I have given an introduction to Depth of Field here.  There I explain why the depth of field is so immense with mobile phones and most small digital cameras that differential focus is not possible.  In other words, everything will be sharp, regardless whether or not this is desirable.  Objects in the surroundings or in the background may be so detailed that they distract the viewer’s attention from the subject chosen by the photographer.

Control of what is in focus and what is out of focus within the image only begins to become possible to some extent with cameras that have a film or sensor format of 24×36mm (now commonly referred to as “full frame”).  Most “35mm” cameras had/have this format.  However, real control of focus with such cameras is often only possible with longer-than-standard lenses, for instance, with 90mm or 100mm lenses, or longer, on a full-frame 35mm camera.

For reasons explained on the above page, control of in-focus and out-of-focus zones within the images first becomes easy to achieve with medium format cameras such as the Pentacon Six.  On that page I also stated:

For these pictures I chose five, small Lego figures. This grab shot was taken hand-held with a digital camera using a 50mm Carl Zeiss Jena Tessar lens at a wide aperture, and it is not sharp throughout, but it does show the setup used. Lighting was from natural daylight entering a window to the right, and the camera was also positioned to the right, low down, just above the surface of the table on which the figures were standing.

		All of these pictures were taken with a Pentacon Six TL with the 80mm Biometar lens mounted on the 10mm tube.  The film was Fujicolor PRO400H.  A slower-speed film (for instance, 160 ISO) would have yielded images with finer grain, but this was the film that I had in the camera at the time.  Obviously, with slower-speed film I would have needed to give longer exposures. The width on the film of the images as cropped here is approximately 37mm, or 70% of the total width of the film frame.  If I had moved closer to fill the frame better, the depth of field would have been even shallower. Biometar on its maximum aperture of f/2.8 Shutter speed 1/30 sec Tripod No cable release, no MLU Focussed on 1st figure from the right. (Using a cable release is normally to be preferred for macro photography, but with a steady tripod and 1/30 sec I was confident that I could release the shutter gently and not move the camera during the exposure.) Note the extremely shallow depth of field when this 80mm lens is used at its maximum aperture with the 10mm tube. [C549_10_1st_fig_m.jpg]
		Focussed on the second figure from the right Other settings as in previous picture. [C549_12_2nd_fig_m.jpg]
		Focussed on middle figure. Changing focus changes the size of the subject on the film, something that must always happen, since the further the lens moves forward, away from the film (as when focussing on closer objects), the larger the image that is projected by the lens onto the film.  In most normal photography, the differences are so tiny as not to be observable, but in macro photography, such differences immediately become clear in the viewfinder. [C549_13_3rd_fig_m.jpg]
		Focussed (approximately!) on 4th figure from the right. In fact, focus is probably a little too far forward, a consequence of trying to work too fast.  Macro photography requires patience and time – and unchanging lighting conditions, if possible! [C549_15_4th_fig_m.jpg]
		Focussed – supposedly! – on far-left figure, although again focus is slightly out.  This does of course demonstrate why it is extremely unwise to shoot at maxium aperture when doing macro photography, since – even with perfect focus! – depth of field is extremely shallow. Stopping down the lens (any lens) has many advantages: it can mask any unintentional focussing error it increases the depth of field, bringing other components in the image into sharper focus with most lenses it will increase the image resolution, its sharpness and therefore its apparent contrast. It does of course have one disadvantage (at least, with moving subjects): the need to increase the exposure time (to give a much longer exposure). The normal solution with moving objects is of course to use electronic flash, which will enable the use of smaller apertures while still achieving a much shorter exposure that will in most cases “freeze” any movement by the subject.  However, the flash should not normally be mounted on the camera, since in that position it is likely to project a shadow of the lens onto the subject!  In addition to this, evenness of illumination across the whole of the image area must also be achieved as far as possible, often by using two flashguns. [C549_16_5th_fig_m.jpg]
		Stopping down to f/16 has massively increased the depth of field (to a depth of about 20 centimetres or 8 inches), although this is not quite enough to encompass the full distance from the nearest figure to the one farthest away. As the smaller aperture lets much less light pass to the film, I have had to increase the exposure time to 1 second, and have of course therefore used a cable release, to prevent the transmission of any movement from my body (breathing! heartbeat!) to the camera. The depth of field extends both forward of and behind the point of sharpest focus and as the lens is stopped down, the increase in focus is greater behind the point focussed upon than in front of it.  For this reason, in this image I have not focussed on the middle figure but somewhere between it and the image to the right of it in this picture (the second figure from the right). The increased depth of field now enables one to perceive (slightly out of focus) the front edges of the table and the point where the back of the table reaches the wall. [C549_17-18_2nd-3rd_f16_m.jpg]
		Here, without changing the point of focus, I have stopped the lens down to its minimum aperture of f/22, and this has increased the depth of field and brought the farthest figure (the one on the extreme left in the image) into sharp focus. Naturally, I have had to double the exposure time (to 2 seconds), to compensate for the halving of the light intensity caused by stopping down the lens from f/16 to f/22.  Cable release used, of course. [C549_19_2nd-3rd_f22_m.jpg] Remember that the closer the subject on which the lens is focussed, the shallower the depth of field.  This happens with all lenses.  In macrophotography, the depth of field will be very shallow at maximum aperture, and the longer the focal length of the lens (for instance, with a focal length of 180mm), the shallower will be the depth of field. The opposite is obviously also true: the shorter the focal length of the lens (for instance, with a focal length of 50mm with the Pentacon Six), the deeper will be the depth of field. For this reason, it can sometimes be good to use wide-angle lenses for macro photography, providing that you are not so close that you either frighten your subject or cast a shadow on it.

For more on this subject, see the pages on this website on

• focus (also covers bokeh and hyperfocal focussing) 
• exposure
• digital
• bokeh
• macro
  

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© TRA First published: April 2017