Focus adjustment - again

Has anybody found a relationship between the +/- 10 steps in the Custom Menu and the um values in the Debug focus adjustment?

Having one manual lens (Pentax-A 1.7/50) I was thinking of adjusting this lens using Debug, and compensate the other lenses using the Custom Menu.

Assuming that the Debug adjustment is global, and that the Custom Menu would be based on the basic (global) setting.

The Pentax-A 1.7/50 is a manual focus lens. Focus adjustment is for AF lenses. If your manual focus lenses are FF/BF, then you need to adjust your focussing screen with shims.

Disagree

focus adjustment is a perfectly normal thing for manual focus lenses.

Focus is OK when green hexagon is lit NOT when the image on the focus screen is in focus.

On an autofocus lens the 'focus ring' is turned by a motor on a manual focus lens the focus ring is turned by hand. A focus adjustment effects when the hexagon is lit regardless of the method by which the focus ring is turned.

So if a manual focus lens is lighting up the green hexagon but has a FF/BF issue then doing an all lens adjustment for one manual focus lens followed by specific adjustments for auto lenses recognised by the camera's library of adjustment for known lenses is a perfectly sensible thing to do.

Adjusting the focus screen with shims only effects the focus of the image seen in the viewfinder and I would suggest that the green hexagon is more usfull and (if adjusted correctly) more accurate than the viewfinder image to determine if the lens is in focus.

I have 4 Pentax DSLRs and 6 out of my 22 lenses are manual so I do have some experience of using manual lenses on cameras with focus adjustment.

Thanks for the clarification, Bob. This is also my understanding. And the green hexagon is very helpful also with manual lenses, especially when wearing spectacles.

Do you agree to my assumption that the Debug mode provides a basic adjustment, and than the Custom menu provides offsets from the basic setting?

yes, with the reservation that I haven't tried it!

Don't forget that on the K20D there is an 'all lens' adjustment in the menu which will apply to any lenses which do dont have a lens specific adjustment set up. I would adjust with your K20D before replicating the effects on your K200D as the changes should be easier to backout of.

Thanks, Bob

My original question still remains, though. What is the relation between the +/- steps in the Custom Settings menu (item 35) and the um (micrometres) scale in the Debug Mode?

I am referring to the K20D in both cases.

I'm afraid I have to disagree with your disagreement...

Focus adjustments apply small corrections to the autofocus system. A manual focus lens does not make use of the autofocus mechanism.

After installing a Katz eye and calibrating the autofocus for my autofocus lenses, I found that the correct focus point for my autofocus lenses were ever so slightly off (ie the green hexagon did not match the sharp focus point on the focus screen). In conversation with Katz eye, I was informed about focus screen shims and bought a few from Pentax. I found my Pentax k20d required a slighly smaller shim than the one that was shipped. Actually the real reason was that the Katz eye screen was slightly thicker than the standard Pentax focus screen. After changing the shim, the correct focus point as seen on the focus screen now matches exactly with the autofocus settings. And my manual focus lenses now match exactly with the appearance of the green hexagon.

Hope this helps,

Dick

yes it does!
You can have the AF active while you manual focus and it give you a signal when the AF thinks the lens is in focus.

Also with the rest of your comment you don't adjust the AF with your focus screen. You should adjust the AF with the help of photos you take and do the same with the focus screen.
The Sensor is the point you calibrate around.

Hi Stefan, That's exactly what Dick said, each one is adjusted independently so that they agree with one another.

Greg

You sure Greg, looks to me Dick was comparing the focus indication of the AF with his focusing screen. He never talked about the focus of his photos and that's what's all about.

No, how can one ever be sure about anything, it's all subject to interpretation. Maybe I read it the way I wanted to understand it.


Greg

But the green hexagon does, it confirms focus, even when using a manual lens. Therefore I find it useful to calibrate AF also for manual lenses.

Hi Stefan,

By the term "calibrate the autofocus lens" in my reply, I meant the process of shooting a target and changing the focus settings until all manner of front focus and back focus were removed. I used Yvon Bourque's target to accomplish that.

http://pentaxdslrs.blogspot.com/2008/06/part-1-autofocus-adjustment-for-pentax.h...

Once I was satisfied that the auto focus system was focusing correctly, I noticed that the sharp focus point set by the calibrated auto focus left the image on the focus screen slightly out of focus.

I then began a new set of tests using manual focus lenses, ignoring the green hexagon and focusing using the focus screen. The Katz eye makes this very precise with it's split image focus feature. That was when it became clear that the focus screen was not properly positioned under the pentaprism - ie a smaller shim was necessary.

When using manual focus lenses, I prefer to focus on my chosen target via the split image on the focus screen. After replacing the shim, this focus point matches the green hexagon perfectly.

Hope this clears the matter up...

Dick

When you don't have a Katz Eye, and your own eyes are not what they used to be, I find it easier to focus manually with the assistance of the autofocus system, i.e. the green hexagon focus confirmation. For that to work one needs to calibrate the AF system.