HOW I BUILT A SINGLE FOCUS ANAMORPHIC LENS.

 

This is not intended to describe each process in a specified sort of way, rather as an detailed overview biased towards my thinking process and how I solved issues and developed new concepts.

 

I forget why I opened up my first anamorphic adapter, but two discoveries stand out for me. One of those would help anyone using adapters in a traditional dual focus setup, and the other was a key finding that led to my single focus design.

 

What I discovered firstly is that anamorphic adapters are tuneable, as the twisting alignment between the front and rear elements is absolutely critical to sharpness. Because this is adjustable, it stands to reason that many are not set correctly, and probably leads to many of the online complaints about sharpness of these adapters. When correctly set, by loosening the three screws in elongated holes that allow the two parts of the adapter to twist relative to each other by a small (but very significant) amount and then tuned visually before tightening up again, the adapters shine in terms of sharpness, and at the very least have acceptable wide open sharpness for cinematic use, which is why you would use anamorphic anyway. If out of tune the sharpness can be awful, although at least improving as the taking lens is stopped down. Many users talk about having to use smaller apertures to achieve sharpness and put that down to the inherent design of the adapter, when in fact a simple tune might solve that.

 

The second discovery got me thinking. In standard form the adapters focus by rotating a focus ring much like a normal (taking) lens. The focus ring causes the two parts of the adapter to move closer together or further away from each other. Except that instead of getting shorter when focusing towards infinity, the lens as a whole gets longer. This is opposite to the taking lens (at least for lenses that don't focus internally) and a critical optical design that we can use as a hack of the century to our advantage, and save the $6000 that single focus anamorphic lenses start at.

 

Most budget anamorphic setups require one to focus the taking lens and then the anamorphic adapter (or vice versa), often in a fiddly iterative process to get proper sharpness, making them useless for focus pulls, run and gun filming or anything requiring enjoyment.

 

I figured that if the taking lens is getting longer as it focuses on closer and closer subjects, then if it is mounted solidly together with an adapter it could be simulaneously pulling the back element of the adapter backwards if the front element of the adapter is fixed in place, then this will effectively be focusing the adapter. But in order to get critical focus you would need a taking lens that extends by exactly the same amount as the adapter needs to get shorter from one focus point to another. It just so happens that if you remove the front ring on the adapter you disconnect the main focus ring from the front element housing and focusing the anamorphic becomes an exercise in push-pull. It is the amount of push-pull that matters here, as we want a lens that matches it exactly.

 

Let's call this specification the “focus extension' of the lens. Unfortunately despite Google knowing everything this is something it doesn't know and so a good deal of trial and error, accurate measurements and a supply of adapters and legacy lenses is needed. But some basics became apparent. Most anamorphic adapters focus to about 6 feet or 1.5m as their closest point. So for simplicity I settled on my measurement as the amount of lens extension when focused from infinity to 1.5m, and as I already had an adapter I knew what that adapter's 'focus extension' was. And this varies from adapter to adapter so sometimes a little luck goes a long way.

 

And I found luck. I bought a Vivitar series 1 macro lens off Trade Me, and as it had some undisclosed fungus that the buyer wasn't aware of I actually wondered about completing the deal, but I'm glad I did. Turns out the same seller was selling off her recently deceased father's collection and when I asked her if there was anything that said 'anamorphic' on it she surprisingly said there was, and I ended up with a bargain price Elmoscope II anamorphic adapter which turned out to be far superior to my adapters already in my collection (a Kowa Prominar 16D and a Sankor 16C). The Elmoscope is shorter overall, but has significantly wider glass making it more suitable for both wider aperture taking lenses as well as having an advantage in optical coverage. Where smaller adapters start vignetting, the Elmoscope doesn't, allowing wider angle lenses to be used. Every little counts, as this is a significant shortcoming of anamorphic in general. Even more importantly, the focus extension of the Elmoscope was significantly less than the other two adapters (about 5.5mm rather than about 10mm), and this in general terms means that short lenses will be suitable, giving wider anamorphic coverage with the potential for single focusing. I like wide coverage, and if you need tighter shots you can always punch in on 4K or use a teleconverter if your rig allows one to be fitted, or shoot on APS-C or super-35 rather than full frame.

 

Getting back to the story, the luck didn't end there. I had already experimented with single focusing using the concepts above but nothing matched and I had created a series of cumbersome “gears” to attempt to equalise the focus extension of adapters and lenses as I knew I was onto something. And then some measurements showed that the Vivitar 105mm macro and the Elmoscope were directly compatible.

 

That was all the easy part.

