How do cameras focus 1

Focusing the analog camera: focusing made easy

Those who also take digital photos will mostly use the autofocus with these cameras: This is precise and fast. Of the analog cameras, on the other hand, only “younger” models from the 1990s (and late 80s) have automatic focusing. However, the older models are usually much more interesting and some of them have different solutions that enable precise focusing. These are explained here.

The classic The analog camera is made of metal, maybe has a built-in light meter, but otherwise works completely mechanically - like clockwork. Younger models from the 1990s can then also be made of plastic and their appearance hardly differs from digital SLR cameras. After all, these have an autofocus.

One of the more modern analog cameras from the 1990s: They look like digital cameras and have lenses with autofocus (here Canon EOS analog).
However, the “classic” mechanical camera usually cannot offer such an autofocus. The focus here is by eye or manually - but this works quite accurately.

There are three methods by which analog, older cameras can be focused:

Focussing by means of a cross-sectional image indicator and a microprism ring

The best-selling analog camera is the single-lens reflex camera based on the system principle:

You are guaranteed to be familiar with such a picture. Many manufacturers built their 35mm SLR cameras according to this principle. Behind the lens of these cameras there is a small mirror that redirects the light that passes through the lens upwards. And in the upper part there is a small screen.

Most models have a so-called screen in the middle of this screen Marker let in. This is a small circle with a (mostly) horizontal line. This indicator is also known in some places as a “measuring wedge”, “cross section wedge” or as a “cross section rangefinder”.

On this illustration you can see the aforementioned marker. The photo shows the small screen of a 35mm SLR camera. With some models, these can be removed or exchanged. The said measuring wedge is more visible in the enlargement (right). Furthermore, there is a so-called wedge around this sectional image Micro prism ring, which is an additional help for focusing.
The following graphic explains exactly how this is used in practice:

Your attention should be drawn to the two red arrows: the lower one points to the cross-sectional image indicator and the upper one to the microprism ring. Some cameras (or focusing screens) do not have the latter. Some focusing screens do not have a measuring wedge either. This is particularly the case with digital cameras: manual focusing is much more difficult here than with an analog camera with an appropriately prepared screen.

The graphic is self-explanatory: If you are not properly focused, then you are

  1. vertical lines on the marker postponed and
  2. structureless surfaces within the microprism ring blurred or. cheesy shown.

However, if you have focused exactly on a certain object, then this is not shifted within the entire ring and is clearly displayed.

Many medium format cameras also have a standard screen with a microprism ring that surrounds a sectional image indicator. With some focusing screens, the latter can also be arranged diagonally.

First of all, (vertical) lines - z. B. such a tree trunk - necessary. If these are not present in the subject (e.g. in a portrait), the micro prism ring can be used to focus.

Focusing with rangefinder cameras with a double image

With so-called rangefinder cameras there is no focusing screen and consequently it is not possible to focus according to the above-mentioned principle.

This is a Fuji medium format rangefinder camera for 6 × 9 film format. It is not a single lens reflex camera, it is mirrorless, so to speak. This has the advantage of a relatively compact design and a relatively low weight.

But if there is no screen or mirror installed, how do you focus with such a completely manual camera? Using one Mixed image rangefinder:

Note: The devil of errors has crept in here. In fact, in the case of a rangefinder, only the image within the green spot is displayed twice if the focus is incorrect, not in the entire viewfinder image (as shown here).

In the viewfinder of such a camera there is a (mostly green-yellowish) spot. With some cameras, this is sometimes not immediately visible to the untrained eye: You must not look through the viewfinder at an angle.
Focusing is now very easy: If the targeted object is out of focus, it will be within the green circle double reproduced. If it is in focus, then both individual images are correct Mixed imagematch. This type of focus can be done very quickly after a little practice. The famous analog Leica cameras (and also the digital ones!) Also work according to exactly this principle.

In particular, such mirrorless 35mm cameras are ideal as “always with you” cameras that you can always carry with you in your jacket pocket. They also use the “rangefinder principle” with the mixed image viewfinder to focus.

shown is an "Agfa Selectronic S"

Focus using zone focus, scales and tables

The third possibility of focusing a manual or analog camera is sometimes called “zone focus”. The bulky and the less beginner friendly The term “hyperfocal distance” is also one of them. This is about focusing according to very specific values, which are either printed on the lens or can simply be printed out using a table. This method works with everyone Camera that can be focused manually and that has a distance scale on the lens.

The advantage of the zone focus is that you can sort of look at it Sharpness zoneslay can: The focus area starts at z. B. two meters in front of you, you go to eight meters and then everything is out of focus.

