How to adjust focusing screen

Started Dec 21, 2008 | Discussions thread
Terrance13
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Re: How to adjust focusing screen
In reply to Joseph S Wisniewski, Dec 21, 2008

Joseph S Wisniewski wrote:

Worse yet, it turns out that this is standard for the Olympus E-volt
series
of cameras. They don't adjust the focusing screens at the factory,
except for in the E-3.
http://forums.dpreview.com/forums/read.asp?forum=1022&message=26593494

I'd try to confirm that with a better source than a single internet
poster that doesn't even use his full name. Like tea leaves...

Goffen is well known in these forums. I also ran across this, and I have
just started looking, now that I realize what the problem is:
===================================
http://photo.net/olympus-camera-forum/00L8St

Peter Free , May 14, 2007; 08:49 a.m.

Having owned an Olympus E-500 two-lens kit for eighteen months, I agree
especially with Jim Covill and Claude Batmanghelidj.
I would recommend against buying into an Olympus 4/3 system today.
The below comments are based on well over fifty years in photography.

(4) Manufacturing Quality and Consistency May Be Questionable.

The sensor and viewfinder in my E-500 body are not properly aligned
and my viewfinder appears to be asymmetrically distorted from
side-to-side. I have to move my head back from the body to see
that it is properly horizontal or vertical. At first I attributed
this to my difficulty in using the tiny viewfinder. Now I
recognize that it's just an example of cost-cutting.
============================================

Now Peter Free was describing a different alignment problem, but it's still
viewfinder to sensor alignment being bad.

So Olympus won't fix it. The focusing screen is considered fixed, and
non-adjustable. So I have to fix it myself.

Did you actually try sending it in, or is this more tea leaves?

Actually, I must confess that I didn't call them on this, because I already
sent the camera back for warranty repair for several problems, and they didn't
do anything with the viewfinder.
And now my camera is out of warranty.
But I will email them and see what they say.
What do you think that the odds are that they will fix it for free now?

Up. It has to be moved closer to the optical path.

But remember, you've got three planes of focus to consider: main
sensor, focusing screen, and AF sensors. If the AF sensors agree with
the focusing screen and not the sensor, you need to shift the sensor
back (shims under the screws that hold the sensor board).

No, AF and sensor agree. The auto-focus is very sharp, when it works
correctly and actually focuses. (Which is a sometimes thing, and I already
sent it back for warranty repair for that. No such luck.)

To shim the screen, you need the shims that Oly uses. Most camera
makers supply shims in an assortment of thicknesses to their service
centers. Your chances of making some that will work are pretty slim.
If you want to try making your own, 27 microns (a hair over 1/1000
inch) will change the plane of focus 10mm at 1 meter when using a
50mm lens. You could probably get away with working at 50 microns
(two 1/1000 inch).

Okay, thanks for the input. Now I know where to start.

Are there any equations or approximations that could help in guessing
how much I need to shim the ground glass? How many thousandths of
an inch are we talking about, roughly, to shift the focusing distance by
maybe 10%?

10% at what range, with what lens?

Is it a MF lens? Remember, with many lenses, spherical aberration
causes a "disagreement" in focus plane that depends on aperture: the
focusing screen sees an f4 aperture, the actual shot could see a
wider aperture if using a faster lens.

Reshoot your test at f4, see how much disagreement there is.

-- hide signature --

Rahon Klavanian 1912-2008.

I did tests with the Olympus Zuiko 14-45 kit lens, in aperture priority
mode so that I could lock the aperture at F3.5 for minimum depth of
focus.
At a distance of about 3.5 feet, the actual focus point appears to be about
one inch in front of the target that I focused on. I repeated the test to
make sure it wasn't an accident of my hands or eyes.

I know that is a lot less than 10%. I was just pulling that number out
of the air for a ball-park guess. Your number of 27 microns moving
the focal plane 10mm at one meter is much more precise. Thank you.

I can repeat the test with lots of other lenses, including manual focus
legacy lenses. And in essence, already have.
I've been fighting with soft focus while doing manual focusing for a year,
and couldn't understand why I got so very few really sharp photographs,
no matter how carefully I focused, and it didn't matter much which lens
I used.
Now I have a clue. My eyes and technique aren't really that bad.

-- hide signature --

'Now I know what it's like to be high on life.
It isn't as good, but my driving has improved.'
== Nina, on 'Just Shoot Me', 13 Jan 2006.

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