Adjustment for Flange Focal Distance w/ RB67 lenses on *RZ*67

[yessammassey]

Mamiya RZ67 manual states:

Because of the differences in flange back between the two series of lenses, the Distance Scale of the RZ67 body does not apply when using RB67 lenses.

I am thinking about 'switching' from an RB67 Pro-S to an RZ67. But I have a 65/4 KL lens for the RB and it's just about the sharpest thing I've ever seen in the medium format world. (Not a Hasselblad user, sadly.)

The 65, like all C- and KL-series RB67 lenses, can be used on the RZ67. The thing is, the KL has the infamous 'Floating System' where the user has to manually set the position of part of the lens to correct for field curvature. This is done by reading the Distance Scale. The Distance Scale is on the body, the Floating System is part of the lens. The user has to manually transfer the reading of the Distance Scale to the distance ring of the Floating System.

The Distance Scale is on the right-hand side of the bellows. Per the RZ67 manual, when using RB lenses, infinity is 7mm 'out' on the bellows from where it is for RZ lenses.

Let's say you're using the 65 KL on the RZ. You need to set the Floating System. Could you get the correct setting for the Floating System by:

1.) Focusing on whatever you want.
2.) Drawing the bellows back 7mm and looking at the Distance Scale
3.) Setting the Floating System according to the 'corrected' reading on the Distance Scale
4.) Re-focusing on the subject.

?

I'm thinking that since RB & RZ primes all focus as 'blocks' on rack & pinion bellows, with no internal movement for focusing, that 7mm offset should be constant throughout the focus range.

Of course, even if it was possible to do this, that doesn't mean it would be convenient or desirable. When I found out that the RZ had a different flange focal distance than the RB, my enthusiasm for making the switch was dampened. But maybe I'll offload the 65 KL as well and get the RZ equivalent.

As an aside, is the 90/3.5 'Z' for RZ67 regarded as much better than the 90/3.8 'C' lens for the RB67?

 

[MattKing]

If 7mm of displacement comes close to matching the line for the 50mm lens, you could just use it instead.
Personally, with my RB, I focus first and then just eyeball the distance for the purpose of setting the floating element. The focus scale on the RB and RZ cameras is far from precise.
If I was looking for precise, flat field reproduction of a flat surface, I would use a tape measure for close distances.
It is only for flat surfaces at close distances that the position of the floating element is even close to critical.

 

[flavio81]

The thing is, the KL has the infamous 'Floating System' where the user has to manually set the position of part of the lens to correct for field curvature. This is done by reading the Distance Scale.

1. It is NOT infamous. It is easy to use and it does improve performance.

2. You can just estimate distance instead of having to read the distance scale. That's how i work.

And if you're really meticulous you might want try to refocus after moving the floating system ring.

 

[yessammassey]

1. It is NOT infamous. It is easy to use and it does improve performance.

LOL. Yes, it is very simple to use. I have seen some threads where people seem to be completely baffled by it, for whatever reason.

If framing at close range, I can actually see features stretch/flatten in the corners as the ring is adjusted. It definitely helps improve the image when set correctly.