by being interlocked to the focussing barrel, similar as groups are moved in zoom lenses.
Recently we had a thread about a floating group at an MF lens actually having to be manually set by a dedicated ring. I guess it was about your lens.

 

[peterB1966]

Typically a "floating" group is displaced automatically by being interlocked to the focussing barrel, similar as groups are moved in zoom lenses.
Recently we had a thread about a floating group at an MF lens actually having to be manually set by a dedicated ring. I guess it was about your lens.

Thanks for the reply - not sure if I am misunderstanding, but on the RB67 the lenses don't have focusing barrels... you focus with the bellows on the camera body?

 

[AgX]

Uuh, I forgot about the bellows focussing...
However this explains why in such case the floating elements are to be set directly.

 

[cramej]

You set the floating element to the same distance at which you are focusing. Forgetting to set it will not have a detrimental effect on the image, though setting properly will yield an improvement in sharpness.

 

[Ian C]

What Mamiya refers to as a floating unit is more commonly called a field flattener. Many helicoid-focused lenses, especially wide-angle lenses, have this cam-actuated inside the lens assembly.

It does essentially nothing at infinity and almost nothing at medium focusing distances (assuming that the float ring is at the infinity setting) . Nikon uses the term CRC (Close Range Correction). It’s all the same. Lenses, especially fast wide-angle lenses, generate field curvature as the subject distance becomes close. That can soften the image radially outward. The field flattener on the RB and RZ lenses use a cemented doublet that is moved independently of the main focus to flatten the field near the image plane.

The following gives the correct focusing method for use on RB67 and RZ67 lenses equipped with the independently adjusted field flattener (“Floating System”).

Mamiya-Sekor_Macro_C_140mm_f4.5.pdf (mamiyaleaf.com)

 

[AgX]

The term common at camera lenses seems "floating elements", I have not yet come across the term "field flattener" at publications from camera manufacturers or such.

 

[reddesert]

"Floating element" describes the mechanics - a lens that moves separately from unit focusing. "Field flattener" describes the optical function. It is a common term in optics and in telescopes, especially when used for astrophotography. https://en.wikipedia.org/wiki/Field_flattener_lens

 

[MattKing]

The floating element term does more comfortably apply to an element that automatically moves (floats) as you focus the lens.
A manually adjustable, movable element is probably better called something else, but often isn't.
And K/L designation doesn't necessarily mean that there are floating elements. In fact, only the 65mm, 75mm and 140mm K/L lenses for the RZ67 offer a manually adjustable floating element.
As for the RB67 lenses, the earlier 50mm, 65mm and 140mm macro lens have the manually adjustable floating element. If there is a manually adjustable floating element on the 90mm K/L, it will most likely have marks for close and far "leave it here if you can't adjust" settings.

 

[peterB1966]

What Mamiya refers to as a floating unit is more commonly called a field flattener. Many helicoid-focused lenses, especially wide-angle lenses, have this cam-actuated inside the lens assembly.

It does essentially nothing at infinity and almost nothing at medium focusing distances (assuming that the float ring is at the infinity setting) . Nikon uses the term CRC (Close Range Correction). It’s all the same. Lenses, especially fast wide-angle lenses, generate field curvature as the subject distance becomes close. That can soften the image radially outward. The field flattener on the RB and RZ lenses use a cemented doublet that is moved independently of the main focus to flatten the field near the image plane.

The following gives the correct focusing method for use on RB67 and RZ67 lenses equipped with the independently adjusted field flattener (“Floating System”).

Mamiya-Sekor_Macro_C_140mm_f4.5.pdf (mamiyaleaf.com)

Much appreciated - will look through it

 

[Neil Grant]

.. the instructions for setting the floating elements (link) are specific to the 140mm macro C and not necessarily the other RB lenses with floating elements. The 140mm macro can show a slight but noticeable focus shift when the FE control is adjusted. The focus will then need touching up. Compare this with the situation when adjusting the FE's on the 50mm C and 65mm C lenses - no observable focus shift occurs. Not sure if the FE's on the 90mm KL cause a focus shift - but if they do, the lens focus should be adjusted.

