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AJ Young

B&H Anamorphic Projection Lens Mod

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I've been deep diving into the world of DIY Anamorphic lenses and now I can share some of my experiences. Recently, I modified an old anamorphic projection lens so I could use it on set. My website has a full version of this post as well as a PDF, but I wanted to share it here in its entirety for discussion. WEBSITE LINK

The Bell & Howell Anamorphic Lens (BH16-2) is an old projection lens originally meant for projecting and de-squeezing 16mm film. Cinematographers can easily modify and adapt this lens for practical use on set with minimal additional parts. The following guide gives close to a step-by-step tutorial on how to modify the BH16-2 for practical use in cinematography and photography. However, there are some steps that won’t be explained, such as how to grease a helicoid, use a spanner wrench, or align an anamorphic lens.

Acknowledgements

  • Tito Ferradens for his saint like work on DIY Anamorphic
  • Chris Bold for paving the way of trial and error
  • Richard Gale for shining a light when we needed it

Key Concepts

Before beginning the modification, the BH16-2 has a key concept about its original design. A built in variable diopter makes the BH16-2 an easy and affordable lens to modify in comparison to other projection lenses. Variable diopters are a clever and simple way to circumvent the double focus anamorphic lenses require.

An anamorphic lens contains an anamorphoser and a spherical lens. The anamorphoser compresses/squeezes the image horizontally; additionally, it controls the horizontal focus of the image. The spherical lens controls the vertical focus of the image and aperture (not present on fully built projection lenses). These two lenses are focused at the same time mechanically in high end anamorphic lenses, called single focus.

When building a DIY anamorphic lens, cinematographers typically use the anamorphoser from a fully built anamorphic projection lens and clamp it together with a different spherical lens. Both the anamorphoser and spherical lens, however, will need to be focused at the same time, called double focus. These fully built DIY anamorphic lenses lack any mechanics for controlling both focuses at the same time, so cinematographers have to manually pull focus on both parts by hand.

Variable diopters, on the other hand, take advantage of optics to control the focus of the two parts. In photography/cinematography, diopters are filters that decrease the maximum focus distance of the lens, allowing the user to focus closer than the lens originally can. Diopters are often used in macro photography, but have a prominent application in anamorphic cinematography. A diopter can have a positive or negative optical power. When diopters of different powers are combined together, they can increase or decrease in power.

A variable diopter uses a combination of two diopters that, when close together, equal a small power, but grow in power as they seperate. The larger the power of the diopter, the closer the maximum focus.

Setting both the anamorphoser and spherical lens to infinity guarantees they are focused to the same point. Then, attaching and using a variable diopter can move that infinity point while keeping both lenses focused on the same point. A variable diopter makes the fully built anamorphic lens a single focus lens.

This is what the three main parts of the DIY anamorphic lens looks like:

4e33617bbac5f224-DIY_anamorphic_graphic03.jpg

All three of these items are clamped/built together to create a DIY anamorphic lens. The original BH16-2 is exactly like this, a variable diopter built onto the anamorphoser that is screwed onto the spherical lens:

58bf8d1205752031-bh16-2001.jpg

The downside of the original anamorphic lens is that the variable diopter requires numerous full rotations to pull focus from infinity to a close focus. Most lenses for cinematography rarely reach a full rotation from infinity to close focus. Additionally, the original spherical lens has no aperture and is near impossible to mount to any camera. This modification fixes the over rotation, corrects infinity, gives a better close focus, and allows for attaching various different spherical lenses.

How to Modify the BH16-2

bc219542b5725779-IMG_20191219_105523.jpg

From left to right are the three main parts of the original BH16-2: Spherical Lens, Series 7 Adapter Ring, and the anamorphoser with built in variable diopter. For this mod, we will:

  • Replace the spherical lens with one of our own
  • Convert the adapter ring to our new spherical lens
  • Replace the variable diopter helicoid with a new helicoid

Parts & Tools

You will need the following parts:

  • BH16-2 with original Adapter Ring
  • Nikkor 85mm AIS F2 Lens
  • 58mm to Series 7 Step Up Ring
  • 58mm Circular Polarizer
  • Rubber Gasket about 54mm big with an interior diameter slightly smaller than 45.95mm
    • These are approximations. When in doubt, use bring the removed variable and helicoid with you to find the right size gasket.
  • [Alternative to Rubber Gasket] 3D Printed Diopter Holder
  • 58mm to 58mm Helicoid Focusing Ring 17-31mm
  • Vid Atlantic Lens Clamp, 77mm
  • Appropriate step-up/down rings from 77mm to the 58mm Helicoid Focusing Ring
  • 1/4 inch 20 lens support point from a Rapido FMJ
  • Appropriate bolt size to mount this support to the Vid Atlantic Lens Clamp
  • PVC Tape 

You will need the following tools:

  • Flat Head Screwdriver
  • Lens Spanner Wrench
  • Rubber Gloves
  • Cotton or cotton like gloves
  • Hex Keys
  • Knife or Dremel Tool

1 - Replace the Spherical Lens

This is the easiest step. The original spherical lens has no aperture control, projects a small image circle, and is near impossible to mount to a camera. Instead, we’ll use a photography lens that can do everything the original spherical lens can not . For this project, we’ll use the vintage Nikkor 85mm AIS F2:

5ba4a1e73fc42e21-nikkor85mmf2.jpg

The Nikkor 85mm AIS F2 is a reasonably priced lens that delivers sharp, neutral looking pictures. It doesn’t have the clinical feel of modern lenses, but still maintains the sharpness for even the largest of screens.

Of course, you’re not limited to this focal length, maximum aperture, or lens. The BH16-2 is a narrow lens to begin with, so anything wider than an 85mm vignettes on a S35 sensor. However, tighter lenses like a 105mm or 135mm work well with this anamorphoser.

2 - Convert the Adapter Ring 

The adapter ring that comes with the original lens has a specific thread on the inside that screws to the anamorphoser. The thread on the rear of the anamorphoser isn’t an industry standard thread and requires the original adapter ring if a cinematographer wishes to use step-up rings to attach the new spherical lens. If you do not have the adapter ring, then you’ll have to use another lens clamp to attach the spherical lens to the anamorphoser. This guide will focus on using the original adapter ring.

db044e47d84a09d3-IMG_20191219_105705.jpg

The rear exterior threading of the adapter ring is Series 7. In the above photo, a 58mm to Series 7 Step-Up Ring is screwed snugly onto the adapter ring. Additionally, the adapter ring is then screwed back onto the anamorphoser.

In Section 3 of this guide, the anamorphoser will be modified to stay locked in alignment via 15mm rod support. Currently, the adapter ring with the step-up ring attached will make it impossible to correctly mount the spherical lens to the camera because there is no ability for the lens to rotate. To fix this issue, a modified circular polarizer (CPL) will be attached.

028cc3b74c7fa9f2-IMG_20191219_105802.jpg 0b421c81b261ad73-IMG_20191219_105814.jpg cdd32951d31ee884-IMG_20191219_105845.jpg

Using a spanner wrench, remove the polarizer glass from the CPL. Screw this empty CPL to the modified adapter ring. Now you can mount the spherical lens to the anamorphoser and still rotate the spherical lens into the camera mount.

3 - Replace Variable Diopter Helicoid

The next, and most complicated step is to replace the variable diopter helicoid (VDH).

db106e852ea23674-IMG_20191219_105950.jpg

Two flat head screws prevent the original VDH from being completely screwed off. Remove these two screws:

 cd7bb7b0258be58f-IMG_20191219_105912.jpg 627ae462d1473599-IMG_20191219_105933.jpg

Once the screws are removed, twist off the original VDH completely:

a13dee6aab835482-IMG_20191219_110053.jpg 4e62cf307e6d0186-IMG_20191219_110126.jpg

The original VDH only contains one of the diopter elements, the other is built onto the anamorphoser. Our mod will remove the diopter in the original VDH and place it into the new VDH.

40764868ff9d70cb-bh16-2002.jpg

Using a spanner wrench, unscrew the ring that holds the diopter in the original VDH. This ring will be tough to unscrew and will require considerable amount of force. It’s best to lock the spanner wrench and use rubber gloves to grip the VDH. Other cinematographers have tried lightly tapping the exterior of the VDH to help loosen the ring. There is no glue in the rings of the VDH. Once the ring is removed, push out the diopter with your finger. (It’s recommended to use cotton or cotton like gloves to avoid smudges and scratches)

25e7c5ee5cb12db5-IMG_20191219_110324.jpg

Above are the three removed items: the original helicoid, the ring that held the diopter, and the diopter itself.