 

Building the anamorphic rig has taken what I estimate to be over 50 different iterations, experimenting with more than one different taking lens (each has their pros and cons), various supports to hold the lens and front part of the adapter in rigid connection, but all iterations to date have used the Elmoscope II adapter. It is now unrecognisable, surrounded by hardware with its focus rings removed. In a bold iteration somewhere in the middle of the process I worked out that the closer the 2 parts of the adapter get to each other the closer it can focus, and that the limitation was in the mechanical design of the lens housings, not the optics. So a significant internal removal of material has resulted in an adapter that can focus down to about 0.7m, a vast improvement over (all?) other anamorphic lenses.

 

Any anamorphic rig following the above process to create single focusing must have:

 

A taking lens that matches the adapter in focus extension, that has:

a focal length that doesn't vignette too much on any given sensor size

A way of holding the front part of the adapter in place

A method of joining the adapter to the lens

Something to join the front of the adapter to the back of the taking lens, or to the camera.

 

Beyond those five requirements my iteration process has also addressed the following:

(1) Finding the ideal taking lens, perhaps in image character, bokeh, maximum aperture, size and weight etc. Whilst some lenses are really liked by indie filmmakers for their character and when used anamorphically with an adapter, such as the Takumar 50mm f1.4 or the Russian Helios 58mm f2 44, these and many other lenses do not match anamorphic adapters' focus extensions and so are not suitable for simple single focus projects without intermediate gearing of some kind, and also don't effectively cover full frame with most adapters (most users are probably using them on a micro 4/3 sensor).

(2) Achieving the widest view, either by using a wider lens, a wide angle adapter or a Speedbooster

(3) Getting a more rigid method of holding the front of the adapter, that is also adjustable for tilt, so as to align the non-spherical lens horizontally to the sensor (to achieve correct horizontal flare and vertical bokeh).

(4) Ways of joining the lens and adapter together that is neat, simple and allows removal if needed. The closer the taking lens sits to the back of the adapter the better the image quality and coverage. A perfectly aligned rigid joiner is ideal but in an imperfect world it can help to have slight side to side play to ease tolerances on the focusing mechanism. Front to back slackness might not be acceptable, however, as this can manifest as achieving critical focus when turning the focus dial in one direction, but not the other, as the play puts the adapter in a slightly different effective relative position depending on whether you are pushing it (no slack) or pulling it (maximum slack).

(5) Perfecting the rig. The way of joining everything together has resulted in the most iterations. I have used modified bellows units, macro photography platforms and Manfrotto and Metz flash brackets. But the only really suitable solution in terms of rigidity and therefore adjustment stability has been the most recent iteration using Zacuto 15mm rails and a baseplate on each end. This has also facilitated the compact fitting of a removable follow focus unit.

 

The current setup:

Setup 1 – best image quality and soft bokeh, manual focus.

In summary:

A heavily modified Elmoscope II anamorphic adapter paired with a heavily modified Nikkor 85mm f2 taking lens, connected to the camera through a standard Metabones adapter, all held together using a 15mm rod setup using mostly Zacuto parts, but with donor parts from countless sources.

 

The adapter can be swopped out for a Speedbooster within minutes as required. On full frame sensors the speedbooster vignettes but once corrected for the 2x anamorphic squeeze in post processing (and therefore the far edges of a 16:9 sensor lost) the coverage is sufficient.

 

The rig can be removed from the camera body exactly as you would normally remove a lens.

 

The rig single focusses from 0.85m to infinity from an effective f4, and from 1.5m to infinity at an effective f1.4.

 

The Adapter:

Elmoscope II anamorphic adapter with focus ring removed, internal housing machined to allow front and back elements to get closer to each other and therefore allow closer focusing, and a 52mm male filter ring pressed securely on the rear to allow direct attachment to the front filter thread of the taking lens without any play in the join. The adapter's front ring has been machined smaller to fit an existing bracket (a rotating tripod collar from an old zoom lens, which now holds the front of the adapter to the rig). The three tuning screws for internally aligning the lens are readily accessible and are covered with a rubber grip, which causes some air drag in the focusing of the adapter unless it is pulled back slightly. The adapter is optically excellent with fairly minimal flare (which can be a disadvantage).

 

Nikkor AIS 85mm f2 taking lens.

 

The lens is incredibly small and light which has allowed other parts of the rig to be beefed up for rigidity whilst everything still being hand-holdable. The focus extension specification matches the adapter. It replaced the Vivitar 105mm f2.5 which was bigger, heavier and had relatively stiff focusing.

 

The silver grip ring between the focus rings and aperture ring has been drilled and tapped to accept a Metabones foot (so that it has a tripod socket), to allow micro adjustment of lens alignment when in place on the rig, and having this also attached to rig helps to prevent flexing through the lens stack. Any unwanted flexing can cause micro shifting of the image particularly when focusing, and also then the focus ring drag can change when a camera is mounted, or the rig used upside down for example.

