As you may recall, towards the back end of last year I had a play around with the focusing screen of my SLR. Specifically I ordered a split image microprism focusing screen as a replacement for what I believed to be a scratched normal screen.
6 months on, and I’ve just switched back to the normal screen (although I may yet go back again).
The split image screen in itself is great – far easier to see when the subject is in focus, and generally what’s going on, and, all other things being equal I would run with it everytime. They’re not perfect by any means, and in particular the way they collect light is different, and so at apertures smaller than about f/5.6, or if light levels are low, the middle bit blacks out. Obviously the f/5.6 isn’t a huge issue, as you tend to preview fully open, and if you have stopped down for depth-of-field preview the precise focus point is less critical.
However, there are 2 specific deal-breakers for me with the specific one I purchased (which was dead cheap):
- The provided shims didn’t really do the job.
- The focus confirmation lights don’t show.
The first is the big problem. It came with 4 or 5 bits of thin plastic shaped in the same way as the real metal shim. (I should add that the purpose of the shim is to ensure that the screen is the correct distance from the lens, so the focussing is correct). These were immensely fiddly to fit, and I don’t think made quite the right gap. This in turn meant the focus was ever so slightly off – actual focus on the sensor didn’t match the screen. It was a tiny amount, but enough to shake my confidence in the focus – which makes the whole exercise kinda pointless.
The other problem is the pathetic plastic shims don’t sit flat – they slipped out and are visible in the viewfinder (but obviously not the images).
The second is less critical – and apparantly you can draw little pencil marks on to make them show up again.
All of this said, I’ve just fired a couple of test shots with the old screen, and I don’t like it half as much! I may yet switch it back, and persist with the shims to try and sort out the focus point.