It would seem that there are several universal adages and urban myths that permeate the motion picture and television industry. One of them is the desire for faster, bigger, cheaper, lighter smaller, heavier and other superlatives of extreme in our choices of equipment. Lenses are subject to this as well. The sheer variety of lenses can make selection most difficult.
There are Ultra-Primes, Master-Primes, Super Speeds, PL mounts. OCT19, Nikon, Canon FD and EF/EOS, and many, many more. The question of specification will inevitably come up. The rating of optical efficiency, known as “F-Stop” relates to how much light passes through the lens, and how much light is lost. The less light loss, the lower the aperture and the faster the lens is considered.
Remember high school Physics class, remember the section on Optics and glass? There are three general effects that occur when light passes through medium, such as glass. 1. Reflection, 2. Absorption and 3. Refraction. Our concern is generally centered around Absorption, the proportion of light entering and exiting the lens itself. Yes, linearity and distortion are concerns, but most modern glass lenses (that aren’t the cheapy $50 stuff) handle this well and are not of specific concern.
In slower lenses, what happens to the light? Where does it go? It has to go somewhere. It does. The light is absorbed by molecule-sized impurities and actually converts to heat. Not a lot of heat, but some. But that’s more thermodynamics, and covered in an upcoming blog.
The faster a lens (read: the ones that absorbs the least light) costs more to rent or purchase and is a reflection of the lenses component quality, materials and overall efficiency. Clearer types of glass with less impurities are able to pass more light through unobstructed.
But the question remains – is a faster lens better? It may be, but the real answer depends on several factors.
How much light does your camcorder need to work? Is there a known “number” associated with a particular camcorder that produces the best results? The answer to both is YES, but it’s not that simple.
Most modern camcorders do very well with light handling. That, coupled with the fact most recording occurs in areas of sufficient light make the specification somewhat less important. Sony’s PMW-EX1 and EX3 are rated at 0.14 (fourteen hundredths of a lux, about as low as you can go this side of infrared). If you eye can see it, then your camcorder can see it. As light level drops, as with the human eye, you start to loose color rendition, that is to say the scene starts to transit toward black & white (gray scale). Take away more light, and you begin to loose edge formation on solid objects. Take away more, and you’re in the dark.
Many camcorders have a “sweet spot” in their exposure. This is the aperture where the imaging sensor (or sensors) are getting everything they need to produce the best picture without overloading (overexposure). My rep’s tell me this number is about f/3.5 to f/4.5. Keep that number in mind for a moment.
Another consideration is whether you are using a depth-of-field adapter like a Letus. By passing the light through a optical condenser (diopter) and a prism, there is some light loss. With the Letus products, it is about ½ stop.
Though Letus is amongst the most efficient with light, other manufacturer’s devices may be somewhat less an additional device to up-right the image. Light loss occurs in that inversion device as well.
Faster lenses are generally more expensive, and can be rarer. You can even get some lenses that are below f/1.0. By way of example, a set of 6 Zeiss Master Primes can rent for over $1200 daily, and cost more than a brand new Cadillac. They clock in at T/1.3. Zeiss Ultra’s are T/1.9. A set of 6 is about $600 per day. We carry the Nikon Nikkor and Canon SSC lines. Their apertures run from f/1.2 to higher as would be in the case of longer telephoto-type lenses (the 500mm Nikon is an f/8.0), very wide and fisheye’s and zoom-able lenses. We have tested them and find them to be very sufficient for professional work, from EX1s to RED’s.
Angeneux, Zeiss, Cooke, Lomo, Red are all great lenses, but may not always be particularly fast. Almost every manufacturer offers a set in the f/2.8 area, still considered to be quite usable, if not desirable. Recall the mathematics: Take a lens with a f/2.8 rating, add a Letus for ½ stop (0.5 stops). When added, that totals f/3.3; ‘kinda right where you want to be.
We have all seen over-exposed video. It looks really bad, and is not easily correctable in post even with Apple Color or a DiVinci. Under-exposed looks dark, but is the better option of the two if you’ve made an exposure error. You can always brighten, though with increased noise. The pursuit of really, really fast glass may prove to be pointless in most shooting situations.
What we’ve discussed thus far is all well and good for sufficiently light scenes such as studio, under lighting or a exterior shot. But what about night or very dark scenes such as you would have in a spooky horror or thriller, or even a steamy bedroom scene at night?
Under low-light or no-light conditions, if you can’t sneak in the “light source coming from nowhere” thing, and you’re not into DFN’s (Day-for-Night” filters) then you will need faster lenses to take advantage of available light.
In this circumstance, faster IS better. Instead of stopping down your lens to avoid blow-out, you would be either go wide open, or nearly so. We stock many 2.0-and-below lenses, several f/1.2’s, f/1.4’s and f/1.8’s. I’ve tried to spread them out over all focal ranges so you don’t get stuck with a night shot at distance or too when your frame is very close up
Recall, wider and longer are less efficient and will have higher apertures. Try to remember this while scripting and setting up your shot list.
So what’s the bottom line?
Fast lenses are more costly all the way around.
Fast lenses are not always required.
Under-exposure is better than over-exposure.
Very expensive lenses are great, but not always required.
Well, that’s it.
As always your comments and opinions are welcomed.
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