Modification to lens focus ring on Fotric 226b camera

[Fraser]

I have just added a little modification to my Fotric 226b camera.

As some will have noticed in my previous post on the Fotric 226 and my 226b thermal cameras, my 226b unit has a stubby lens fitted that protrudes only around 12mm from the face of the lens mount. The lack of length made it challenging to operate the manual focus and the narrowness (6mm) of the focus ring caused my fingers to appear in the thermal scene whilst operating it. The standard 226 lens is larger and longer and more like a standard C mount lens found on a CCTV camera. I wanted to increase the size of my 226b lens housing to make it easier to use.

I began searching for a manual CCTV lens in my collection of such items with a view to gutting it and creating a shell to fit over the 226b stubby lens to increase its size and ease of focus. I also considered gutting a M37 mount Camcorder Supplementary telephoto converter lens. I really just needed a lens shell into which I could install a 3D printed ‘chassis’ that would mount on the stubby lens focus ring. Whilst searching eBay for suitable candidates of supplemental video lenses I stumbled upon the lens mount converters used with some compact cameras to permit use of standard photographic filters when a camera lens does not have a threaded mount for such. These adapters sit around the cameras lens and extend beyond it. That looked like a promising design for adaption to my needs. I just needed to find a suitable size. I decided upon the UM-E2 lens adaptor from Nikon that normally mounts on an 800 series compact camera. This adapter is unusual as it is not a straight extension barrel, it is a approx 41mm barrel threaded at the camera end and presenting a step down M28 filter mount at the other end. This creates a nice bull nose lens shell in to which I could install the 3D printed plastic chassis to adapt it to my 226b lens focus ring shape.

I bought the UR-E2 adapter and set to work making the chassis to go inside it. The design was very simple as it is just a cylinder with two different internal diameter sections. I prototyped the ABS plastic chassis to achieve dimensions that were a clearance fit into the UR-E2 barrel but an interference fit on the 226b lens focus ring. I was amazed at the accuracy of my Tiertime UP! BOX 3D printer when creating a model with a 0.05mm differential dimension to create the desired fit of the chassis. That printer is so precise when working with ABS.

Once the 3D printed ABS chassis was perfected, I inserted it into the Nikon adapter barrel and used carefully located spots of UHU glue to secure it into the bull nose front and along its sides. The result is a solidly fitted plastic chassis inside the aluminium barrel, yet it can be removed by force in the future if required.

I am very pleased with the resulting extended lens barrel and the relatively narrow field of view of the 226b lens means I do not have any problems with vignetting.

I love my 3D printer !

This approach could be employed for other cameras that have manual focus lenses that are challenging to operate due to small size.

Fraser

[Fraser]

Continued...

[Fraser]

Just tested the new focus ring operation and it has transformed this cameras ease of use  The manual focus feels just like on an SLR now. Easy to grip and fine adjust. An absolute pleasure to use now. I checked how close I am to getting vignetting at the corners of the image and it looks like it starts with an opening of around 24mm diameter and my opening at the end of the UR-E2 is 28mm diameter. If the UR-E2 had caused vignetting, there are other Nikon adapters in the UR-E series that are basically straight through tubes (just like conventional lens extension tubes) so I could have used one of those.

I attach three sample images of my Hi-Fi as it was just an easy target that was available whilst writing this on the sofa   

The first is a standard image, the second is with the noise reduction operating and the last image is with Edge enhancement active. No signs of vignetting or other issues as a result of the modification. I can remove this modification easily if ever required. Note that the 3D printed chassis is an interference fit on the aluminium focus ring so is very tight and does not require any adhesive 

I can see other dongle type cameras benefitting from a larger manual focus ring so such an approach could be repeated for them as well. Alternatively the Nikon UR-E2 adapter could be deleted from the design and a fully 3D printed larger focus barrel could be employed. I wanted a nice aluminium barrel though. My Mk1 prototype was a fully 3D printed barrel to test the idea and I was awaiting the arrival of the UR-E2. As I print in ABS plastic I can fill, sand and paint any 3D printed items to improve their looks.

Fraser

[Fraser]

The Mk1 prototype that I produced to test the idea of an extended focus ring and lens housing. This is where 3D printers are so useful. It was soooo easy to create the design as it is not complex and the accuracy of the printed parts dimensions was amazing. A perfect fit on the first attempt. I experimented with tiny changes in the diameter of the plastic that grips the aluminium lens focus ring to establish the best interference fit that was not too loose or too tight. To do this I just printed 9mm high rings to try on the lens and assess grip. I also experimented with fill densities and resolutions of print, just for interest. I ended up with a normal resolution and 65% fill. Some attempts at higher fill amounts ended poorly due to the thin wall of the plastic adapter where it fits around the focus ring. The rejected prints are visible in the last picture. prints took between 40 minutes and an hour, depending upon resolution and fill settings. The white areas on the ends on these prints is just dust from sanding the ends on 600 grade wet & dry paper. One print (bottom left) was painted with matt black enamel paint in the area ahead of the lens but this proved unnecessary so was dropped in the final design.

Fraser

[Fraser]

My original post on the Fotric 226b camera.......

https://www.eevblog.com/forum/thermal-imaging/the-story-of-a-canon-g5-digital-camera-and-a-fotric-200-series-thermal-camera-)/msg4423027/#msg4423027

Fraser

[Fraser]

If the Nikon UR-E2 had proven unsuitable for my application I had another Nikon adapter, the larger UR-E5, on its way to me as a backup plan  It has just arrived and, as can be seen, is more of a straight through design. It is now spare, to await other similar applications.

Fraser

[Fraser]

Quick teacup test to check for vignetting Sadly the saved pictures have inserted graphics obscuring some of the corners but I had a clear view of each corner. No vignetting found so all is good. I am pleasantly surprised on this front as I was unsure whether the 28mm viewing aperture and extended front to the lens barrel would cause some vignetting at the corners. Clearly not. The 260b uses a 30 Degree HFOV lens which is pretty narrow compared to some common consumer thermal cameras.

[Fraser]

Those test pictures were ruined by the graphics so I repeated the test with the graphics overlay and measurement options removed.