Full Frame envy? Focal reducers to the rescue: a review of the Camdiox focal reducer for Fuji (part 1)
Full frame cameras, as we well know, are the craze among mirrorless users these days, particularly after Sony released a string of quite affordable models during the last year. If we try to be concise and to the point, these are the main arguments in favor of "Full Frame" superiority:
- Inherent ability to achieve shallow DoF
- Better "light gathering" capability, resulting in superior ISO performance
Other advantages such as increased dynamic range and color depth are rarely mentioned in relevant conversations.
First of all, let's state it again, just in case Full Frame Junkies weren't paying any attention the previous one million times this was mentioned: sensor size by itself has no effect whatsoever on DoF. Nada. Zilch. Please re-read the excellent article about different formats at Photographylife.
What's meant by the DoF statement, is that, the bigger the imaging surface (i.e. the sensor, in digital terms), the easier is to achieve shallower DoF with a wider angle of view, at a given aperture. A 50mm lens will provide the same DoF for any sensor, but the larger sensor will give the coveted blurred background effect at a wider angle of view. So, in essence, we have better control of DoF with smaller focal lengths.
"Light gathering" had emerged as something akin to quantum physics' "spooky action at a distance" statement, but let's try to keep it simple: among similar technology sensors, the larger size ones will demonstrate better results at the same signal amplification ("ISO") values. Which means that, e.g. for a APS-C sensor to reach a comparable image quality, it has to "claim" approximately one stop ISO over a full frame one.
And this is the point where a new breed of adapters come in, offering ammunition for smaller sensor size equipped cameras. Of course, they only work with adapted lenses (chiefly manual, but there are AF-enabled ones also). This may be a disadvantage to many, but as we've seen, there is a certain degree of technical and creative freedom in having the vast choice of legacy and modern glass through adapting (check previous article here).
Focal reducers are an exciting proposition, the technical details of which I don't even pretend of fully understanding. As far as I can figure it out, they work like inverse teleconverters, de-magnifying the image circle by use of a specially constructed optical element.
Metabones was the first company to popularize focal reducers with their Speedbooster adapters. They are using patented technology developed a while back by J. Brian Caldwell of Caldwell Photographic. Here is a link explaining the inner workings of Speedbooster and this would be applicable in principle to any other brand too.
- With a focal reducer in front of a APS-C sensor, the angle of view is expanded (practically, but more precise mm measurements later) to that of a FF sensor, effectively eliminating "crop factor" in that respect.
- The lens "gains" one stop in terms of effective aperture. This means that, with a APS-C sensor you "claim back" that one stop in DoF, making the frame "equivalent" to FF. For example, a f/2 max aperture lens "becomes" a f/1.4, which, translated in equivalence terms (1.5 crop factor) makes it exactly the same as FF.
Here's the kicker: the final image is "equivalent", but the smaller sensor also gains a stop of light, which can be translated to either shutter speed or ISO, making the combination "one better" on the same lens setup on a FF body. This can be seen as eliminating, under certain circumstances, the ISO advantage of the larger sensor.
There is a number of other advertised benefits also: for example, chromatic aberrations are said to be reduced (since they are actually getting smaller) and even MTF resolution improved. The latter is because the image circle is "projected" into a smaller area, similar in effect to what happens when you resize an image; because it's compressed, it seems to be sharper overall. Finally, for similar reasons, border and corner illumination seems to be improved.
It is probably apparent that videographers are primarily benefited by using focal reducers. It is especially difficult to achieve a nicely blurred background by using a m43 (or smaller, see Blackmagic cameras) sensor and system lenses. Since manual focusing is a normal practice for video anyway, having access to the vast range of manual lenses, with wide angles of view, is virtually a godsend.
Soon after the original Metabones focal reducer became available, a number of Far East variants appeared in the market, such as the Lens Turbo, and others. These are now (as is the Metabones) in their second generation, so to speak, apparently having ironed out some early issues.
The specific brand I've been using is one branded Camdiox, and it's the version for the Fuji X-mount. It's almost certain by now that the various "knock offs" are not direct copies of the Metabones, but it's more than probable that they use the same design principles. I am not exactly sure if the Camdiox is the same as other similar products; in Europe, the Roxsen company is one primary outlet for this brand, but not the only one. Because the original Metabones is quite expensive (besides any quality advantage, having to pay royalties to Caldwell doesn't help with pricing), it is rather difficult to justify, if you only use it infrequently. The Camdiox is under 100€ shipped, and it remains to be seen if the actual image quality is there, through real-world examples.
I have to provide a fair warning for anyone looking for chart shooting or any other formal testing methodology: I don't do that and have no interest whatsoever in doing it. This and any other reviews I'll ever publish, will always be of a practical "in the field" nature. If you're looking for a laboratory style review, this is not it. This is also why sample photos are normally processed, the same way I'd process any other photo I take (with "regular" native lenses). My point is that this levels the playing field, so to speak, and processing isn't in any way excessive, in any case.
I have used the adaptor with both the X-M1 and the X-E2 and a number of manual lenses for the OM and M42 mounts. In part 2, we will see more image examples, as well as a more in-depth evaluation of the adapter, considering its pros and cons and reaching an overall conclusion on its value. Stay tuned for more!
Update: please click here for part 2!