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12-28-2010, 07:49 PM   #61
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james,

I am sorry but you misread my post.
I did not dismiss the possibilty.

I said that w/o doing a controlled experiment, there is no reason to discuss the theory beyond the point it already has. That's how our civilization evolved beyond mysthicism. BTW, doing a controlled experiment is easy enough.

01-09-2011, 09:13 AM - 1 Like   #62
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I'm not qualified / smart enough to say anything about K-5 and CA&PF, but today I met two fellow Pentaxians and while having good discussions about Pentax cameras and lenses I took a few quick snaps with K-5 and K20 and couple of lenses (DA 40 Limited, FA 77 Limited, DA* 16-50, Tamron 28-75, DA 21 Limited). This wasn't a controlled test and the conditions weren't good (overcast, very foggy weather). On some shots the K-5 was worse, on others it was on par with K20 using same lens, and some lenses didn't produce any CA/PF worth to mention or at all.

Since it wasn't a controlled and good test, only four 100% crops from two lens:
K-5 and DA* 16-50
K20 and DA* 16-50
K-5 and FA 77 Limited
K20 and FA 77 Limited

Unfortunately I forgot to use my Sigma 30 f/1.4. Hopefully next time we'll have better weather and can set up a controlled test.
01-09-2011, 09:51 AM   #63
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QuoteOriginally posted by simico Quote
I'm not qualified / smart enough to say anything about K-5 and CA&PF, but today I met two fellow Pentaxians and while having good discussions about Pentax cameras and lenses I took a few quick snaps with K-5 and K20 and couple of lenses (DA 40 Limited, FA 77 Limited, DA* 16-50, Tamron 28-75, DA 21 Limited). This wasn't a controlled test and the conditions weren't good (overcast, very foggy weather). On some shots the K-5 was worse, on others it was on par with K20 using same lens, and some lenses didn't produce any CA/PF worth to mention or at all.

Since it wasn't a controlled and good test, only four 100% crops from two lens:
K-5 and DA* 16-50
K20 and DA* 16-50
K-5 and FA 77 Limited
K20 and FA 77 Limited

Unfortunately I forgot to use my Sigma 30 f/1.4. Hopefully next time we'll have better weather and can set up a controlled test.
That's (by far!!) the best post wrt the topic. It is the only one helping to clarify the topic. Thanks a lot.

The samples illustrate two points I did already make:

  1. The K-5 has a higher pixel density making the purple seams appear wider. That's a trivial fact of course.
  2. The K-5 has better dynamic range and in many circumstances, the dark parts of an image will turn out brighter (shadow is boosted more, either in camera or in post processing or by selecting a corresponding exposure). This will boost the purple fringes too which however, still come from the lens.
So, I still see no evidence that the K-5 sensor amplifies PF.
01-09-2011, 10:32 AM   #64
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QuoteOriginally posted by falconeye Quote
That's (by far!!) the best post wrt the topic. It is the only one helping to clarify the topic. Thanks a lot.
Agreed! Very good.

01-09-2011, 11:32 AM   #65
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QuoteOriginally posted by simico Quote
I'm not qualified / smart enough to say anything about K-5 and CA&PF, but today I met two fellow Pentaxians and while having good discussions about Pentax cameras and lenses I took a few quick snaps with K-5 and K20 and couple of lenses (DA 40 Limited, FA 77 Limited, DA* 16-50, Tamron 28-75, DA 21 Limited). This wasn't a controlled test and the conditions weren't good (overcast, very foggy weather). On some shots the K-5 was worse, on others it was on par with K20 using same lens, and some lenses didn't produce any CA/PF worth to mention or at all.

Since it wasn't a controlled and good test, only four 100% crops from two lens:
K-5 and DA* 16-50
K20 and DA* 16-50
K-5 and FA 77 Limited
K20 and FA 77 Limited

Unfortunately I forgot to use my Sigma 30 f/1.4. Hopefully next time we'll have better weather and can set up a controlled test.
Its a good start. But Klaus of Photozone shows the DA*16-50mm as having higher than normal CA at all settings!

And Klaus of Photozone says the FA 77 has low CA but high PF! And the cause is the sensor!

"However, lateral CAs are only one aspect - purple fringing is another one. At large aperture setting this kind of CA can indeed be a problem. Knowing how to force the problem I was able to produce the following 100% crops:
Please don't let you put off by this problem though. This happens only in extreme contrast situations when the bright portion is at or beyond the contrast latitude capabilities of the sensor." He is using a K10D with a CCD however, does not apply to CMOS I believe?

