Mamiya RB67 Pro SD Bellows Distance Scale Differences?

JWMster · Dec 8, 2023

Love the bellows scale. Kind of curious though that in watching David Hancock's video on the RB his camera had a different scale. The scale on his EARLIER version Pro or Pro S (not the Pro SD) scales the bellows adjustment from 0 stops to 2 stops. The scale on my PRO SD camera scales only from 0 to 1 stops. Did light just suddenly get brighter? Is it possible someone replaced the original scale with a scale off another camera? The list of lenses on this includes the 140 Macro that the earlier scale on Hancock's does not.... so it SEEMS it ought to be the right one. I'm just a bit puzzled.

Thanks for your help.

JWMster · Dec 10, 2023

Turns out the part number for this on the PRO S is 5001-15471. What I think I'm after are photos of the different RB models (plain, Pro S and PRO SD) to see what the differences are? Maybe nobody shoots this thing any more? So below is an iPhone photo of the distance scale on my RB67 PRO SD and based on the youtubes I've seen, it looks to be missing a bellows adjustment halfstop or two. Thoughts?

reddesert · Dec 11, 2023

Bellows factor is just a formula for the increased exposure needed when the lens is racked out fairly far. The plate just shows you a focusing distance scale, since RB67 lenses don't have a focusing ring where the distance scale usually goes. As a bonus, the plate also tells you the exposure increase needed, since you're probably not metering TTL.

For example, to focus a lens at a distance of 10 times the focal length, you need to extend the bellows by roughly 1/10 the focal length. (VERY roughly - it's really more like 1/8 the focal length.) So for the 150mm lens focused at 1.5 meters, the extension would be roughly 150/10 ~ 15mm, and more accurately 150/8 ~ 19mm. That's what the upper scale in mm shows, following the curve for the 150mm lens.

The bellows exposure factor goes as the square of the (total bellows draw / focal length), or (169/150)^2 = 1.26. So you would need to increase exposure by a factor 1.26, which is about 1/3 of a stop. The lower scale in steps (or stops) shows that Mamiya has approximated this as: with the 150mm lens, from focus distances of 1.8 to 1 meter, you should use a compensation of 0.5 stops.

This is explained (without the math) in the user manual sections on distance scale, close-up photography, and exposure compensation. Read the manual. Then stop worrying about it unless you work at close-up ranges (< 10 x the focal length).

MattKing · Dec 11, 2023

I expect the scale may reflect user feedback - as the camera went through its various versions, it probably became clearer which lenses were being used more at closer distances.
The variation on the Pro-SD might also reflect realities imposed by the change in available focal lengths, as well as the larger "throat" in the SD's lens mount area.

Dustin McAmera · Dec 11, 2023

Pacific Rim has the instruction book for the Professional (no S):

https://www.pacificrimcamera.com/rl/01200/01200.pdf

The exposure-comp sale is covered on page 24-26. As you say, the scale is different, apparently recommending a factor +0.5 at about 4mm extension; that seems ridiculous.

reddesert · Dec 11, 2023

For clarity, I am attaching a screenshot of the image of the focusing scale in the original RB67 Pro manual.

You guys are reading the lowest bar of the Pro scale incorrectly. The lowest bar is like a legend, not a position scale. It tells you what pattern of hashmarks corresponds to 0.5, 1.0, 1.5 stops of compensation, but its positioning only corresponds to the bellows extension distance for the next-lowest row, which is a focus distance of 1 meter. This scale is also confusing because it makes the next-lowest row look like it's for the 50mm lens, but actually the 50mm lens is the rightmost curve, not a row (this is a little clearer from the matching colors in JWM's photo). In fact, the bellows factor of 0.5 at 5mm extension would only happen for the 50mm lens focused at 1 meter. The longer lenses need much more extension before requiring an 0.5 factor.

Mamiya appears to have figured out that the scale was confusing and improved the graphic design for the later model in JWM's photo above. They also eliminated the +1.5 and +2 hash markings, perhaps because hardly any lenses were being used in the regimes where the +1.5 and +2 factors would apply.

In the Pro SD scale, the borders of the 0.5 and 1.0 regions aren't a smooth function of focal length, I don't know why that is but I suspect it has something to do with the lens optical designs (something about the principal planes not being the same as the focal length distance, for retrofocus lenses).

_T_ · Dec 11, 2023

The manuals for the pro sd and the pro are on butkus and they show that mamiya clearly updated the compensation indicator plate at some point.

You can also see that the maximum bellows extension has not changed between the two versions.

Also the magnification tables show the same values and the focusing charts match for all of the focal lengths.

So something doesn’t add up.

