The Pentacon Six System
by TRA

Filter Systems for Pentacon Six lenses

A “square” filter system for the Pentacon Six?

The Background & The Problem

Traditionally, filters have been round, and they screw into a filter thread on the front of the lens (or many decades ago occasionally were push fit, held in place by friction).

Cokin filters

However, in 1978  the French photographer Jean Coquin introduced a system of square filters. These filters slid into a holder that was mounted onto the lens.  Eventually, this system was commercialised world-wide with an anglicised spelling of his name: Cokin.  Square (or in some cases rectangular) filters have various advantages:
  • They can be mounted via adapter rings onto lenses with different-sized filter mounts.
  • Jean Coquin introduced graduated filters, in which the intensity of the filter effect varied from the top of the filter to the bottom.  This can be used, for instance, in landscape and seascape photography to reduce the brightness of the sky and avoid over-exposing it.
  • The graduated filter can be slid up or down in the holder, to align with the horizon, which does not have to be at the mid point of the image, which is seldom the best position, from a compositional point of view.
However, some of the best landscape lenses for the Pentacon Six have very large diameter front elements, so that the filter mount on the two wide-angle Flektogon lenses is 86mm, with a thread pitch of 1mm, whereas Coquin’s original system was for filters with a mount diameter up to 62mm – far too small for use on most Pentacon Six lenses.  (For information on the Coquin/Cokin system, I am referring to the “Cokin” entry in French Wikipedia, here.  Page accessed on 29th September 2019.)  This was the “A” (“Amateur”) system.  The company subsequently introduced a “P” (“Professionnel”/“Professional”) system, with maximum thread diameters of 82mm, still too small for many Pentacon Six lenses.

Cokin subsequently introduced two further sizes:
  • “Z-Pro” with sizes for lenses with filter mounts up to 96mm diameter
  • “X-Pro” with sizes for lenses with filter mounts up to 112mm diameter.
At last there was a size for the 50mm Flektogon!  However, if the 96mm system were used on this wide-angle lens, I would be concerned that there might be vignetting (darkening) of the edges or corners, since most filter holder have two or three slots, in order to hold a series of filters in front of the lens at the same time, so these filter holders can extend forwards up to a centimetre or more from the rear mount that screws into the lens.

Meanwhile, other manufacturers have entered the same sector of the market.

Lee filters

One of the best-known in the U.K. is Lee filters.  At the time of writing, they have information on a 100mm system, which can be accessed here.  (Link correct on 29th September 2019).  Even this can be too small for some wide-angle lenses, and so Lee have now introduced a 150mm system.  They call it “SW150”.  I would guess that “SW” stands for “Super-Wide”.  Information on that system can currently be accessed here.  This certainly sounds fully suitable for Pentacon Six lenses.  However, I have no experience of it, having followed another route.

Voigtländer lenses and NiSi filters

A couple of years ago I bought the superb 10mm (!) Voigtländer “Hyper-Wide Heliar” lens.  Such an extreme wide-angle lens could not be made even for a 35mm SLR, and it was previously only available for Rangefinder cameras.  However, when mirrorless digital cameras were introduced, Voigtländer made this lens available in the Sony FE “35mm full frame” mount.  It is of course a superb lens.  However, it does not cover 6 × 6 format and cannot be used on a Pentacon Six.  But ...

For such an extreme wide-angle lens, one on-line review recommended the NiSi 150mm Filter Holder System, and I bought the holder immediately, in case it was discontinued (which seems to have happened!!).

Here are some pictures of the NiSi holder on the 10mm Voigtländer lens, on a Sony mirrorless full frame 35mm camera:

As indicated by the name, this filter holder takes rectangular filters that are 150mm wide.  It is shown here and in the picture to the right with no filter in place.

This closer view reveals how the holder is slipped round the petals of the built-in lens hood.  The central section of the holder is mildly conical, which has to be the case so that the filters will clear the front of the lens hood petals.

This side view enables us to appreciate how the holder is attached to the lens.  Again we can see the conical shape of the inner section of the holder.  Here we have inserted a 3-stop hard graduated ND filter into the holder.

Front view with the graduated filter in place.  This is a grey graduated filter.
The brownish-reddish colour visible here is the colour that is reflected by the multi-coating on the filter.  A totally-neutral grey is what is transmitted by the filter.


Note that while most NiSi filters are square, the graduated Neutral Density filters are 150mm wide × 170mm tall, to permit adjustment of the filter to match the height of the horizon (or other transition from light to dark) in the image.

The NiSi holder has two separate components:
  • a central, “dished” component that is round, which slides onto the lens
  • an outer component that is rectangular, which holds the filters.
The back of the rectangular component has a narrow recess all round the opening, and the front of the ring sits in this recess.  On one side, the round component is held in place by two small tabs in the rectangular component, and the edge of the ring is tucked under these tabs when it is inserted into the larger component.  On the other edge of the opening, there is a small spring-loaded tab.  The edge of that tab can just be seen in the photograph to the right here, on the right-hand side of the opening.  This tab is pulled out by the user, gripping the knob that can be seen in the photo.  The rest of the ring is dropped into place, and the knob is released, enabling the ring to be securely held in place by the tab.

