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08-16-2013, 10:00 PM   #1
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K10D - Getting Sharp focus in NON-AF region

I recently got a K10D for myself from ebay. It has firmware 1.10

I prefer using manual lenses on my Pentax bodies and so I mounted a 50mm 1.7 & 1.2 on the K10D. As expected there were some focusing issues and so I went to debug mode and calibrated af area 1 with a number of 40+ and getting very sharp focus on the part where camera is focused and I get the focus confirmation signal.

Now when I shoot pics where subject matter is not in centre of the pic and is instead on the sides outside of the focus confirmation region I tend to get out of focus shots, even though I can see through the viewfinder the image seems to be in very sharp focus. I went to debug mode and increased and decreased the numbers but no luck its always out of focus. My viewfinder's dioptre has been calibrated perfectly so I doubt it's that.

I have uploaded two pics to illustrate the problem, they can be seen at the end of the post.

I shot the top right corner of my computer screen [my way of judging focus was to see strong 'etchings' or moire like patterns appearing in viewfinder to confirm its in sharp focus]

I want to know if any of you experience a problem like this and if yes whats the work around to it?

I also want to know is it true if you use lenses with very wide apertures such as pentax 1.2 the pentaprism + viewfinder on the k10d might not be able to handle the large amount of light passing through that it shows image in focus when in fact its out of focus?

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Last edited by aruk5; 08-16-2013 at 10:10 PM.
08-16-2013, 10:12 PM   #2
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I've had to fine-tune AF on my K10 as well. I would suggest going outside in daylight to make adjustments. I could never accurately fine-tune the AF using indoor lighting on my K10. I think indoor lighting, especially tungsten, plays tricks on the AF system.
08-16-2013, 10:28 PM   #3
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Perhaps the lens is to blame? If you're focusing on something outside of the AF region, wouldn't you need to use manual focus instead of auto focus?

Adam
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08-16-2013, 10:33 PM   #4
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I have the K10D and can confirm that light with a strong red component (tungsten) will trick the AF system. Use daylight if you can -- or just use consistent lighting when doing tests.

If you want to use the pktether software, you can enable debug mode which will give your K10D the ability to move the AF focus setting. I have identified the proper setting for my bodies for tungsten vs daylight. Flourescent lights are a tough one as they could be amber or blue. Under those lights, I use my eyes.

I found that the AF setting of 140 um works for daylight and 90 um works for tungsten.

Note that there are different steps for tuning the AF system and tuning the focus screen. Do the AF first, then you can do the focus screen. THe stock screen on the K10D was known to have issues with handling bright lenses as it would show more available DOF than the lens would provide -- you'd see more in focus than was actually captured. Several aftermarket screens solve this issue.

EDIT:

On re-reading your note, I think I see what you are asking:
You are looking through your viewfinder at a target that is off center. Looking at the display of moire patterns on a computer screen is actually not a confirmation of focus. I just tried it with my monitor. What you are seeing with that pattern is interference between the grain of the matte of the focus screen and the lcd display. Instead, look for sharpness of lines - or if you have a diamond mesh area in the center of the field of view - a clear view that's not fuzzy.

Another thing to check is to ensure that the diopter of the viewfinder is set properly for your eyes. You will need to adjust the slider above the viewfinder until the guidelines are sharp. Your eye should be as relaxed as you can be. A trick is to not focus on anything and just look at one line as you rack the slider back and forth. You'll see a point where the lines are sharpest. This is the spot you want as you are viewing the image cast on the ground glass and you'll want it to be in focus so that you can judge proper lens focus.

...And don't blow away that 1.10 firmware. If you go to higher than 1.30 (current firmware is 1.31) then you can't hack to get the quick method of defeating SDM. Although, there are ways of loading lens firmware now so this is not as big of a deal.


Last edited by smigol; 08-16-2013 at 10:47 PM.
08-16-2013, 10:53 PM   #5
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Using the optical focus screen to calibrate the AF does not work very well. As smigol mentioned above, the stock screen shows DOF equivalent to about f/4 regardless of the true maximum aperture of the lens mounted. Live view is the better solution, but you need a newer camera to get that feature. I have used the moire method with good results, but it only works with a taken image or live view of a special test pattern*. Moire in the viewfinder is not the same since it is interference of the screen dots with the fresnel lens not the plane of focus. The bias can be significant.

That being said, using focus confirmation for manual focus is sort of hit or miss. The AF system is really not that precise at best and missed focus is pretty much the norm with faster lenses. I was pretty unhappy with my results with faster lenses until I got a Katz Eye aftermarket screen with a split image focus aid. Suddenly things were sharp where I wanted them to be sharp.

As for things only being sharp in the center AF area...that would be a lens issue.

Note: AF fine adjustment using debug mode on the K10D is specific to a single lens only...the one used for the adjustment.

Steve

* Link to article on how to do this...very cool: http://www.northlight-images.co.uk/article_pages/cameras/1ds3_af_micoadjustment.html

Last edited by stevebrot; 08-16-2013 at 11:14 PM.
08-16-2013, 11:24 PM   #6
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QuoteOriginally posted by stevebrot Quote

Note: AF fine adjustment using debug mode on the K10D is specific to a single lens only...the one used for the adjustment.

