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12-08-2010, 11:59 PM   #1
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Severely Backfocussing Lens - options?

Hey all. So, with the magic (measurebating) of focus charts, I found out my K-x overall backfocuses quite a bit. Luckily, with a bit of googling, I found the debug mode, and with an adjustment of +120 (which seems a bit severe), most of my lenses are pinpoint accurate - I actually shot a basketball game today with my FA50, and even at F2 under relatively dim (gym) lighting, I got quite a few keepers.

I assume then, that that means it's my K-x backfocussing, and not (most) of my lenses, since the +120 more or less fixes all of them.


However, I've found, also, that my favorite lens, my D-FA 100/2.8 WR, backfocuses quite a bit - in fact, it takes a +200 to get it perfect, and anything less or more than that gets both it and my other lenses totally OOF on most shots. Since it's still under warranty, but I bought it from B&H (I live in Canada), what are my options?

-Do I have to send it to the US to get it repaired?
-How long will it take, and would I have to ship my K-x with it? I can live for 6 weeks without my 100mm, but 6 weeks without a camera...

Thanks for your help

12-09-2010, 06:21 PM   #2
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C'mon guys, 119 views and nobody knows a thing?
02-25-2012, 05:05 AM   #3
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Took a while but here it is. I've got the same problem but then in front-focus.
And the thing that worries me is that is appeared suddenly. Situation: I recently got my DA 35/2.4 AL and out of the box it took spot on, tack sharp images. Yesterday however I noticed that sharpness has disappeared, whatever I tried. Needed even to switch to manual focus mode to improve things. Unfortunately, manual focus with the small OVF without split-screens etc. and my ageing eyes is not as good as the standard autofocus normally.
Created the debug mode file and started experimenting. It turns out that somewhere between +13 and +14 the ideal correction should be but this can not be set. It seems that the numbers are cm's in front or back of the target so I'm still 5mm off. I used a coarse grained piece of paper with written lines to focus on.

Question is, how can the focus change so suddenly? I cannot remeber dropping or bumping the camera so it shouldn't be a mechanical issue.
Does anybody know what the other test items in the menu mean and how to use them?
02-25-2012, 12:39 PM   #4
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sorry jaieger am not here to lend a hand but the other way around...
have the same problem with my tamron before, problem is i cant copy the debug file on my card. can you possibly show me how? am not a techie person... thanks. by the way i also have the k-x

02-25-2012, 01:03 PM   #5
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Is the lens still in the returning period? since the body problem is solved for most lenses maybe you can return and change the 100mm lens... Even if you changed your camera you would still have the problem either with the bulk of lenses or the 100mm since they seem to be quite apart.... I would ask myself what has changed since before the charts to start bothering me.
You can always save up and buy or upgrade to a body with the microadjustments for the lenses...
How long have you owned the camera? because if it's out of the return period i find it pointless to send it back since you already figured out how to solve the problem with the debug mode...just try an average adjustment that'll work reasonably well with the enses you own and the settings you normally use...
02-25-2012, 01:06 PM   #6
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QuoteOriginally posted by HoBykoYan Quote
sorry jaieger am not here to lend a hand but the other way around...
have the same problem with my tamron before, problem is i cant copy the debug file on my card. can you possibly show me how? am not a techie person... thanks. by the way i also have the k-x
The easiest way is to create the new file on your pc, if you use Windows open Notepad.exe or another text editor, type the following:
[OPEN_DEBUG_MENU]
hit enter so the prompt jumps to the next line
Then save and close the file.
Then rename the new file to MODSET.xxx, in every case people used 492 for the xxx in case of K-x, so did I and it works. (So it is called MODSET.492 then...).

Now the question remains why you can't copy the file to your SD cart. Is it write protected? Is it full? Can your computer read the contents of the SD?
Do you insert the SD directly into the computer or do you use a USB-cable to connect the camera? Is it an SDXC so you need to update drivers (and also firmware on K-x) to be able to use it?

Perhaps try another SD to copy the file and insert that one...


Additional to the above, the distance measured to correct probably incidentally coincides with the number of 'um' of the correction scale. Now I'm still interested what 'um' is... Unless they mean micrometer, which can only mean some internal correction, whatever it may be.
02-25-2012, 06:11 PM   #7
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QuoteOriginally posted by Twarp Quote
It seems that the numbers are cm's in front or back of the target so I'm still 5mm off. I used a coarse grained piece of paper with written lines to focus on.
There is no way to know which line the camera tried to focus on - it isn't necessarily the one directly under the red dot for the focus point you have selected. Those red dots are just approximations. The camera can legitimately choose to focus anywhere in general vicinity of that red dot.

