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Jumbo 300mm Canon extension tube with autofocus

by thenickdude Aug 6, 2019
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I've just come back from field-testing a new Version 2 of this tube, and the results are excellent. By reshaping the aperture at the camera end to be rectangular (sensor-shaped), the vignetting has been eliminated, and by using matte spraypaint on the inside, the central hotspot is gone and the contrast is now superb.

I hope to publish the new version soon.

EDIT: Published now! I've updated this Thing with the new version 2 model.

Bug photo

I saw this post on hackaday and was great timing. I'm working on the exact same thing for using my Samsung NX lenses for an astrophotography camera. Only difference is I've made it as small as possible. Finding those pogo pins was so much better than the diy job I was prepared to try out. I've also included a port to pull data from the camera on what happens with lens focus so I can reproduce it without the NX1 body on an arduino. I've bought enough sets of pins for 3 of these. So if all goes well I'll print your one out as well and take photos of really small things. Great post! Thanks. Once I've finished my NX mount I'll post it up here.

for the internal reflection I suggest you to modify the design so the inner tube contain tiny grooves this will take longer to print maybe but will help fixing the reported issue (probably) without the need of post processing... otherwise using a smokey candle to coat the internal surface can be better than most spray paint... the ideal solution will to use vanta black but that's overkill.

The internal grooves can exploit the layer effect and make even layer have a smaller diameter than the even and this will not slow down the printing like if they grooves are parallel to the tube (both need to be tested maybe to see which offer the optimal solution), material choice is key as well as some filament tend to be less shiny and refelective than others... and maybe using the Cura jerking feature can help as well but also make the exterior look nicer as it add some texture to it.

Yes, the design already includes inner grooves in the tube.

If there exists a matte PETG that would be really interesting!

This is good.

Can the slight vignetting be eliminated by adding a rectangular cutout aligned with the locked-on-camera position of the extension tube to the last couple inches of the parts in the assembly?

I think the vignetting is due to the internal diameter being 35mm, which matches the Kenko and Canon tubes, but with the exit pupil being so far away it's effectively at infinity, limiting the resulting image circle to 35mm diameter. This isn't enough to cover the full frame.

Yes, I suspect that the cross-section of the internal cavity needs to be rectangular by the time it reaches the camera end in order to solve this.

Came here from Hackaday. As a fellow hacker, scrolling through your blog I looked only at the images and knew exactly how it works and what risks there were. Why not put some intricate design on the outside of the tube instead of having it look like a dull concrete pylon?

Thanks for the idea on the decoration, I was able to create a new prototype design using photos of insects I've taken!

Decorated tube

It's so cool to have something decorated with my own artwork!

This print is effectively a prototype, so I wasn't thinking about decoration so much. Now that you mention it though, I can imagine a bunch of neat possible surface designs!

Maybe for my next revision!

Came here from PetaPixel. That is a great write up of the production and use of the lens extension! Well done.