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01-11-2009, 08:26 AM   #31
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Interesting that we look at the same photos and come to different conclusions. I believe the 18-250mm photo is sharper. Look at the sky around the sails. The 18-250 is showing texture in that area that the 50mm is losing. I noticed this because I did some cereal box tests with my DFA 100mm macro to see how sharpness compared with the 50mm. The 100mm shots were showing this same banding effect much more clearly than the 50mm. I could barely see any banding when I looked at the box with my naked eye. With a magnifying glass, it was there, just like the 100mm said it was. I suggest you get the box and a magnifying glass out and see if I'm right. Pixel level crops show more than the unaided human eye can see.

At the very least, your photos are very close in sharpness. Other than the sky around the sails, I don't see what makes you think they aren't the same. My tests with the 18-250 and 50mm on a K20D show they are not close at all. The 16-45mm outresolves the 18-250 and is outresolved by the 50mm. If you really want to know what's what, take your lenses and your memory card to a camera shop. Shoot some advertising posters using your lenses and your memory card and see for yourself. The 50mm outresolves the 18-250, and there's no room for doubt. I bought the K20 after I saw how it could distinguish between lenses. I still love the K100's image quality for most forms of photography, but with the cropping I do for wildlife shooting, there's really no comparison.

PS. You cannot compare my photo set to yours given a different subject, different lighting, different setup, different processing.

01-11-2009, 11:33 AM   #32
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Imho... There is something fundamentally wrong with these tests... K20 is known for the best JPG output in Pentax lineup... K100... for one of the worse... (only K200 is worser)

I'll leave drawing conclusions up to you fellas...
01-11-2009, 11:54 AM   #33
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QuoteOriginally posted by alexeyga Quote
K20 is known for the best JPG output in Pentax lineup... K100... for one of the worse... (only K200 is worser)
This is hardly anything generally "known" at all. dpreview is probably the *only* reviewer that didn't like the default K200D JPEG, and they *loved* the K100D JPEG. In fact, I don't know of any reviews that criticized the K100D JPEG. As for the K200D, even dpreview point out that their issue was only with the *default* settings. And in any case, these kinds of concerns are completely subjective, anyhow (eg, one reviewer likes highly sharpened and saturated images, another likes them more natural). So I have no idea what you are talking about.
01-11-2009, 12:25 PM   #34
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Mark please... My point was that we should compare RAW conversions rather than default JPG-s... Anyways, this topic isn't about trashing the K200, so no need in defending it so vigorously...

01-11-2009, 01:01 PM   #35
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QuoteOriginally posted by audiobomber Quote
I believe the 18-250mm photo is sharper.
Look at the sky around the sails. The 18-250 is showing texture in that area that the 50mm is losing.
This is the reason why I speculated that I probably hit a better AF fine calibration for the 18-250 compared to the 50mm. The print raster actually manages to excite some moire, it appears.

However, there are plenty of areas where the 50mm image is definitely sharper. I understand sharpness to be a combination of resolution and contrast. Look at the "T-SHIRT" writing at the top right corner of the image. Less blurry with the 50mm. Look at the fine print below the fish pic tarting with "Package includes". Less blurry with the 50mm. The most dramatic difference can be seen in the writing "Kellog has introduced..." at the top left corner of the image. It looks like the blurriness of the 18-250 may come from a non-flat focal plane or corner weakness but still overall, the 50mm image is more contrasty and has less blur in many areas.

I agree with you that the 18-250 pulled out the texture better in a part of the image, but I put that down to a better AF result.

QuoteOriginally posted by audiobomber Quote
At the very least, your photos are very close in sharpness.
Please have a look at the areas I pointed out. The differences are not subtle at all. I'm not saying you have this problem, but I noticed that when I view these pages with Firefox, then any differences in sharpness become totally blurred as Firefox has a wrong DPI setting for my screen and therefore resizes (enlarges) the images. When I view them with Seamonkey, 1 image pixel becomes 1 screen pixel and the differences are much easier to see. If the 800 pixel wide images on these pages look larger/smaller than a 800 pixel wide image in a photo browser with 100% magnification then resizing takes place, making it extremely difficult to still see the original sharpness (differences).


QuoteOriginally posted by audiobomber Quote
The 50mm outresolves the 18-250, and there's no room for doubt.
My test result confirms this. Probably not to the extent possible, because I believe the AF calibration for the 50mm was not optimal, but the 50mm images is sharper in many ways then the 18-250 image. I agree with you that my result seems to indicate that the 18-250 shows higher resolution for some part, but the explanation "better AF result" solves this puzzle.

EDIT: One difference between our tests appears to be that you did a heavier crop than I did and only showed the centre performance of the lenses. Admittedly, my results mainly show that the prime performs much more uniformly then the super zoom.

QuoteOriginally posted by audiobomber Quote
I still love the K100's image quality for most forms of photography, but with the cropping I do for wildlife shooting, there's really no comparison.
Fine. But note that I'm not discussing this point at all. What I took issue with was the quality of your K100DS shots. If even my 18-250 can see the print texture, your 50mm should have seen it all the more. Unless the AF result wasn't optimal. However, if your AF result wasn't optimal then this would explain why you obtain a result that contradicts the expectations and experiences of other forum members.