2928c140580efa6e-IMG_20191219_111300.jpg

Next, we will place the diopter into the new helicoid. The helicoid that works best with the BH16-2 is an M58 to M58 Focusing Helicoid Ring 17-31mm. This specific size perfectly fits over the anamorphoser.

Most of these new helicoids are too stiff from the factory. The best practice is to re-grease the helicoid before installing the diopter.

ba014aec98283d14-IMG_20191219_111335.jpg

Next, the diopter will be inserted into the helicoid. A rubber gasket will hold the diopter in place within the helicoid. [Alternatively, a 3D Printed Diopter Holder can be used]

bd8765a42ccdecb7-IMG_20191219_111453.jpg f4d7f0ea75548a48-IMG_20191219_111504.jpg

This particular rubber gasket has an interior diameter that is too small, so a knife or Dremel tool was used to widen the diameter. The diameter should just smaller than the diopter itself because the rubber will stretch around it and hold the diopter snugly in place. Before installing the diopter in the gasket, install the gasket into the helicoid by pushing it in:

faaf1bb996eb3743-IMG_20191219_111521.jpg

Once the gasket is pushed into place, push the diopter into place:

1b33c805605d4f27-IMG_20191219_112015.jpg dc19a4109c2ed3a1-IMG_20191219_112019.jpg

Above are the front and back of the new VDH with the diopter held by the rubber gasket. Next is installing the new VDH securely to the anamorphoser. The sturdiest solution is to use a clamp like one of the Vid Atlantic anamorphic clamps.

62719dc78de62629-IMG_20191219_111213.jpg

The particular clamp used in this guide has a front 82mm thread and a rear 77mm thread. Once the lens is complete, it will be too heavy for the camera mount and adapter ring. The clamp will also become the lens support point.

bdfc2569dc9c415c-IMG_20191219_111158.jpg 7be5b1e17a713e09-IMG_20191219_111203.jpg

The female 1/4 20 support point from a Rapido FMJ was used for this clamp mod. Additionally, step up rings were attached to the front 82mm thread. Once the step up rings are attached, the new VDH is screwed into place on the lamps clamp. Finally, the new VDH will be clamped to the anamorphoser.

4e929a90dc7b68ed-IMG_20191219_112048.jpg 6421426596233dec-IMG_20191219_112331.jpg

Before attaching the new VDH, use PVC Tape to cover the anamorphoser. The tape only needs to cover where the bolts of the clamp will touch. Doing this protects the anamorphoser and gives extra grip for the bolts of the clamp. Once taped, attach the VDH!

facb0176c5814783-IMG_20191219_120805.jpg

Screw the anamorphoser + new VDH to the spherical lens. The newly modified lens is nearly complete, but the anamorphoser needs to be aligned. Attach the lens to a camera, then attach the rod support, and finally align the anamorphoser by loosening the VDH clamp and rotating the anamorphoser until alignment is correct. Once it is, lock everything down. 

It’s important to use rod support with the mod because the various step-up rings and the spherical lens are too weak to hold the weight of the anamorphoser and variable diopter. It also locks the alignment of the anamorphoser and spherical lens. The added stability of the lens support is a requirement for the BH16-2 to be practically used on set.

The final step is to set the spherical lens to infinity and the lens is ready to shoot!

A Few Notes

Infinity on the spherical lens largely depends on how accurate the focal flange distance is of the camera mount. In most cases, the infinity markings on the spherical lens won’t be the infinity you set the lens to. The best way is to mess with the focus of the spherical lens and variable diopter until they line up. Once they do, you’ll only need to pull focus with the variable diopter.

The anamorphoser is already set to infinity. However, these lenses are old and it may have been dislodged over time. This guide doesn’t address how to fix the anamorphoser and it is recommended to seek professional services for the anamorphoser.

The diopter element within the rubber gasket will need some adjustments. Collimation is the accurate alignment of optical elements and the diopter will most likely be aligned incorrectly once it is installed. The easiest solution is to adjust the diopter element within the rubber gasket until sharpness is even across the image.

Additional Resources

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