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Old Dec 3, 2011, 2:44 PM   #1
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Default Pentax K5 - chromatic aberration

I'm looking to upgrade my K10 to the K5 but having shot a few images at my local dealer with a Tamron 18-250mm noticed CA on a few shots.

Attached image shows CA along the edge of the roofing 'bargeboards' and around the light socket - ISO 200, 375mm, f13, 1/250S

Looking at the images of the skyscrapers on the review at Digital Camera Resource for the Kx which shows considerable CA, I've also read that the K5 with the 18-135mm lens is particularly bad in this respect; CA is noticably absent on ALL Nikon images i.e. D90, D7000

Staining has been an issue with the K5 sensor but is CA just limited to the lens or is the sensor used on the K5 partly to blame.

Feedback from you K5 users would be greatly appreciated.
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Old Dec 3, 2011, 4:42 PM   #2
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I don't have a K5 so I can't comment on your specific question, but it's my understanding that CA is caused by the lens, and is not affected by the sensor. Am I wrong about that? I'm totally guessing about this, but I wonder if the reduced incidence of CA in Nikon bodies could result from Nikon's firmware?
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Old Dec 3, 2011, 7:09 PM   #3
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It is the lens not the camera.
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Old Dec 3, 2011, 8:43 PM   #4
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The CA or chromatic aberration, is localized in the lens. Its the lens inability to focus all the colors on the sensor plane.

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Old Dec 3, 2011, 11:43 PM   #5
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I don't think the CA I see with my K5 is much different than what I saw with my other Pentax cameras. I have a couple of lenses that show CA and several more that show none (or almost none, if it's there it's not noticeable enough for me to correct). I read some people theorizing that the K5 was worse for CA when it first came out, but I don't see it at all with my equipment.
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Old Dec 4, 2011, 12:32 AM   #6
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I have also read in professional reviews that the K5 can exacerbate the CA produced by certain lenses to a minor degree (nothing worth worrying about in 99.99% of shots) though it should be remembered that for by far the greater contribution is from the lens itself.

The shot you have posted is of a very high contrast scene and in this situation almost all lenses are going to show some CA (easily removed in PP if you e.g. crop and find it noticeable). Even very high quality lenses can produce noticeable CA under extreme conditions.

Executive Summary : Where the K5 is concerned there is nothing in the slightest to worry about.
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Old Dec 4, 2011, 12:10 PM   #7
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Quote:
Originally Posted by mtnman View Post
I don't have a K5 so I can't comment on your specific question, but it's my understanding that CA is caused by the lens, and is not affected by the sensor. Am I wrong about that? I'm totally guessing about this, but I wonder if the reduced incidence of CA in Nikon bodies could result from Nikon's firmware?
The Tamron 18-250mm is not that wonderful a lens (but a good 'walkabout' lens nevertheless) & does in itself suffer from CA/vignetting so I wasn't that surprised to see it at the edge of the frame - what 'concerned' me was a review of the Pentax 18-135mm lens & a users comments which left him most disappointed.

I did wonder if the Nikon firmware could have been used to suppress CA.

Quote:
Originally Posted by Frogfish View Post
I have also read in professional reviews that the K5 can exacerbate the CA produced by certain lenses to a minor degree (nothing worth worrying about in 99.99% of shots) though it should be remembered that for by far the greater contribution is from the lens itself.

The shot you have posted is of a very high contrast scene and in this situation almost all lenses are going to show some CA (easily removed in PP if you e.g. crop and find it noticeable). Even very high quality lenses can produce noticeable CA under extreme conditions.

Executive Summary : Where the K5 is concerned there is nothing in the slightest to worry about.
Image quality at high ISOs is what lets down the K10 with the Tamron 18-250mm. In order to reduce vignetting, across the focal range, it's necessary to use as small an aperture as possible which means increasing the ISO to achieve a shutter speed that prevents camera shake (even with SR switched on).

The attached image compares ISO 12800 with ISO 400; I should point out that I initially though I was using ISO 128 so it was a mistake on my part but it does indicate the performance of the K5 at high ISOs. The ISO 12800 images have been noise suppressed using the Imagenomic filter in PS CS5; post processing has been used on all images to enhance quality. The bottom 2 images are stand alone and not enlargements from the top 2!

Thanks to all for the feedback.
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Last edited by Catbells; Dec 4, 2011 at 12:16 PM.
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Old Dec 4, 2011, 3:53 PM   #8
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G'day CB

I think that you are overly worried about too much - and the micro-enlargement of the overhead lamp shows "exactly what would be expected" from a 'commercial / consumer quality' zoom lens

If you were to be shooting professionally [nat geographic etc] then your lenses would cost in the $thousands, not $hundreds, and I believe therefore the results you are seeing are quite 'normal'. Equally, if you want 'perfect IQ' forget all such zoom lenses, go to a series of individual prime lenses ... and sell your car to pay for them :-)

Regards, Phil
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Old Dec 4, 2011, 4:16 PM   #9
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I beg to respectfully, politely and cordially disagree on the Tamron 18-250. I find it to be an excellent all around lens I shoot professionally for a newspaper. Example below at full zoom. CA is usually not a problem with most lenses unless you are zooming in beyond the reasonable.
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Old Dec 6, 2011, 5:20 AM   #10
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CA is a function of the lens, so if you had ca with the k10, you'll also have it with the k5, and the K5 will have it more. Simply because you've got more pixels on the sensor so a 3 pixel CA on a k10 would become a 4 pixel CA on a K5.
But this is as normal as can be expected.

One of the other 'problems' that was found by measurebaters was a purple sensor blooming, when pushing images in post processing to higher ev's (+3 and more), sometimes a purple shine appeared over the image. nothing to do with CA, but it's purple.
I haven't seen it myself but I think when you work towards it, you might notice them.

For as far as I know the only problem with the K5 have been the sensor stains and that was fixed by Pentax in a great way.

Just my 5c

Ronny
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