Understanding dual focus and single focus is important to planning an investment in anamorphic lenses.
The vast majority of anamorphic lenses are dual focus lenses. This means that focusing is done with both the taking prime lens and the anamorphic lens. There are some fine dual focus anamorphic lenses such as the Isco Micro- small, tack sharp, high build quality, and very adaptable to almost any DSLR camera. But single focus unlocks the power of the lens, allowing you to work quicker, rack focus, and even macro focus anamorphic.
Dual focusing can be easily learned- it’s pretty much muscle memory- and perfectly usable for many run-and-gun type shoots, but it doesn’t allow for easy rack focusing between two subjects.
Fortunately, most dual focus anamorphic lenses can be turned into single focus anamorphic lenses via two methods- the Rangefinder, and the Dual Follow Focus.
The Rangefinder (Variable Diopter Method)
As explained in our close focusing anamorphic article, a rangefinder is a set of two precisely-powered achromatic diopters that allow focusing to be achieved solely with the rangefinder. Simply adding a rangefinder to the front of your anamorphic lens (make sure you have a front filter on your anamorphic- our ready to shoot packages have this modification built in) will turn any dual focus lens- Kowa, Isco, Sankor- into a single focus anamorphic setup. Check out this article on single focus anamorphic lens calibration to see how this works in detail.
Popular rangefinders include
- Our Premium Optics Rangefinder ($649)
- SLR Magic Rangefinder ($599)
- Focus Module Lens (740 euros- for Schneider lenses)
Pros of anamrophic rangefinders
- they can work with virtually any anamorphic lens
- they can be removed if desired to save weight or minimize rig size
- rack focusing is simple to set up
- they can even be used to significantly decrease your anamorphic lens minimum focus distance for crazy macro shots
- smaller profile than a follow focus
- lower quality glass might increase chromatic aberration and other artifacts
- if coated, they may affect anamorphic flaring
- they add weight to the front of the camera setup (if you’re using a gimbal, we recommend purchasing a dedicated single focus lens instead)
The Isco Rangefinder, SLR Rangefinder, and Aivascope all work very well to affordably turn dual focus anamorphic lenses into single focus. The Isco Rangefinder is the highest quality glass (as with all Isco lenses) and by nature of the glass also acts as a 0.65x wide angle converter. The SLR Magic and Aivascope are not as high quality, but are more compact as helicoid focusing instead of push-pull. The Aivascope makes up for its optical weaknesses with a competitive price. The FM Optic lens is good quality glass but very heavy and large especially when added to an already significant rig.
We have also developed a brand new single focus rangefinder developed specifically for the Isco Micro. Based on our experience with all of the above systems, we developed a compact, high quality setup that smoothly focuses without adding significant wight to the rig or the budget.
The Dual Focus Follow Focus System
A more mechanical solution for single focus anamorphic involves a calibrated dual follow focus. Instead of optically modifying the focus chain as a rangefinder would, a dual follow focus system is as the name implies- one follow focus controls two lenses. The new Rapido Single Focus setup is an example of this system.
Pros of dual follow focus systems include:
- identical optical performance to the original anamorphic
- no possibilities of added vignetting or abberation
- smaller profile- discounting the system itself
- a larger profile, as this needs a follow focus, lens gears, and power
- generally more expensive
- calibration is required, making switching lenses time consuming
If it is important to you that your anamorphic lens setup has the ability to focus with only one element, definitely consider either of these methods as a way to achieve this feature. If you are a single operator, run and gun shooting with a dual anamorphic lens is completely possible and once you’ve gotten the hang of it, is quite easy.
If you’re unsure about where to go, we’d definitely recommend starting with a dual focus anamorphic lens instead of a dedicated single focus anamorphic. You can get the hang of anamorphic shooting, and decide if single focus is an investment you need later.
If you’re looking to shoot anamorphic next week, definitely purchase a single focus lens. The ease of use and ability to dive right in is an invaluable benefit in time savings for time-critical production.
If you have found this article interesting and are further interested adding anamorphic to your toolbox as a cinematographer, please visit our anamorphic lens store for demos and examples. We have spent several years collecting, modifying, and testing anamorphic lenses to weed through the junk, make needed modifications, and assemble ready-to-shoot packages.