Blue screen of Basic

My DeVere 504 has the original electronic timer which looks a lot more fanct than it is. You set the tiem with a couple of rotary swithces on top. But it's not a digital circuit, dividing down a master clock. It's just a 555 monotstable, the switches vary the number of resisotrs in-circuit. Fortunately the DeVere system is quite modular, the timer plugs into the votlage stabiiser, and one of the first things I did when I got the enlarger was to trace out schematics. So I can make a digital timer to plug into the smae socket if I want to. THere are at lest 6 books. Two of them are brand-specifc -- Leica and Nikon (note the latterc covers the S series ragefinder camers, the reflex cameras and the Nikonos). The otehr 4 books are more general. Camera Maintenance and Repair VOlumes 1 and 2 have gneral repair tips, methods and how to make test instruments in the first half of the book and then some details on taking apart 'representative' models. Restoring Classic and Collectable coamers covers pre-war camers, how to mke bellows, tc. Repairing the Great Collectable Camers is post-war models and covers some very interesting designs. None of them, IMHO, are a substitue for the manufacturer's service manual -- if you cna get it. And there are plenty of thigns I would do differently. But the books are worth reading. Make one! Although there is a trap for the unwary that most comemrical testers get erogn too. The point is that no shutter opens and closes instaneously. Not even folca plane shuytters -- due to the spacing between the curtains and the flim, you get a slight penumbra round the slit image. So while you would like the light .vs. time curve to be a rectangle with vertical sides (along the 'light' axis), in fact it has sloping sides (which may, or may not, be linear). Now, what actually matters, to a very good apporxiamtion, is the integral of that curcve, the area under it. So what you should do is integrate the light coming throug hthe shutter and compute the equivanet 'open time for a perfect shutter'. What most, if not all, testers do is simply set a light threshold and measure the time for light to be above that threshold. This is fine for slow speeds, it can give wildly wrong resutls for high speeds (and can cause people to complain that the shutter is not accurate, when in fact the totla ligth transmitted is correct for the marked time). However, such a simple tester will pick up gross probles, like a sticking escapemet. Just don't expect the higher speeds on the shutter dial to agree with the timer. If in doubt, take a series of photographs of the same illuminated grey card with different speeds, adjustign the aperture to give the same exposure each time, and compare the densities of the negatives. That will pick up any major erors in one of the speeds. -tony