He may be wrong as I think the lens can PF as well? In your tests the K20D is showing much less purple through the pic with the FA 77 versus the K-5, much less. With the K-5 almost every single branch has PF and or a tint why? EDIT: its because the shadows are lighter from the K-5. The K-5 lifts the shadows up more revealing the same amount of PF in this pic.

Also I want to buy the K-5 in a couple months. This is not to knock it, its a superior dSLR. I just want to know if, what, when, why because I hate (a strong word I know) PF. Its not a huge deal, so ignore my 'thing' LOL.... with PF and enjoy the K-5. Just digging.

It's an interesting read -

Pentax SMC-FA 77mm f/1.8 Limited - Review / Test Report - Analysis

Your statement that "On some shots the K-5 was worse" is the question, why? Where they fairly identical shots? On another post a K-5 with a DA55-300mm is showing PF/CA with no cropping to 100%. I can't get my K20D to do this without going to 100% and cropping. Thats my question, how and why is the K-5 showing PF/CA without cropping, when the K20D does not unless you crop to 100%?

The sun was blinding, it looks darker that it was because the K20D preserves highlights and lower EV. This is how to get the most out of the K-5 BTW you want to expose for the highlights as you have superior shadow detail and plenty or room to lift the shadows!

This was for another post but it fits here. It proves nothing however just interesting I have a strong interest because I want to know.

Manufactures are in business to sell cameras. Sometimes they neglected IQ to increase mega-pixels thats pretty much a fact. Because mega-pixels sell! Now are we in the same situation, except high ISO sells yes/no? Will it take time, the next sensor fix problems if there are any? Believe me the next model Pentax makes will have features and performance that will make you want to sell your K-5; it must thats the only way Pentax, Sony, Nikon... stay in business.


All shot with the K20D and DA55-300mm at f/5.6 and 300mm.









This pole was way down the street at least 300' away!




Last edited by jamesm007; 01-09-2011 at 12:41 PM.
01-09-2011, 01:40 PM   #66
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QuoteOriginally posted by falconeye Quote
That's (by far!!) the best post wrt the topic.
+1

Reputation points awarded.

I agree with Falk's analysis and his conclusion. It may furthermore be the case that the K-7 chooses a slightly different focus in such situations. Note that the green fringing appears to be stronger in the K20D shots, suggesting that the K20D may hit a better compromise in terms of green and purple fringing. One can trade off these two against each other by adjusting the focus correspondingly (see this Fig. 3 of an article about CA).



QuoteOriginally posted by jamesm007 Quote
And the cause is the sensor!
Strictly speaking Klaus doesn't point to the sensor as the source. He might be just saying that the PF coincides with contrast levels which stress the sensor. I believe he's wrong either way. In any event, you shouldn't treat this statement by Klaus as gospel.

Last edited by Class A; 01-09-2011 at 01:45 PM.
01-09-2011, 02:19 PM   #67
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QuoteOriginally posted by Class A Quote
+1

Reputation points awarded.

I agree with Falk's analysis and his conclusion. It may furthermore be the case that the K-7 chooses a slightly different focus in such situations. Note that the green fringing appears to be stronger in the K20D shots, suggesting that the K20D may hit a better compromise in terms of green and purple fringing. One can trade off these two against each other by adjusting the focus correspondingly (see this Fig. 3 of an article about CA).




Strictly speaking Klaus doesn't point to the sensor as the source. He might be just saying that the PF coincides with contrast levels which stress the sensor. I believe he's wrong either way. In any event, you shouldn't treat this statement by Klaus as gospel.
Umm could that be the reason I wrote "he may be wrong" that I believe it is lens that do the PF? Read my post again carefully. Its much more open than your interpretation of it, really

There is no green purple trade off in the sample above, its just the K-5 lifting up shadows making CA/PF seem stronger. As Falk says its the K-5 lifting up the shadows the make some inherent PF/CA more prominate. Thats problem 1. Next problem is the K-5 has at times 'perhaps' stronger CA/PF then any explanation works with. That no one knows yet.