Making the holder in two separate components has two advantages:
  • It enables the manufacturer to offer centre sections for different lenses.  A NiSi brochure lists 15 different lenses from a wide range of manufacturers, including Voigtländer, Zeiss, Nikon, Canon, Sigma and others.
  • It enables the user to rotate the filter holder, for instance, to get the best effect when using a polarizing filter, or for a slanting horizon when using a graduated filter.
It also has an advantage for us Pentacon Six users!  It enables us to replace the centre section with one that will fit our preferred lenses!!  More than two years ago I wrote directly to NiSi and to one of their U.K. distributors, to enquire about obtaining alternative centre sections.  I also asked the same question of the staff on their stand at the Photography Show in Birmingham in March 2019.  However, up to the time of writing (at the beginning of October 2019) I have not received a reply.  I therefore decided to seek the solution elsewhere.




Regular visitors to this website may have seen how SRB have helped me in the past.  Their website is now here.  (Last accessed on 30th September 2019)
  • Years ago, they made a ring that enabled me to mount a Hasselblad Compendium Lens Shade onto the 600mm mirror lens.  (See here.)
  • And years ago they designed the components that enabled Tom Page to mount the prototype Schneider-Kreuznach 40mm Curtagon lens into an Exakta 66 lens body.  (See three pages, starting here.)
Over the years they have also made or supplied from stock other lens adapter rings (not reported on in this website).

I therefore asked them if they could make some custom rings for me.  The result can be seen in the image to the right.

Because of the petal lens hood of the 40mm Zenzanon lens (see pictures of it here), they had to make a deep ring, which slides onto the petals and has a locking screw to hold it in place.  All the other rings are essentially flat discs with a uniform outer diameter and profile to fit into the rectangular component of the NiSi filter holder, and differing internal apertures and filter threads, depending on the lenses for which they are designed.  In the picture to the right, the front of the ring is up for the 40mm Zenzanon, 58mm, 86mm, 95mm & 105mm rings, and the back of the ring is up for the 67mm & 82mm rings.

Here is a summary of the principal lenses with a Pentacon Six mount that these rings will fit, and some Pentax 67 lenses that will mount on one of my Pentacon Sixes, via a special lens mount ring (see details here), plus
a few lenses for other cameras:

Custom tube with locking screw (Top left in picture on the right)
40mm Zenzanon

105mm × 1
40mm Curtagon

58mm × 0.75mm
80mm Biometar & Planar
80mm Tessar
90mm Vega-12

67mm × 0.75
45mm Mir 69
120mm Biometar
180mm Meyer-Optik Primotar
Exakta 66 60mm, 80mm, 150mm & 250mm lenses

82mm × 0.75
45mm Mir 26B
& shift & shift/tilt lenses derived from it
150mm Kaleinar
250mm Jupiter-36
300mm Telemegor
45mm Pentax 67 lens
300mm Pentax 67 lens
(and also lenses such as the 23mm Fujinon GF for Fuji GFX)
86mm ×1
50mm & 65mm Flektogons
180mm & 300mm Sonnars
140-280mm Variogon (with front ring removed)
(and also lenses such as the 17mm Laowa GF for Fuji GFX)
95mm × 1
75-150mm Variogon,
140-280mm Variogon (with front ring in place)
300mm Pentacon/Orestegor
400mm Tele-Ennalyt
500mm Arsat APO
55-100mm Pentax 67 lens
90-180mm Pentax 67 lens
The 80mm Planar is a (West) German Carl Zeiss Planar lens that someone has cleverly mounted into an East German Carl Zeiss Biometar lens body.


Click on this image to see it larger.

Note that while SRB-Griturn are always prepared to consider orders for special, one-off items, experience has taught them not to produce bespoke items based on dimensions measured by customers – or even from specifications published by other manufacturers! – as these can be inaccurate.  They work to fractions of a millimeter, and so do their own measurements of the components to which custom items are to be attached.
Step-up rings

Other lenses can be catered for by using a larger-sized ring, with a step-up ring from the lens to the ring.  For instance, for the Arsenal Vega-28B 120mm lens, which takes 62mm × 0.75 filters, the above 67mm ring could be used via a standard 62mm to 67mm step-up ring.  One must only be careful using step-up rings when using wide-angle lenses, as the greater depth of the accessory caused by the step-up ring could result in vignetting.  However, this is only really a potential problem with the widest wide-angle lenses, which is why rings of the right diameter for these lenses have been made, to avoid the need for step-up rings in such cases.

