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01-06-2009, 12:59 PM   #16
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thnx, asdf.

01-06-2009, 11:49 PM   #17
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EDIT: Scroll down to a newer post with possibly a more meaningful pair of cropped images.

I promised outdoor shots, but first I wanted to give a fair comparison with the 18-55II kit lens. After few dozen shots of pretty much the same composition I finally decided that my K200D noticeably front-focuses with the kit lens, every single time. Strange!

I used ufraw to convert from RAW to png and gimp to crop and finally convert it to jpeg! PHEW!

The AF was supposed to focus near the word "Park." I used Av mode (5.6 aperture, 50mm and 53mm) a tripod and the built-in flash, but my conditions were far from ideal. The first shot is done with the kit lens; the second is done with 17-70.

EDIT: Also, pay attention to the whiteness of the paper in both cases. I used a flash in both cases.
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Last edited by asdf; 01-08-2009 at 01:18 AM.
01-07-2009, 10:55 AM   #18
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I seems that your target was not parallel to the camera sensor and it was very close as well. At those distances even minor errors in focusing will show up, so don't worry about FF/BF for now, and DOF is so small that it will be really hard to judge anything.

To do a proper test I would suggest the following:

1) This is the major point: always use manual focus. The idea here is to test optical quality of the lens, not accuracy of the AF system. In addition, to avoid your errors in MF here is how to do it: (1) defocus completely; (2) focus manually; (3) take a picture; (4) defocus again; repeat the process at least three times (I do 5). Once done, choose the sharpest result. This way you will likely eliminate both AF and MF errors and actually test the lens.

2) To test corner sharpness take separate series following steps similar to those described in #1, but look at the corner target and focus there, NOT in the center! This is especially important at close distances. The reason is mainly field curvature and spherical aberration. For more details on lens aberrations see here:

Photographic optics

BTW: One of the key design differences between regular and macro lenses is that macro lenses are designed to provide so called "flat field" (translation: minimized field curvature and spherical aberration). So an average lens is even not expected to provide corner sharpness that matches center sharpness are close distances.

3) Finally, to compare color rendering set white balance to MANUAL (according to your shooting conditions).
01-07-2009, 11:21 AM   #19
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As far as I can see, there is a slight back focus on the second sample. "In the" before word Park is in focus........

One more thing, when you do this test, always use first aperture , 2.8 , 4.0 , whatever it is.........

01-07-2009, 01:14 PM   #20
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I'll keep shooting and post any interesting observations.

BTW, I was around a meter away and the images were cropped without scaling. The white balance was set to the flash preset. I don't have studio lights and at first I didn't want to introduce noise due to long exposure, so I used flash.

QuoteOriginally posted by Ivan Glisin Quote
I seems that your target was not parallel to the camera sensor and it was very close as well. At those distances even minor errors in focusing will show up, so don't worry about FF/BF for now, and DOF is so small that it will be really hard to judge anything.

To do a proper test I would suggest the following:

1) This is the major point: always use manual focus. The idea here is to test optical quality of the lens, not accuracy of the AF system. In addition, to avoid your errors in MF here is how to do it: (1) defocus completely; (2) focus manually; (3) take a picture; (4) defocus again; repeat the process at least three times (I do 5). Once done, choose the sharpest result. This way you will likely eliminate both AF and MF errors and actually test the lens.

2) To test corner sharpness take separate series following steps similar to those described in #1, but look at the corner target and focus there, NOT in the center! This is especially important at close distances. The reason is mainly field curvature and spherical aberration. For more details on lens aberrations see here:

Photographic optics

BTW: One of the key design differences between regular and macro lenses is that macro lenses are designed to provide so called "flat field" (translation: minimized field curvature and spherical aberration). So an average lens is even not expected to provide corner sharpness that matches center sharpness are close distances.

3) Finally, to compare color rendering set white balance to MANUAL (according to your shooting conditions).
01-07-2009, 01:24 PM   #21
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I guess so, but take these shots with a grain of salt: I was impatiently working in a dark cramped room and may have bumped into the tripod a couple of times. But I did turn on the 2s mirror lockup.

What was interesting to me was color rendition: in both cases, flash was used and white balance was set to the flash preset. The kit lens produced a slightly bluish white. But again, it's probably safer to assume that I messed something up.

QuoteOriginally posted by klika Quote
As far as I can see, there is a slight back focus on the second sample. "In the" before word Park is in focus........

One more thing, when you do this test, always use first aperture , 2.8 , 4.0 , whatever it is.........
01-07-2009, 04:10 PM   #22
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QuoteOriginally posted by asdf Quote
BTW, I was around a meter away and the images were cropped without scaling. The white balance was set to the flash preset. I don't have studio lights and at first I didn't want to introduce noise due to long exposure, so I used flash.
With K200D, at 1m camera-to-subject distance, 50mm setting and f/5.6 depth of field is only -4.12cm/+4.49cm (in front of/behind the subject). So you have total DOF of only about 9.5cm, and very minor shift in focal length may affect the image.

In contrast, with identical settings at 5m camera-to-subject distance DOF will increase to -91.5cm/+144.3cm, giving you over 2m of total DOF!

WB on flash and flash use for this type of tests works the best. Tripod may be of great help as well.
01-07-2009, 05:39 PM   #23
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Keep in mind, pentaxforums compresses the images further making them look less sharp.

