VMI have recently and uniquely removed the coatings from a set of Zeiss distagon lenses in order to bring this very popular ‘vintage’ look into an affordable pricing sphere to produce a set of Zeiss ZF Uncoated DSLR lenses for hire.
We believe that this may be the first set in the world to have been uncoated and as you can see from the examples, the effect can be as dramatic or subtle as required.
This article seeks to explore the effects that removing the lens coatings can have on an image
The reasons behind the Coated ‘purple’ look
Essentially, the AR (anti-reflective) coating on a lens provides a secondary internally reflective surface in order to cancel out the reflections that occur when light goes from air to glass, or glass to air. This cancellation of stray/unwanted reflections also increases the contrast of the lens, as ther is reduced unwanted light degrading the image.
The basic idea is that a ray of light hits the glass. Some light passes through the lens, some is reflected. If a thin film, or coating, is applied to the lens, of a specific thickness, then the reflected light is again reflected back out of the lens. This second ray is by now "out of phase" with the original ray. Obviously there are multiple frequencies of light, and therefore one needs many coatings (multi-coating) for this to work effectively. This is sometimes known as ‘quarter wave’ coating. For the full theory and Maths (If you are interested!, look up Lord Rayleighs thin film work from 1886)
Of course the wavelengths of incident light striking the lens are anywhere in the visible (or into the IR) spectrum so lens manufacturers have to decide which wavelength each coating of the multi layer coating will reflect. The visible spectrum of light measures from 400nm to 700nm, so generally the coatings are pitched in the middle at around 500-550nm. This therefore is the yellow part of the spectrum that does not reflect (or more correctly has had it’s reflection cancelled by a reverse polarity wave) so the complementary colour not ‘sucked in’ will appear as a blue-purple reflection. This is easily seen on most lenses and multi coating is basically just a ‘pimped’ up version of the above targeting a wider spectrum of frequencies/colours of light.
What Uncoating Achieves :
Simply put, it removes all the reflection based optical technology of the last half-century. The coatings exist to reduce flare and increase the transmission of contrast and therefore by extension, definition and perceived sharpness.
However, an uncoated modern lens still retains its ability to transmit colour and most of its clarity and the effect can be very subtle.
All comparisons were shot on a Canon 5DMkIII using coated and uncoated Zeiss Distagon/Planar lens sets with all other settings the same per test.
It may be difficult to see any variation in the above comparison once it is in web resolution but the originals demonstrate a ‘kind’ and benign tone to the uncoated shot with an ability to attenuate some of the digital harshness in the cheaper ranges of large sensor cameras. Producing an image somewhat akin to that of an ARRI Alexa.
Equally, when approaching a more challenging ‘light source in shot’ situation, the effects will be much more dramatic.
Colour transmission will be broadly similar when there isn’t a heavy light source actually in the image as below, but because there is a ‘wash’ of ambient light hitting the uncoated lens, it is unable to deliver the same degree of contrast as the coated lens.
At night or in darker surroundings, the lack of ambient light will allow the uncoated lenses to maintain a higher degree of contrast. But again any strong in shot source will create a dramatic effect.
Also, as there is a similar current trend to pursue the anamorphic ‘flare’ look, we thought we’d combine the two by adding a 2mm Blue steak filter to some of the tests. Please see below, unlabeled so you can make your owns minds up.
Hopefully, the above images go some way to demonstrating the broad gamut of effects achievable with uncoated lenses.
We have specifically dealt with the Zeiss Distagons as they are unique to VMI, but we also carry uncoated Cooke Mini S4s for those wishing to use PL mounted cameras.
Some of you may be a little surprised at the amount of detail and colourinformation that the uncoated lenses can carry and we think it is important to understand that for a lot of images we see on TV, there is an element of ‘turbo boosting’ the vintage effect by shooting in Log C (or variants) and not fully returning the contrast and colour information in post.