It could be that the compensation chart for one of the models is off by up to 1 full stop or it could be that they’re both off.

wiltw · Dec 11, 2023

The chart in Post 6 does not quite makes sense...50mm FL with 50mm extension achieves 1:1, which entails a 2EV increase in exposure.
Yet the graphics show +2EV being needed at 43mm extension.

At 1/2 mag, the exposure increases by 1.5EV, and the scale correctly shows that.

Dustin McAmera · Dec 11, 2023

reddesert said:
The lowest bar is like a legend, not a position scale.

Aha! That makes more sense now. Ta!

JWMster · Dec 11, 2023

Thanks to all of you here. Discussion is helpful. Guess more of what I was seeking was confirmation that my eyes weren't deceiving me and that indeed, the presentation on the chart had changed. Cause remains undetermined but what we have here are 3 possible explanations - two from Matt:

1) Change in lens mount throat (which might argue the KL lenses differ from the C and earlier)
2) User feedback
3) User confusion

Maybe some combo of the above.

Good case to be made by reddesert that it's just better to read the distance and do the math. FWIW, time constraints have meant my first rolls are still undeveloped - so no real world personal feedback yet. At this point, I've simply been dealing with assuring myself that the gear works and I understand how to operate the controls for the system, and fairly, I'm just trying to put the pieces together for getting the photographs I bought this for - including some tests for off camera flash with a cold shoe.

FWIW, my Mamiya PRO SD manual (downloaded from Butkus or similar) appears a bit different. Discussion on page 27 addresses the "Distance Scale" and page 32 begins (as section 22) on Close-up Photography continuing on to page 33 where the adjustment factors on the chart given on my camera ARE in fact the exposure compensation value. There is also a table. And I digress to this level of detail to assert that this is how I have been using it in my 3 rolls so far which is a relief to many perhaps. Moreover, while I am in fact reading Dostoyevsky's "Idiot" as a "How to Manual", that remains a work of fiction whereas operating a camera like the RB something else. So far, I'm enjoying both.

But no, I did not think to check the older manuals for the OTHER versions of the RB, but doing so now there is a fair amount of better detailed information than in mine - especially on the lenses. And I would have seen this. My apologies, but also my thanks.

xkaes · Dec 11, 2023

One big factor that needs to be added in to manual exposure adjustment calculations is the FLANGE focal length of these lenses -- which varies tremendously. For example, the 37mm RB lens has a flange focal length of something over 100mm -- same thing with the other short, wide lenses. The longer lenses are the opposite. So simple calculations can't be done.

MattKing · Dec 11, 2023

wiltw said:
The chart in Post 6 does not quite makes sense...50mm FL with 50mm extension achieves 1:1, which entails a 2EV increase in exposure.
Yet the graphics show +2EV being needed at 43mm extension.

At 1/2 mag, the exposure increases by 1.5EV, and the scale correctly shows that.

The different lenses attain infinity at different amounts of bellows extension, but the actual physical extension doesn't necessarily match the focal length for the retro-focus wide angle lenses and the telephoto longer lenses.
Thus the need for individualized curves.
And yes, use the bottom bar as a legend.

Arthurwg · Dec 11, 2023

I have yet to use my Pro SD for closeup work, but I've considered fudging the bellows factor by simply adding 1/2 or 1 stop when that becomes necessary. At least with BW film there should be enough range to handle any discrepancy.

MattKing · Dec 11, 2023

The advantage of the scale is that it incorporates the factors that the flange distances vary between the lenses, and that some lenses are retro-focus, while others are telephoto.
Those factors make it impractical to do exposure adjustment calculations based on bellows extension.

wiltw · Dec 11, 2023

MattKing said:
The advantage of the scale is that it incorporates the factors that the flange distances vary between the lenses, and that some lenses are retro-focus, while others are telephoto.
Those factors make it impractical to do exposure adjustment calculations based on bellows extension.

Aha, the insight that comes only with ownership of the stuff, and reading user documentation!

Dan Fromm · Dec 11, 2023

wiltw said:
The chart in Post 6 does not quite makes sense...50mm FL with 50mm extension achieves 1:1, which entails a 2EV increase in exposure.
Yet the graphics show +2EV being needed at 43mm extension.

At 1/2 mag, the exposure increases by 1.5EV, and the scale correctly shows that.

Sorry, extension needed to get 1:1 is 2f, regardless of focal length and lens design.

JWMster · Dec 12, 2023

I would circle back to the possibility that the differences in the appearance of these scales between the PRO SD (post # 2) that I have and earlier (post # 6)... and hope that it is not due to the change from C to KL lenses. And I would hope this BECAUSE it would suggest that if you're putting a C lens (like my 50mm C) on a PRO SD made for KL lenses, then you are SOL, and I can't imagine Mamiya would want to mess with me like that... so that I'd have to use ONLY KL lenses on the PRO SD.

