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07-10-2015, 12:36 AM   #1
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Is my kit lens faulty?

Hi,

Just brought a Pentax K-50, and compared to the D5100 i was using its fantastic. Its a joy to hold and use, and the pentaprism is so much better than the pentamirror in the nikon. However im having an issue with the Kit lens at 55mm.
At F/5.6-7.1 im noticing a weird glow. It happens on all my 5.6-7.1 images. I've attached the best sample of this issue. Is this normal of the kit lens, or did i receive a duff lens? This is an extreme example, but it does happen in all lighting situations. I've tried a couple of portraits at this length and they look like ive added a cheap photoshop filter over the whole image.

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07-10-2015, 01:05 AM   #2
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looks very nice/dreamy there is some people buying expensive "soft" lenses to achieve this look :-) how much did you crop?
it seems not to be normal...
07-10-2015, 01:23 AM   #3
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I say nay but I'm going more so off your description as the single image without cropping and exif data doesn't give much to go from. At F7, even kit lenses should be sharp in ideal lighting conditions. If you could, and for the benefit of others to judge, take a flash photo or daylight (light behind you) at F7 and +1/125 sec and post it with a crop of the centre.
07-10-2015, 01:36 AM   #4
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are you using a hood?

07-10-2015, 01:39 AM   #5
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At every situation (45-18 wide to f11 (havn't shot below f11), and 55mm at f8+ (f7.1 isnt bad, but the glow isnt an issue at f8)) the lens is sharp, sharper than the d5100 kit lens, and has better colours, the only issue i have is this lens at 55mm f5.6-f6.3 (again its a little pronounced at f7.1, but that one is just me being super fussy).
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07-10-2015, 01:55 AM   #6
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Very difficult to determine whether this is a problem with the lens or not. Given the size of the bee, the image is appears to be cropped. If not cropped then the image must have been taken at or near the minimum focusing distance at the maximum focal length for this lens. My DA 18-55 AL WR tells me the minimum focusing distance is is 0.25 metres. At that distance, at those apertures, you will have virtually no depth of field. The glow you are seeing could be out of focus blur. It could also be camera movement or subject movement or both. Flowers and bees are not good subjects for determining lens performance in my opinion, as they move.

In any zoom lens the performance is often not at it optimum at its maximum focal length, I think this this would be true for the kit lens more so that a top line zoom.

A finger print on the lens can cause effects like this. Filters can also reduce image quality. In fact one method to get a soft image such as this is to deliberately smear Vaseline on a UV filter.

In summary I can not say for certain if your lens is faulty. I would suggest a more controlled test, with camera on tripod and a fixed subject such as a test target.

I would also not judge the lens too harshly if it does not achieve perfect IQ at the extremes of its physical limitations. I have a kit lens in my bag, I do know it has limitations but it is often my lens of choice.

I hope it all turns out well
07-10-2015, 02:32 AM   #7
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The "pseudo-macro" position of the 18-55 is worth next to nothing in my experience as well.
Don't expect good performance unless stopped down a fair bit (f/9.x, f/11).
07-10-2015, 02:39 AM   #8
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Either this is a lens defect, or the image is simply mis-focused (more likely) based on the second photo you posted. Try to blow up the image in live view and see if you still get artifacts when focused correctly. If so, I'd get the lens serviced or exchanged.


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07-10-2015, 02:46 AM   #9
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It happens on every 55mm f5.6-6.3 image, don't get me wrong i am a beginner, so I know that my technique is bad, and that the lens is probably fine, but I would like to make sure that I don't have a defective lens.

This leaf crop shows the difference between f5.6 and f7.1, this issue doesnt appear at less than 45mm, and yes while 45mm f4.5 is soft compared to 45mm f7.1 it doesnt have this 'glow'.
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07-10-2015, 02:48 AM   #10
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I just had a look back at some old photos I took with a plastic Sigma kit lens on a *istDS. What I see in mine are limits to sharpness and resolution typical of the lens and sensor I was using, but not the glow you have. Even cropped down to pixel level there is no halo effect at play. It's only one image, but I'm guessing you've taken all manner of shots in all conditions and you're seeing the same thing. If this is the case and I were in your shoes, I'd be taking it back.

If you PM me your e-mail address I'd be happy to send a full size image so you can compare for yourself. I have some 18-55mm Pentax lens images my Father took on a K-x and the same comment applies.
07-10-2015, 07:01 AM   #11
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I've returned it to amazon for a replacement, hopefully the replacement doesnt exhibit this problem.
07-10-2015, 07:22 AM   #12
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Looks to me that your lens has a front-focus issue (as in one of the pictures your have shown - nothing is in focus).... in general, if you stop down a bit more, it will get something in focus. Try something like F8 to F10 to see if you can get that. I am also not familiar with the k-50, and not sure if you can use AF fine adjustment to correct it.

You should also try to see if the same behaviour exhibited at other focal lengths. Kit lenses are generally not so good at either end of the focal lengths.
07-10-2015, 09:54 AM   #13
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no matter what is in focus, and the focal distance at 55m everything has a glow, but its more pronounced in those images. But again only at f5.6/6.3/7.1 at 55mm. Other than that focal length/apertures, its a good lens, which leads me to believe it is a defect rather than the lens. At f8, f9, f10 everything is sharp all focal lengths, even 18-45mm are fine wide open.
07-10-2015, 11:37 AM   #14
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QuoteOriginally posted by Jedipottsy Quote
no matter what is in focus, and the focal distance at 55m everything has a glow, but its more pronounced in those images. But again only at f5.6/6.3/7.1 at 55mm. Other than that focal length/apertures, its a good lens, which leads me to believe it is a defect rather than the lens. At f8, f9, f10 everything is sharp all focal lengths, even 18-45mm are fine wide open.
?
Actually, I'd say quite the opposite...
07-10-2015, 05:24 PM   #15
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I see the lens has been returned so this is probably academic but I have done a table top test of my DA 18-55 AL WR and I can confirm what the OP is saying. The lens is very soft at the extremes of its physical parameters.

  • Minimum focusing distance of 0.25 metres
  • Maximum focal length of 55mm
  • Maximum aperture of f5.6
With the above settings the image is virtually unusable, nothing is sharp. Stopping down the aperture to f7.1 - f8 improves matters considerably. Whilst I was not expecting great results, I was surprised by the extreme softness displayed. Despite my experience, I am not prepared to say this is an indicator of a faulty lens. I see it as an example of what happens when attempting to push the performance of a budget lens to the extreme. I would have no hesitation in recommending the DA 18-55 AL WR to anyone for general use but for extreme close up work, a dedicated macro lens has no equal.



I fear the OP will get no joy from the replacement lens.
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