Precise Scale focusing with a RB67 - Is it possible?

akaa · Jun 24, 2011

I ask because I am new to MF and am used to the relatively "accurate" focus marks on my Canon FD gear. I find the focus scale on the side of the body fairly difficult to use, along with the fact that currently I have the 150mm SF lens, which isn't depicted on the RB67 Pro S. I decided to try and use the marks along the top of the scale and I found a couple formulas for bellows extension, but I am either using them wrong, or they are the wrong formula for what I want to do.

Any advice greatly appreciated!

polyglot · Jun 24, 2011

You can't accurately focus using the scale on the bellows, you have to use the ground-glass with the magnifier in the WLF popped up.

If it's anything like the RZ, there is a circular pattern to the grinding which means that fine detail in your subject will start to exhibit moire patterns on the GG when it is properly focused. I find that I can nail the focus at f/2.8 (with RZ 110/2.8) unless the light is quite dim and since all the RB lenses are a bit slower, you should be able to accurately focus those too.

tomalophicon · Jun 24, 2011

Yep, use the groundglass for accurate focusing. Then you can get real fine focusing.

BetterSense · Jun 24, 2011

The focusing scale is basically worthless on the RB, at least for shorter lenses. I don't understand why they didn't make the lines skinnier, because it would have helped.

akaa · Jun 24, 2011

So, If one wanted to focus at a certain hyperfocal distance and shoot at will (think kids B-day party) what would you do?

Hikari · Jun 24, 2011

If I had adequate DoF, I would focus about 1/3 of the way into the scene. Most likely I would always be adjusting the focus with the RB.

brucemuir · Jun 24, 2011

you'll need to stop down quite a bit for zone focus to work on 6x7

tomalophicon · Jun 24, 2011

akaa said:
So, If one wanted to focus at a certain hyperfocal distance and shoot at will (think kids B-day party) what would you do?

I'd use a Canon FD.

MattKing · Jun 24, 2011

Take a look at the depth of field tables for your lens. You can use the information there to determine some target distances, and then confirm them with a tape measure.

If you don't have depth of field tables for your lens, you could use the information on the 127mm and 180mm lens tables included in this manual from Mike Butkus' site:

http://www.cameramanuals.org/mamiya_pdf/mamiya_rb67_interchange_lenses.pdf

markbarendt · Jun 25, 2011

tomalophicon said:
I'd use a Canon FD.

Yeah, small format, as well as a short lens and lots of light.

Athiril · Jun 25, 2011

I just look where it's sharp on my RB67. I mainly shoot wide open though.

Otherwise, if you want background to maximum foreground, set you desired f-stop, focus to the background or furthest you want in focus (or closest if vice-versa), hit the DoF preview lever and adjust slightly.

hpulley · Jun 25, 2011

It's an SLR, why use zone focusing? Use a prism finder then focus, shoot, wind, repeat. It is fast to focus. I shoot my daughter on her bicycle sometimes with my RB67 and it works great, believe or not. For action shooting my AF, AE, high speed motor driven EOS bodies are better even than my FD equiptment but you can shoot action with an RB67.

400 speed film helps of course and on a bright day outdoors f/16 1/400 gives you room for focus errors.

paul ron · Jun 25, 2011

How about getting a split image (rangefinder) focusing screen?

If you are looking to do zone focusing DOF, what I have done is put a piece of white tape on the top of my front standard. I predetermine the range I want to cover at say F22, then preview in on my focusing screen the depth of focus as form "here to there" till I am satisfied with the zone coverage. Now put a fine pen mark on the tape where the standard meets the body. repeat this for a couple different F-stops till you have everyting you need.

When in the field, just advance the focus to the mark n lock it in, set the proper F_stop n speed and off you go... sports finder!

You'll notice the ifference between different F-Stops is only 1/32" or sometimes almost the same. The slight difference is a lot in termes of coverage.

polyglot · Jun 25, 2011

IMHO the only zone-focusing attempts you should bother with on formats that large is by focusing on a point that you've eyeballed or even measured as being a certain distance away, and even then probably only bother if you're at f/22 and doing hyperfocal, but that won't be any good for people-shooting. Ignore the scale still.

One option you have is to prefocus on a particular point (chair/table/post/whatever) and just trip the shutter as people pass that point.

David Brown · Jun 25, 2011

akaa said:
So, If one wanted to focus at a certain hyperfocal distance and shoot at will (think kids B-day party) what would you do?

Use a different tool (camera). The RB is my principle camera and I love it. But, it was never intended to be used for candids.

2F/2F · Jun 25, 2011

akaa said:
So, If one wanted to focus at a certain hyperfocal distance and shoot at will (think kids B-day party) what would you do?

