I often describe photography as a combination of art and science. Consider, for a moment, the sorcery that goes into conjuring an image from paper infused with silver particles. While exposing, developing, and printing images requires a knowledge of chemistry, photography is also heavily dependent on the tools required to make an image - cameras! Modern cameras and lenses are triumphs of mathematics, optics, and engineering.
Camera makers have long competed to place innovative technologies into high quality tools, each taking different approaches to answer the demands of consumers and professionals. Advancements in image-making have resulted in cameras that can record rapid sequences of motion, capture images with minimal available light, or even produce instantaneous prints without the need for external processing - a feat that still blows my mind.
Today's mobile phones incorporate miniscule but complex and capable cameras. Never take for granted that this technology was made possible by 200+ years' worth of refinement. While digital photography is sometimes viewed as an absurd arms race - with companies touting numerical specifications that matter only to professionals and those with an excess of disposable income - there are occasionally new tools that are as affordable as they are useful.
Many photographers have never used a "focal reducer", which are also referred to as "speed boosters" or "lens turbos" depending on the distributor. It's unsurprising - they have a very specific use and weren't around during the era of 35mm film. Focal reducers are primarily intended for use with cameras adapted to use lenses from cameras with larger film formats or sensor sizes; today's mirrorless cameras fit this bill.
There are many advantages to using a camera with a small sensor; they're more compact and lightweight, have greater depth of field, and can use lenses from almost any other camera system, with appropriate adapters. It's now fairly common for photographers to use vintage, manual focus lenses from old film cameras on modern digital cameras. "Legacy lenses" can be cheap and are widely available. Unlike today's ultra-sharp and highly-corrected glass, vintage lenses can provide a unique rendering and give photos a very different aesthetic.
Many mirrorless cameras have small sensors. Full-frame cameras have a surface area 1.5x larger than an APS-C camera, for example; APS-C is considered to have a crop factor of 1.5x (this varies slightly depending on the actual sensor size, which differs amongst manufacturers). Small sensors require shorter lenses to capture a normal field of view (simulating human perspective). Full-frame cameras have long set 50mm as the default focal length. On APS-C, focal lengths would need to be reduced by about 0.72x to achieve the same field of view as full-frame. The standard lens for APS-C is approximately 35mm. If a photographer adapted a full-frame 50mm lens for use on APS-C, part of the lens' image circle is goes beyond the edges of the small sensor. The light that does hit the sensor provides a narrower field of view and shallower depth of field, working as a portrait length lens. Perhaps this isn't what the photographer wants, so it is for this reason that focal reducers were designed. How can we use legacy lenses on crop-sensors to get a normal field of view, aside from buying wider focal lengths?
The answer begins with a technology that's been around since the earliest SLRs: teleconverters. A teleconverter is an adapter that increases the focal length of a lens (by 2x, for example); a glass in the adapter channels the light coming in from the lens to a narrower perspective. This allows photographers to shoot in multiple ranges without carrying extra lenses. Teleconverters have a side effect of reducing the amount of light gathered by the lens by one stop. A 50mm f/2 lens used in with a teleconverter will perform like a 100mm f/2.8. In addition, teleconverters increase the magnification of a lens, at minimum focus distance.
Focal reducers are essentially the opposite of a teleconverter in every way. They also use glass elements but instead of letting the large coverage area of the lens go to waste, it is channelled to the small sensor with approximately the same field of view that would be portrayed on full-frame. In addition to this, the lens can now provide one stop value more light. This is significant - it means that you could use a faster shutter speed or a lower ISO in certain situations. My Fujifilm X-T10 setup includes a vintage Super Takumar 50mm f/1.4 (a screw mount lens usually found on Pentax 35mm cameras). The lens functions like a 75mm f2 with a standard adapter, but maintains the look and feel of the 50mm f/1.4 when used with a focal reducer. Another way of saying it is that the Takumar performs like a 35mm f/0.95 lens designed for a cropped sensor - such as the Zhongyi Speedmaster.
The combination I mentioned cost me $265 ($100 for the lens, $15 for a basic adapter, and $150 for the focal reducer). You could definitely find the lens for less with patience. By comparison, Fuji's native 35mm f/1.4 lens retails for $600, and the 56mm 1.2 retails for $1,000. It's now clear that I would have to spend roughly 6x what I paid to get two lenses that cover the same duties as one lens with two adapters.
Here are a couple of sample images for comparison between the standard lens adapter and focal reducers; let's start with comparing field of view. I took these two photos from the same position in sequence. As you can see, the focal reducer allows me to capture more of a scene without stepping back. Note that the shutter speed increased with the focal reducer due to the fact that it increases the lens speed.
Next, let's compare magnifications from the minimum focus of the lens - 45cm. In this instance, you might say that using a standard adapter would be better for macro and detail work due to the higher magnification. Depth of field is shallower at the portrait/tele focal length but bokeh is more visible from the wider point of view.
Lastly, I wanted to show you what it looks like when you try to capture the same composition with different adapters - this is mostly for people interested in bokeh and blur in their images, and would be helpful for shooting portraiture. It goes without saying that I had to scoot a bit closer to get roughly the same proportions. The focal reducer emphasizes the outline of the out-of-focus highlights (on the left side of the image).
In the end, I think that focal reducers are a welcome accessory to my tool kit, giving my lenses more range and allowing me to capture low light scenes that I may otherwise struggle with. Of course, there are a few gotchas:
1. Using legacy lenses with adapters or focal reducers would mean working without autofocus. Only lenses intended for the Fujifilm mount will have AF. Fuji does provide excellent manual focus assistance, including split-screen or focus peaking, which outlines areas in focus in the highlight color of your choice.
2. You won't be able to record EXIF data automatically; this doesn't particularly matter to me. I should note that the X-T10 DOES have a menu that allows me to set up three manually-entered lens settings, but you would have to access this menu and adjust your selection every time you changed lenses or adapters.
3. You get what you pay for. A cheap focal reducer won't have the same quality of glass components as a pricier one would. Glass is image quality! A cheap reducer could have result in image softening, especially at the corners, which is something pixel-peepers would want to know.
What do you think? Would you add something like a Lens Turbo to your tool kit? See below for more image samples using the X-T10, Lens Turbo, and vintage lenses.