The below article describes how to improve brightness of a viewfinder of a YashicaFlex TLR camera. The same tricks would work just as well with many other old TLRs. If you can barely see anything through your TLR’s view finder, I hope you will find this article useful.
Below a picture of my self-serviced YashicaFlex TLR.
I bought the camera from an eBay vendor in Japan. It didn’t cost much, sold as-is. It arrived in a poor shape,. There were many many problems, as described in another article, all of them succesfully resolved 🙂
One of the biggest problems was the view finder. You could barely see anything through it. Even with an an otherwise functioning camera, this is a major deal-breaker. Composing an image and focusing, they both require as good visibility as possible. My camera in that aspect was only just-about usable outdoors, while indoors you couldn’t see anything.
The diagram below shows how a picture makes it from a photographed object to your eye, on a TLR camera. The light goes into the camera through the viewing lens. It bounces off a mirror placed at an angle, then goes up towards the eye. There the light falls on a ground glass screen, where the picture forms. You look at this picture from above, to compose a scene and to focus the camera.
To make the view as clear as possible, both elements require attention – the mirror and the ground glass screen.
Cleaning the mirror and the ground glass screen.
The ground glass screen of my camera was very dusty on both sides. I disassembled the view compartment and took the screen out. Then I took out the mirror, also covered with a thick layer of dust. Nobody has cleaned this thing, ever!
It’s quite easy to remove both parts. Once removed, I washed them with soap and polished gently with a microfibre cloth. I reassembled the camera and the picture got a bit better.
Better, but still far from ideal… I now could see the view indoors, but still very dark. The mirror simply lost its lustre over the decades. There were dark spots all over the surface. 65 years means a lot of oxygenation of the reflecting silver layer. It’s the exact same process which makes silver cutlery require regular polishing 😉
I decided to replace the mirror with a new one. I thought of buying a piece of mirror of similar thickness and cutting it myself. Then I’ve discovered that it cannot be just any mirror. It has to a first-surface mirror. It’s a mirror whose reflecting surface is not at the back of the mirror, but at the front.
If you’d use a typical cheap “second surface” mirror, focusing could become an issue. Here’s why:
The additional layer of glass through which the light goes in a conventional mirror before it bounces off the reflective layer, introduces secondary (ghost) reflections, slightly shifted. Light becomes weaker. Accurate focusing can become difficult.
I found some vendors of first surface mirror glass of the required thickness but prices weren’t worth it. They don’t seem to be particularly interested in selling me a single 10×10 cm piece 😉
So I went to eBay and bingo! There’s a nice guy in USA selling first-surface mirrors, already cut to proper sizes for variety of cameras, including my YashicaFlex. Find him here: $7 for a new shiny piece of a fitted mirror doesn’t seem an excessive price at all!
I ordered the mirror, waited a week, got it, peeled off the protective film (what a pleasure!), placed it inside the camera, and the view has gotten better again!
Nearly there… Why nearly? Well, there was still a lot of vignetting. Vignetting is a phenomenon where light on the ground glass screen is the most intense in the center, but becomes darker and darker towards the edges. It nothing to do with the camera, that’s just how things work with optics. Here’s an example:
Few weeks later I bought another TLR camera for repairs – a Zeiss Ikoflex. It was dirty like hell but hey, that viewfinder! The picture was bright, and no vignetting. How come?
I took a closer look and there I saw it. A Fresnel screen in the viewfinder.
Getting rid of vignette with Fresnel lens
Fresnel lens is a clever contraption by Augustin-Jean Fresnel, who came up with a cheap solution to boost brightness of light beams from lighthouses. It has been called the invention that saved a million ships. It’s a flat surface covered with concentric grooves which bend and focus light just as a lens would do – but all this without the lenses’ bulk, thickness and cost.
Nowadays cheap Fresnel lenses help senior citizen read their books and newspapers. They’re made of plastic and sold in bulk for peanuts, as can be seen here on eBay
I bought a sheet big enough, cut it to the required size, so that it would fit inside the ground glass screen compartment of my Yashicaflex. I’ve fixed it under the ground glass screen and it just worked!
The vignette is practically gone, while focusing still works fine (which was my biggest concern). This is such an improvement!
Below some pictures of the operation.
Ground glass screen of the Yashicaflex:
Fresnel lens cut to size:
Fresnel lens placed under the ground glass:
New bright viewfinder:
(c) Tomasz Waraksa, Dublin, 2020