 

The focusing threads have been cleaned of most of the manufacturer's grease and light oil applied to make the ring very easy to turn with practically no drag. This also means that the follow focus works better even with the extra drag of the anamorphic adapter's sliding focusing, and the ring on its own is a joy to focus with. It is sufficiently smooth and loose that it can be focussed with a light touch with one finger, and can actually be hand focused whilst on a steadicam without causing rotation of the balnced rig. Anamorphic images/footage don't like camera rotations as it causes unpleasant and amateur looking distortion, so in general terms the lighter the focusing action the better with an anamorphic lens to avoid any twisting of the camera during shooting, and a stiff focus ring imparts torque to the rig, obvious particularly when hand holding or on a steadicam. In this way the follow focus helps, as it makes the torsional force become front to back rather than side to side, so it doesn't cause that unpleasant optical distortion, but the mechanism needs to be loose enough for it to turn freely. Obviously no movement as a result of focus control is preferable, in fact essential for professional usable footage.

 

The focus ring has a removable Zacuto follow focus gear with a random little bracket to provide a small handle to focus with. To focus, this little handle can be operated with one finger by the hand holding the camera grip, whilst the left hand supports the weight of the rig from underneath.

 

Because of the modification to the close-focusing distance of the adapter, it does depart slightly from a linear focusing progression between 1.5m and 0.85m (the close limit imparted by the the Nikkor 85mm, although the adapter could go a bit closer in reality), and so, even with correct focus extension matching, sharpness is significantly diminished unless the distance between the front of the adapter and the camera is adjusted whilst in that range. My rig allows that adjustment, but a little cumbersome and as stopping down to f5.6 brings both ends of the range into acceptable sharpness, if I need to do a focus pull from one extreme to the other then I use f5.6, or f8 (slightly better), and then no other adjusting is needed. In fact for this and a few other reasons, f5.6 or f8 is the sweet spot.

 

But I needed to improve bokeh at those apertures, as the Nikkor 85mm out of the factory has seven straight sided aperture blades and so bokeh suffers noticeable from f2.8 downwards (and so very much so at f5.6 or f8). I particularly do not like hexagonal (actually heptagonal so even worse) edged bokeh, particularly in obvious out of focus points of light (it even finds its way into cinema), but it also imparts lack of softness to the bokeh in general. So I have modified the aperture blades of my 85mm to be more rounded, becoming perfectly round at f5.6. Like all my modifications this required some ingenuity so as not to destroy the blades in the process. The bokeh is now cleaner than at f2 (which exhibits halos), let alone how it used to be with the aperture pattern in it.

 

Of course all those apertures are effectively one stop wider if I am attaching the camera body using a Speedbooster. So then I'm getting single focus sharp footage at an effective f1.4, with some spreading of highlights at a magnified level which are gone by f2.8 (effectively f2). This is obviously a technical description but I should add that sharpness is largely irrelevant to creating emotion in film.

 

The Rig

The front of the rig uses a modified tripod collar from an old 100-500mm zoom lens to hold the front of the anamorphic adapter, drilled and tapped in three places with allen head grub screws to hold the adapter securely and allow rotational adjustment to align the adapter to the camera sensor. It bolts through the rig using a modified Manfrotto tripod plate screw. It has a 77mm filter thread glued to it, strong enough for a very heavy Cavision wide angle adapter but normally used for ND filters and/or a rubber lenshood. The wide-angle adapter has edge softness but brings the closest focus point closer, although cannot achieve any more angle of view than the setup already enjoys.

 

The collar bolts to an as yet unmodified baseplate from a Tilta cage, which has a modified piece of the cage bolted in an offset position underneath at the balance point of the lens to provide a place to mount the lens to a tripod, steadicam or slider. The baseplate slides on Zacuto rails with a Zacuto clamp bolt, allowing the position of the adapter to be tuned to the lens. On the camera side of the rails is a zacuto base riser plate mounted upside down and through it are two tripod screws attached respectively to the base foot of the mount adapter (Speedbooster) and to the custom base foot on the 85mm lens. Getting the shims/clearances/tightness etc right with these two screws is critical to focusing performance and the rig holding tune.

 

Between the baseplates is the rod mount for a Zacuto follow focus unit. The rod sockets on the Zacuto base plate allow for quick attachment of ancillary equipment or carry handles.

 

Is my latest design better than all my other designs? Yes, but not in all respects. A previous iteration was much smaller and lighter, and didn't include the mount adapter/speedbooster in the rigid setup, and so could be quickly mounted on any camera with a suitable mount adapter. But it lacked rigidity and although it could coaxed into having light focusing, if used upside down the focus would stiffen up, and it didn't like having a follow focus attached to it. And optical tuning wasn't as reliable. I wanted perfection in optically tuned sharpness and light focusing and now I have that. A very recent version, and one I can still swop to within a few minutes is auto focus, great for using on a steadicam but overall just not as crisp to use, with less desirable bokeh etc.

© 2020 by mort'mer/mortmer/Bruce Mortimer