'Splain to me Lucy.. Mamiya Floating Element Lens

I found this thread and have and need some help too.
My RB67, 65mm Sekor "C" lens arrived yesterday. It appears to be a "floating element" lens. When I bought it off of ebay there was no mention of a "floating element". The lens is in9 out of 10 condition and everything appears to be working fine. My question is about the floating element adjustment too.
There is a ring closest to the end of the lens that has distance in ft/m. at the two ends of adjustment travel there are detents that feel just like aperture "clicks". When I rotate this ring I can see that the inside of the lens is turning but nothing on the outside is moving.
When I look through the viewfinder, after focusing like normal, I turn the "floating element" ring but can tell not any difference in sharpness or anything else for that matter. Where do I find the distance to use to adjust this element? the scale on the side of the bellows???
How do I use this lens properly???
Does the floating element really make a difference in the quality of the photo or is it a gimmick? I am a real lover of my RB67 system and understand most of the features but this one is a bit confusing...

I'm not quite sure, but believe the thing to do is focus the lens normally, read the distance from the normal scale on the side of the camera, set the FLE ring accordingly, and then refocus.

Generally, floating elements do indeed make a difference, yes.

I hope that is not how this works!!! If so it seems like a real pain....I am afraid your are correct though.

Q.G. said:

I'm not quite sure, but believe the thing to do is focus the lens normally, read the distance from the normal scale on the side of the camera, set the FLE ring accordingly, and then refocus.

Generally, floating elements do indeed make a difference, yes.

Click to expand...

I have a 50mm floating element C lens. There is no need to refocus after you set the FLE ring.

The ring doesn't change the focus on the lens. As I understand it, it changes how the lens corrects for aberrations and/or field curvature.

Usually I don't bother to read the distance off the camera side scale. I just estimate the distance and set it.

The detents are there because if you are working quickly, you can just set the ring to either the close detent, or the far detent (whichever is applicable to your subject) and the floating element correction will be very close to being optimum.

So the floating adjustment is not critical like normal focus? If it is close it is good?

stradibarrius said:

So the floating adjustment is not critical like normal focus? If it is close it is good?

Click to expand...

Well......

The floating element does make a difference, just not as much difference as normal focus.

To use a hypothetical, if you have a subject that is 10 feet away, and you are off by 1 foot with the setting of the floating element (say you have the floating element set in error for 9 feet), the affect on the image is a lot less than the affect if you have the normal focus off by 1 foot (again, say you have the normal focus set in error for 9 feet).

One thing I'm not sure of, and would appreciate knowing, is how much of the correction supplied by the floating elements relates to flatness of field.

MattKing said:

I have a 50mm floating element C lens. There is no need to refocus after you set the FLE ring.

The ring doesn't change the focus on the lens. As I understand it, it changes how the lens corrects for aberrations and/or field curvature.

Click to expand...

Theoretically, it does change focus.
Moving bits around inside the lens changes the focal length, and without changing the lens to film distance too, focus will change as well.
But (i don't know this particular FLE lens) it may well be that the change is so small that it is less than the already small error always present in focusing, i.e. too small to be noticeable and worry about.

The floating element does indeed change focus, if you watch the focusing screen closely as you adjust it, it is visible but minimal.
The Mamiya lens is designed to be at optimum value when the FE ring is set to the distance set on the focusing rail.

The scale on the rail seems so imprecise??? Probably it's that I just don't really know how to use it...

Reviving this thread.

I have recently become an Rb67 owner with a 90mm floating KL lens kit - and I have the question as to where do I look on the wlf to get the floating element just right - corners? Center?
Also, if the floating element is gonna change focus, then, what ultimately is the final focusing? It should be that we get as close to perfect focus and then adjust with the floating element, right? (else we'd be on a focus adjustment loop)



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analoguey said:

Reviving this thread.

I have recently become an Rb67 owner with a 90mm floating KL lens kit - and I have the question as to where do I look on the wlf to get the floating element just right - corners? Center?
Also, if the floating element is gonna change focus, then, what ultimately is the final focusing? It should be that we get as close to perfect focus and then adjust with the floating element, right? (else we'd be on a focus adjustment loop)



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Click to expand...

