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03-26-2011, 08:24 AM   #1
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The epic focusing screen saga comes to a close (sort of)

Hey all.

I've been wrangling with a manual focusing issue with my K100D for awhile now & I have it sort of done, I think.

I bought a generic split screen from e-Bay and installed with a moderate amount of hassle thanks to the crap plastic tweezers they sent me for the job. The focus was off so I ordered a new set of shims from Pentax, which arrived yesterday. This morning I spent 3 hours (!!!) installing, testing, uninstalling, installing the next one up, testing, etc... and finally I think I have it as close as I can get. Two things: First off, the supplied shim was way the hell off. I wound up using the thickest shim in the set to get it to focus correctly. But it would be nice if Pentax would get it right before they ship it out the door. One of the big selling points for me on Pentax was the ability to use older MF glass with it. What good is that, when all your shots are out of friggin' focus?!??!

(OK.. rant off...)

The other thing is, I used my 50mm 1.4 MF prime set to f1.4 to test it. When I focus on anything over about a foot at f1.4, there is just a shade (like 1-2 mm) of backfocus. But when I focus on something very close to the lens with a close up filter, it's frontfocused about 1-2 millimeters. If I stop down to f2, there's sufficient DOF to make it negligible.

Is it normal at a very wide f-stop like 1.4 to have this kind of focus disparity (albeit very minor) at different distances? I know, it's only a millimeter or so... But it would seem that if it's front-focusing very close, and slightly rear-focusing farther away it would be impossible to get it absolutely dead-on accurate at every distance.

I know... I'm splitting hairs, and maybe it's normal, I dunno... Just thought I'd see if anyone else knew the answer.

So, good news is I have the screen about as calibrated as I think it's ever going to get. Bad news, there's a buttload of dust on it from repeated installs & uninstalls, so I'm gonna need to get a can of air and I'll have the thrill of removing it yet again for the eleventy-billionth time to clean it. Oh, joy...

Bobbo :-)

03-26-2011, 10:29 AM   #2
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QuoteOriginally posted by GibbyTheMole Quote
...First off, the supplied shim was way the hell off. I wound up using the thickest shim in the set to get it to focus correctly. But it would be nice if Pentax would get it right before they ship it out the door.
Pentax probably had it right. Your split screen is more than likely not the same thickness as the original; that's why there are shims.
03-26-2011, 12:12 PM   #3
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@Gibby: Where did you get the shims BTW?
03-26-2011, 02:40 PM - 1 Like   #4
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Original Poster

Ordered them from Pentax parts department. Phone number is: 720-988-2653. It was around 6 bucks for the shims & $8 for shipping.

Their tech support line, by the way, is: 800-877-0155.


That makes sense, except the focus was a little off with the original screen too. Also, according to info from Katz-Eye, the focus screen thickness is irrelevent as the focusing takes place on the ground glass surface which is on top of the screen next to the pentaprism, just the same as the original screen focus would be.

Bobbo :-)

03-26-2011, 02:53 PM   #5
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You can order shims from Pentax(directly).
I usually grab the entire batch(8-10 of them) when I pick-up a new body.
Though I'm still on the fence with the K-5 given it's advanced LV capabilities.

Either way, screen shimming is always a bit of a chore.
And your experience is a great reminder of the implications that come with them.
However, if its of any help, you can wash your screens back to a pristine condition by washing them in baths made-up of mild dish soap distilled water. I usually set-up a few foam cups(1 x wash and 2 rinse) with distilled water. After which I dry the screen off with a blow-drier(careful not to blow it away!) and dabbing the drops off onto a tissue(for absorption).

Also, I would advise never to handle your screens with bare hands. Even though the installation tweeters are essential to installing/removing the screen, it is far better to have full contact access to the mirror box and such without worrying about the effects of oils and dust from your hands.

Oh. and I don't know if this applies to you or not, but do remember that screens can or will affect your metering at some stage. So I guess it end-up being a commitment of sorts for those who chose to use them. My own resolve, was to commit a body to MF and install and use a Katzeye with it exclusively(called it our manual).

Hope this helps.

PS. you can micro-calibrate a shim() with 3m tab tape which is very thin and easy to work with.
03-26-2011, 03:24 PM   #6
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Thanks for the helpful info... The only thing I see on the screen is dust, so I'm gonna pop it off (again...) and hit it with some canned air, being careful not to blow it across the room, of course... ;-) If I should ever need to give the screen a bath though, I'll remember the tip...

Haven't really noticed a metering issue, though MF lenses tend to meter a stop or so slower than my AF lenses. Being an old manual guy who cut my teeth on all-manual cameras, (K1000, Nikon F2s, etc...) that's just what I'm comfortable with.

Bob :-)

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