Last edited by jamesm007; 01-09-2011 at 02:30 PM.
02-24-2011, 08:47 PM   #68
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Hi guys,

I'm new here, I just bought a K5 after 4+ years as a Nikon shooter (D50, D300). I absolutely love the camera, except for one minor issue. I get this really bad CA/Purple fringe with bith my DA35 F/2.4 and my FA50 F/1.4 at wide apertures.

I have never experienced this on either Nikon with the Nikkor 50mm F/1.8 or the Sigma 28 F/1.8 (my 2 Nikkor primes). Here is an example from the 50, not sure if the issue is with my camera since both lenses do it.



If anyone has any thoughts/ideas/suggestions, I'd really appreciate the help. I'd prefer not to have to stop down, as I bought the primes for the DOF. Is this common with Pentax lenses?

Thanks!

-Sean

02-24-2011, 08:59 PM   #69
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Neither of those lenses is the cream of the crop as far as CA on digital goes, as they were both designed for use on film cameras, which are much more forgiving in this respect (the DA 35/2.4 uses the same optical formula as the FA 35/2, just with smaller glass).

Furthermore, wide-open, you'll always get more CA than stopped down- that's just optics. There are many lenses that do a great job of handling it, however, such as the FA limiteds, DA limiteds, or the new DA zooms.

BTW, the above photo is overexposed, and that also worsens CA.

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02-24-2011, 09:16 PM   #70
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Good call on the overexposure. As I'm still learning the new camera system and taking lots of test shots I'll be mistake-prone. I'm definitely still getting used to the controls, they're significantly different. Thanks for your help. If you were to return one of the two lenses to save for a limited, which would you keep?

While it's off-topic to this thread, I also wanted to mention that my K5 focuses perfectly in tungsten light and has no sensor stains. Those were my greatest worries when I decided to switch and it has been perfect. I think the AF is actually more accurate than my D300, albeit with fewer AF points (which I don't care about). This camera is so well built, can't wait till I get the hang of it.

EDIT: I just took out my D300 and was able to induce it by overexposing. The CA colors are just a bit less noticeable than on the K5. Interesting. This is a different test shot since I'm at home, but you get the point. D300:

Last edited by sweendiggs; 02-24-2011 at 09:48 PM.
02-25-2011, 11:51 AM   #71
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Update:

I contacted Pentax to see what they thought of the images (I took some that weren't overexposed and some where they asked me to change settings) and I was told that especially with a DA lens, this should not be happening. I was advised that it may be a sensor issue.

I'm not sure how helpful that is for any other users experiencing this, but support has been very helpful, it can't hurt to contact them if you're seeing these issues.
02-25-2011, 03:50 PM   #72
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Seems like you received this information from some Pentax USA or some other not to technically minded place. I wouldn't trust it one bit.
02-26-2011, 04:27 AM   #73
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This is completely normal, and similar to what I see with the DA70 @f/2.4 on the K10d.
02-26-2011, 08:06 AM   #74
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QuoteOriginally posted by Class A Quote
Seems like you received this information from some Pentax USA or some other not to technically minded place. I wouldn't trust it one bit.

Pentax USA, yes.

It may be normal, but seems odd to me as someone who just switched from another brand. I have tried to recreate this with a couple of lenses on my D300, and even wide open (50mm F/1.8, 28mm F/1.8) I have to actively try to get fringing to occur. I have to turn the flash on and set the camera to +2 EV to start really seeing it, and the fringing is still less noticeable than on the Pentax when I'm stopped down, flash off, -1 or 2 EV, etc. It's more of a bluish tinted white fringe rather than intense purples and greens.

Is this a picture that I'd typically shoot? No. Does it worry me that this may happen when taking an important picture of something else? Yes.

This tells me that either the cheap Nikon glass is superior to the cheap Pentax glass, or the camera's processing is better at handling this CA.

Thanks again for the info guys, I do appreciate the input.

-Sean
02-26-2011, 05:29 PM   #75
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Hmm. Looking at your picture a second time on a better screen, I have to admit that it's strong, given the subject. As I said, I do see similar behavior with my DA70, but usually with much stronger highlights. It's difficult to compare your two pictures, though, the CA is visible in the D300 shot, too, but it's much darker and seems to have less strong light reflected on the white letters.

Here's an example (K10D + DA70) with very strong highlights (frost with strong sun):


100% crop of the above:


Several of Pentax' lenses have a fairly pronounced "bokeh CA" like this. It seems to be found on lenses which also are known for their nice rendering and soft bokeh transitions.
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