RB67 50mm Lens Floating Element Test

[Andrew O'Neill]

 

[Donald Qualls]

I thought I'd been told (in another thread here on Photrio) that the 50 mm doesn't have a floating element, that's only the 65 mm. The similar scale on the 50 mm is just a DOF indicator. Or did I recall that incorrectly?

 

[Alan Edward Klein]

Thanks for doing the test. For whatever it's worth, here's some instructions. How this effects your test I don't know.

 

[mshchem]

I could never see much with Mamiya RZ67 FLE lenses. On a Hasselblad with the 50mm and an Acutematte screen I can definitely see a snap of sharpness and contrast when the lens is dialed in on close objects, it's subtle and the lens is wide open. I think at f8 it wouldn't be noticeable.

 

[Andrew O'Neill]

I thought I'd been told (in another thread here on Photrio) that the 50 mm doesn't have a floating element, that's only the 65 mm. The similar scale on the 50 mm is just a DOF indicator. Or did I recall that incorrectly?

The 50 and 65 both have floating elements.

 

[MattKing]

Andrew,
The biggest reason to use the floating element adjustment is to improve flat field performance.
So with your test subject, it would be quite difficult to evaluate the effect.
As an example, if you were photographing something like an 8 person wedding party in limited light, the bridesmaid and groomsman at the opposite ends will come out better if the ring is set correctly.
And with respect to Donald's observation, between the 50mm and the 65mm lenses, there are a number of versions, and at least one of them doesn't have the floating element. I just can't remember which one(s)!

 

[Trail Images]

Thank you taking the time to perform the test(s) here, Andrew. I have both lenses, use the 65 more often, but can't say I've fussed with the FLE enough on either to see any differences.

 

[Andrew O'Neill]

Andrew,
The biggest reason to use the floating element adjustment is to improve flat field performance.
So with your test subject, it would be quite difficult to evaluate the effect.
As an example, if you were photographing something like an 8 person wedding party in limited light, the bridesmaid and groomsman at the opposite ends will come out better if the ring is set correctly.
And with respect to Donald's observation, between the 50mm and the 65mm lenses, there are a number of versions, and at least one of them doesn't have the floating element. I just can't remember which one(s)!

Mine has floating elements. The extreme edges in my examples should show a difference between corrected and uncorrected. I saw no difference, although someone commented on my youtube channel that they could see a slight difference...

 

[MattKing]

Mine has floating elements. The extreme edges in my examples should show a difference between corrected and uncorrected. I saw no difference, although someone commented on my youtube channel that they could see a slight difference...

I can't remember - what aperture were you using?
Because if the variation fell within the depth of field, you might not be able to see the difference.
Mostly, they don't change the resolution - they change the focus!

 

[Andrew O'Neill]

I can't remember - what aperture were you using?
Because if the variation fell within the depth of field, you might not be able to see the difference.
Mostly, they don't change the resolution - they change the focus!

f/22. So floating lens correction is more beneficial if using large apertures? I'll have to do another test shooting wide open...

 

[MattKing]

f/22. So floating lens correction is more beneficial if using large apertures? I'll have to do another test shooting wide open...

And a subject that has a flatter field
This would have been a good one :

 

[Andrew O'Neill]

And a subject that has a flatter field
This would have been a good one :

View attachment 341256

You should see this little church now! It has been completely renovated.
I think I'll photograph my fence

 

[Donald Qualls]

I'll try to double check, but I believe my 50 mm is one without the floating element.

 

[ic-racer]

I got a new appreciation of manual adjusted floating element lenses after repairing my Rollei 28/f2 lens. The floating elements in that lens are linked to the focus ring with a second helicoid. Getting both helicoids in synch did require testing with film and a loupe during the re-assembly process.

 

[MattKing]

To clear up these statements, the standard 50mm (which came in two versions, which were identical optically, but the W version had half-stop marks between the full aperture detents) does not have floating elements. Some people criticize this lens because the corners, particularly at wider apertures, are to them unacceptably unsharp. (I have the original 50mm, and I don't mind--I usually don't shoot anything where the corners need to be sharp, and the center is certainly sharp enough.) These lenses can usually be found fairly cheaply. The 50mm L ULD *does* have floating elements. It's reputed to be one of the best RZ lenses ever, largely because the floating elements allow you to get excellent sharpness across the frame even wide open (assuming those bits are actually in focus), and is quite expensive in comparison to the other 50s. The 50s all had maximum apertures of F4.5.

Similarly, the 65mm came in two early versions, which again were optically identical, the W version merely had half-stop marks on the aperture indicator, which the very first version lacked. The 65mm L-A had floating elements. All had F4.0 maximum apertures. The difference in performance here is probably not as pronounced as in the 50mm, as I've heard several people express satisfaction with the original 65mm. And the original 65mm weighs about 300g less and is 33mm shorter than the L-A version, so much lighter and more compact. I have the L-A version, I've never owned the original so I can't vouch for its performance. But the L-A is *really* sharp. The nice thing is the price gap is also not as great as it is with the standard 50mm vs. the ULD version.

If you'd like a detailed summary of *all* RZ67 lenses, you can find a very useful one here.

I believe you are referencing the RZ67 lenses, not the RB67 lenses that are the subject of this thread.

 

[Donald Qualls]

RZ67 lenses

I have an RB67, not an RZ67. My 50 mm is a Sekor C, and I recall being told it does not have a floating element. Given it was a late version of the RZ lens in each of these focal lengths that has this, did any of the ones that fit an RB67 actually have it?

 

[Andrew O'Neill]

The Sekor C has floating elements.

 

[Donald Qualls]

Hmm. Does that also affect barrel distortion, or is that coming only from the 0.45x filter I had on that lens the one time I've got rectilinear subjects with it?

 

[Andrew O'Neill]

That's a good question. But, I've never seen any such distortion in all the years I've used this lens...

 

[Donald Qualls]

I figured as much. I've blamed the $40 wide angle filter. I actually bought it for 35 mm pano, and I don't think the effect will be noticeable with that (but even if it is, that's wider than an Xpan). Even just the 50 mm is plenty wide for most things, though, and ought to be sharp enough for my needs, especially if I remember to adjust the floater.

 

[rulnacco]

I believe you are referencing the RZ67 lenses, not the RB67 lenses that are the subject of this thread.

I have an RB67, not an RZ67. My 50 mm is a Sekor C, and I recall being told it does not have a floating element. Given it was a late version of the RZ lens in each of these focal lengths that has this, did any of the ones that fit an RB67 actually have it?

My apologies, gentlemen! Somehow I read RZ instead of RB--and gave you information that, while interesting, was totally useless to the discussion. Duuuuuh. I'll slow down next time and make sure I'm on point before jumping in!

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.

 

[Donald Qualls]

Yep, that little tab almost opposite the MLU selector. Now I'll need to test it...

 

[Andrew O'Neill]

I really believe that all that ring is good for is to determine depth of field...

 

[Donald Qualls]

That's what I've been told before, but if there's a floating element, there has to be some way to control it. The tab I mentioned before is actually on the aperture ring, so that isn't related; there's no other reason to put a movable ring with distance on the lens (there's a DOF scale on the right side of the body above the cocking lever). The "focusing" ring on the front of the lens has indents like a, well, focusing ring. I've ignored it in the past because I was told it was decorative, but I'll run a test roll and see what I get with it set correctly at close focus, vs. set all the way wrong. Field curvature is what I expect, meaning I should see a significant difference in corner sharpness from "right" to "maximum wrong" setting...

 

[reddesert]

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.