I don't have time to study this out this morning because of an upcoming meeting, but maybe the graphed adjustments between the 2 scales don't actually change while the presentation does? If so, then that would confirm that Mamiya was really motivated to eliminate user confusion. Note that I don't at this time own a lens extension.

MattKing · Dec 12, 2023

JWMster said:
I would circle back to the possibility that the differences in the appearance of these scales between the PRO SD (post # 2) that I have and earlier (post # 6)... and hope that it is not due to the change from C to KL lenses. And I would hope this BECAUSE it would suggest that if you're putting a C lens (like my 50mm C) on a PRO SD made for KL lenses, then you are SOL, and I can't imagine Mamiya would want to mess with me like that... so that I'd have to use ONLY KL lenses on the PRO SD.

I doubt you have anything to worry about with the C lenses.
But I would point out that the scale is an aid - designed to help make some things simpler and easier. If you have a lens whose flange distance differs from the more current version, you might not have access to that aid - you might need to do more manual calculations, based on magnification. That of course is what just about every LF photographer does.
You can always check by seeing if the distance scale matches up to reality. If it does, the close focus exposure adjustment will as well.

wiltw · Dec 12, 2023

Dan Fromm said:
Sorry, extension needed to get 1:1 is 2f, regardless of focal length and lens design.

magnification = [length of extension] / [focal length of lens]

so 1:1 (or 1X) = 50mm extension / 50mm FL of lens

Source: Ernst Wildi (author of the 'Hasselblad Manual') Medium Format Photography c.1987, p.289

MattKing · Dec 12, 2023

wiltw said:
magnification = [length of extension] / [focal length of lens]

so 1:1 (or 1X) = 50mm extension / 50mm FL of lens

Source: Ernst Wildi (author of the 'Hasselblad Manual') Medium Format Photography c.1987, p.289

I believe one of you is speaking of bellows extension for lenses without a flange distance, while the other is speaking of how much extension to add to a lens with a flange distance.

wiltw · Dec 12, 2023

MattKing said:
I believe one of you is speaking of bellows extension for lenses without a flange distance, while the other is speaking of how much extension to add to a lens with a flange distance.

For clarity, the equation provided by Wildi does not need to consider the 'flange distance', which varies from manufacturer to manufacturer/design

Canon R mount flange distance = 20mm
Canon EF mount flange distance = 44mm

yet for 50mm FL lens, both EF lens and RF lens would use 50mm extension with 50mm FL lens to achieve 1:1

MattKing · Dec 12, 2023

But I believe that the Wildi equation refers to how much extension needs to be added to the (Hasselblad) lens.
So with a 50mm lens, you need a total distance of 50mm (the extension) + 50mm (the focal length of the lens) = 100mm for 1:1.
Without the added extension, a 50mm lens focused/extended to the 50mm focal length focuses at infinity - not closer.
In contrast, Dan is talking about the total distance between the film and the nodal point of the lens, not extension plus the focal length.

Dan Fromm · Dec 12, 2023

wiltw said:
magnification = [length of extension] / [focal length of lens]

so 1:1 (or 1X) = 50mm extension / 50mm FL of lens

Source: Ernst Wildi (author of the 'Hasselblad Manual') Medium Format Photography c.1987, p.289

Please consult:

Lefkowitz, Lester. 1979. The Manual of Close-Up Photography. Amphoto. Garden
City, NY. 272 pp. ISBN 0-8174-2456-3 (hardbound) and 0-8174-2130-0 (softbound). A
thorough discussion of getting the magnification, lighting, and exposure. Especially good
on working above 1:1. Extensive bibliography

before shouting at me.

Oh,, and by the way, I measure extension as the film-to-lens' rear node distance.

wiltw · Dec 16, 2023

Dan Fromm said:
Please consult:

Lefkowitz, Lester. 1979. The Manual of Close-Up Photography. Amphoto. Garden
City, NY. 272 pp. ISBN 0-8174-2456-3 (hardbound) and 0-8174-2130-0 (softbound). A
thorough discussion of getting the magnification, lighting, and exposure. Especially good
on working above 1:1. Extensive bibliography

before shouting at me.

Oh,, and by the way, I measure extension as the film-to-lens' rear node distance.

For the record, I was NOT shouting...I had emphasized one word and the FL (and book title...I have one guy who compulsviely critcizes every omission of references) for very easy readability purposes. It is not the same as bolding entire sentence(s).

Since i do not have a reason to get the referenced book, and for other readers of the thread, could you please extract the essence of what you refer to, and post it in this thread?

Mamiya RB67 Pro SD Bellows Distance Scale Differences?

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