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07-15-2008, 10:50 AM   #1
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Front focusing while wide open???

I’m new to DSLR world and not sure if this is normal thing or some kind of AF problem. My K200D with DA 15-55 II lens attached front focuses on close shots when lens wide open. It’s not just soft, it’s definitely FF. I tried couple of tests and found that at max aperture (all focal lengths) it is 5-10 mm front focused, and focuses correctly when stopped down approximately 1 stop (sometimes 1 1/3). Particular numbers came from test I found here: Nikon D70 Focus Chart

I used to have DA 15-55 (not mark II) and did not notice any problems. However, with a new Mark II lens, I just got, focus on some of my “macro” shots is off. It’s especially evident when I shoot in Av mode and open lens all the way: many of the pictures not just soft, but focused on the wrong part of the subject. I haven’t noticed this with DA 55-300, but with min focusing distance of 1.4 m a few millimeters don’t make a big difference anyway.

I assume that AF is off, but I can really see it when lens is wide open and the depth of field id the shallowest. Is this a problem that I need to worry about or it’s just a normal practice?

Here is a sample image of what I described: http://www.aimagehosting.com/images/tr5nc0kypak89tf2wvb.jpg


Last edited by x_goal; 07-15-2008 at 11:46 AM.
07-15-2008, 01:42 PM   #2
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Hmmm

From your description and test shots, if you did them "by the book", it seems your problem is of "back focus", not front focus. But to be honest, the sharpest (at wide open) seems to be around the 2 mm line, and probably between the target text line and the 2 mm line. As you stop down, the depth of field increases towards the back of subject (as it should).

Considering such test was done at "closest focusing distance" with this lens, I would say that such test results prove that your lens is "within acceptable tolerances).


Anyone correct my if I'm wrong, but IMHO, such minuscule difference is nonsense with this "kit lens".

RB
07-15-2008, 02:05 PM   #3
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I assumed it's front focus because following picture is described by Tim Jackson (Nikon D70 Focus Chart) as back focus.



What I've got is kind of opposite - the focus seems to be in the front of the subject, not behind. However, I might be wrong.
I tried to the best of my ability set camera at exactly 45 degrees to the chart and keep it still... And the test shots showed missed focus at high aperture very consistently. the set I posted is just a representation of about 15 sets of shots I took with different focal length and distance.
I just wasn't sure is it's within tolerances or this camera-lens tandem is not working properly

Thanks
07-15-2008, 02:27 PM   #4
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One word of advice when testing. Do it in natural light, not artificial light.

07-15-2008, 02:42 PM   #5
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QuoteOriginally posted by pschlute Quote
One word of advice when testing. Do it in natural light, not artificial light.
Well, It was done in artificial light: incandescent light + flash... If it is not acceptable, just let me know - I'll try to set this up outside when weather is good!
07-15-2008, 03:37 PM   #6
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QuoteOriginally posted by x_goal Quote
I’m new to DSLR world and not sure if this is normal thing or some kind of AF problem. My K200D with DA 15-55 II lens attached front focuses on close shots when lens wide open. It’s not just soft, it’s definitely FF. I tried couple of tests and found that at max aperture (all focal lengths) it is 5-10 mm front focused, and focuses correctly when stopped down approximately 1 stop (sometimes 1 1/3). Particular numbers came from test I found here: Nikon D70 Focus Chart

I used to have DA 15-55 (not mark II) and did not notice any problems. However, with a new Mark II lens, I just got, focus on some of my “macro” shots is off. It’s especially evident when I shoot in Av mode and open lens all the way: many of the pictures not just soft, but focused on the wrong part of the subject. I haven’t noticed this with DA 55-300, but with min focusing distance of 1.4 m a few millimeters don’t make a big difference anyway.

I assume that AF is off, but I can really see it when lens is wide open and the depth of field id the shallowest. Is this a problem that I need to worry about or it’s just a normal practice?

Here is a sample image of what I described: http://www.aimagehosting.com/images/tr5nc0kypak89tf2wvb.jpg
Your case is almost exactly the same happened to my.....Normal!!!!!!!!
My K200d+kit Mk2, when open its F- number at F4.5, F4, F3.5... Picture found soft in portrait shots. Sharpness only acceptable starting from F8 onwards. I took shot at F4.5 on one street in Sham Shui Po at 5-6 pm. The focus almost run away.
After checking (indoor and outdoor), it was front-focusing (8-10%). The amount of F-F depends on the F-number. In fact, I concluded that the focus depnded on the F-number really.

I sent it to repair, afterwards, picture sharpness is OK. But at wide angle end (18mm,24mm,30mm) and at F3.5, F4, F4,5 or even F5.6, when shot objects far away (more than 8-10m) by using AF, the focus ring turned passed through the infinity mark and hit the hard-stop end.

Then I try the DA 18-55 old version in a shop in Hunghum, found no problem. I also bought DA 35 F2.8 macro limted... No such problems.

The problem is partially caused by the Mk2 Lens. But I also think the CCD position of K200d is constructed or placed a little bit too backwards that it left almost no margin for the technician to make fine-tune. (Believed a production QC problem there)

Good luck.

PS: When I was checking, I tried taken picture at 0.35m, 0.8m, 1.5m and 2.2m always also

Last edited by ckanthon; 07-15-2008 at 05:28 PM.
07-15-2008, 09:21 PM   #7
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my 1.4/50 front focuses severly when autofocus is used with halogen lights. nateral light no problem. halogens, front focus.

