I recently acquired a Yashicamat twin-lens reflex medium-format camera from eBay, and although it’s in pretty good condition for it’s age (at least 35 years as they were discontinued in 1971!) the viewfinder was distinctly grubby.

Cleaning it up was actually fairly straight-forward. There are four small screws that secure the viewfinder to the body; remove these and the whole viewfinder assembly lifts out. Then you can get at the mirror to clean that - there’s a black metal clip on the top edge that secures it in place. The ground glass screen is actually in two parts - there’s the upper glass surface which is ruled with gridlines, and a plastic fresnel screen underneath. Both are held in place by two spring clips which you can remove with a bit of fiddling with a screwdriver.

As the view lens chamber isn’t sealed particularly well, there was thirty-odd years-worth of dust and debris inside, including a couple of pieces of confetti! A quick swipe around with a blower brush will get rid of most of it, particularly if you hold the body upside down - and you’ll notice a definite difference in the brightness of the finder screen once it’s done. With any luck, this one should be good for another thirty-something years…