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09-09-2007, 10:03 AM   #1
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Need help evaluating results from focus test

Ever since I got my K10D I've been a little vary about the AF. Today I decided to test the AF using this test procedure.

When looking at the results they are not conclusive and I need some help. This is wher you come in , could you please spend a few minutes helping me evaluating these JPEGs directly from the camera and post you opinion.

F 100mm macro at f/2.8

FA 50mm at f/1.4

FA 35mm at f/2.0

DA 16-45mm at 16mm and f/4.0

DA 16-45mm at 34mm and f/4.0

Thanks in advance
Paul


Last edited by pdmlmember; 09-18-2007 at 10:29 PM.
09-09-2007, 12:15 PM   #2
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Maggie
Looked at your posted photos (The largest versions) and if I had to pick at the results this is my take:
The 16-45, slight back focus ( both at 16 and 34)
FA 35, looks perfect to me
FA 50, slight front focus
F 100 macro, slight front focus

Just my 5 cents worth.....

Cheers...

Jan
09-09-2007, 12:17 PM   #3
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Maggie, these look OK to me as far as I can tell from these small pics. A crop of the central area would help.

The AF system is not perfect but as long as the central bar is sharp it means it is within the depth of focus - thats as good as it can get when you think about it and means what you shoot will look sharp too.

You will find each lens will vary a bit between shots too depending on which direction the focus moves and lenses themselves are not perfect either.

Of course "perfect" focus would mean the sharp field would extend 1/3 in front and 2/3 behind but thats almost impossible to achieve using an AF system every single time. A lot of dedicated pros get their cameras and all lenses professionally calibrated by the factory.
09-09-2007, 12:39 PM   #4
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Although not perfect, in these sizes they all looked acceptable to me.

09-09-2007, 01:03 PM   #5
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QuoteOriginally posted by Maggie Quote
Ever since I got my K10D I've been a little vary about the AF. Today I decided to test the AF using this test procedure. (snip)

It's very difficult to make fine distinctions, Maggie, because camera shake caused some fuzziness in each picture. The center point is not really crystal sharp in any image. However, disregarding this, the focus itself looked reasonably fine in the three or four images I looked at (the larger versions).

So, if these are typical of your images, it appears you need to address camera shake far more than focus. Go back to the basics of proper arm placement for holding the camera steady, holding your breath during the exposure, and pressing the shutter release button gently to avoid jerking the camera. In lower-light situations, use a strong (not cheap) tripod to keep the camera steady during longer exposures, or raise ISO to allow faster shutter speeds, or add light to the scene to increase shutter speeds, or a combination of these.

Of course, make sure the anti-shake feature of the K10D is turned on, but this is not a cure-all for weak camera technique. You still need to make a reasonable effort to hold the camera steady, especially during longer exposures. If that is just not possible, then you need to avoid longer exposures by somehow increasing the shutter speeds as described in the previous paragraph.

stewart

Last edited by stewart_photo; 09-09-2007 at 01:08 PM. Reason: spelling
09-09-2007, 01:25 PM   #6
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First of all thanks for your input, keep it coming.

Stewart,
All these photos were taken with the camera on a tripod using a wireless remote and 3s mirror lockup. Also the antishake was turned of and single spot (center) AF used. The only thing I can see causing camera shake is the floor. Your comment makes me wonder, is there something wrong with my camera?
09-09-2007, 01:41 PM   #7
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Maggie,

I do not want to cause a firestorm amongst those who are more technically-minded than me, however, I feel you should do yourself a favor and go shoot some photos of people and other scenes you might normally use your camera for.

If you are happy, then forget about all this front focus, backfocus and all of it and enjoy your camera, if you arent, then investigate further.

I sell photos to clients (wedding and portrait) and to date, even with all the discussion about this lens or that, I have not had any problems or complaints about my photos.....you'd think with all the lens dicussion, I'd at least get one bad lens...eh?

Anyway, just my thoughts.

PS
09-09-2007, 02:15 PM   #8
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QuoteOriginally posted by pentaxshooter Quote
Maggie,

I do not want to cause a firestorm amongst those who are more technically-minded than me, however, I feel you should do yourself a favor and go shoot some photos of people and other scenes you might normally use your camera for.

If you are happy, then forget about all this front focus, backfocus and all of it and enjoy your camera, if you arent, then investigate further.

I sell photos to clients (wedding and portrait) and to date, even with all the discussion about this lens or that, I have not had any problems or complaints about my photos.....you'd think with all the lens dicussion, I'd at least get one bad lens...eh?

Anyway, just my thoughts.

PS
I agree with pentaxshooter.

Looking at the images you posted, focus in all is well within what I would regard as 'normal limits'. As has already been pointed out, different lenses have different characteristics and will therefore give slightly different results.

All your test shots were at or close to widest aperture and lenses generally do not perform so well at the extremes.

There is a tendency to expect that modern electronics can give perfect results time after time, which simply is not true. And test cards do not equal real-life situations.

You can drive yourself crazy looking for problems because you will find them! In the end photographic technique is what produces the best photos, not the camera....

Enjoy your photograohy.

09-09-2007, 03:07 PM   #9
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Maggie

Any possibility you can post some photos from your town? Perhaps some people shots too (especially closeups?)

You come from a beautiful part of the world....it would be nice to see it from the K10D's perspective.

PS
09-09-2007, 03:59 PM   #10
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QuoteOriginally posted by Maggie Quote
(snip) All these photos were taken with the camera on a tripod using a wireless remote and 3s mirror lockup. Also the antishake was turned of and single spot (center) AF used. The only thing I can see causing camera shake is the floor. Your comment makes me wonder, is there something wrong with my camera?