No idea why.
07-15-2008, 11:01 PM   #8
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May I suggest you check this out:

AF adjustment test chart to help with the Pentax K20D Custom Setting No.34 - Digital Cameras - Zimbio

PART-1. Autofocus Adjustment for the Pentax K20D, Custom Setting No 35 - Digital Photography - Zimbio

PART-2. Autofocus Adjustment for the Pentax K20D, Custom Setting No 35 - k10dbook - Zimbio

These are specific articles to using this fellow's focusing charts with Pentax cameras. He is a Pentaxian and is in talks with Pentax about having his charts made "official" with them.

NOTE: The first link is good to see how to fold the chart. The second and third links are for the "newchart" which he also has posted at his website. I don't think he wants anyone to use the chart that is shown in the first link anymore.

Especially read and re-read his description of how to read the results.

Kent


Last edited by ksignorini; 07-15-2008 at 11:04 PM. Reason: Added info.
07-16-2008, 01:05 AM   #9
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QuoteOriginally posted by KungPOW Quote
my 1.4/50 front focuses severly when autofocus is used with halogen lights. nateral light no problem. halogens, front focus.

No idea why.
I have no idea why either, but I noticed variations in A/F under artificial light. This is why I suggest to the OP to test outside.

Given his location, he should have less trouble than me in finding a dry bright day!
07-16-2008, 11:11 AM   #10
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Thanks you all, guys! I did the tests with the test charts developed by Yvon Bourque (see above links posted by Kent) and guess what… It was just my lack of experience combined with wrong testing techniques, nothing more than that. But I have to tell that AF checking chart he developed is much better than others I’ve seen and easier to use as well.
The only one thing from his directions that I did not follow – I flipped chart upside down, so I did not need to set camera too high (I don’t own tripod or grip). This way I just found a book of right thickness and set camera on it. However, this should not matter because chart was at 45 degrees to camera; only numbers are upside down… Also I set everything next to the window so there was enough of natural light. This time the focusing with wide open lens was consistently on the target (I would say 90% of the shots).
The only disadvantage of the chart – the paper of the target must be of good quality and flat. Otherwise, the focusing point and markers on the sides might be in different planes. We are talking here fractions of millimeter, but still worth checking.
Just for comparison I post another sample of shots taken at approximately the same focal length that first sample.

http://www.aimagehosting.com/images/88280rqoka0yc0fam6p7.jpg

So, I’m happy with my lens and camera; just need to work on “shake reduction” in my hands and developing good photographing techniques…
Thanks all!
07-16-2008, 11:08 PM   #11
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QuoteOriginally posted by x_goal Quote
Thanks you all, guys! I did the tests with the test charts developed by Yvon Bourque (see above links posted by Kent) and guess what… It was just my lack of experience combined with wrong testing techniques, nothing more than that. But I have to tell that AF checking chart he developed is much better than others I’ve seen and easier to use as well.
The only one thing from his directions that I did not follow – I flipped chart upside down, so I did not need to set camera too high (I don’t own tripod or grip). This way I just found a book of right thickness and set camera on it. However, this should not matter because chart was at 45 degrees to camera; only numbers are upside down… Also I set everything next to the window so there was enough of natural light. This time the focusing with wide open lens was consistently on the target (I would say 90% of the shots).
The only disadvantage of the chart – the paper of the target must be of good quality and flat. Otherwise, the focusing point and markers on the sides might be in different planes. We are talking here fractions of millimeter, but still worth checking.
Just for comparison I post another sample of shots taken at approximately the same focal length that first sample.

http://www.aimagehosting.com/images/88280rqoka0yc0fam6p7.jpg

So, I’m happy with my lens and camera; just need to work on “shake reduction” in my hands and developing good photographing techniques…
Thanks all!
Thanks for your attached test result. Good for my reference as well. Thank you.
07-18-2008, 10:01 PM   #12
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QuoteQuote:
my 1.4/50 front focuses severly when autofocus is used with halogen lights. nateral light no problem. halogens, front focus.

No idea why.
The AF used by pentax (SAFOX VIII ) is wavelength dependent ... is a well documented problem of the pentax AF.

RiceHigh's Pentax Blog: AF Accuracy's Dependency on Lenses and Yellow Light
11-27-2010, 12:03 AM   #13
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I do have a problem with my K5 and TAMRON 17-55/2.8
At 2.8 aperture at 55 mm there is front focussing . stopped down to 4.0 the issue is gone.
Any suggestions ?
11-27-2010, 10:32 AM   #14
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The K5 has a calibration option in the custom menu. Read the user manual; page 126

Please show some pictures that demonstrate the issue.
11-28-2010, 12:42 PM   #15
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Hi Sterretje , thanks for reply. I had the camera and lense combo callibrated by PENTAX (de Beukelaer) . I had tried myself to callibrate the initial delivered camera but had to go beyond - 10 in this .
Now the AF after "repair" is spot on in daylight but in dimmer light and with use of flash the focus is completely off. When I take a pic at 50mm 2.8 with my TAMRON 17-55 2.8 lens (that was send together with the camera to callibrate) with flash in artificially lit room it is a total blurry (front focussed again) shit ! Tried the same with my K7 . Same lens and other variables and here the pics get sharp. FAULTY K5 or General problem ?????
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