Steve

* Link to article on how to do this...very cool: AF microadjustment for the 1Ds mark III, 1D Mk3, 5D Mk2, 7D, 1D X
The K10D adjustment is for the body - thus effecting all AF lenses. I believe that the later cameras had AF adjustments that were lens-specific.
08-16-2013, 11:34 PM   #7
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Hey all! Thank you for quick replies! Nice to know this forum has active participants!

Paul - My problem is while using manual lenses such as the pentax 50mm 1.2 or 1.7. The 'AF' I am referring to is actually the focus confirmation centre dot you get while using manual lenses. Regarding your point about the differences in white balance settings I am yet to try it but will do so soon!

Adam - I doubt my pentax 50mm 1.7 or 1.2 are faulty as pics look super sharp when shot using focus confirmation its only the off-centre portion of the pics which appear to be out of focus even though when i view through the viewfinder they appear to in focus and unfortunately the k10d doesnt give any focus confirmation when clicking images off centre or away from the focus confirmation area [which is in the centre of the viewfinder]

smigol - Well although I used a computer monitor to demonstrate my point I must mention that I also tried the same with coarse fabric or the carpet where you get some etchings or markings or straight lines when seen through the viewfinder but they too appeared to be out of focus. My diopter has been calibrated to my eyesight. I will check out the pktether software and see if it helps. The option of moving af settings seems interesting.

stevebrot - Your point about the dof of the stock screen designed for f4 makes sense as when I use the pentax 50mm 1.2 or 1.7 at widest aperture the off centre portion is out of focus but when I use it at f4 and above the focus accuracy is much better! I will certainly consider going in for katz eye focus screen as lots of pics i shoot are at wide apertures.
08-17-2013, 07:17 AM   #8
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QuoteOriginally posted by smigol Quote
Another thing to check is to ensure that the diopter of the viewfinder is set properly for your eyes. You will need to adjust the slider above the viewfinder until the guidelines are sharp. Your eye should be as relaxed as you can be. A trick is to not focus on anything and just look at one line as you rack the slider back and forth. You'll see a point where the lines are sharpest. This is the spot you want as you are viewing the image cast on the ground glass and you'll want it to be in focus so that you can judge proper lens focus.
An easier way to set the viewfinder diopter is to remove the lens and point the camera at a uniformly lighted surface. Adjust the diopter so the in-viewfinder text is sharpest. The point here is to not be distracted by the image. Both the text and the focusing screen are meant to be viewed at infinity - which is what the viewfinder optics do and the diopter adjustment tweaks for the user.

By the way, IF you swap out the stock focusing screen and need to use shims, do the above first and then without changing the diopter setting, swap shims until the image with a lens focused at infinity is as focused as the text.

08-17-2013, 08:36 AM   #9
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a late discovery i just made is that under debug mode when you have set af mode to 1 [both horizontal and vertical points enabled] and the af dial is set to sel you can toggle the af points to your choice! I was under the impression that unlike the k-x and k110d's debug mode which let you select the af point, the k10d didnt allow you to do so [when manual lenses are mounted on them]. it wont if af mode is set to 0 but when set to 1 it does! well this has solved my problem to a great extent as now i can compose off centre shots and use the left or right af points for focus confirmation.

Jim - i use the same method to set my viewfinder diopter. I Keep the lens out of focus and adjust diopter till the view finder marking appear sharpest. this method is ofcourse not useful with cameras such as the kx which dont have any viewfinder markings on them! anyways thanks for the reply

Last edited by aruk5; 08-17-2013 at 08:50 AM.
08-17-2013, 09:54 AM   #10
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QuoteOriginally posted by aruk5 Quote
not useful with cameras such as the kx which dont have any viewfinder markings on them! anyways thanks for the reply
I guess you misunderstood what I meant by in-viewfinder text. Of course the K-x has this information. The shot below is taken from the K-x manual. If you move the diopter lever so this text is in focus, you don't have to worry about whether or not the lens is properly focused when setting the viewfinder for your specific vision.
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08-17-2013, 10:31 AM   #11
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QuoteOriginally posted by JimJohnson Quote
I guess you misunderstood what I meant by in-viewfinder text. Of course the K-x has this information. The shot below is taken from the K-x manual. If you move the diopter lever so this text is in focus, you don't have to worry about whether or not the lens is properly focused when setting the viewfinder for your specific vision.
Jim - My mistake! I got a bit confused when I posted my reply! Ofcourse the kx does have the markings but what they dont have are the focus indicator lights/markings. Another reason why i think I said that was the markings on my kx are very light and hardly visible most of the time that I stopped noticing them plus I shoot most of the pics using live view that i rarely use the viewfinder! Anyways thanks for pointing out the error! cheers!
08-19-2013, 08:26 PM   #12
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QuoteOriginally posted by smigol Quote
The K10D adjustment is for the body - thus effecting all AF lenses.
This is true. Any adjustment will effect all lenses. Unfortunately, changing the factory setting may not be a good idea. AF focus bias is usually not an issue of body calibration, but may instead be related to how well the lens focuses light, the focus mechanicals, and how the AF system works*. Debug mode on the K10D does indeed adjust the body, but perfect for lens "A" may not be so good for lens "B". Adjustments as part of the menu system was introduced with the K20D and are always specific to the lens mounted and are also limited to AF lenses. Ditto for subsequent models.


Steve

*I used to have a link to a great discussion with animated illustration showing how the AF system works and why calibration is needed for some lenses.

Last edited by stevebrot; 08-19-2013 at 08:35 PM.
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