QuoteOriginally posted by audiobomber Quote
You cannot compare my photo set to yours given a different subject, different lighting, different setup, different processing.
Please note that I have stated this myself. However, one of the differences is that you used the "bright" setting. Your images, using AF as I did, should therefore be sharper than my "natural" images. Also, if some of my images are sharper than yours then this suggests that either the K100DS has worse JPEG output than the K100D or that you could have obtained better results. If the latter is the case, it questions the validity of your conclusion.

Last edited by Class A; 01-11-2009 at 05:44 PM.
01-11-2009, 01:36 PM   #36
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QuoteOriginally posted by alexeyga Quote
There is something fundamentally wrong with these tests...
I agree that the tests are lacking in a number of ways.

With a flat subject the focus has to be spot on and it usually is not using AF (on different lenses). As I've written, I don't think my quick tests proves anything, except that it throws some doubts on the OP's original results and conclusion.

I also agree about using RAW and one RAW->JPEG converter rather than out-of-camera JPEG. I made this point earlier on already.

QuoteOriginally posted by alexeyga Quote
K20 is known for the best JPG output in Pentax lineup... K100... for one of the worse... (only K200 is worser)
The only JPEG criticism I know of is that about the K10D. DPreview thought that using RAW+ a good converter yielded a much better result then JPEG out of the camera. As Marc wrote, they loved the JPEG from the K100D.

Judging from a comparison done by RiceHigh the only Pentax camera with a really inferior JPEG output was an *ist model. The K100D JPEG is visibly better. The K10D JPEG output using "bright" is very close the a K100D JPEG output using "normal".

Last edited by Class A; 01-11-2009 at 01:47 PM.
01-11-2009, 03:09 PM   #37
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Just to see whether I could get more sharpness out of the prime, I did a further run with a different AF calibration setting for the prime. I left the calibration setting for the zoom at the value where it achieved best sharpness in the last run.

Below are the results. The crops are showing ~76.7% of the original images and have been resized to 800 pixel width (~3.4 x reduction) with Picasa. Except for "Auto Contrast" no other PP has been done. Sharpness setting at the camera was "natural" and "+0" (neutral).

First the zoom still recovering the print texture. Sorry for not getting exactly the same field of view in comparison to my previous shots. I put more effort into the parallel alignment of the package with the camera this time and ended up with a different positioning of the package.

Then the prime. Probably still not the best AF fine tuning, but at least it now also shows the print texture. As before, many areas are rendered with more local contrast by the prime compared to the zoom.

Because of the challenges with AF fine adjustment and invariable AF variations, this test perhaps doesn't say anything about the K100D's 6MP sensor showing resolution differences. It sure does demonstrate that using a prime vs a super zoom on a K100D results in visible differences. The original OP's comparison didn't show these differences. Therefore, I conclude that the OP's comparison wasn't optimal (probably due to AF not working optimally on the K100DS) and hence the validity of the conclusion made is questionable.

BTW, I did the same shots at f/8. The results are as expected by Marc. The difference between f/5.6 and f/8 in the prime shots is almost not there. The difference between f/5.6 and f/8 in the zoom shots is very noticeable. In some image areas the f/8 zoom images is close to the f/5.6 prime image. In other areas, one can still see a pretty obvious differences.

Last edited by Class A; 08-07-2010 at 09:21 AM.
01-11-2009, 08:04 PM   #38
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Surely these tests would require a Weetbix box to have any validity ?


;

Pete



01-11-2009, 09:23 PM   #39
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QuoteOriginally posted by Class A Quote
The original OP's comparison didn't show these differences. Therefore, I conclude that the OP's comparison wasn't optimal (probably due to AF not working optimally on the K100DS) and hence the validity of the conclusion made is questionable.
Sorry man, in the first set the 18-250 was sharper. In these photos they are virtually identical, it's a pick'em. Rather than disproving my statement, you've proven it. All you have to do now is admit it to yourself.

I've compared the 18-250 and 50mm on my K20D. There's a clear difference in resolution, a difference which the K100D does not resolve. Bokeh, colour rendition, sure, but not resolution. My statement still stands, the 18-55 and 18-250 are bumping against the K100's resolution limits. A 6mp camera cannot demonstrate the FA 50mm's higher MTF capability.
01-11-2009, 09:29 PM   #40
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QuoteOriginally posted by audiobomber Quote
My statement still stands, the 18-55 and 18-250 are bumping against the K100's resolution limits. A 6mp camera cannot demonstrate the FA 50mm's higher MTF capability.
I sure wish I still had my DS to take some test shots and post them. All I can say is, at f/5.6, the difference between the 18-55 and the M50/1.7 was *excruciatingly* obvious to me.
01-11-2009, 09:33 PM   #41
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QuoteOriginally posted by alexeyga Quote
My point was that we should compare RAW conversions rather than default JPG-s...
OK - actually, I had no idea what your point was, and was completely confused by your statements about the relative JPEG quality of the various cameras, because they appeared to come form out of the blue. This test is not comparing one camera against another, but different lenses on the same camera. So I don't see what JPEG quality has to do with anything here.
01-11-2009, 10:06 PM   #42
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Dan,

QuoteOriginally posted by audiobomber Quote
Sorry man, in the first set the 18-250 was sharper.
AF is not perfect. There are always small variances.