Bottom lime: your test is invalid. Chances are, thee is no problem at all, and it's just faulty testing methodology fooloing you into thinking thee is a problem. It is much, much easier to conduct a completely bogus focus teat than to do it right.

Feel free to post same images and we'll probably be able to explain how and why the camera is simply choosing to focus somewhere other than where you intended, and how you can take steps to make the camera focus focus where you want. But thee is practically zero chance that this is a lens problem based on your description.
02-26-2012, 06:34 AM   #8
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Marc, you are right when you say there's no scientific ground in my test. However it is clear that without correction it suddenly focuses in front of the center spot of the focusing screen. Unfortunately the K-x doesn't have any red dots. Then it was trial and error to finally conclude sharpest focus should be in between a correction of +13 and +14um. Trying to focus on a grainy, contrasty brick wall from a distance of 1m is also only acceptable with these corrections made. In every case I made sure that AF was in AF-S mode and used only the center spot, wherever it may be in relation to the real center, it seems to coincide altogether. I always use lens hoods whenever possible so also in this case.

Reset the AF correction to zero, disabled debug mode, switched off and removed the batteries. After inserting them again took some shots at different distances. When enlarged 16 times, the center spot is blurry at each distance in the room.
Went into debug mode again, set it to the +13um correction I found out yesterday, reset everything again and repeated the first shots. Now quite some improvement in sharpness at the center spots, almost as good as it can be I guess.

Did a quick cross check with the kit zoom 18-55 and this one is as sharp as the 35mm (after the correction set). I conclude therefore that there's nothing wrong with the lenses but something happened with the K-x. I'm getting a bit tacky now: no red dots to show what it is really intending to do, wandering focus... Time to upgrade?

My test SD with the debug hack-file is only 32MB (use it only for firmware updates) so it had to be erased several times during test shooting. Think I'll put the file on every SD I have, just in case...

02-26-2012, 06:45 AM   #9
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Hi Adam, i already copied it to my sd. problem is i cant access the debug mode. tried the av+\- together with the on switch nothing happens. thanks and pls bear with me.
02-26-2012, 08:49 AM   #10
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QuoteOriginally posted by Twarp Quote
Marc, you are right when you say there's no scientific ground in my test. However it is clear that without correction it suddenly focuses in front of the center spot of the focusing screen.
Then can you post the tests that demonstrate this? As I've said many times, it is much easier to screw up a focus test than to get it right. Nothing you've posted here suggests you'd be the exception. The brick wall test is perhaps better than the paper with lines.
02-26-2012, 05:02 PM   #11
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QuoteOriginally posted by HoBykoYan Quote
Hi Adam, i already copied it to my sd. problem is i cant access the debug mode. tried the av+\- together with the on switch nothing happens. thanks and pls bear with me.
Try following the more specific directions HERE.
02-26-2012, 08:58 PM   #12
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QuoteOriginally posted by HoBykoYan Quote
Hi Adam, i already copied it to my sd. problem is i cant access the debug mode. tried the av+\- together with the on switch nothing happens. thanks and pls bear with me.
Soo sorry for this, just noticed it now... This should be for Marc (my fault)...

@mgvh:
this is the same link i've been following but i don't know what's wrong since i can't access to the said debug mode...
i'll try to make it one more time and create a file.
02-26-2012, 11:26 PM   #13
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i really don't know what am doing wrong right now... i really can't open the debug mode... help....
02-27-2012, 02:08 AM   #14
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i have the Version 1.00 does this mean anything? will it help to solve the problem?

Thanks in advance
02-27-2012, 05:44 AM   #15
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@HoBykoYan: from the Ricehigh blog above it is clear that it works from any K-x firmware version to date, I have 1.02, perhaps you can try to upgrade first?
Can you define what you see when you switch on the camera? Did you make sure you hit [ENTER] when typing the line in de modset-file; the cursor needs to blink on the next line when you save it...

@Marc: in the previous posts I referred to a front-focus. Now such definitions are in the same league as stating 'the bridge is open', or saying 'sitting in front of the PC' versus 'sitting behind the PC'. I meant to say that the sharpest point in view was further away from the lens than the point-of-aim, thus 'more in front'. In all other posts that means back-focus so I'll switch to that point of view then

Since I'm not at home now till tomorrow there is no way to post pics to show the results of the correction now.
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