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02-13-2014, 12:03 PM   #31
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A little side trip here. What causes the purple fringing?

02-13-2014, 12:08 PM   #32
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Purple fringing - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Chromatic_aberration
It's kind of a prism effect- and seen in high-contrast situations.
02-13-2014, 12:09 PM   #33
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Open mouth ... stay quiet ... open mouth... stay quiet ... open...

I'll just say +1 to the OP sentiments. I have 3 AF lenses of which the WR 18-55 and the F35-70 is a second. the 18-55 is my only WR lens, and the only lens I have below 28mm (and that is a MF lens). So I find I have to pull it out now and then. It can produce some good images, but never do I come back and look at all the pictures and think it is has done a great job or that the colors have a lot of pop. It works, it has a purpose, but it will always produce some level of disappointment.
02-13-2014, 12:10 PM   #34
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it's not the lenses fault, its the Pentax AF system. I've ranted enough in other posts, so I won't go into it here.
I noted that the snow in front and to the left of the bird IS in focus. Your CAMERA decided that's what it was going to focus on because it had better "edges" compared to a soft feather bird.
It's not the lens, it's the camera.

02-13-2014, 12:12 PM   #35
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QuoteOriginally posted by nomadkng Quote
it's not the lenses fault, its the Pentax AF system. I've ranted enough in other posts, so I won't go into it here. I noted that the snow in front and to the left of the bird IS in focus. Your CAMERA decided that's what it was going to focus on because it had better "edges" compared to a soft feather bird. It's not the lens, it's the camera.
Open mouth ... if it is the AF system's fault, wouldn't it also create problems with other lenses. Just to keep the comparison reasonably fair with two lenses of similar range and speed - I'll be a lot more excited about the images coming out of my F35-70/3.5-4.5 than the kit lens. It is like the sharpness and colors just aren't there with the 18-55.
02-13-2014, 12:14 PM   #36
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Snow always fools the meter and the bird appears to be completely out of focus. My guess is that the AF let you down here, not the lens. Some motion blur possibly. In some conditions, especially snow with an overcast sky, the light is very flat and the camera doesn't do well. I shoot motorcycle and ATV ice racing throughout the winter and I use an MF lens because because the AF just doesn't do well. I have talked to Canon and Nikon guys at the events and they have the same problem.

I have found the kit lens to be a decent performer overall. It has it's limitations but it's capable of producing good shots.
02-13-2014, 12:16 PM   #37
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QuoteOriginally posted by dansamy Quote
A little side trip here. What causes the purple fringing?
The basic is that each color of light in the spectrum focuses to a different point. The greater the difference in light, contrast, and focus distance between two points in the picture, and the larger the aperture, the worse it becomes.

Here is a much better explanation. Chromatic aberration - Wikipedia, the free encyclopedia
02-13-2014, 12:20 PM   #38
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QuoteOriginally posted by nomadkng Quote
It's not the lens, it's the camera.
Or possibly the camera's AF settings. I'm using center-point AF using the 1st version 18-55 & ancient K10D & *istD, and rarely miss focus when the subject is so near. Reeftool makes some valid points as well. I'm not sure about the OPs problem - I still suspect possible lens condensation or backfocusing issues.


Last edited by paulh; 02-13-2014 at 12:22 PM. Reason: added comment
02-13-2014, 12:21 PM   #39
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Well, kit lenses tend to be lower quality and a little soft when they are wide open. You can't expect amazing quality from something that most probably sells for like $35 - $50.

However, it doesn't mean you cannot get some decent pictures with it.
Stepped down, with the right WB, light and metering, you can get some decent quality images.

In the conditions you have taken your first images, any lens... actually any camera, not lens, will have trouble getting the right exposure.
That's why is always a good idea to take control of the exposure.

So I wouldn't blame the lens yet. AF is a camera issue or user isue (stady hands, small movements, etc), not the lens issue (unless is misaligned) and the WB and metering is a camera issue as well.
02-13-2014, 12:21 PM   #40
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QuoteOriginally posted by MSL Quote
Open mouth ... if it is the AF system's fault, wouldn't it also create problems with other lenses. Just to keep the comparison reasonably fair with two lenses of similar range and speed - I'll be a lot more excited about the images coming out of my F35-70/3.5-4.5 than the kit lens. It is like the sharpness and colors just aren't there with the 18-55.
it really depends on the circumstances. the "old" (pre k3) PDAF prefers hard edges such as reeds or railings, or perhaps in this case the snow, to softer, furred or feathers subjects. it's quite common for the AF to lock on a target half a frame away. maybe this is the first time he has actually notice the phenomena because of his subject matter.

it has everything to do with relationship of the edges to the intended target, focal length and aperture. maybe he's managed to avoid issues with greater DoF before. maybe his subjects haven't been animals that often and so they tended to fill the screen more.

we could spend hours investigating every picture he ever took to determine why he hadn't encountered this problem before, and we could come to different conclusions.
I KNOW for a FACT I have this issue with my K5iis and I have read enough posts by both forum members and others in the blogosphere that have documented this AF "quirk".
therefore, I have concluded this matches a characteristic tendency of Pentax DSLR that I have a lot of experience with.

why the OP never noticed it before is beyond the scope of this thread, if you are claiming that Pentax DSLR have no AF issues that's a different tangent.
I was offering my opinion of his dilemma based on my experiences.

yes, I agree the 18-55 is not pro quality glass, but there is a reasonable level of expectation of IQ that this presented image does not meet. I do not believe the kit quality IQ of the 18-55 entirely explains the poor image.