Due to the misspelling, I don't know if you meant the anti-shake system was on or off in the paragraph above. Of course, the anti-shake system should be off when using a tripod. Also, you didn't say which mode (RAW or JPEG) you were using during the test. The JPEG image algorithms could easily cause some fuzziness like this in the resulting images (an intentional effect intended to simulate the overall appearance of film in the final prints). Conversion of RAW files into JPEG afterwards could cause similar results.

Regardless, I don't think there is anything wrong with your camera unless you're seeing real problems with the final images. If that is the case, then consider having the camera repaired. Otherwise, I agree with the others; don't worrying about it. Some variations in focusing are routine, even within the same camera from time to time. These variations rarely impact images in the real world since they're all well within the tolerances offered by depth-of-field and so on.

stewart
09-09-2007, 10:50 PM   #11
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As a clarification for Stewart, you're right the anti-shake was turned of. Also I shot directly in JPEG.

Finally, thanks for putting my mind at ease. To me the results looked ok, but I wanted a second (& third) opinion. I normally don't do this kind of testing since I know myself being a little bit anal. I promise that I'll post some pictures of my part of the world later. Thanks everyone for your help.
09-10-2007, 02:10 AM   #12
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Glad to offer some comfort, Maggie. Of course, if you see any problems with your actual images, please feel free to follow up with a sample or two so we can perhaps offer something more. However, I suspect you'll find the end results very satisfying instead.

By the way, I just noticed the flickr site hosting your test images includes the EXIF data. Had I known that earlier, I obviously would not have asked which mode was used.

Anyway, welcome to the forum and the Pentax community as a whole. I hope you enjoy both and stay with us for a while. Take care.

stewart
09-10-2007, 05:23 PM   #13
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I just performed a focus chart test last night and would like to share my experiences.

I recently took some shots at a night concert using tamron 28-75 and fa50, and a lot of people commented that my shots are front focused. So I did a focus check using the famous D70 test chart.

I have Tamrom 28-75/f2.8, DA50-200 and FA50/f1.4. Since the tamron is my walkabout lens, I tend to focus on this lens first. Using the test chart and as per the author's instructions, I find that the lens is very much front focused indeed.

I then proceeded to set the "focus corr" value via the K100D debug service menu. After many trials and errors, I find that I need to set it to -220. A more detail test confirmed that this is incorrect. I need to set it to -350!! Now that is not a typo.

Then I tried the FA50/1.4, I need to set it to -80.

Then I tried the DA50-200. Due to the small aperture, the depth of field is much greater than the tamron and FA50, so the focus chart test is non-conclusive.

Now, K100D service menu can only have one focus corr value and out of desperation, I set it to -350 to suit my tamron. I thought this is all well but when I actually use the Tamron in real life shooting, the focus run back focus so much that it is not usable!

Put the k100D and tamron on the test chart again, the combo performed perfectly with -350 compensation. So I was freaked.

Then I decided to forego the test chart and adjust the focus corr myself. I set it to -100, -150, -200, etc and test and test. All no good. Finally, I set it to -50 and tested it!

Focus is spot on! With -50 focus corr, I also tested the FA50 and again spot on. This is the final value I settled with and I am not going to calibrate further.

My experience is that the test chart may not be that accurate afterall.

Of course, other people's experiences may differ.
09-10-2007, 07:20 PM   #14
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QuoteOriginally posted by raider Quote
I did a focus check using the famous D70 test chart.

I then proceeded to set the "focus corr" value via the K100D debug service menu. After many trials and errors, I find that I need to set it to -220. A more detail test confirmed that this is incorrect. I need to set it to -350!! Now that is not a typo.

Then I tried the FA50/1.4, I need to set it to -80.

Now, K100D service menu can only have one focus corr value and out of desperation, I set it to -350 to suit my tamron. I thought this is all well but when I actually use the Tamron in real life shooting, the focus run back focus so much that it is not usable!

Put the k100D and tamron on the test chart again, the combo performed perfectly with -350 compensation. So I was freaked.

Then I decided to forego the test chart and adjust the focus corr myself. I set it to -100, -150, -200, etc and test and test. All no good. Finally, I set it to -50 and tested it!

Focus is spot on! With -50 focus corr, I also tested the FA50 and again spot on. This is the final value I settled with and I am not going to calibrate further.

My experience is that the test chart may not be that accurate afterall.
This is very interesting.

I too would have thought the focussing chart was the more critical and accurate way of checking focus.

The only things I can think of this large discreprency - are either -

1) the K100D was set to AF using multiple sensors so and the camera was using the sensor(s) that were the closest - so very front focussed (I take it that you did use central single point focus - but had to put this in for completeness).

or

2) the K100D/Tamron combination is behaving differently when focussing on close objects (eg: focus chart) and normal/distant objects.

If it is the latter (2) - are your close-ups and macro shots still accurate on "real-life" objects with your current (-50) correction?
09-10-2007, 07:32 PM   #15
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This might be a dumb question, but in reading about early autofocus while researching another issue separately, it discussed the use of contrast detection as part of the autoficus process. Thsi, plus my own experiences with autofocus and errors got me thinking.

Does the autofocus behave differently as a function of what direction it approaches focus from??? I.e. do you achieve the same focus point when you approach from infinity as opposed to minimum focus distance?

Has anyone deliberately focused on a target always from one specific starting point?
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