Time to go mythbusting again and test out if flipping the rear element of the Century Optics adapter really brings all those benefits people claim about close focusing.
Hello ladies and gentlemen. Tito Ferradans here to test out another myth related to the small
Century Optics adapter.
Back to business, if you have ever considered getting a small Century Optics, there’s a great chance you came across one – or more – posts by people claiming that flipping the rear element of the lens will improve its close focus capabilities and still allow for infinity focus.
“Diopters simply allow you to get really close focus, something that is often a issue in anamorphic world, since old anamorphic lenses typically have garbage CF. However, you are talking about an adapter, which makes things a bit different from the normal anamorphic lenses which is the base of my experience.
To my knowledge, the only way a diopter would make a lens sharper, is if the anamorphic adapter was not properly aligned to begin with, and the diopter serves to correct the adapter to it’s expected working condition. For example, if you have a diopter on your lens, and you can focus from relatively close distances to infinity… there was something wrong with your set-up before. The diopter didn’t improve your image, really than fix it. That may seem like semantics, but it would be giving the diopter too much credit otherwise.
For instance, read the first post in this:
http://vimeo.com/groups/anamorphic/forumthread:232783Ryan Patrick O’Hara, 2012
or
“The Optex has a 1.33x squeeze ratio and produces more subtle flares than 1.5x or 2x anamorphic adapters. However, if you point it directly at a bright light, ala Spielberg, it will give you long horizontal flare beams.
Anamorphic adapters typically use two lens elements to produce a non-focused wide-angle adapter with different magnification ratios in horizontal and vertical directions. To produce sharp results, the astigmatism of the two lens elements must be aligned to converge close to the focal plane of the normal lens that you’re using with the adapter. The “focus” ring on an adjustable adapter allows you to converge the anamorphic elements manually.
On a fixed anamorphic adapter, the lens elements are set to converge at infinity and typically have a working range down to about 6-8 feet. You can use a diopter in front of the adapter to pull it in for close-focus shots. The Optex happens to have a rear anamorphic lens element that can be removed and put back in an inverted position, which makes it work in close-focus range without needing a diopter.” – LPowell, 2011
The question here is, if turning the glass around would bring such benefits, why weren’t they originally made that way? It’s time to check out if this works.
I’ve reached out to Brian Caldwell – designer of the glass for the Metabones Speedbooster – asking for his input on what I should expect after turning the glass inside out. Here’s what he said:
“Assuming the rear group is a cemented doublet with a leading negative element, then flipping it would move the principle plane of the rear group towards the front group. This is similar to focusing the adapter for a closer object distance. However, I expect that the aberration balance would be completely trashed, especially at longer focal lengths where you use the entire rear aperture of the adapter. Also, the squeeze ratio would drop, just like it always does when focusing a dual-focus adapter to a closer object.
Personally, I wouldn’t do it except as a fun experiment. I would expect much better results with a diopter.” – Caldwell, 2016
So here we go for an exciting round of testing!
On the first test I’m racking focus between 75cm (the first Lego set), 1.4m (the AT-AT Walker) and 2.5m at the wall. Since the goal is to test faster apertures, lenses are all wide open. Results are very poor at close focus for the unflipped Century. The +0.5 achromat improved focus for both the AT-AT and the wall, but not much for the close focus mark. I must say it was surprising to see how much better things looked with the flipped rear element – especially at the wider end.
Contax Zeiss 35mm f/2.8
Canon EF 40mm f/2.8
Contax Zeiss 50mm f/1.4
Then I went on to test chromatic aberration. With Canon’s 40mm I found myself an interesting scenario with lots of high contrast between bright and dark, with a relatively easy subject to focus on. Also known as “rug hanging on a tree”. Chromatic aberration is pretty bad on either cases, so, fortunately it’s not a big deal to have the rear element flipped or not.
Canon EF 40mm f/2.8
Canon EF 40mm f/2.8
From that I moved to test infinity focus on super wide shots. This is where the flip really struggled, as I could see the loss of sharpness much more easily, and the edge compromise creeping in much further into the frame.
Contax Zeiss 35mm f/2.8
The last test is for longer lenses and I used a Jupiter 9 – 85mm – at f/2.8 to see how it performed and if the stretch factor was affected by the flipped rear element. I won’t deny the mod is much sharper than the original configuration for close focus, but the stretch factor indeed decreases. In my case, I was getting around 1.25x. Also, you can notice the diamond shaped bokeh indicating that there’s something wrong with the setup (much like what I mentioned about the SLR Magic Anamorphot 1.33x-50)
Jupiter 9 85mm f/2
If you wanna do the trick to your own Century, just unscrew these two small screws at the back – they don’t come off completely – and remove the cover. Then take out the glass, flip it and close it back. Be careful because the entire back of the body comes loose when you do this! The process doesn’t take 5 minutes.
I believe it’s a useful technique for medium close ups. If you can’t afford a +0.5 diopter (seriously?!), I’d say it’s a reasonable solution. The edges become more messed up, but they’re already pretty bad on the original, so it’s not a huge deal.
The biggest issue is that now you’ll have to play to the Century’s strong side, using wider lenses and stepping away from pretty much anything above 50mm.
I’ll admit that the results for this video were very surprising, and I expected image quality to drop much more. What about you? Let me know if you’ll be flipping your Century, or keep on using diopters! If you want more tips, tests and tricks now’s a great time to subscribe to the channel, and if you want information in writing, head to the blog for an even larger amount of articles! See you soon, Ferradans out.