You cannot always see the effect of the floating element in the finder. It deals mostly with flatness of field and certain lens aberrations.

The most accurate way to set the floating element is to pre-estimate the distance and set the floating element there.

Then focus.

Then check the actual distance, and adjust the floating element to that distance.

If you are moving more quickly, focus first and then set the floating element to match.

And if you are really in a hurry, guess the distance and leave the floating element set there while you adjust focus for each shot.

MattKing said:

You cannot always see the effect of the floating element in the finder. It deals mostly with flatness of field and certain lens aberrations.

The most accurate way to set the floating element is to pre-estimate the distance and set the floating element there.

Then focus.

Then check the actual distance, and adjust the floating element to that distance.

Click to expand...

Actual distance - you mean on the scale? Or how?

MattKing said:

If you are moving more quickly, focus first and then set the floating element to match.

And if you are really in a hurry, guess the distance and leave the floating element set there while you adjust focus for each shot.

Click to expand...

I generally have a good estimate on the distance, so after focusing I just do what you suggested above.

But where do I get to see the effects? On print/scan?


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Yes, on the scale.

And yes, on print/scan.

As I mentioned, a lot of the benefit is with respect to flat field performance, so if you are not shooting flat field subjects, you may not notice that benefit.

Not just flat field, but correction of aberrations that cause radial smearing in the corners. The ground glass is too low-resolution to perceive it, but the difference is quite apparent in a good print. Try a closeup composition that has sharp corner details with the adjustment set to infinity for the first frame and set correctly for the second frame. Print them both and look in the corners.

MattKing said:

Yes, on the scale.

And yes, on print/scan.

As I mentioned, a lot of the benefit is with respect to flat field performance, so if you are not shooting flat field subjects, you may not notice that benefit.

Click to expand...

I see, thank you, I'll try taking a look at my next print/scan. I am a little confused by what you refer to as flat field performance, could you explain that further?

polyglot said:

Not just flat field, but correction of aberrations that cause radial smearing in the corners. The ground glass is too low-resolution to perceive it, but the difference is quite apparent in a good print. Try a closeup composition that has sharp corner details with the adjustment set to infinity for the first frame and set correctly for the second frame. Print them both and look in the corners.

Click to expand...

Ah, so is this mostly about corners then? (I'll try what you've suggested - should make for a good test!)

Are there any mamiya or other guides around this?



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yes there was a booklet for the camera and each lens
the descriptions were simpler than on this thread
there was also a soft focus lens

Flat field performance refers to the ability of the lens/camera system to record flat items sharply on the film.

Think of copying something like artwork. You need to have excellent contrast and resolution across the entire negative, revealing all the details of the artwork.

You cannot have the centre of the artwork in focus, with the corners of the artwork (which are farther away) out of focus.

The plane of sharp focus needs to be flat, not curved, and that performance needs to be possible at different distances.

Good flat field performance also requires being able to render an image without distortion - rectangular subjects need to be rendered as a rectangle, not a barrel or pincushion.

Ah right! Will try shooting something like that for the exercise!

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MattKing said:

Flat field performance refers to the ability of the lens/camera system to record flat items sharply on the film.

Think of copying something like artwork. You need to have excellent contrast and resolution across the entire negative, revealing all the details of the artwork.

You cannot have the centre of the artwork in focus, with the corners of the artwork (which are farther away) out of focus.

The plane of sharp focus needs to be flat, not curved, and that performance needs to be possible at different distances.

Good flat field performance also requires being able to render an image without distortion - rectangular subjects need to be rendered as a rectangle, not a barrel or pincushion.

Click to expand...

two queries
a) if you want e.g. to copy art work you would use a process lens?
b) a RB67 open aperture performance may be limited by film flatness as well as lens performance if the film retains a memory from the film feed roller path...

Xmas said:

two queries
a) if you want e.g. to copy art work you would use a process lens?
b) a RB67 open aperture performance may be limited by film flatness as well as lens performance if the film retains a memory from the film feed roller path...

Click to expand...

Are you sure those are queries?

A process lens is good for artwork, but the process cameras are a bear to use on location.