I own a DA 50-135, Sigma 100-300 F4 and a Tokina 80-200 f2.8. I can regularly and repeatedly recreate this exact same image with THOSE lenses while using the K5iis PDAF with center point only selection. I have seen this exact result (soft animal, perfectly focused sharp edged object in another part of the frame) many many times too often in my own images, much to my heartbreak and dismay. So I feel reasonably assured in my hypothesis that it is the AF system

Last edited by nomadkng; 02-13-2014 at 12:30 PM.
02-13-2014, 12:30 PM   #41
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QuoteOriginally posted by mrNewt Quote
However, it doesn't mean you cannot get some decent pictures with it. Stepped down, with the right WB, light and metering, you can get some decent quality images.
Quoting just this post, but there are several here making similar arguments. The way I read the OP post was that the kit lens did not work for him as a slap it on, pick some reasonable settings and get a decent image out under a wide range of conditions lens. And in that respect I agree with him. I don't know if he is arguing he can't get any decent images, just that it doesn't perform well a lot of the time.

QuoteOriginally posted by nomadkng Quote
we could spend hours investigating every picture he ever took to determine why he hadn't encountered this problem before, and we could come to different conclusions. I KNOW for a FACT I have this issue with my K5iis and I have read enough posts by both forum members and others in the blogosphere that have documented this AF "quirk". therefore, I have concluded this matches a characteristic tendency of Pentax DSLR that I have a lot of experience with. why the OP never noticed it before is beyond the scope of this thread, if you are claiming that Pentax DSLR have no AF issues that's a different tangent. I was offering my opinion of his dilemma based on my experiences.
I wasn't trying to get into a discussion of the AF system. It is well documented and a frustration I have with my K5. But there is more to the dismal images than just being out of focus. Maybe part of the problem is that the kit lens is pretty slow, and so the AF worked a lot better with his 35/2.4. That is a reasonable question to consider. And at the end of the day, whether it is the AF system, or the quality of the glass, or that you have to work a lot harder with the 18-55 to get a good image out - there is a reasonable case to be made against using the lens as a general, walk around lens under many conditions.
02-13-2014, 12:35 PM   #42
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QuoteOriginally posted by MSL Quote
... But there is more to the dismal images than just being out of focus. Maybe part of the problem is that the kit lens is pretty slow, and so the AF worked a lot better with his 35/2.4. That is a reasonable question to consider. And at the end of the day, whether it is the AF system, or the quality of the glass, or that you have to work a lot harder with the 18-55 to get a good image out - there is a reasonable case to be made against using the lens as a general, walk around lens under many conditions.
I think part of the apples to oranges comparison is the FoV for the 2 lenses gives one margin for error. 35mm compared to 55mm focal length can mask some problems.

and for what it's worth, I don't think the 18-55 is worth the plastic one could recycle it for, so yes I agree with the premise that it should be donated to goodwill or better yet, some high school photography program and not counted on to produce ANY images of value. If the OP has reached that level of "sophistication" and demands for image quality, the 18-55 should never see the light of day again in his journeys.
02-13-2014, 12:38 PM   #43
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QuoteOriginally posted by nomadkng Quote
I think part of the apples to oranges comparison is the FoV for the 2 lenses gives one margin for error. 35mm compared to 55mm focal length can mask some problems.
That is why I compared the 18-55 with the 35-70 as they have a decent amount of overlap in focal range and are both about the same speed (or slowness), and I find the 35-70 produces better colors (independent of an AF issues). I'm not as harsh about the lens as you are - partly because the WR version brings that advantage to the table. But I can see most folks not using it unless they have a specific reason to do so that no other lens that they own can provide.
02-13-2014, 12:40 PM   #44
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QuoteOriginally posted by MSL Quote
Quoting just this post, but there are several here making similar arguments. The way I read the OP post was that the kit lens did not work for him as a slap it on, pick some reasonable settings and get a decent image out under a wide range of conditions lens. And in that respect I agree with him. I don't know if he is arguing he can't get any decent images, just that it doesn't perform well a lot of the time.
Is true, kit lenses are not the best out there.
My coment is based on what images he posted... from them, I do not see a lens issue but rather in camera settings issues.
In this case, based on the images presented, the camera failed to get the right exposure and focus properly, not the lens.

Lenses gives other kind of issues - like PF, CA, soft corners, lens flare, vignetting, barrel distortion, etc.
02-13-2014, 12:40 PM   #45
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QuoteOriginally posted by MSL Quote
That is why I compared the 18-55 with the 35-70 as they have a decent amount of overlap in focal range and are both about the same speed (or slowness), and I find the 35-70 produces better colors (independent of an AF issues). I'm not as harsh about the lens as you are - partly because the WR version brings that advantage to the table. But I can see most folks not using it unless they have a specific reason to do so that no other lens that they own can provide.
so we concur the 18-55 does and performs like a kit lens and the OP is basically correct in his conclusion...lol

however, he is using the wrong example photos to illustrate his point. poor images that is a result of AF errors rather than lens IQ does not valid the hypothesis. 2 identical subject images at identical focal lengths an apertures that are technically sound and in perfect focus would validate his conclusions. He is using faulty data.
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