Tuesday, July 24, 2007

Split Image Focus Screens

A replacement split image focus screen inside the K10D.

The standard focus screen in a Pentax DSLR is really nice, but if you have a camera that supports replacement screens, like the *ist D, *ist DS, or the K10D, then you owe it to yourself to see if any of the alternatives appeal to you. Pentax makes alternate focus screens with various lines for cropping and scale (such as the rule of thirds), which are just etched graphic changes to the standard matte fresnel design. All the Pentax replacement screens come with a little tab for easier handling and placement, and the expert packaging is such that you get a nice container for your old screen. They aren't even that expensive, typically around $50. B&H Photo usually has stock of screens for past cameras, like the DS.

But I've always wanted a split image focus screen to help with manual focus. There are a few places who make them, all non-OEM, and all of varying quality. Katz Eye is easily the most trusted name out there for Pentax, using premium glass and really refined production techniques. They even make screens for the K100D, which isn't considered as having a "replaceable" screen system. There's also Beattie and Haoda. Conversely, you can also try your luck and order from China thanks to eBay. Expect to pay between $20 and $150.

About Split Focus Screens

People familiar with older SLRs and rangefinders will remember split image focus screens as having a divided center circle prism that appears sliced in the middle. As the focus moves, objects in both sides of the circle either align or slide askew. Rather than just get blurry, you can observe that objects are not in focus by the tell-tale fracture in parallax alignment within the circle. For added confirmation, sometimes on the outside of the split prism circle, you'd also have a microprism ring that gave the appearance of a half-tone screen as things move out of focus (the Pentax K1000 had a standard screen with just a center microprism circle). These types of classic screens are a great help for manual focusing, especially in low light, but they just aren't as necessary as they used to be now that autofocus rules the roost.

Problems?

Pentax hasn't made any such replacement themselves, perhaps due to quality concerns about obstructing the digital exposure and autofocus. Split image screens are notoriously difficult for accurate digital spot and multi-segment exposure when your lens aperture is less than fast (F4 or smaller). You can't blame Pentax for that. For manual focus, they've already given you a huge viewfinder, a bright screen, and given you the option of getting focus confirmation (the center red focus point will flash and you can choose to hear an audible beep). Cut Pentax some slack for having thought carefully about the situation. But because more than a few Pentax owners enjoy using older glass, such as old M42 Super Takumars, or even Pentax SMC-M and SMC-A manual lenses, the demand for split focus screens is still out there. Sometimes people want to trust their eyes more than the camera's AF system, and that's okay. You just have to accept that no one can guarantee perfect results.

Trying One Out, Cheap

I was really curious about split image focus screen replacements for my Pentax K10D and my *ist DS, but I wasn't entirely sure I was going to use it that often, so I followed the path of least resistance and ordered one off a recommended seller on eBay who modifies old K1000 screens for use in Pentax DSLRs (RJ Camera Accessories). Katz Eye and Pentax have higher standards, include a great installation kit, and have great customer satisfaction, so trying this out is always a risk. For $25, I expected the quality to be a little sketchy, which it is, but I was also happily surprised. I had contacted the vendor for 2 special requests: a diagonal 45º angle split in the center circle and a little tab, like Pentax has on their screens. Both of these requests were done well. The quality of the replacement screen is pretty good, even if the glass cutting doesn't seem 100% exact, because everything is sized correctly and optically it's perfectly clean and bright. It will also work in both my *ist DS and my K10D.

The package received from China.

What I got in the mail was a tiny padded envelope that contained the replacement screen wrapped carefully (and placed inside an SD card plastic container, too) and a set of cheap tools ($3 extra). Honestly, I just wanted the extra finger gloves, because I thought they would make me feel more competent and look cool. I was wrong, but oh, well.

Finger Gloves

Installing it in my K10D was pretty straightforward. I prepped a dust-free work area, laid out all the tools and materials, and gave my camera a good cleaning in advance with a rocket blower, microfiber cloth, and some canned air. I can't stress how important a dust free workspace is when you're working with your viewfinder system. Dust and your own fingers are your worst enemies with this procedure, because you'll likely introduce dust into your camera and you have to be particularly careful not to allow your fingers (oil on your fingertips, etc) or the tools to touch the mirror or scratch the glass.

All I had to do was lower the hinged focus screen door above the mirror and swap out the screen for the new one using the provided tools to grip the screens' tabs. Afterwards, I followed up by blowing out the inside of the camera a few times to remove any dust. Pentax includes instructions for replacement screens with their camera's manuals, but if you don't feel comfortable doing this, by all means get a professional to do it for you. Katz Eye offers this service, or you can ask a local camera technician.

Results

In the end, I haven't experienced any autofocus or exposure problems, and for that I'm pretty lucky. However, I wouldn't trust AE with a telephoto lens without checking the histogram first. My experience has been very similar to this account (link). Everyone's mileage seems to vary, although Katz Eye is confident you shouldn't experience any problems with their non "Opti-Brite" screens. Using wide angle manual lenses has become a new pleasure, but at least my DA lenses seem to autofocus just as well as they ever did for me. If I find that I'm using this more often than not, I'll probably choose to invest in a Katz Eye version, which can even have custom lines etched onto the surface of the screen (I'm a big fan of the golden proportion, myself).

Viewfinder mock-up

Links: RJ Camera Accessories, Katz Eye, Pentax K10D Replacement Screens, CameraMentor's Split Image Focus Experience, Haoda Replacement Screens, Boris D.'s Pentax Vintage Focusing Screens Page, Beattie Intenscreens

2 comments:

daniel said...

rad, thanks for the write-up, i've been really curious about the SPS and think you've helped me make a decision to go for it!

Miserere said...

Changing the focus screen will not affect the AF funtion because it is underneath the mirror, at the bottom of the camera, so it uses light that has not gone upwards towards the focusing screen (which is why AF cameras have darker viewfinders than MF ones).

The light meter, on the other hand, is upstream from the mirror, so it can be affected by the split prism. In my experience the effect is negligible, if any.

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