[almo]

I am thinking about replacing my K20's focus screen with a split image focus screen to better aid in manual focusing. What i don't know, however, is how this will effect auto focusing. Can anyone enlighten me?

[Photonz]

Hi Almo. Any modification to your focussing screen can NOT affect autofocus. That is because your camera use phase detection to focus, and the phase detection sensors sit below your mirror. Some users do report that exposures is affected by 0.3 to 0.6 EV stops. But that is easily fixed by dialling in the correct exposure compensation value.

In my personal experience with a K100D and split-prism viewfinder, stop-down exposure metering on manual lenses is 100% accurate and exposures on my 18-55mm kit lens is most of the times accurate but my Sigma APO DG Macro 70-300mm is usually 0.6 stops too dark - so I just dial in the appropriate exposure compensation. For the benefit of accurate manual focussing that is hardly any inconvenience.

Cheers!

[david94903]

I have a K20d that I installed a Katseye split focus screen in years ago. There is no issue with it affecting autofocus for the reasons mentioned in Photonz reply. Also, I've never experienced any issues regarding exposure EV stops either.

[almo]

Awesome answers guys! Just what I wanted to hear. Since the Split screen doesn't effect the AF ability, does it effect the focus point overlay? If that is the right thing. The little red square that flashes when it locks on? Probably not a deal breaker for me, but good to know.

[Photonz]

It's a pleasure. No, the focus point overlay is unaffected. Just make sure the function is enabled in the camera's advanced functions menu, for when using manual lenses.

[jawsy]

I've got a Katzeye on my K20D. Generally agree with previous comments. No change to E/V for full screen weighting, +0.3 for centre weight and up to +1.7 for spot metering (which I rarely use.)

I also had to shim the screen to calibrate the prism. This also fixed a long running battle I'd had trying to calibrate my FA50.

I cannot recommend a split screen highly enough. It's one of those things that after buying I wished I'd done sooner.

[Lowell Goudge]

Something to remember, the K10/K20 has a highly irregular exposure for manual lenses. I found metering improved on my K10 overall with a split image screen

[almo]

Does the brand matter much? There are the $20 ones on ebay from China, and then the Katzeyes which are considerably more. Probably a dumb question, but I'm just tossing it out there.

[6BQ5]

I bought a cheaper generic Chinese made screen from a fellow forum member to see what screen was like. The metering was waaaaay off. Every shot was over exposed because the screen had poor light transmission to the meter behind the prism. The camera thought I was in perpetual darkness. I would avoid the cheaper screens. They are cheaper for a reason.

[narual]

just remember it's probably going to make spot metering fairly useless, and that you can't move the split, so if you want to focus on something that isn't dead center, you'll need to recompose, and if you're using a really fast lens, you may not have enough area in focus to do that safely. (you may have to, say, focus on the tip of the nose instead of the eyes, so that when you move the camera so the subject is to one side of center, the eyes are in focus.)

[dms]

I did the switch (on K20d)--but for my theater photography it made spot metering a real problem, especially w/ non A lenses. At f5/6 and smaller (f/5.6~f/16) it resulted in +3 e.v. exposure. I would not do it again. BTW I only use MF so I cannot speak to impact on AF--if any. My results were:
f/2.8.... +0 e.v.
f/3.3.... +1 e.v.
f/4 .......+2 e.v.
> f/5.6 .+3 e.v.

[Pioneer]

I do not own a K20D but...

I have one on my ist DLS and it works like a charm.

I have on on my K10D and it is wonderful.

I rarely spotmeter with 35mm or aps-c, so I notice no exposure issues. If I do need a spotmeter I use my Pentax spotmeter.

Any auto focus problems I have are not caused by the focus screen.

I only work with Katzeye screens and am absolutely thrilled with the quality and service, so have no experience to report with the ebay varieties.

[narual]

In case you're unaware, there's a different option -- a matte screen intended for large aperture lenses. They don't have any split screen or microprisms or anything to help you focus, but they accurately reflect sharpness below f/4 or 5.6 or whatever the effective limit is for the stock focusing screen.

The downside is if you're using a slow lens, the image in the viewfinder will be a bit darker, and if you get one with lines etched in it, SteveBrot and possibly others have said it can affect metering a bit on at least the k3.

[stevebrot]

SteveBrot and possibly others have said it can affect metering a bit on at least the k3.

The S-type screen with AF area markings from focusingscreen.com affected the metering a lot (2+ stops) on the K-3. That tidbit aside, I liked the S-type screen. The main caveat is that it dims significantly between f/2.8 and f/4. Focusingscreen.com also sells several other screens. Their prices are good as is the product quality. Post-sale customer service was poor in my case, but other's have had no problem.

I put a KatzEye screen in my K10D in 2008 and was very pleased with its performance on that body. I initially bought the standard version (no OptiBrite), but traded that for the OptiBrite version after about a week of ownership. OptiBrite results in a screen that is slightly brighter than the stock Pentax screen and is absolutely worth it, IMHO. I currently have a KatzEye on my K-3.

I have never tried any of the eBay screens. Fotodiox is also selling a split-image screen now and I believe at least one PF member has tried it. Edit: Alas, not for any of the older bodies.


Steve

[reeftool]

Does the brand matter much? There are the $20 ones on ebay from China, and then the Katzeyes which are considerably more. Probably a dumb question, but I'm just tossing it out there.

I haven't had good experiences with the cheap screens.