Helicoid focusing ring explained

Let's start at the beginning, what does helicoid mean? 

According to the Oxford Dictionary it means: 

noun

• a helical or spiral object.
•  Geometry a surface formed by simultaneously moving a straight line along an axis and rotating it around it (like a screw thread).

So on a manual focusing lens it means that the front lens rotates and moves forward or back whilst you are twisting the focusing ring.

Video explanation here:

For old timer photographers who grew up with manual focusing lenses on their cameras, the "helicoid focusing ring" was something that was always there - but we just didn't call it that. It was just called a "focus ring". The term helicoid focusing ring has really come into favor of late because of the fad of using old m42 and m39 enlarger lenses on modern digital cameras.

Of course in modern lenses we try to eliminate the rotating movement so that polarising filters can be used without having to constantly re-position them, and eliminate the forward-backward movement to reduce any change in the angle of view.

Here's a simple comparison of the travel of manual focus lenses against a helicoid focusing ring.

In these photos we have two manual focus lens and one helicoid focusing ring. In the photo on the left they are are retracted. On the right they are all extended. They all move varying amounts. The large Takumar 35mm lens at rear moves the front lens 4mm, the Chinon 50mm lens at front left moves the front glass 7mm to infinity focus. The helicoid focusing ring at front right has a huge 14mm of travel (although they can be purchased with other amounts of travel).


So is 14mm bigger and better? No not at all and in fact it is a bit of a pain because it doesn't stop at infinity focus. So if you are doing video work it is possible to go out of focus beyond the infinity point which then stuffs up your shot (of course this won't happen to a trained focus puller if you can afford one.)

Have a look at my other post regarding the bits you will need so that you can mount enlarger lens on your GH2, NEX, Nikon, Canon, etc, etc, etc.

How to mount an enlarger lens on a digital camera.

Let me know what rig you have enlarger lenses mounted on.

Enlarger lens compared to modern kit lens on a digital camera

Panasonic 14-42mm kit lens appears to tower over the Nikon EL 50mm enlarger lens sitting on its adapter set.

How do enlarger lens compare with modern lenses? Well let's have a look at a simple comparsion. I'm using a Nikon EL-Nikkor 50mm enlarger lens, that cost me $20, on my Panasonic GH2 and I'm comparing it with the 14-42mm kit zoom lens that comes with the GH2. Of course, to mount the enlarger lens I also needed a helicoid focusing ring ($28), a M4/3 to M42 adapter ($12) and a M39 to M42 step down ring ($2) - but these can now be used to mount other enlarger lens.

The range of Nikkor lenses is huge. The EL in this case stands for Enlarger Lens. This particular lens is a lower quality one in the EL range having only 4 elements compared to the usual 6 elements. That said, I got this one "well used" from a commercial photo-lab so I guess they were happy with its performance.

Obviously it would have been preferable to compare them at the same focal length as the the shorter focal length lens will show greater depth of field.

For a look at the adapter set up click here.

Here's a few examples that show how an enlarger lens stacks up against a modern kit zoom lens. The test demonstrates both still shots and video work. Lets have a look at the results:

Here's the video results:

The old Nikon is certainly prone to flare, but that is not surprising as this lens was never designed to be used outdoors much less pointed anywhere towards the sun. So you should always remember that enlarger lenses are really just for fun. The enlarger lens is certainly tough to focus in low light, and I now understand the value of the split screen focusing in my old Pentax Spotmatic F. By the same token, as the video proves, a modern auto focusing lens can be caught short very easily.

And here's the photos:

Nikon enlarger 50mm f5.6

Panasonic at 42mm f5.6

Nikon enlarger 50mm f16

Panasonic at 42mm f16

Nikon enlarger 50mm f5.6

Nikon enlarger 50mm f16

Panasonic at 42mm f5.6

Panasonic at 42mm f16

So is it worth getting an enlarger lens? Well just for the fun factor it's a big YES! Take a couple of lens and go for a walk in the park, or to that old church, maybe do some portraits of your loved one. But if you had to shoot a wedding for a friend on the cheap, well I'd be grabbing the kit lens and going full auto.

For shooting video? Well that's a different story. The enlarger lens can hold its own in a lot of situations. Especially as you would be pulling focus manually to get the best results. Again, if you've got to run and gun at a wedding you will be wanting the kit lens.

You should never buy one thinking that it will be some cheap alternative to more expensive camera lenses that have coatings on their glass.

How to mount enlarger lenses on digital cameras

Are you think about getting into enlarger lens for your digital camera? Or maybe you've already got one and can't get it to work - well let's look at what parts you will need to get you started. Enlarger lenses don't have the ability to focus by themselves. Whilst you can change the aperture setting there is no focusing ring on the enlarger lens. So the parts you will need are an adapter, a helicoid focusing ring and, possibly, a step-down ring.

Here are the parts laid out... (from left) M39 enlarger lens, M42-M39 step-down adapter, 17-31mm helicoid focusing ring, M42 to camera mount adapter.

Here they are ready to assemble ...

The majority of the enlarger lenses seem to be M39 mounts so you will need a step down ring. These M42 to M39 rings are very cheap on eBay - less than two dollars. (I purchase most of my camera accessories from eBay simply because it is convenient for me.)

Helicoid in, helicoid out ...

The 17-31mm helicoid focusing ring is a key part. It moves the lens in and out to allow the focusing. It is described as a 17-31mm model. That just means that it is moving the lens in a 14mm range.

They come in various sizes but I recommend that the M42 to M42 version as it seems to be the most economical to purchase. In comparison, the M42 to M39 was more that double the price.

The other critical part is the adapter mount that allows the helicoid focusing ring to be mounted on your camera. It is critical that you purchased a thin mount. The one that I am using is 5 millimetres in depth, 10 mm overall as another 5 mm disappears into your camera.

One thin, and one wide - M42 to M4/3 adapters ...

In the picture above, the adapter on the left is for use with helicoid and enlarger lens. The one on the right is for use when mounting regular M42 camera lenses. Each has its own purpose and whilst they can be physically interchanged they will not allow correct focusing if swapped.

Have look at the video below to see how it all fits together ...

Any questions? Just ask in the comments below.

What are some of your favorite enlarger lens?