McCaffrey DIY Budget Focuser

• Focuser by DIY
• Single Focus : Variable Diopter
• Mount: 77 MM

Welcome to the review of the cheapest DIY single focus solution I ever tried to make. The tutorial for building this thing is somewhere on the screen right now and I gotta thank Chase McCaffrey for sending me the instructions on how to put this thing together.

Today I’ll be talking about what you should expect from it, if you decide to build one. This focuser is pretty small, which makes it a better fit for smaller scopes. I didn’t have any small scopes, so I tested it a the Schneider Cinelux anyway.

It weighs 340g, or ¾ of a pound. Construction is pretty basic, if you watch the build tutorial. Focus comes from infinity to 2 feet, Nikon style, and has 180 degrees of throw. I didn’t add a focus gear to this one as the lens extends from the back too, moving the focus ring a lot. Needless to say, there’s no witness marks on this focuser!

I made 3d-printed 77mm rear threads and 82mm front threads to keep this super easy to attach it onto scopes as well as to add diopters and other filters. If you don’t love printed threads - they’re kind of finicky - I’d suggest adding regular step rings or blank rings there to refine the focuser.

The price for this thing is somewhere between $50 to $100, depending on how you source your materials.

When looking at these charts it was crazy to see how much red tinting happens when the taking lens is wide open. The red tinge goes away as you stop your taking lens down. Sharpness is okay in the center, but it's really gone as we move towards the corners. I noticed it's something that happens not only towards the corners but top and bottom in general more than the sides. Performance is best at 35mm and 50mm, struggling at 85mm.

The most noticeable change introduced by this focuser is the huge wide angle effect. Here's the Cinelux on its own, mounted on a 50mm lens - which is the equivalent of 72mm on the GH5 + Speedbooster. Now when I put on the focuser, the image gets considerably wider - like a 0.79x wide angle adapter. Plus we get a ton of vignetting.

Speaking of vignetting, while 50mm is mostly fine on the Cinelux alone, once we add the focuser, 50mm becomes a dark tunnel. 35mm, or 50mm equivalent is a no-go even on Micro Four Thirds, as I'm shooting these tests on the GH5. 50mm, or 72mm equivalent still got intense vignetting, but we're almost clear on 2.39:1, and 85mm - 125mm equivalent - is totally clean. Doing all the math, an 85mm taking lens on Full Frame would be clear.

For comparison, here are the naked Cinelux's flares, we get a subtle purple streak and a secondary teal streak. Once we add the focuser, the situation is pretty much the same. No big changes here except, again, the field of view.

Gotta say, while performance is not the most amazing, if you’re getting started now, or if you just want something to experiment with, this focuser is gonna be great for you. I had a blast putting mine together! Building these things makes me a lot more at ease grasping how the optics work, although I’m far from having a full understanding of it all.