This type of focusing is particularly recommended within landscape photography, if you want to z. B. want to do without swollen (fuzzy) foreground.
How it works is easily explained using an example:

 

Take a look at the values ​​printed on the lens in the picture below, especially the aperture values: 32/22/16/8 and 8 \ 16 \ 22 \ 32. B. the two 16s opposite are: 3 meters and approx. 9 meters. The line in the middle is offset by a value of approx. Four meters.
That means: at an aperture of 16 and with manual focus at 4 meters extends the focus range from 3 meters to 9 meters. The depth of field is therefore approx. 6 meters with this lens and this setting.

Using this zone focus principle, you can use the scale and the set aperture to determine exactly which areas are in focus within your image. You don't even have to look through the viewfinder to do this. This procedure is particularly useful when taking pictures with a tripod if you can stop down a long way.

This is the back of a simple viewfinder camera. This has neither a focusing screen nor a rangefinder. So you simply estimate the distance to the subject and focus that way. This is of course better based on the zone focus. However, since the lens does not have any values ​​printed on it, you can simply choose one table use to focus.

If you look closely, the table gives e.g. B. the following:
With f / 16 and a manual lens adjustment to 3 meters, everything from approx. Two to five meters is shown in focus. Very easily.

However, these values ​​are dependent on a) the film format used (small format, medium format, ...) and b) on the focal length of the lens. You can generate such a table individually for your camera on this page: The depth of field calculator.


Feiningers Great photo lesson is one of the most famous textbooks for photography and is now being published in a new edition. The photo theory can be used as the Standard work of analog photography. You can take a look at this book on Amazon.

View on Amazon

display

On this photo you can see the focusing screen of a large format camera on the right. You can also see the table attached there, which you can use to read the depth of field for each point focus at each aperture. Of course, you can also use a magnifying glass to focus directly on the screen. This is at z. B. Landscape shots less useful: Here the sharpness should extend over a very specific area.

In this photograph, the lens was set in such a way (aperture + distance) that everything from about two meters to infinity is shown in focus. In fact, the focus was just behind the protagonist so that the depth of field can extend from the very front to the back. This makes it possible to create almost no visible blurring. The additional flash from the left results in a rather artificial-looking image, as if the protagonist was standing in front of a photo wallpaper.

Conclusion

Of course, a nimble autofocus on a camera is often a great advantage! Most analog cameras don't have one (probably the newer ones from the 1990s). Nevertheless - with a little practice - it is quite possible to focus precisely with an old camera. If you can use a tripod (stop down wide = longer exposure times), you are on the safe side even with cameras without a focusing aid: You simply use a table (or the scale on the lens) for the zone focus.
Once you have adapted an old, manually focussed lens to a modern digital single-lens reflex camera (DSLR), you will quickly find that focusing is far less precise with the eye. This is due to the fact that the built-in focusing screens of the analog SLR cameras are equipped with a microprism ring and / or measuring wedge in order to be able to focus precisely according to sight. There were also magnifying glasses for even greater accuracy. With many medium format cameras, a small, fold-out magnifying glass is already integrated in the light shaft for precisely this purpose. Further precise focusing can be achieved using the rangefinder principle with the overlapping image, which is built into some non-reflex cameras (e.g. Leica). You can recognize these types of cameras ("rangefinder cameras") by the two conspicuous viewfinder windows. With some types of these analog cameras, however, this image overlap is difficult to see in the viewfinder (especially if you look at the viewfinder at an angle).

Article date: 09/17/2016 / last change: March 22, 2021 ▲

Hello! This is where Thomas writes. I have been involved in analog photography for 20 years now and I develop my pictures in the darkroom or "with" the computer.

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Willi | on January 9, 2017

Hello Thomas

I would also like to thank you for your article, which has been made very easy to understand.
I recently bought a Nikon F301 that I got when I was young
was the first to have an SLR, and I am excited about it again. However, notice
I think it takes some practice to focus and focus; the F301 has
Sectional image indicator, micro prism ring, ground glass and 12mm setting circle. Most of the time I am a little confused when looking through the viewfinder whether I have got it right
got on the lens; man has only a limited number of recordings and no delete button
like a DSLR. BUT I think that's exactly why they make a lot of effort at Analog to take the best possible photo and not edit it with a photo program. In my opinion, the result is often no longer a photo.

Greetings Willi

Pascal | on November 24, 2016

Thank you for this great explanation. I have only just started with analog photography and I own a Minolta srT303b with a split image indicator. I always got upset that I couldn't focus when there wasn't a vertical line. But now I know and I am thrilled!


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