How accurate are zone focus scale markings meant to be?

[TheEyesHaveIt]

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Hi all,

I've been trying to get. better with zone focusing and gauging distances by eye. To practice, I laid out a tape measure to around 10 feet and put different objects are various depths. Then I setup my M11 on a tripod at the start of the tape and will set the focus using the scale markings on the lenses - and then double check via the RF patch, the LCD peaking, and finally take a shot and zoom in.

One thing I'm noticing with a number of my lenses is that while the RF patch, LCD peaking, and shots line up as expected on certain marking points, on other points, I have to adjust to get the shot in focus. So for example, if an object is exactly 5 feet away based on the tape measure, if I set the lens with the 5 feet mark dead in the center, I find that I have to adjust it a bit left or right to get the object really in focus / line up the RF patch / LCD peaking.

So are these scale markings meant to be just rough estimates or am I doing something wrong?

Cheers!

[madNbad]

Mostly they’re a guide to give the user an idea of what should be in focus at a particular aperture. The nice thing about using a digital camera is it makes it easy to experiment and find the proper marks for your lens. 
Put a handful of props at various distances and have some fun!

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[hepcat]

"Measured with a micrometer, marked with chalk, and cut with an axe."

Rangefinders are NOT high-precision devices.  A rangefinder is to get you close enough for the DOF to carry the shot.  That's why large apertures are so difficult to use well on a rangefinder camera.    Use digital focus-peaking if you really want to see how close your rangefinder really is to being accurate on your M11. 

Photography is, entirely, a pursuit of "close enough" and tailoring your other settings to cover any error introduced.    I frequently use preset settings on my camera.  I set the aperture at f/8, set infinity at the far f/8 DOF mark and be aware of the closest f/8 distance.  If that's not sufficient, go to f/11.  If you want to shoot wide-open and close to the camera using only the rangefinder, well... good luck.   All of us have done it for years, but it's hard to do well. 

[RexGig0]

If he DOF is so shallow that inches or centimeters are enough to matter, keep in mind that the distance is from the film plane or sensor plane, not the end of the lens.

[Jeff S]

Jeff

[TheEyesHaveIt]

Ok sounds good - thanks all. Just wanted to confirm it wasn't something with the lens(es) or the RF patch.

[Stuart Richardson]

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Unless you are using a very precisely calculated helical with distance markings (like in an Alpa technical camera, for example), the distance markings are usually a rough guideline. When they adjust the lens in the factory and when they adjust the rangefinder in the body, that is going to shift around the exact point of focus, in relation to the scale on the lens. Infinity is a good example...is it at the hard stop? Is it in the middle of the infinity symbol? The right side? The left side?? This can even change due to thermal expansion and contraction, which is why Leica R telephotos focus past infinity, for example. It might be slightly different at 40C than at -20C. On a contemporary M camera, the most accurate way to focus is to use the live view (obviously not the quickest or most fun way), otherwise the rangefinder is the most accurate method...it can be very accurate indeed if the lens and rangefinder are well paired and well adjusted, and your eyesight is capable of very good contrast discrimination. This is only becoming a greater problem as the megapixels increase, however....it is a huge challenge to focus a 90mm Summilux wide open at 60mp...so much so that it is probably better on the SL2. 

P.S. Zone focusing is always going to be a very rough affair, unless you are mostly thinking small prints and are using something like a 28mm or wider and an aperture of f8 and smaller. It is always better to focus if you can...I would suggest setting your camera up with a preset range that you think will work for the scene and then if you are trying to capture a quick moment, if you have the chance just focus normally. If you don't have the time, then by all means fire away with the zone focusing...

Edited August 26, 2023 by Stuart Richardson

[dpitt]

When I zone focus, I always locate an object at the intended distance. Then I focus with my RF patch on that object. After that, I find subjects that are at a similar distance and shoot...

[pop]

What you do is not 'zone focusing'. It's just focusing.

The term 'Zone focusing' describes a method where everything within a rather deep zone appears 'acceptably sharp' in your image. The scales and marks on my rather nice 35mm lens tell me that everything between 1.5m and infinity will appear sharp in my picture when I set the aperture to 1:11 and the distance on the scale to a bit more than 3m. It all depends on what you deem 'acceptably sharp'. This procedure has been invented early in the twentieth century, I believe, when no one blew up pictures as much as we do today. No pixel peeping was possible at that time.

You mention three ways of (actually) focusing, and each has of course its own set of advantages and disadvantages. Please don't expect me to exhaustively list all of them in the space of a single post.

First, there's scale focusing: you measure the distance between the camera and the subject and set your lens to that distance by means of the distance scale engraved on the lens. By some very old convention, the distance has to be measured between the subject and the plane of the film (which is the surface of the sensor, nowadays). Many cameras have a line engraved on the body which indicates the exact location of that plane. In my experience (and according to the literature), the scales on well made lenses are quite accurate (possibly to about 1% of the value indicated), but you will not be able to set your lens with that accuracy on account of the lens not having any tick marks beneath the scale. You mentioned that you put some objects on a measuring tape in order to test the scales on your lenses. Be aware that the camera must be aligned exactly in parallel to the tape, otherwise the distance between camera and object will be greater than indicated by the tape. Hence, the object to be photographed must be at the same height as the camera.

In the Leica world the obvious means of focusing the lens is by using the rangefinder built into the viewfinder. In my experience, this is a very accurate method, provided it works at all for you. For it to work you must see reasonably well, but with a bit of practice you can even use it when your acuity is less than perfect. Obviously, it works only well enough when there is enough light to see by. Additionally, the construction of the rangefinder in a Leica camera is such that you can use it only when there are reasonably prominent vertical edges within your frame. (Actually, the edges have to be parallel to the shorter side of the image frame, so you can cope with horizontal edges by turning the camera by ninety degrees or, indeed, any other angle). Another shortcoming is that the rangefinder operates in the very middle of the frame only. Focusing first and then pointing to another part of the scene will undo your focus. The rangefinder in your Leica camera works only from a given minimal distance of some 0.7m and it's not accurate enough for longer lenses.

Most digital cameras that can do live view will offer focus peaking as an 'alternative'. Focus peaking works by highlighting the places in the image with the greatest contrast with another color. It's not particularly accurate if you look for the sharpest spot in your image, as other places in your image might have more contrast than the place you want sharpest. Often, you can judge where the plane of focus lies by watching the marked area in front and back of your subject. This is particularly handy if there are fine structures in your image such as a gravel path.

Also, you can focus by eye. Just observe the image by eye while changing the focus of the lens. Digital cameras usually can magnify the image in the viewfinder so that you can better judge the sharpness of the image. This method might be slower than others. When you require a great magnification factor, holding the camera steady might become an issue. This method relies heavily on your visual acuity, of course.

Finally: many pictures that became famous did so in spite of being slightly or even much out of focus.

[hansvons]

Distance marks on still lenses are never accurate, even on the most costly M lenses.

And they are not meant to be as they are missing proper witness marks. Cine lenses, on the other hand, are another story. They have accurate witness marks, are shimmed to meet the exact focal distance, and the mount (PL, LPL) is super-sturdy and locks the lenses with a screwcap. 

This zone focusing procedure only works for smaller prints and when focus is not critical to the photographer. Regardless of how much you stopp down, on a 50mm and 35mm lens in close to medium distance (10m), there will be a specific focus distance visible. Only at infinity 100+ meters and stopped down, the depth of field will take care of critical focus.