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06-30-2014, 02:32 PM   #1
Robert Perrie
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Lens not focusing at wide angle

Hey everyone.

I have just brought a Sigma DC 18-250 lens.

After looking at some wide angle shots of landscapes I took I have noticed that the point that should be in focus is not and comes across as soft focused.

I did some testing and looked at the test shots on 100% and above zoomed in.

I tried different apatures and focal lengths. This is what I found.

Zoomed in it did not matter what apature I used the area I focused on was pretty sharp. With a wide focal length (between 18 and say 25) if I was close to the subject (about 7 inches away) once again the area focused on was pretty sharp. I did notice that sometimes in the test shots the area I thought was being focued on was actually to the left or behind where the focus point was pointed on.

Then in the final test shots I tried were with a wide angle focal length (as above) in both wide and narrow apatures but about 2 foot away from the subject. When reviewing the image at 100% plus I could not find the sharp focal point. It seems the lens cannot get a focus point for subjects at a certain distance. This is also what I found with my landscape shots which were taken at around 2 in the afternoon on a sunny day. My test shots were done on a tripod with a 2 second timer and my landscape shots at 18mm had a 1/80 shutter speed. Once again I would say the photos were not out of focus but where soft looking.

Does this sound like I need the lens looking at or is this something that just happens with certain lenses.

Thanks.

06-30-2014, 03:02 PM   #2
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You should post a picture so we can see... since it could be anything (or nothing).
06-30-2014, 03:19 PM   #3
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The Sigma 18-250mm isn't the world's sharpest, lens but the photos should certainly not appear soft except when you really blow them up. A few samples photos would help us identify the problem

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07-02-2014, 04:00 PM   #4
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Ive attached some pictures i took. IMGP81895 is f6.3 / 180mm IMGP819030 is f18 / 180mm IMGP81871 is f3.5 / 18mm IMGP818825 is f18 / 18mm.

I focused on the silver clip in all the photos. The 18mm photos are not sharp at that point but the 180mm hotos are sharp at that point.

I have looked into AF fine adjustment but have not tried it yet.

My camera is a K30, by the way.

Thanks

Attached Images
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PENTAX K-30  Photo 
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PENTAX K-30  Photo 
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PENTAX K-30  Photo 
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PENTAX K-30  Photo 
07-02-2014, 10:47 PM   #5
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Sorry I'll try again. The first and third shots are the 18mm (wide angle) shots.

Thanks
07-07-2014, 02:33 PM   #6
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Hi I was just wondering if anyone had any answers to the problem I am having.
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