Mamiya RB 180mm C DOF Scale - help!?!?

Atracksler · May 16, 2015

So I just got a RB67 (yay!). And a 180mm C Lens.

On the front of the lens is a DOF Scale, which rotates pretty freely around, I'm assuming I have to set it based on my focus. Does anyone have a dummies guide/explanation of how to use the DOF Scale on the lens?

Much obliged.

Xmas · May 16, 2015

Confirmed there are two types of RB C lenses

Those with a floating group.

Some merely have a manual depth of field scale.

In either case you read the distance from the scale on the body and copy it to the lens ring.

You can 'prefocus' with either type of lens.

There are (free web) manuals for the body and for the lenses. But the system has quite a lot of variations.

Alan Klein · May 16, 2015

These are from the manual. Note that there is also a DOF preview lever on lenses so you can get an idea of the DOF on the focusing screen as well.

Using the depth-of-field scale 1. Turn the distance scale lever and align the figure representing the focused distance with the center index on the depth of field scale. 2. The two distances (on both sides of the center index) opposite the same figures as the actual lens aperture on the depth-of-field scale are the near and far limits of depth for a given distance and lens aperture.

Using the focusing screen to see DOF1. Set the desired aperture by turning the aperture scale ring and then adjust the focus. 2. Depress the depth-of-field preview lever (A) and the depth-of-field can be observed on the ground glass focusing screen. Upon removing your finger, the lever will return to its original position and the lens aperture will fully reopen.
The curve for each lens is marked with a white dot. Since the dot coincides with the right-hand lens indicator, use it to quickly find the curve on the scale for the lens used.

Pro S D Manual http://www.google.com/url?sa=t&rct=...00gfKNdR2scCt-rrA&sig2=XWURWDL81cKtQna-t0CvHw

Pro S Manual: http://www.google.com/url?sa=t&rct=...00gfKNdR2scCt-rrA&sig2=XWURWDL81cKtQna-t0CvHw

Atracksler · May 16, 2015

Sounds like visual check with the DOF preview is the way to go, the two scales just seem confusing....

nwilkins · May 17, 2015

it's not that confusing but the system is not just not very useful in pratcice. it works just the same as other lenses with helical focusing, excpet you have the intermediate step of the side scale because the camera uses bellow focus.

so you just focus the lens. then you look on the side to find out how far away your point of focus is. then with this information you can theoretically use the DoF scale on the lens to see what your depth of field will be at a given aperture.

alternatively you could determine zone focus with the DoF scale on the lens and then that will tell you how far away your point of focus should be, and you set that using the scale on the side.

but in practice the side scale is pretty imprecise so it doesn't work very well unless you're using a pretty wide lens. and generally using a DoF scale on a 180mm lens isn't going to be very practical on most cameras, even with helical focus.

Kyle M. · May 17, 2015

I don't know about the RB (never payed attention when I had mine) but on my RZ the distance scale on the side is every bit as precise at a tape measure, sure it doesn't go to the nearest inch but is certainly accurate within a foot or two.

paul ron · May 17, 2015

Its just a DOF calculator in a sence like your hand held meter. You have to know the distance you are focused at, set that distance on the calculator, now you can see the different DOF is for each F-Stop.

Xmas · May 18, 2015

paul ron said:
Its just a DOF calculator in a sence like your hand held meter. You have to know the distance you are focused at, set that distance on the calculator, now you can see the different DOF is for each F-Stop.

The general case is for the floating group lenses when it is more desirable to set the distance on the lens ring.

For C lenses 55, 65 and 140mm I think.

flavio81 · May 18, 2015

Atracksler said:
So I just got a RB67 (yay!). And a 180mm C Lens.

On the front of the lens is a DOF Scale, which rotates pretty freely around, I'm assuming I have to set it based on my focus. Does anyone have a dummies guide/explanation of how to use the DOF Scale on the lens?

Much obliged.

First congrats on your RB! I just bought a 180/4.5 C lens this saturday, and just finished cleaning the lens elements yesterday.

Adding to the explanations above,

The depth of field tables provided in the user manual (which you can download at the BUTKUS website property of a saint named "butkus" who has sacrificed himself to make such manuals available to us) are more useful than the DOF ring of the lens, which is a simple calculator.

But then, some people feel that such DOF calculations are too relaxed. That is, that they consider a big circle of confusion. In other words, that some people would find the actual DOF narrower than what the tables or DOF ring lists.

My rule of thumb is: use 2 stops smaller aperture than you would in 35mm terms. For example if shooting with a 90mm lens at f2.8 (in 35mm format), you would then use the 180mm RB lens (equivalent angle of view to the 90mm lens on 35mm format) at f5.6 to get a similar depth of field.

Still, due to the much higher resolution of the 6x7 negative, on high enlargements you will still find the depth of field narrower -- because there is more capacity for recording detail.

Trail Images · May 18, 2015

The general case is for the floating group lenses when it is more desirable to set the distance on the lens ring.

For C lenses 55, 65 and 140mm I think.

I have these 3 lenses, and yes they do have floating element rings to adjust.

flavio81 · May 18, 2015

Xmas said:
The general case is for the floating group lenses when it is more desirable to set the distance on the lens ring.

Note that you need to set the (approximate) shooting distance on the "floating" lens ring, and then focus the lens as usual. You still need to focus the lens.

Xmas · May 18, 2015

Yes good point but I normally adjusted
- the lens ring first
- focused
- made fine adjustment to lens ring

But the user needs the user manual to hand otherwise the lens will be the least of his problems.

Mamiya RB 180mm C DOF Scale - help!?!?

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