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03-15-2008, 03:56 PM   #1
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Is this a bad copy of 16-50*?

Hi, everybody, I am a new comer here, however, I have taken photos with my K100d and Sigma 24-70/2.8 for almost a year. On the Jan/27/2008, I bought a DA* 16-50 from Amazon. And before this, I haven't heard of the QC issue of this lens(heard impossible :P), so I haven't test it after I got it.
These days, during taking some photos with it, I found that the edge sharpness is not so good, but I don't know if it is the "normal" status of this lens. If I send this lens to Pentax USA for adjustment, does it possible for Pentax Customer Service to make it better?

Attached is the link which includes a original photo(K100D, 16mm, F2.8, ISO200, without any filters like UV and CPL) and the 100% crop of the four corners and center. Would you please help me to confirm that may I send this back to Pentax USA for adjustment? Thank you so much.

Picasa Web Albums - Adonishong - 16-50.judgement


Last edited by adonishong; 03-15-2008 at 04:41 PM.
03-15-2008, 04:58 PM   #2
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Your right side isn't looking so good. Are you sure that the lens is completely parallel to the brick wall?

I can't comment on how well Pentax USA will calibrate it as I haven't tried that yet.
03-15-2008, 05:03 PM   #3
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Left hand corners look sharper than right hand corners. But it could be because sensor is not parrallel to wall and DOF is not covering.

Take a shot of an average scene at 16mm f2.8 in good daylight of a contrasty subject situated at 4.5 to 5 metres from the camera and post 100% centre and corner crops. If possible use tripod and mirror lockup with remote or cable release.
03-15-2008, 05:28 PM   #4
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QuoteOriginally posted by drivel Quote
Your right side isn't looking so good. Are you sure that the lens is completely parallel to the brick wall?

I can't comment on how well Pentax USA will calibrate it as I haven't tried that yet.
QuoteOriginally posted by selar Quote
Left hand corners look sharper than right hand corners. But it could be because sensor is not parrallel to wall and DOF is not covering.

Take a shot of an average scene at 16mm f2.8 in good daylight of a contrasty subject situated at 4.5 to 5 metres from the camera and post 100% centre and corner crops. If possible use tripod and mirror lockup with remote or cable release.
Thank you to both drivel and selar, I will do the test you mentioned later. Thank you so much.

By the way, in fact, I have test from f/2.8 to f/22, the result with f/2.8, f/3.5, f/4, f/5.6 looks like the same...

03-15-2008, 07:28 PM   #5
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Thanks so much to drivel and selar.

I will do the test as selar said soon.

If I wanna do a newspaper test, how long shall I set for the distance between newspaper and lens?
03-16-2008, 10:30 PM   #6
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QuoteOriginally posted by adonishong Quote

By the way, in fact, I have test from f/2.8 to f/22, the result with f/2.8, f/3.5, f/4, f/5.6 looks like the same...
That's not good

I would fill the frame with the whole piece of newspaper. It gets more difficult to get parallel at those close distances, however.

Let us know how it works out
03-17-2008, 12:20 AM   #7
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To fill whole frame with newspaper at 16mm, he would need a very large newspaper, or get to the 30cm close focus limit of the DA*16-50, at which distance the depth of field is very little, about about 2/3rds of a centimetre at f2.8.
I would call that extreme shooting conditions for this lens, its not a macro, so plane of focus will be curved, adding to the bad impression he will get of the lens.
Best to test the lens by taking a shot representative of normal usage of the lens. If the lens is defective, the defects will show up even in normal shots.
03-17-2008, 12:37 AM   #8
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That's certainly true.

My guess is that if he does a quick newspaper test around 50mm he's going to see the defect immediately.

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