I wouldn't do it with that camera. I would focus each shot as well as I could by eye, and I would use a prism viewfinder. You are going to look through the lens to frame the shots anyhow, so might as well just focus IMO. On RZs (maybe RBs too), there is this twisty thing on the lens that lets you figure out a hyperfocal distance and then transfer it to the scale, but setting the lens at an exact focusing distance via the scale, especially with the wider lenses, is difficult and inaccurate. Any hyperfocal focusing is not as consistently sharp as actually focusing on the main subject shot by shot. The high magnification of 6x7 format makes this even more so.

And for a birthday party, I would shoot 35mm, or digital, more likely. Why do you want to use so much film real estate for party pix? Small format is a much better tool for the job, and you can get outstanding quality from it with today's films. You also are going to tire of chasing people around with a hand held RB, and you are going to stick out like an [annoying] sore thumb. I would really just be more low key about this. Travel simple and light, and have a good time. Save the RB for when it is the best tool for the job. It is not in this case.

lxdude · Jun 25, 2011

akaa said:
So, If one wanted to focus at a certain hyperfocal distance and shoot at will (think kids B-day party) what would you do?

I'd tell Will to dammit stand still.

akaa · Jun 26, 2011

Thanks everyone for the reply's. I think I wasn't asking the right question and gave a bad example, though I was interested in taking pictures of the kids.

What I would like to know is if there is another way to determine focusing distance using the mm scale at the top of the chart on the RB. If I am out shooting a landscape and know that I want to use the hyperfocal distance of, say 8 feet, for me it would be easier to do the math ahead of time and know that it is "X"mm of extension with the 90/3.5. Trying to set that with the curves on the chart is very fiddly.

On a side note, I did try some zone focusing and some static focus shots - I was my baby girls 1st birthday

We'll see how they turn out.

BetterSense · Jun 26, 2011

This thread inspired me to cover the focus scale on my RB with a white sticky label. Now I can draw my own damn lines for the 3 lenses I actually own, including hyperfocal marks.

markbarendt · Jun 27, 2011

BetterSense said:
This thread inspired me to cover the focus scale on my RB with a white sticky label. Now I can draw my own damn lines for the 3 lenses I actually own, including hyperfocal marks.

That is a great idea.

Athiril · Jun 27, 2011

David Brown said:
Use a different tool (camera). The RB is my principle camera and I love it. But, it was never intended to be used for candids.

Well I've been using it like that, and hand held at night in the city haha.

Ian C · Jun 27, 2011

Hyperfocal Focusing Table for 150mm f/3.5~f/32 lens for 6x7cm format (circle of confusion c = 0.059mm).

The entries are: aperture, hyperfocal distance (actual distance focused), the near limit of acceptable focus (1/2 the hyperfocal distance), lens increment Δ forward of the infinity position.

f/3.5, 109.1m, 54.6m, 0.21mm

f/4, 95.5m, 47.7m, 0.24m

f/5.6, 68.2m, 34.1m, 0.33mm

f/8, 47.8m, 23.9m, 0.47mm

f/11, 34.8m, 17.4m, 0.65mm

f/16, 24.0m, 12.0m, 0.94mm

f/22, 17.5m, 8.7m, 1.30mm

f/32, 12.1m, 6.0m, 1.89mm

Hyperfocal Focusing Table for 90mm f/3.5~f/32 lens for 6x7cm format (circle of confusion c = 0.059mm).

f/3.5, 39.3m, 19.7m, 0.21mm

f/4, 34.4m, 17.2m, 0.24mm

f/5.6, 24.6m, 12.3m, 0.33mm

f/8, 17.3m, 8.6m, 0.47mm

f/11, 12.6m, 6.3m, 0.65mm

f/16, 8.7m, 4.3m, 0.94mm

f/22, 6.3m, 3.2m, 1.30mm

f/32, 4.4m, 2.2m, 1.89mm

Example: To get hyperfocal focusing with the 150mm lens at f/8 youll set focus at 47.8m on the focusing scale or by moving the lens 0.47mm forward of its infinity position.

BetterSense · Jun 27, 2011

Where did you get that data? I could be wrong, but to focus on 4.4m with the 90mm lens, it sure seems like you have to move the lens more than 2mm forward!

Ian C · Jun 27, 2011

Starting with the thin lens equation

1/f = 1/i + 1/p

we get

i = pf/(i p)

For a lens to subject distance p = 4.4m = 4400mm and f = 90mm

i = 4400mm*90mm/(4400mm 90mm) = 91.88mm (film to lens)

The lens increment from its infinity position is

Δ = i f = 91.88mm 90mm = 1.88mm

I think the program I wrote to generate the hyperfocal table rounds off slightly differently to 1.89mm due to a longer chain of calculations.

As you focus closer than 4.4m the rate of increase of lens increment accelerates rapidly.

akaa · Jun 27, 2011

Thanks Ian, and I'm not saying your math is incorrect, but this is exactly what prompted this thread. With the formula I had, the far distances seemed plausable, but as I calculated distances that were closer, ie. 4.4m, it seemed less and less likely that it was correct. IIRC, 4.4m is somewhere around 6-8mm for the 90mm/3.5

Precise Scale focusing with a RB67 - Is it possible?

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