I've been shooting with a tripod so far, 2s mirror lockup. This time I also used a cable switch and cleaned the 18-55 II. I did a lot of shooting.

Here's the set up: manual focus, manual exposure (0.5s shutter speed, F5.6, ISO100), reported (in EXIF) focal lengths 50mm for the 18-55 II and 53mm for 17-70. No flash this time. I set the white balance separately for each lens with inkjet photo paper as my white card. PEF->PNG->cropped JPG.

I attached cropped but not scaled images for pixel peepers. The word "miracles" is near the center of the original image. The book is Robert Park's "Voodoo Science" which I thought would be appropriate for this activity.

Conclusion: 18-55 II seems much softer in this spot of the DOF. You can actually see jaggies with the 17-70.

QuoteOriginally posted by Ivan Glisin Quote
With K200D, at 1m camera-to-subject distance, 50mm setting and f/5.6 depth of field is only -4.12cm/+4.49cm (in front of/behind the subject). So you have total DOF of only about 9.5cm, and very minor shift in focal length may affect the image.

In contrast, with identical settings at 5m camera-to-subject distance DOF will increase to -91.5cm/+144.3cm, giving you over 2m of total DOF!

WB on flash and flash use for this type of tests works the best. Tripod may be of great help as well.


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Last edited by asdf; 01-09-2009 at 08:01 PM.
01-08-2009, 01:45 AM   #24
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If you're going to be doing focusing tests you have to target more isolated subjects. The AF "cross-hairs" are larger than what you see on the viewfinder. I usually choose newspaper headlines or just write well-spaced lines on a whiteboard. There has to be a clear target that you're going for. If it's too cluttered it may go to the other targets.

Unless you're shooting an object that's completely flat and parallel to the sensor's plane.

How's it using the lens though? I mean, your experience with it. Is the AF fast enough, the feel of the zooming etc
01-08-2009, 10:54 AM   #25
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Even with all the uncertainties, which are hard to remove completely, it seems pretty evident that the 17-70 is sharper than the kit lens, but not overwhelmingly so.

Have you found any differences in more "real" shooting conditions?
Thanks for all the effort in testing and answering questions here!
01-09-2009, 02:58 PM   #26
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I'll try to find the best adjectives here. The focus ring is loose compared to my PENTAX-M 50mm F1.7 and goes through 45 degrees; but the resistance is constant. The zoom ring is smooth, heavy with constant resistance and also goes through 45 degrees.

It was cloudy outside, but I felt it was a good day to test the expected chromatic aberration at 17mm. I haven't done pictures with the kit lens in the same situation, yet, so I'm not posting the cropped corners, yet: so check out the photezone.de review. I tried the "cloudy" white balance. The attached photo is shot (hand-held) with F8, 1/30s shutter speed, ISO100, at 17mm (Av, autofocus, autoexposure +2.0).

BTW, this was the only blue sky I found.

EDIT: pentaxforums.com seriously degraded the sharpness of this photo.

EDIT 2: Here's the flickr version:


QuoteOriginally posted by soccerjoe5 Quote
If you're going to be doing focusing tests you have to target more isolated subjects. The AF "cross-hairs" are larger than what you see on the viewfinder. I usually choose newspaper headlines or just write well-spaced lines on a whiteboard. There has to be a clear target that you're going for. If it's too cluttered it may go to the other targets.

Unless you're shooting an object that's completely flat and parallel to the sensor's plane.

How's it using the lens though? I mean, your experience with it. Is the AF fast enough, the feel of the zooming etc

Last edited by asdf; 01-22-2009 at 03:57 AM.
01-09-2009, 03:10 PM   #27
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QuoteOriginally posted by EricT Quote
Even with all the uncertainties, which are hard to remove completely, it seems pretty evident that the 17-70 is sharper than the kit lens, but not overwhelmingly so.
pentaxforums.com compresses the image further, degrading the sharpness. In my last photo, more of the tiny branches were visible in the original scaled jpg but on the board, they smeared.

EDIT: My guess is that the difference would've been even more pronounced on the K20D.

QuoteQuote:
Thanks for all the effort in testing and answering questions here!
No problem.

Last edited by asdf; 01-09-2009 at 10:38 PM.
01-20-2009, 04:32 AM   #28
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so...

Not to beat a dead horse, but what is the consensus?

That the kit lens is softer or the 17-70mm?

p.s. : sorry if you feel we've gone over this enough.
01-20-2009, 05:02 AM   #29
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QuoteOriginally posted by crispy0009 Quote
Not to beat a dead horse, but what is the consensus?

That the kit lens is softer or the 17-70mm?

p.s. : sorry if you feel we've gone over this enough.
The kit lens is definitely softer at 50mm, f/5.6. With 17-70, you can see jaggies at the edges of letters--at least on K200D's sensor. The kit lens is more anti-aliased.

Doing accurate sharpness tests requires some care (when I was doing the shots above my tripod setup wasn't steady--I didn't intend it to be a sharpness test--but the difference was still noticeable):

Mirror Lock-Up

Also, telephoto ranges magnify any existing vibrations.

You can check out photozone.de's reviews--even if they're not very careful, you can at least compare how the lenses perform under the conditions they set up.

Last edited by asdf; 01-20-2009 at 07:14 AM.
01-20-2009, 03:43 PM   #30
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Thanks.

I think I've got it now.
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