Installing Focusing or Fresnel Screens

Installing Focusing/Fresnel Screens | Digital SLR | Film SLR Cameras

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Installing Focusing or Fresnel Screens

In this article, I will reference the Fresnel lens or focusing screen as the “screen”.

Most SLR users know this but I have talked to many customers over the years who didn’t, so I am going to say… when using a digital or film camera SLR, none of the spots, debris or dust specs you see in the viewfinder will be part of the final image. All of that debris is in the viewing system only.

Why install a new screen in your SLR camera?

Because of all the specs and dust have accumulated on it over the years of using the camera and you changed lenses a lot? Not really.
Mostly because the camera owner tried to clean a small spec from the exposed side of the screen and damaged it.
I saw a YouTube video that shows you how to clean it or just touch the screen with scotch tape to remove something on the bottom side. That never works 100%.

Old mirror cushion foam or anything else that touches that screen will permanently damage it. Not totaled but the marks will always be visible.
As a tech I tried everything method and chemical or cleaning solution made and nothing would clean a screen where it looked brand new.

With the screen installed and the lens removed, anything on the bottom side of the screen will show as a slight gray area when looking through viewfinder, a more definitive mark when a lens is installed.

You cannot touch a focusing screen with anything other than clean filtered compressed air.
Canned air users sometimes end up blowing liquid onto the screen, mirror and other parts of the focusing system unless you are extremely careful.

Focusing screens are probably the most easily damaged and most fragile part in a camera that they are easily accessible by a user.

I have document somewhere in the shop about the focusing screen designed by Minolta engineers for the XD where the screen is made up of a million or so little pyramids. The Minolta design became a standard and eliminated much of the light loss of typical ground glass or concentric circle type screens.

Installing Focusing or Fresnel Screens

Enough of my rambling and onto installing the screen.

You need to have steady hands, not be nervous or shaky when working with focus screens or you have a greater chance in damaging a new screen.

For the most part, I do not recommend using the tools supplied with retail boxed screen replacement kits supplied by some manufacturers. Holding a screen with those tools just gives you more leverage and amplifies the small movements of your fingers or hand, making it easier to damage the screen during the install.

Be gentle on the screen frame latch, it never takes a lot of force to release it. Some customers damage them. Years ago, you could purchase a new screen frame separately.  Lately, most of the screen frames are part of the mirror cage assembly and not available separately.  Even though you may be able to easily remove it and take it out of the camera, it is not a separate part supplied by the manufacturers.

Some cameras use screen focus shims* and those may drop down with the screen when you push the screen frame latch. It is a good thing to know what’s there by looking at a parts list before you push the frame latch. Part lists we have online are listed here.

Also, pushing the frame latch and dropping the screen onto your work surface will be OK since you are replacing the screen anyway. Though you need to pay attention to the order of parts that are present. Shims fit first in the camera, then the focusing screen in the frame that latches into place.

Work over a clean desk and preferably a technician’s work mat.

For the most part most techs, including me, hold the screens on the sides between their fingers. Some screens that have a tab on the front, I may hold the screen by that sometimes. How I hold them depends mostly on how I have to place the screen in the frame.

I find it easier when the camera is steady by keeping it contact with my work mat then I just drop or place the screen onto the frame then latch it into place. When shims are used, sometimes I find it easier to work with the top cover on the work mat. It is rather difficult put the screen on the frame then stack the shims on top of screen and keep things lined up to fit when latch the screen frame in place.

Needless to say, first practice, practice, practice with the old screen until you are able to install and remove it easily. Then you will be ready to install the new screen without damage.

Hope this helps you and as always, I invite your comments.

Gray

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*Shims are used to put the screen at the correct distance from the lens mount for sharp focusing at infinity that also matches the lens mount to the image sensor or film plane.

**The attached image from the Canon XT DSLR parts list shows you the screen frame, screen and shims are used on that model camera. Since camera parts made to exacting standards, it is rare that different shims would be required when installing a new replacement screen.