 

[Alan Edward Klein]

Link to a discussion about the floating ring.
https://www.flickr.com/groups/42161461@N00/discuss/72157607240612842/

 

[Alan Edward Klein]

I have a 50mm with floating ring:

Here are some of the instructions. See link for complete.
https://rb67.helluin.org/lenses/50mm-f4-5c/

• Floating Element: This lens has a floating element which is moved by a separate ring marked with green numbers, located in the front of the shutter speed ring. Most lenses, like this one, are designed to have the best sharpness when focused at infinity. Other lenses, like many macro lenses, are designed to have the best sharpness when focused closely. The floating element allows you to get the best sharpness at a range of focusing distances.
• Notes: Acceptable results can be had by setting the floating element ring at infinity. This will give acceptable focus from about 7 feet to infinity. Setting the ring at 3.3 feet gives acceptable result from 3.3 to about 7 feet. If focusing closer, set at 3.3 feet at stop down as much as possible.
• Using: To use the lens, first focus with the bellows focusing. Second, use the focusing scale on the side of the body or a tape measure to find the focusing distance. Third, align the floating element ring so that the green number matching the distance lines up with the red dot on the depth of field scale

 

[MattKing]

.. the instructions for setting the floating elements (link) are specific to the 140mm macro C and not necessarily the other RB lenses with floating elements. The 140mm macro can show a slight but noticeable focus shift when the FE control is adjusted. The focus will then need touching up. Compare this with the situation when adjusting the FE's on the 50mm C and 65mm C lenses - no observable focus shift occurs. Not sure if the FE's on the 90mm KL cause a focus shift - but if they do, the lens focus should be adjusted.

I believe that all the floating element lens adjustments cause some focus shift, however the amount of shift is so relatively small with the 50mm or 65mm that it is difficult to observe.
In any event, I used the same technique with all three.

 

[peterB1966]

I shoulda known there would be the inevitable discussions of is it reallllly a floating element etc, so should have just put it to bed with a snapshot of the lens. See below:

 

[AgX]

... while the fora on the RZ67 seems to indicate the DOF calculator at the front of the RZ67 lenses is just that, a calculator, the K/L actually tells [it ontrols a] floating element ...

Can't one just look at the lens and see what it is doing when turning that ring?

 

[peterB1966]

Can't one just look at the lens and see what it is doing when turning that ring?

Not really, as this may have a really subtle effect on the edges at the best of times, and I am viewing via a speckled, decades-old viewfinder/magnifying glass combo

 

[AgX]

I did not mean looking through the viewfinder, but looking at the lens direcly.
(One must do the same for instance when trying to differ between a plain triplet and a Tessar type, or when to fo find out where a speck sits.)

 

[peterB1966]

I did not mean looking through the viewfinder, but looking at the lens direcly.
(One must do the same for instance when trying to differ between a plain triplet and a Tessar type, or when to fo find out where a speck sits.)

In which case, no.

 

[MattKing]

I shoulda known there would be the inevitable discussions of is it reallllly a floating element etc, so should have just put it to bed with a snapshot of the lens. See below:

View attachment 284052

There must be two 90mm K/L versions, because the ones I have seen (admittedly not many) didn't have that marking.
The Mamiya RZ system brochure also doesn't include that version of the 90mm in the list of floating element lenses.
I would suggest using the procedure specified in the manual for the 140mm macro lens.

 

[Dirb9]

There must be two 90mm K/L versions, because the ones I have seen (admittedly not many) didn't have that marking.
The Mamiya RZ system brochure also doesn't include that version of the 90mm in the list of floating element lenses.
I would suggest using the procedure specified in the manual for the 140mm macro lens.

All of the Rb67 90/3.5 K/l lenses have a floating element. The confusion might come from not all of the K/L lenses having the green "floating system" engraving, it seems that Mamiya started that engraving in the mid 90s, a few years after the lens was introduced, however all RB67 lenses with the rubber ring have true floating elements. The lenses with a small simple plastic or metal ring to check DOF are not floating elements. The earlier Sekor C 90/3.8 did not have a floating element.
As for the RZ67 version, you are correct, it is a drastically different design, much simpler in a 6e/6g configuration with no floating element, as opposed to the 11e/9g arrangement in the RB67 K/L. I don't know why the more advanced 90 never was introduced in an RZ67 version.
The basic procedure of focus, read the distance, and set the ring works fine, and actually pretty fast once you get used to it. And, as other people have mentioned, it really makes the most difference at close focusing ranges, so you don't need to worry about it for landscapes.

