Upgrading a Nikon D40 viewfinder to split-prism focus screen

Since being given a Nikon F60 SLR some twelve years ago or so, I’ve struggled with the standard viewfinders provided on modern consumer-grade SLR cameras.  My annoyance was further amplified when I bought my factory-reconditioned D40 in 2008.

The problem shared by both these cameras is that the viewfinder is not terribly precise.  It’s easy enough in most lighting situations to see whether the frame is generally in or out of focus, but to do so with any precision is challenging at best.  Quite often I find my eye automatically compensates  for poor focus by focussing on the subject “through” the screen itself.  I do this without even thinking about it, despite whatever conscious effort I make to prevent it happening.

Specific to the D40 is the issue that the viewfinder is about 1.5x smaller than the F60 I had been used to, and certainly smaller than the more professionally-oriented devices Nikon currently offers.  Not only is it smaller, but it’s also dimmer.  Sure, I willingly bought the D40 knowing about these issues, but they’ve become more of a show-stopper as I’ve grown to move away from shiny new auto-focussing lenses to older manually-focussing units.

I did some research into possible solutions that didn’t involve buying a new camera body, and I soon found that like pretty much every other Nikon SLR out there, the focussing screen on the D40 is easily removable – presumably for cleaning.  This also opens the way to replacing the existing screen with something more suited to the way I want to work – that is to use split-prism and/or microprism focussing rather than relying on the built-in autofocus system.

I won’t explain how split-prism focussing works, as it’s done so much better here.


The screen I chose was a generic (no brand name) cheap unit found on eBay, but it’s like this one. Instructions were found online here, which gave me enough information to know what to expect.  Lacking specialist tools, I washed my hands and used my index finger (and nail) to operate the latch that holds the screen in place, and used clean fingers to drop the shim and screen into place.  The wrapping on the new screen was enough to place between the mirror and the latch to prevent scratching.

I’m not always the most practical of people, and yet this installation job was easily done in less than 20mins including making some tea and reading the manuals – and I’ve never done anything like this before!


The concept proved itself very rapidly in ‘everyday’ snapshot situations. But something was wrong: when I manually focussed using the new screen, the image turned out with the actual focal point being shifted a little behind what I’d focussed on.  Pants.

Given that my lenses hadn’t changed, and given the assurance I’ve had from several sources that the choice (or even presence) of screen does not interfere with the camera’s built-in autofocus sensors, there was only one answer: the screen was out of alignment.

Back to Google and Flickr forums I went, and found that this is a common enough issue experienced when installing and using custom screens – particularly cheap ones like mine. Whether this problem reflects the quality of the cheaper screens, or whether it’s caused by the quality of calibration carried out in the manufacture of the camera itself, I cannot tell.

Before going any further, I found and printed a focussing test chart (more on the issues that brought up here!) and took some autofocus-assisted shots of it with the kit lens. First with the new screen, then with the old, and finally even without a screen.  This confirmed what I had read, namely that the autofocus works as it should.  Good – just the manual focussing to sort then.

The research I’d previously carried out into the problem suggested using some special tools to recalibrate the mirror, so it naturally rests in a different place.  In this camera this would inevitably mess up the autofocus system too, which I felt would be too complex a job to realign with the tools and time I had at my disposal.  There had to be a simpler solution!

So I gave the issue some thought, and basically I cheated.  I figured that if moving the mirror in relation to the screen can solve the problem, then why not move the screen in relation to the mirror instead?  If this can be done without putting too much pressure on the screen assembly (and damaging either the screen in the camera in the process) then it has to be worth a shot – right?


I pulled the screen and shim back out of the camera, and first decided to try installing the new screen without the metal shim.  This moved the screen further away from the mirror.  Took some test shots, and soon saw that the back-focus problem had gotten worse.  Okay, then if that was the case then perhaps instead I needed to effectively thicken the shim to move the screen closer to the mirror?

Buying a second shim to test this theory seemed like too much work, not to mention that this would mean throwing yet more time and money at the problem, with no guarantee of a workable solution.  What if the spendy new shim added too much thickness?

So instead I thought to try sticking some appropriately-sized paper strips to the shim to thicken it slightly.  Five minutes with some Pritt-Stick, scissors and an old till-receipt was enough to prepare the existing shim for testing.  I reinstalled the shim and screen, and took several hundred (!) test shots.  The situation was now bearable but the back-focussing problem was still present enough to be annoying.

Back to the cutting-board I went, this time removing the paper strips and replacing them with similar sized strips cut from a used rail-ticket, as that was about double the (estimated) thickness of the original paper strips).  Pritt-Stick, scissors and patience were still the tools of choice.  Eventually I put it all back together and “Hurrah!” – manual focussing with the split-prism now works even more accurately than auto-focus.  Problem solved!


Despite, and perhaps even because of, the work I’ve had to put in to get things calibrated properly I’m now very pleased with the end result.  I now have a camera that still works very well with autofocussing lenses, but also has the capability to give me even sharper results with manual focussing.

I would heartily recommend such a screen upgrade to anyone who is struggling with manual-focussing their modern DSLR rig, but I would perhaps suggest that they buy an official screen either from the camera manufacturer (Nikon, in my case) or a much more trusted third-party manufacturer such as the Katz-Eye products linked earlier in the article.

With all of that said, I cannot vouch for either of these more expensive solutions as I have not tried them – so as always your mileage may vary.

One thought on “Upgrading a Nikon D40 viewfinder to split-prism focus screen

  1. What a great write up. I was just surfing around to find info on DIY focus screens. Stumbled on your post. I have a spare D40. I might give such a screen a try. Anyway, thanks for blogging this;)

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