One exception is the Pentax 67 55mm lens, which has a filter mount diameter of 77mm.  A 77mm male to 82mm female step-up ring could have been used with the above SRB 82mm ring, but to avoid any risk of vignetting I have preferred to use a 77mm male up to 95mm female step-up ring, as the extra inner diameter of the SRB 95mm ring means that vignetting is less likely when an adapter ring is used on this wide-angle lens.

Using the NiSi system with the SRB rings on the Pentacon Six

The 45mm Arsenal Mir-69 wide-angle lens
with the NiSi filter holder mounted via the SRB 67mm ring,
with a NiSi 3-stop hard grad filter in place.


The 50mm Carl Zeiss Jena Flektogon wide-angle lens
with the NiSi filter holder mounted via the SRB 86mm ring,
with a NiSi 3-stop hard grad filter in place.


No vignetting occurred when using these combinations of SRB rings and the NiSi 150mm filter holder with these wide-angle lenses!

Using filter systems is of course not limited to wide-angle lenses; this system can also be used on standard lenses (as illustrated at the top of this page) and even with long telephoto lenses.  In the following pictures we can see the system on a 400mm lens and a 500mm lens.

First we can see the filter holder on the Arsat 500mm APO automatic aperture lens, via the SRB 95mm × 1 adapter ring.  Here we are using the NiSi two-stop medium grad ND filter.


This view enables us to see the integrated lens hood that is permanently mounted on this lens.
It is simply slipped fully back in order to accommodate the filter system.  More information on this lens can be found here.


And here we see a super classic lens from the 1960s, the Enna Tele-Ennalyt 400mm lens, again using the same SRB 95mm × 1 adapter ring!  Here we have again mounted the NiSi two-stop medium grad ND filter.

With the Tele-Ennalyt, we have simply unscrewed and removed the standard Enna lens hood.  More information on this lens can be found here.

Using the NiSi system with the SRB rings on the Exakta 66

The NiSi 150mm filter holder will naturally mount on all the fixed focal length Schneider Kreuznach lenses for the Exakta 66 other than the 40mm Curtagon, as they all have a 67mm × 0.75 filter thread, so here we shall concentrate on the two Schneider Kreuznach zoom lenses, the 75mm-150mm and 140mm-280mm Variogons.

The 75-150mm Variogon M in Exakta 66 style, with its lens hood fitted and the front cap to the right.

When we remove the lens hood, we find that it has a thread diameter of 100mm, but behind it there is a ring that we can also remove, revealing the 95mm diameter thread on the lens itself.

Here we have mounted the SRB 95mm × 1 ring onto the front of the 75-150mm Variogon, after removing the ring that normally goes between the lens and the lens hood.

And here we have “clipped” the filter holder onto the 95mm ring, where it is securely held in place by the three tabs round the edges of the opening in the holder.  We have also put the 2-stop medium graduated ND filter into the holder.


The 140-280mm Variogon M in Exakta 66 style, with its lens hood fitted and the front cap to the right.

When we remove the lens hood, we find that it has a thread diameter of 95mm, but behind it there is a ring that we can also remove, revealing the 86mm diameter thread on the lens itself.
So with the longer Variogon we have two filter-mounting options:
  • We can remove the adapter ring that holds the lens hood and mount an 86mm × 1 filter or filter ring, the same as we used on the 50mm Flektogon and that we could use on the 65mm Flektogon and on the 180mm and 300mm Carl Zeiss Jena Sonnars
  • Or we can leave the adapter ring in place and use the 95mm × 1 filter or filter ring that we used on the shorter 75-150mm Variogon (and on the 500mm Arsat APO lens and the 400mm Enna Tele-Ennalyt!).

Here we have mounted the SRB 86mm × 1 ring onto the front of the 140-280mm Variogon, after removing the ring that normally goes between the lens and the lens hood.
And here we have “clipped” the filter holder onto the 86mm ring, where it is securely held in place by the three tabs round the edges of the opening in the holder.  We also have the 2-stop medium graduated ND filter in the holder – in fact, we saved time by merely unclipping the holder from the 95mm ring that we were using with the 75-150mm Variogon.

Here we have left in place the 86mm to 95mm ring that sits between the lens mount and the lens hood, so we have been able to add the very same 95mm × 1 ring from SRB that we had used on the 75-150mm Variogon.

And here we have “clipped” the filter holder onto the 95mm ring, where it is securely held in place by the three tabs round the edges of the opening in the holder.  We again have the 2-stop medium graduated ND filter in the holder.  With a wide-angle lens we would not want to “stack” rings in this way, because of the danger of vignetting being introduced, but with a lens that has as long a focal length as this, and a filter holder that is so wide, there is no risk of vignetting occurring.

The first test shots have been taken, but we may need to wait until next spring or summer before shooting seascapes with this system, as the coast is at some distance from here.

To see the introduction to using filters, click here.

To go back to the Frequently-asked Questions front page, click here.

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© TRA October 2019 Revised January 2022