& Exposure Factors
The manual tubes consist of a front tube (“A” in the image on the right) with a mount to receive Pentacon Six lenses at one end and a screw thread at the other, and a rear tube (“B” in the image on the right) with a mount to go on the Pentacon Six body at one end, and a screw thread at the other. Each of these tubes is 9mm long, and both tubes are needed at all times, either just joined together, or with one or more of three spacer tubes of different lengths between them.
The screw thread used appears to be 68mm, apparently with the normal pitch for this size of 0.75, although I have yet to check that.
The dimensions of the other tubes are:
Tube I 8mm
The various combinations provide (without any gaps) image scales on film from 0.21:1 (fractionally more than one-fifth life-size) to 0.98:1 (fractionally under life-size), when used with the 80mm Biometar lens and making use of its focussing ring.
The big disadvantage of the manual tubes is that there is no automatic operation of the lens diaphragm pin, so it is necessary to open up the lens fully to focus, and then stop it down to the chosen aperture before taking the photograph.
This can be overcome by the use of the special extension tube with aperture control, and a double cable release. This tube is 20mm long, and it can be used on its own or with the manual tubes, providing image scales from 0.24:1 to 1.02:1 (fractionally over life-size)
|Here the manual tubes are being used with the special
extension tube and double cable release in order to retain
automatic aperture operation.
The special extension tube is labelled “Z” in the chart below. Pentacon’s order number for this tube was 208 560.
For a long time I believed that these manual tubes were
only ever available in plain metal finish outside (they
are matt black inside). However, thanks to a
Pentacon collector who is a renowned expert, I now know
that some manual tubes were made with a black
finish. They are seldom seen!
|This chart shows the entensions obtained, image scales,
image size and other information for photography using the
manual tubes with the 80mm Biometar lens.
This chart gives exposure factors when using the 80mm lens.
For exposure factors with other lenses, please see lower down this page.
In practice, depth of field is extremely shallow with macro photography, and normally smaller apertures would be recommended – either with increased light to compensate (if the subject is moving) or a much slower shutter speed (if the subject is not moving).
If you are use a metering prism, none of this
compensation is necessary, as the meter will give you
the correct reading – an excellent reason to get
and use a TTL metering prism!
Exposure prolongation factors enable you to compensate,
when the light falling on the film will be less bright
than the light falling on a hand-held light meter. Assuming
that you have been careful to ensure that the light
falling on the hand-held meter is the
same as the light falling on the subject to be
photographed, less light will fall on the film
in either of two circumstances:
In either case, the effect on the film will be the same,
and for this reason, filters that do reduce the amount of
light falling on the film (some do not!) should be marked
with an exposure prolongation factor, just like the
factors on the extension tube charts. You will find
a helpful explanation of this on the filters page on this
website, where the factors are, logically, called “filter
factors”. That page also has a helpful chart
that explains this further. You can see the page here (scroll down for the
The Pentacon Order Number for the manual tubes was was 208 530. You can see an illustration of the special extension tube here (scroll down). I have called it an aperture control ring, because that is essentially what it is!
I recommend that if possible you obtain the automatic
tubes. These contain a plunger that transmits the camera
instruction to stop down the lens aperture when firing. The
order number for the automatic tubes was 208 810. Early
versions of these tubes were produced in plain metal finish
outside, although later on they were available with a shiny black
finish outside. All versions are of course matt black
inside. The dimensions of the auto tubes are as follows:
|Tube I 15mm
Tube II 22.5mm
Tube III 30mm
Tube IV 60mm
In conjunction with the 80mm standard lens, these tubes provide image scales between 0.18:1 and 1.62:1.
Image scales, image size and other information for photography using the automatic tubes with the 80mm Biometar lens.
To see more information on the automatic tubes, click here.
You can see the effect of using these automatic tubes here.
There is also a 10mm extension ring which is not intended to be combined with any of the above rings; it merely fills the gap in the image scale between 0.1:1 and 0.18:1, i.e., the maximum extension of the lens (8.5mm) and the No 1 tube (15mm). Pentacon said that if this ring is the first one to be put onto the camera, you should release the shutter before the lens is inserted and locked. Data related to using this ring is in the above chart.
The Pentacon Order Number for the 10mm ring was was 208
811. To see the special ring, click here.
scales & extension factors with other lenses
Pentacon also gave brief information on using the auto
tubes with some other Carl Zeiss lenses.
Pentacon does not give factors for using tubes with other lenses, as they are rarely used in macro photography. However, application of the above principle will indicate that if you added an 80mm extension between the camera and the 180mm Sonnar lens, you would be increasing the distance of the lens from the film by somewhat less than half of its focal length. The exposure compensation would therefore be in the range of about 2. That is to say, you would need to open up the lens by ONE stop OR increase the exposure time by one setting, for instance, from 1/125 to 1/60 sec (assuming that the camera was on a tripod and the subject was not moving!).
You should be cautious about using significant lengths of extension with lenses that were not designed for such extensions, as this can result in unexpected consequences. You can see what I mean here.
The Pentacon bellows provide variable extension nominally from 20mm to 100mm and image scales with the standard 80mm lens from 0.25:1 (one quarter of life-size) to 1.25:1 (larger than life-size).
With a double cable release, lens aperture automation is retained without the need for the special extension tube referred to above.
|Image scales and other information for a range of bellows extensions is given in this table:||
|For extreme close up work, it is possible to mount the 80mm Biometar lens reversed on the bellows (or for that matter, straight onto the body or one or more of the extension tubes), using Pentacon’s special reversing tube (which is illustrated here – scroll down). This results in much greater magnification. Here are the relevant exposure details:||
|With the lens reversed, it is still possible to retain
lens aperture automation by using the special tube
described above in the section on maintaining aperture
automation when using manual tubes (the “aperture control
ring”). This tube was often supplied with the double
The Pentacon Order Number for the bellows was was 208 750.
The Pentacon Order Number for the double cable release was 210050
The four types of Pentacon extension tube sets, from L to R:
manual (chrome), manual (black), auto (chrome), auto (black)
(The size labels that I have added to the black auto tubes may just be visible in this picture.)
To go on to the next section, click below.
To go back to the beginning of the macro section, click here.
The Pentacon Six bellows
© TRA January 2006. Latest revision: September 2017