At least, I hope you have noticed that the 50mm image is sharper than before.
Looking at this shot (taken at "natural" not "bright"), don't you think "Why are my K100DS so damn soft in comparison?"? How can you ignore the obvious shortcomings of your K100DS samples?


QuoteOriginally posted by audiobomber Quote
In these photos they are virtually identical
Of course they are not "virtually identical" across the image. The shortcomings of the superzooms in some areas are plain obvious. With more tinkering with the AF calibration for the 50mm, I'm sure I could get the 50mm images even sharper.

QuoteOriginally posted by audiobomber Quote
Rather than disproving my statement, you've proven it.
Sorry, I cannot help you. I have said more than once that my quick tests do not prove anything. But they certainly should have instilled a lot of doubt in you about your experiment.

One thing they show for sure: Getting the focus right is paramount. A slightly misfocused prime can look worse than a perfectly focussed super zoom. Differences in lens quality cannot be reliably observed unless perfect focus can be achieved. That's why I'm criticising the "flat subject" setup (unless extreme measures are taken that it is in perfect focus for each lens).

My own tests brought me to the conclusion that your K100DS shots are hopelessly out of focus for both lenses. Also, I believe the difference between the two K20D images is probably more an effect of good focus with the prime and mediocre focus with the kit lens. Have you tried to check BF/FF for both of them?

I fully believe that the K20D does the better images and better allows to spot differences between lenses in principle, but I'm more than ever convinced that your images don't demonstrate anything but bad AF.

I'm completely at loss why you cannot see that my prime images are considerably better than my super zoom images. You could try to state that the differences are a result of loss of performance towards the corners by the superzoom (or some other argument), but to state that there are no noteworthy differences just astonishes me.
01-11-2009, 10:14 PM   #43
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QuoteOriginally posted by Marc Sabatella Quote
All I can say is, at f/5.6, the difference between the 18-55 and the M50/1.7 was *excruciatingly* obvious to me.
Do you find my tests as inconclusive as Dan perceives them?

I can see the difference between my f/5.6 shots easily.

Note that the 18-250 is not the 18-55. It is quite possible that the former is a bit sharper around the centre.

For anyone not seeing the differences between the prime and zoom f/5.6 shots: Download both images and flick between them using an image browser. You'll immediately not only see the difference in geometric distortion but also very clearly where the zoom images dramatically falls off in terms of sharpness.

Maybe I should not have done the test without having found the optimal AF calibration for both lenses first. (To do that reliably is a lot of work.) I thought the tests already provided sufficient ammunition against Dan's conclusion. Apparently not so in Dan's book.
01-12-2009, 09:40 AM   #44
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Class A:

We're covering a lot of the same ground and not making headway, so I'll summarize my case and be done with it.

- You cannot compare resolution in your photos with mine, for all the reasons I stated previously.

- I have checked the focus on both my cameras using a focus chart with three primes and a zoom, under tungsten light and daylight. Both cameras performed equally well. AF and MF were spot on at alll apertures in daylight with each lens. Both cameras front focussed equally under tungsten light in MF or AF mode, but only at F/2.8 and wider. The resolution tests in this thread were done in daylight at F5.6, which means that the cameras were performing optimally. I also cross-checked using MF and AF and the AF was spot on.

- You are struggling to show the differences in resolution between a superzoom and a prime, which is exactly what I expected. I have tested these very lenses on a K20D, and I know there are major resolution differences. I can see from your photos that you are nowhere near to showing the magnitude of these differences, yet you're still claiming it's there. That's why I suggested you check out a K20 in a store for yourself. It seems only then will you understand what I'm talking about.

- I have ranked the resolution of my lenses using the K20. Highest to lowest: DFA 100 macro, FA 50mm, Image A 28mm, DA 16-45, DA 18-250, DA 18-55. There's no detailed analysis needed or excuses about maybe the prime was misfocussed. It's just crystal clear when I view the photos at 100% which lens is sharper. (Note that this is with the cereal box test, intended to highlight resolution. Normal photographs will not clearly show resolution differences).

- Mounted on a K20D, the 18-55 has more resolution at 50mm f5.6 than the FA 50mm on a K100DS. Having said that, resolution alone does not determine image quality. It is still worthwhile for an owner of a 6mp camera to buy a good prime for speed, improved bokeh and colour rendition. But before getting carried away with exotic primes, one should consider a camera upgrade. That's my conclusion.


Last edited by audiobomber; 01-12-2009 at 09:51 AM.
01-12-2009, 09:57 AM   #45
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FWIW, I think audiobomber is right. With my old K10D, the Sigma 17-70 and FA50 were close enough that I preferred the Sigma 17-70. After some testing this weekend, the K20D seems to show which lenses are sharper and which aren't more easily...e.g., primes are much sharper when stopped down slightly while the Sigma needs to be stopped down to f/8-11 before it's sharp when pixel peeped.
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