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01-18-2010, 01:28 AM   #1
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Pentax DA 40mm Limited focus question

Hi,

I have a DA 40 Limited 'Pancake' and I've noticed what to me is strange behavior. Areas that are out of focus do not blur as I would normally expect but instead get weird ghosting or halo patterns around them. I include a cropped sample from an image where you can see this clearly. This was shot at f/2.8, which makes the effect worse. Is this normal behavior on this lens, or do I have a defective lens? I also feel that the focus never gets quite as sharp as on my 18-55 kit lens (regardless of aperture), which surprises me. What do you guys think?

Thanks!

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01-18-2010, 01:16 PM   #2
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I have this lens and I have never seen a bokeh like that on my copy....

Kind regards
.lars
01-18-2010, 02:22 PM   #3
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Welcome to the forum Dave.
Whilst I appreciate your concern about the fine lens, this alone cannot tell us whether your lens is defective.
Try some more controlled tests of both the bokeh and sharpness - utilising objects within the frame at varying distances from the camera, focusing on each object to look for focal point sharpness and bokeh rendering under different lighting conditions.

The image above shot out of focus and wide open will not be convincing in assessing true bokeh rendition.
01-18-2010, 02:56 PM   #4
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Hello Dave,

I once thought I had a problem with the bokeh of a used Pentax lens that I just purchased. It was unusually harsh and strange compared to all my other lenses. I realized that the problem originates from the very cheap UV filter that was on the lens. I removed it and bokeh became normal.

See this thread on another forum. I had the same effect on my pictures.

So if you have a UV filter in front of your lens, it may be a good idea to test it without the filter !

01-18-2010, 03:09 PM   #5
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Watch for UV filters and high in-camera sharpening. It should not look like that.
01-18-2010, 04:45 PM   #6
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A UV filter could not cause that unless it's shattered. Wrong image settings in-camera or a defective lens could be the case.

Posting the entire original image file would be helpful.
01-18-2010, 05:19 PM   #7
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Thanks everyone for your replies. How can I post the entire original file? There seems to be a size limit... and it seems even in this crop the resolution was scaled down... the effect is actually more pronounced than it appears here.

There is a UV filter on there, but the camera settings are the same as when I shoot with other lenses and I see nothing like that. I'll try taking some more controlled test shots with/without the filter on.

Thanks,
Dave
01-18-2010, 05:45 PM   #8
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QuoteOriginally posted by daveboettger Quote
Thanks everyone for your replies. How can I post the entire original file? There seems to be a size limit... and it seems even in this crop the resolution was scaled down... the effect is actually more pronounced than it appears here.

There is a UV filter on there, but the camera settings are the same as when I shoot with other lenses and I see nothing like that. I'll try taking some more controlled test shots with/without the filter on.

Thanks,
Dave
You can upload the entire picture on SendSpace ( Free large file hosting. Send big files the easy way! ) for free, among other places. Just a random link while googling.

01-19-2010, 01:15 PM   #9
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Just resize the image to web-friendly dimensions (~1000 pixels on the longest side) before uploading - that will take care of the file size too.

And post one where you think focus is not as sharp as the kit lens (and the same picture from the kit lens). Most likely, it's just the camera picking a different part of the picture to focus on than you intended - random chance, in other words. The 40 should be sharper at the palce of sharpest focus at pretty much any aperture up to f/11.
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