11 September 2010

Manual Focus

I’ve been interested in getting a manual focus screen for my D300 for a while, but the price of the Katzeye screen has put me off. However, I recently found out that you can get focus screens from on eBay for a fraction of the price, so I thought I’d take the plunge.

I chose a 180 degree split, which just means that the split line is horizontal. That means that it’s easiest and most accurate to focus on vertical lines and impossible to focus on horizontal lines. The other common types are:

  • 45 degree single split. This is the same as the 180 degree but with the split line at 45 degrees. One of these screens will let you focus on both horizontal and vertical lines but with less accuracy. For maximum accuracy you’d need to find a 45 degree line.
  • 45 degree double split. As the name suggests this screen has two splits. Apparently the purpose of this is to help get the sensor plane aligned with what you need to focus on and is mainly useful for photography flat objects like coins and books.

Removing the focus screen on a D300 is slightly fiddly as you really need to remove two tiny screws (it’s probably just about possible to change the screen without removing the screws but I wouldn’t recommend it). Once the screws, and small plate they hold, have been removed you just need to unhook the wire holding the screen in and replace the screen. If you plan to do this you should follow some proper instructions.

Unfortunately, so far things have not gone to plan. Fitting the screen is in theory fairly simple. In practice the particular screen I have was about 1mm narrower than the original screen and so the wire clip holding it in slipped off one side and so didn’t hold it as securely as I’d like. To counter this I removed the clip completely, bent it in slightly with some pliers, and then put it back. Not too hard but it shouldn’t have been necessary and required some confidence.

Once securely fitted I tested the screen by setting the camera to autofocus and seeing if the screen agreed. It didn’t. I half expected this as there were two shims between the original focus screen and camera body and I’d read guides that said to leave them in and other guides that said to take them out. So I tried removing one, then both shims. Unfortunately that didn’t really help.

At this point I had to do some more research. One thing I learned is that with a 1.5mm allen key you can adjust the mirror resting position to a small degree by turning a small screw next to the bottom right hand corner of the mirror (as you look into the camera). This helped and got the focus quite close, but I couldn’t adjust it far enough. Also please do note that I later found a few warnings about how this adjustment might mess up your auto focus, however, I found just as many notes saying that people had done this without any problems. For the record I have not seen any problems with my auto focus but haven’t tested it thoroughly.

Finally after more research I’ve found a few people saying that modern DSLRs are simply not set up for manual focus at all accurately (although mostly they’re not far off). Given the general lack of complaints about these screens I think in my case I may have got unlucky and got a camera that is so far away from accurate manual focus that the small adjustments available to me aren’t enough.

So, I’ve admitted defeat and emailed Nikon Service to see what they can do adjust the focusing and how much it will cost. More details to follow as things progress…