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.