And process lenses aren't particularly flexible for general photography - especially the fixed aperture lenses.

While it is true that RB67s may, like other roll film cameras, have some issues with film flatness when shooting wide open, the RB67 lenses probably don't exhibit their best performance when wide open anyways.

Rudeofus said:

Even Mamiya seems to be aware of this, since they market a 140mm macro lens with is supposedly optimized for close range.

Click to expand...

The RB67 140mm has a floating element which has a scale for no, one or both extension rings.

If you are poor it is a reasonable sub for the 127 and 180.

Xmas said:

yes there was a booklet for the camera and each lens
the descriptions were simpler than on this thread
there was also a soft focus lens

Click to expand...

Hmm I see. I shall try looking it up, see if any are being sold on ebay!

stradibarrius said:

The scale on the rail seems so imprecise??? Probably it's that I just don't really know how to use it...

Click to expand...

It did seem like that to me, today, when I was trying out what polyglot suggested

polyglot said:

Not just flat field, but correction of aberrations that cause radial smearing in the corners. The ground glass is too low-resolution to perceive it, but the difference is quite apparent in a good print. Try a closeup composition that has sharp corner details with the adjustment set to infinity for the first frame and set correctly for the second frame. Print them both and look in the corners.

Click to expand...

oh wait. sharp corner detail. Hmm, I dont think it had that, will try again. :| But I did do this, set floating to infinity and then to whatever distance scale said and shot of two snaps. Lets see how those turn up...

Xmas said:

yes there was a booklet for the camera and each lens
the descriptions were simpler than on this thread
there was also a soft focus lens

Click to expand...

I apologize this was abstract - from memory...

My camera came with two booklets for the:-

- camera
- interchangeable lenses

but the latter booklet references further specific booklets for the
37mm, 140mm, 150mm and 500 mm which booklets I never had

The rules in 2nd booklet for the 50mm and 65mm were focus and set the floating ring to distance from focus scale, and a note
'* the floating ring may be turned to set the distance either before or after focusing' which I fair copy.

Except and I fair copy again

'When placing emphasis on spur-of-the-moment snap shots set the infinity mark (red) of the floating ring to the center mark (red) when the distance is from infinity to approximately 7 ft (2m), and if the distance to subject is less than approximately 7ft (2m)m a sufficiently sharp image can be obtained merely by setting 3.3 ft/1m (red) to the index.
* In the case of close up photography nearer than 3.3 ft (1m), set the floating ring to 3.3 Ft/1m, then stop down the lens as much as possible.
* The distance to subject implies the distance from the film plane to the subject'

Except in the same booklets depth of field tables for each of the 50mm and 65mm fair copied again,

'When using the 50mm (sic or 65mm) lens closed then 3.5 feet (1 meter) it is necessary to use a lens aperture of f/16, or smaller, in order to obtain satisfactory lens performance.'

In first bookelt - when using the 360mm the (a) filter needs to be between the rubber hood and lens, either position may be used with the other lenses.

Lastly there is a warning that only the 127mm will be reasonably free from from vignetting when both the type I and II tube are used together on 6x7, but some vignetting will be obtained with the 127mm on the polaroid packs larger image... The other lenses may vignette with two (both) tubes, but will be ok with either one alone.

Note the 140mm would be better than the 127mm, but I don't have the handbook for it... The 140 is a double Gauss (7 element - the rear inner group floats) the 127mm a triplet (5 elements), I'd say the 90mm is already a inverted telephoto.

I don't want to scan the handbooks cause of copyright, although the handbooks don't claim copyright

I find my lenses pretty good the only precaution I take is to shoot all 10 (or 20) exposures over a short interval, for critical work at large apertures, if I'm dong long intervals or cold weather I use the 6x6 TLR Mamiya for film flatness risks,

I do sometimes forget the floating rings, in snapshot mode... even with a warning Avery label on the back caps, it does not help that the 90mm has a similar depth of focus (only) ring.

Noel

Unless you shoot close up (up to 7 feet) the floating element should remain at infinity. I have the 50c and 140 Macro c, both have floating elements although the 140 is only used if used in conjunction with the macro tubes.