Pfocus, in various versions, are DIY single focus solutions/variable diopters based on wide-angle adapters to help with adapting anamorphic projection lenses for shooting purposes.
The general idea was to enable anyone to build a relatively cheap and fully usable focuser with the help of 3D printing and easily obtainable household items. The first unit ever was the Pfocus; I dropped the the along the way as people didn't care for proper naming anyway. Pfocus is a terrible pun on my surname and the word focus.
I was neither the first to use wide-angle converters for focusers, nor was I the first to 3D print them. But I do think I was the first to combine the two and make the files readily available to anyone.
Pfocus units are not general focusers that work with any glass you throw at them, every version is only compatible with a designated pair of donor glass.
the Pfocus was made in part to challenge myself if I actually could pull it off, as well as an opportunistic incident: my friend Tim L sent me the glass of a Fujinon WCV-82SC wide-angle converter as he had a spare; he was as interested if it could be done just as myself. When I noticed I could probably make what I was after, I checked with Tim if he was fine if I share the housing online, for free, with anyone interested. Tim said yes, he let me keep the glass and I made him a housing for his own use.
Since then, I tried numerous wide-angle adapters of various brands to see if I can find a good candidate for new housings. While I tried converters with three and four elements, I found that classic two-element designs not only have an advantage in simplicity, when build into a focuser the image quality is also comparable.
As I have no influence on the glass itself, I worked hard to make everything I can influence as neat as possible. So ideally, the manuals and built of these units is easy enough for anyone to follow and the usability as nice as it can be. I learned dozens of things along the way, and while not everything can be put it any housing I always strived to get it as good as I can. Proper clamp-on mattebox support, the closest focus within the boundaries of an internal mechanism, the widest possible image within body-constraints and ideal image quality.
Wide-angle converters as focusers have various advantages as well as disadvantages:
close focus capability
easy mattebox compatibility
widening the image
Of course, it all depends on the individual wide-angle adapter. Not all of them are even capable of becoming variable diopters, or they may be too small, etc - this list more represents the ones that I made a housing for, compared to commercially available variable diopters.
I put "widening the image" as both, pro and contra. Simply because depending on what you are after, this can be either good or bad.
For a little overview how various Pfocus units compare to other focusers in terms like close focus and weight, you can have a look at this handy table.
Speaking of that, one quite interesting fact that gets overlooked often when considering wide-angle converters for focusers is that they simply get not only wide - it's wider than your scope. You see, inevitably your scope will vignette your image at some point. Be it because of a larger sensor or a shorter taking lens. That is the max width you can achieve when using a common variable diopter. Often the focuser will vignette before the scope, but some diopters (like the Rapido FVD-24a or FVD-35a) will vignette around the same time as the scope or even after them. So, you can't get wider than this, unless you widen the image with another optical apparatus, like a wide-angle converter. Mounting such a wide-angle converter onto such a large variable diopter can be tricky or impossible. But as the Pfocus units are all based one wide-angle glass, the built-in widening takes the headache out of this. And as this widening happens before the scope, making it wider than any common focuser can do on its own. Even though most Pfocus units will vignette sooner than e.g. an FVD-24a, the applied widening still delivers the wider image.
The most important part of any focuser is and always will be the image quality. And I'm not beating around the bush with this: compared to the most popular focusers on the market, the IQ simply isn't on that level. Field curvature messes with the edges, but also in the center you won't achieve the same level of sharpness. Chromatic aberration can become an issue, distortion is amplified. However, that doesn't deem these units completely useless. When looking at charts, it's easy to call off a lens, in normal shooting conditions you can still achieve very nice and pleasing images. It's just important to know their limits.
The best thing to me personally is when someone actually builds one of my focusers; to get a general idea of what you can make with a Pfocus, have a look at Kapitan Hjertes video shot on Pfocus 🅱
In total, I made eight different housings for wide-angle converters (incl functional revisions). However, I didn't release all of them - when I am not happy with the results or realize that the used glass is too exotic or made of unobtanium, I drop the idea of making them available. Mostly because creating the documentation (the worst part of any project, huh) takes just too much time for the two users who can actually build one of them.
So far, there are three different Pfocus units available:
FREE - the first, the classic, using the Fujinon WCV-82SC as donor (internal focus and protruding front available)
$11.21 - a more professional oriented unit with focus markings and improved mechanics, can be built with the Zunow WCX-80 or the good ol' Fujinon WCV-82SC as donor glass
$5.29 - same improved mechanics as Pfocus 🅰, but more of a barebones expirience using glass from the Nikon WC-E80
While Pfocus 🅰 is meant to cater needs of ambitious users, the used wide-angle converters are not necessarily cheap or easy to get. The Nikon WC-E80 used in Pfocus 🅱 however is very cheap - if you already have a 3D printer, you can make it quite easily under $100. At some point I decided to sell the 3D printable files for Pfocus 🅰 and 🅱. This was not an easy decision, but I decided that for the work and time I put into these a little compensation is only fair. For what it's worth, I don't make a lot from this to begin with, but it financed a pretty decent Pizza for me already.
Before I made versions 🅰 and 🅱, I made a unit that I called "the Pfocus 🅱". It was based on a Century Pro-Series 0.75x wide-angle. However, when I gave it a spin after re-housing it the resulting image quality was so bad, I deemed the endevour a total fail. It had crazy close focus and was really wide, yet it was also comically large and heavy; the last nail in the coffin though was the edge performance, which was just so bad. If you are interested in this either way, Pooli sells a housing for this adapter.
Another more interesting focuser I made ran under the codename Pfocus 🅾 - it's based on a four element wide-angle converter, incl one aspherical element. It's large, but the size was managable. Heavy, but tolerable. Crazy wide (as in: vignettes after your scope over the WHOLE focus range). Crazy close focus (around 10cm/four inches). And even with all these aspect, I managed to add a front lip for proper clamp-on mattebox support (which, when attached, would cripple the vignette of course). But the glass so exotic, the build very tedious. I kept it as a nice "what if", but it will not see the light of day like the others have.
how does it work?
To get a good idea of how a wide-angle converter can be used as a focuser, I recommend watching Tito Ferradans video about the original Pfocus
Basically, for a variable diopter a strong negative and a strong positive diopter are paired and cancel each other out. So, a +10 and -10 result in 0, which means no change, which means infinity when you set your lenses to that (it's not as simple as using two diopters of the same opposite value, but you get the idea). By distancing the negative one it becomes weaker, so the positive side takes over and focusses closer. As most two element wide-angle adapters consit of a very strong negative in the front and a strong poisitive in the rear, this can be exploited for our use.
But beware: not every wide-angle converter can be used like this, as the elements may not cancel each other out; this will result in not being able to reach infinity focus. These kinda adapters worked by setting the camera they were made for into a special wide-angle mode, here the camera focussed into macro and helped the (too weak) positive diopter out a bit. My wild guess is they did this to achieve less abberations by using weaker elements.
Regarding wide-angle converters with more than two elements, things do work a bit different and I can mostly make assumptions (based on some insider-info and my own discoveries). However, that would go a bit far for this (already too long) overview :)
This is all I have to say about my Pfocus units in general. If you are left with questions or are interested to learn more, you can reach me through Kontakt.
Please also mind the FAQ if you are interested in me making a focuser from a new pair of glass.