 

[Alan Edward Klein]

All of the Rb67 90/3.5 K/l lenses have a floating element. The confusion might come from not all of the K/L lenses having the green "floating system" engraving, it seems that Mamiya started that engraving in the mid 90s, a few years after the lens was introduced, however all RB67 lenses with the rubber ring have true floating elements. The lenses with a small simple plastic or metal ring to check DOF are not floating elements. The earlier Sekor C 90/3.8 did not have a floating element.
As for the RZ67 version, you are correct, it is a drastically different design, much simpler in a 6e/6g configuration with no floating element, as opposed to the 11e/9g arrangement in the RB67 K/L. I don't know why the more advanced 90 never was introduced in an RZ67 version.
The basic procedure of focus, read the distance, and set the ring works fine, and actually pretty fast once you get used to it. And, as other people have mentioned, it really makes the most difference at close focusing ranges, so you don't need to worry about it for landscapes.

I keep mine set on infinity when shooting landscapes as a matter of procedure in case I forget to set it.

 

[MattKing]

All of the Rb67 90/3.5 K/l lenses have a floating element. The confusion might come from not all of the K/L lenses having the green "floating system" engraving, it seems that Mamiya started that engraving in the mid 90s, a few years after the lens was introduced, however all RB67 lenses with the rubber ring have true floating elements. The lenses with a small simple plastic or metal ring to check DOF are not floating elements. The earlier Sekor C 90/3.8 did not have a floating element.
As for the RZ67 version, you are correct, it is a drastically different design, much simpler in a 6e/6g configuration with no floating element, as opposed to the 11e/9g arrangement in the RB67 K/L. I don't know why the more advanced 90 never was introduced in an RZ67 version.
The basic procedure of focus, read the distance, and set the ring works fine, and actually pretty fast once you get used to it. And, as other people have mentioned, it really makes the most difference at close focusing ranges, so you don't need to worry about it for landscapes.

So the lens pictured is not a RZ67 lens, it is an RB67 lens.
That now makes much more sense. And I now realize that the OP's first reference was to the RB67 K/L version. Unfortunately, he/she immediately started referring to the RZ67 K/L lenses, and I immediately misunderstood what he was referring to. All of my earlier references in this thread are to the RZ67 lenses. My fault.
FWIW, I don't tend to get the RB67 and RZ67 lenses confused, because I never think of them as being the same, even for the few of the K/L lenses that might share the same optical design.

 

[peterB1966]

I

So the lens pictured is not a RZ67 lens, it is an RB67 lens.
That now makes much more sense. And I now realize that the OP's first reference was to the RB67 K/L version. Unfortunately, he/she immediately started referring to the RZ67 K/L lenses, and I immediately misunderstood what he was referring to. All of my earlier references in this thread are to the RZ67 lenses. My fault.
FWIW, I don't tend to get the RB67 and RZ67 lenses confused, because I never think of them as being the same, even for the few of the K/L lenses that might share the same optical design.

I was referring to what I had managed to find, as a jumping-off point, i.e. this is what they say of RZ67 lenses, but what would the situation be with this RB67 lens. Apologies for any confusion.

 

[peterB1966]

All of the Rb67 90/3.5 K/l lenses have a floating element. The confusion might come from not all of the K/L lenses having the green "floating system" engraving, it seems that Mamiya started that engraving in the mid 90s, a few years after the lens was introduced, however all RB67 lenses with the rubber ring have true floating elements. The lenses with a small simple plastic or metal ring to check DOF are not floating elements. The earlier Sekor C 90/3.8 did not have a floating element.
As for the RZ67 version, you are correct, it is a drastically different design, much simpler in a 6e/6g configuration with no floating element, as opposed to the 11e/9g arrangement in the RB67 K/L. I don't know why the more advanced 90 never was introduced in an RZ67 version.
The basic procedure of focus, read the distance, and set the ring works fine, and actually pretty fast once you get used to it. And, as other people have mentioned, it really makes the most difference at close focusing ranges, so you don't need to worry about it for landscapes.

A corollary question, re “read the distance and set the ring”… I presume you are talking of reading the distance of the graph on the side? On the 90mm the graph flatlines after a meter or two… I presume after that you guesstimate?