[Catalana]

I love to shoot with manual lenses and noticed that my K-5 was a bit off in that department, which led me to read up on the subject. First of all, many thanks to all the previous posters and especially those,
that have provided pertinent information on acquiring the little bits and pieces from Pentax.

Once again, the link for the parts:
https://www.pentaxforums.com/forums/pentax-k-5-forum/131473-k-5-manual-focus.html#post1367571

Anyway, once the washers arrived, I decided to first test seven different manual lenses (all wide open) with the factory installed "focus adjustment washer",
just to rule out sample variation of my SMC-M 50mm/1.7 & SMC-M 100mm/2.8, with which I had initially tested manual focus accuracy. I did this on a tripod with shake reduction off and the 2 second timer on.
Diopter adjustment was the same for all shots. All lenses exhibited about the same amount of front focus.
In a previous test I had tested the 50mm and 100mm lenses with the factory installed washer removed, resulting in back focus of about the same margin as front focus.

I had ordered 0.1, 0.15, 0.2, .25 and .3 washers and decided to install the .2 washer, which more or less hit the sweet spot. I may yet try the .15 washer at some later date, to bias the focus a little further to the back.

Here are some images that may help explain it all:

I created the pattern with Excel and turned the LCD display by ~45 degrees.
Through the viewfinder, the green square was in focus to my eyes.


After changing the washer. This shot is not entirely representative of all results; there is a small margin of focusing error in this one, but it's good enough to convey my point.


Some tools I used and a loose washers..., shot after adjustment.


And hopefully a clear shot of the retaining latches and the position of the "focus adjustment washer". The focusing screen has already dropped and is out of view. This is the mirror box from my K-7, which is more or less identical to the K-5.


I spent the rest of the available daylight taking some "wide open" shots in the real world. But even with accurate/improved focus it can still be a challenge to get it right, but for now I'm satisfied.
I rarely shoot wide open. Lets say I'm more inclined to do it more often. Practice, practice and practice...
K-5, SMC-M 100mm/F2.8, 1/800sec @F2.8, ISO 100

[wlachan]

I am not sure how I should feel after reading this. You can't trust the AF, then you can't trust the focus screen. Boy. Appreciate your post anyway.

[kdre]

Thx. for sharing. Very informative.

[Harald]

I am not sure how I should feel after reading this. You can't trust the AF, then you can't trust the focus screen. Boy. Appreciate your post anyway.

Well, I do know people who think that if they have an box of matchsticks, at least the tips are in the wrong end of the box... you seem to be one of them.

[Snydly]

So to understand this completely, the 'washer' can be removed and replaced with a different size? I've seen photos of the focusing screen being removed but thought the metal retainer was just that, a 'tray' to hold the screen in. This retainer can be removed and replaced with a different size which moves the focusing screen to adjust manual focus? What are the shims I've read about and where do they fit in the scheme?

Thanks for the tech...

Bill

[Catalana]

I am not sure how I should feel after reading this. You can't trust the AF, then you can't trust the focus screen. Boy. Appreciate your post anyway.

It is what it is...there always will be sample variation, and this happens to be so on the K-5 I own. But it does not mean that all K-5's have this issue.

[Catalana]

So to understand this completely, the 'washer' can be removed and replaced with a different size? I've seen photos of the focusing screen being removed but thought the metal retainer was just that, a 'tray' to hold the screen in. This retainer can be removed and replaced with a different size which moves the focusing screen to adjust manual focus? What are the shims I've read about and where do they fit in the scheme?

Thanks for the tech...

Bill

The focusing screen sits in a hinged tray that is held in place by a retaining latch.
So , you could replace the screen if you want to, with different types of lines or grids etched into it. These grids would usually aid composition. Then you can also get a "Katz-Eye" focusing screen, which is considered a "focusing aid".

But this is not what I am posting about. Once you drop the focusing screen tray (it is still attached and the focusing screen is resting in the tray, but the assembly is out of view in the images above), the small latch for the focusing screen washer becomes accessible. Disengaging it will allow you to take out the washer (shim). The washer (shim) sits between the focusing screen and the penta-prism.

Here is another shot that should help you visualize the set-up...

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Last edited by Catalana; 04-30-2011 at 10:16 AM.

[Snydly]

I understand now, thanks. So you can get these washers from Pentax? Are there third party equivalents (just curious). I ask because because I would really like to have the ability to Manually Focus better.

[Catalana]

Getting them from Pentax would be advisable. They are less than a dollar each, but shipping is about $8.- (via UPS). Look at the link in my first post.

[Snydly]

I understand all the mechanics now. I also understand you can get Katz-eye screens and some from Focusingscreen.com, but what I'm curious about is the fact that I've read about people using pieces of tape to shim a screen. Are they in fact just adding to the size of the 'washer' you're talking about?

Thanks again...

[Catalana]

I can't answer that question from experience, but it would seem to me, that the screens themselves vary in thickness. Some people have cannibalized and modified screens from older Pentax bodies, even from other makes, like Canon. With some care and a sharp blade, one can cut strips of tape and use them to calibrate the focusing screen. I'll leave that to more adventurous folks. If every Dollar, Peso or Rubel counts, it might be the way to go, but I'd rather have a proper washer in my K-5.

[asdf]

I understand all the mechanics now. I also understand you can get Katz-eye screens and some from Focusingscreen.com, but what I'm curious about is the fact that I've read about people using pieces of tape to shim a screen. Are they in fact just adding to the size of the 'washer' you're talking about?

Thanks again...

I've used postit note paper shims. The idea's the same. I'd rather go the OP route though...

[Gator]

excuse my ignorance but I dont get it, what are you actually trying to acheive ? if you shoot with manual focus you turn the focus ring until the image is in focus what does ajusting the camera do ?

is it something to do with the focus indicator when used manually ?

[asdf]

excuse my ignorance but I dont get it, what are you actually trying to acheive ? if you shoot with manual focus you turn the focus ring until the image is in focus what does ajusting the camera do ?

is it something to do with the focus indicator when used manually ?

When focusing you're looking at the image made on the focusing screen, not the sensor, unless you're using live-view. You want the distance between the mirror and the image on the focusing screen to be equal to the distance between the mirror and the sensor. If something's off by a fraction of a millimeter, you'll get out-of-focus shots.

[jolepp]

excuse my ignorance but I dont get it, what are you actually trying to acheive ? if you shoot with manual focus you turn the focus ring until the image is in focus what does ajusting the camera do ?

is it something to do with the focus indicator when used manually ?

Umm... no. Unless the length of the light path to the ground surface of the focus screen is the same as that to the sensor surface there is going to be BF / FF even when something looks perfecly focused in the viewfinder, hence the shims.

In reality this might be more complex, but that would be the main idea I gather? One thing is that modern focus screens add to the DOF as it appears looking through the viewfinder ... Actually, for best MF results the mirror should reflect all the available light to the focus screen - this would disable AF, of course, but would add about a stop to the brightness of the viewfinder (?).