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12-04-2017, 03:38 PM   #1
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Help me test Pentax 15-30 for decent erring please)

So I've received my new 15-30 today, hooray and all)

However, I'm a bit worried since Adorama did a terrible job packing the lens - they packed the box into a much larger box, and used like 1 sheet of those air cushions. When I received the lens I could hear it sliding back and forth in the box So naturally I'm worried that it might've suffered some damage during the shipment. I want to properly test it for decentering, if I find any I'll want to exchange it for another copy for sure, it's a damn expensive piece of equipment. It's hard to do the test that PF posted in guides - the one where you place the object into each corner of the image and comparing it - with such wide fov.

I took a shot of a brick wall, it looks to be ok, the extreme bottom left corner seems softer than the one on the right. However, the one image I quickly took looks odd to me - church (where I focused) is nice and sharp, however the entire left side of the image is soft, and this is with f8 at 15mm, I thought dof should be very wide and should probably include a lot of the image? Or I'm missing something in terms of field of curvature etc, and image looks normal for the lens and distance to the object? Any suggestions/info are greatly appreciated

Fullres jpegs available here:
Update your browser to use Google Drive - Google Drive Help


Last edited by awscreo; 12-05-2017 at 04:37 PM.
12-04-2017, 04:24 PM   #2
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At 15mm the lens does have a lot of field curvature, so it can be a bit hard to evaluate. If you can shoot a scene were the 4 corners are equidistant, and compare them, that may work as a baseline test.

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12-04-2017, 04:55 PM   #3
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QuoteOriginally posted by Adam Quote
At 15mm the lens does have a lot of field curvature, so it can be a bit hard to evaluate. If you can shoot a scene were the 4 corners are equidistant, and compare them, that may work as a baseline test.
What about the brick wall pic I have in the folder?
12-04-2017, 05:03 PM   #4
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QuoteOriginally posted by awscreo Quote
What about the brick wall pic I have in the folder?
To me it looks OK!


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12-05-2017, 01:24 AM   #5
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Looks like chromatic aberration because of the contrast of the sky behind the trees.
Also, maybe the shutter speed was too slow for the trees, which could be softening the look of things. Sounds stupid, but trees just won't keep still! ;-) Try starting at 1/250 and see how it goes.
12-05-2017, 02:51 AM   #6
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Decentering tests will be more successful after you drop the lens from about three feet.
12-05-2017, 10:33 AM   #7
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QuoteOriginally posted by calsan Quote
Looks like chromatic aberration because of the contrast of the sky behind the trees.
Also, maybe the shutter speed was too slow for the trees, which could be softening the look of things. Sounds stupid, but trees just won't keep still! ;-) Try starting at 1/250 and see how it goes.
There was no wind at all, very still and quiet evening) I'm going to test it more today and tomorrow, I was just wondering if there was a method I can use to do it more efficiently.

---------- Post added 12-05-17 at 10:34 AM ----------

QuoteOriginally posted by D1N0 Quote
Decentering tests will be more successful after you drop the lens from about three feet.
can you post a youtube guide on how to do it properly? I want to make sure I drop my lens properly
12-05-2017, 10:37 AM   #8
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QuoteOriginally posted by awscreo Quote
can you post a youtube guide on how to do it properly? I want to make sure I drop my lens properly
Sure. Send the lens over to me. I will drop it for you

12-05-2017, 11:03 AM   #9
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QuoteOriginally posted by D1N0 Quote
Sure. Send the lens over to me. I will drop it for you
No deal! I want to drop my lens myself
12-05-2017, 01:35 PM   #10
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QuoteOriginally posted by awscreo Quote
No deal! I want to drop my lens myself
maybe try to shoot the starry sky, you can even underexpose the picture, and do not use astrotracer and SR. 10 s at f4, 15 mm. Then elevate exposure in the postprocessing and analyze the image.
BTW, CA are huge in the picture of the church. Is the picture done at f8 too?
P.S. But it seems the same with my lens, he he. As you know, Pentax has more CA compared to Tamron 15-30, but is a little sharper according to Photozone.de tests

Last edited by Medex; 12-05-2017 at 01:44 PM.
12-05-2017, 03:07 PM   #11
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So I've taken few shots just now, and I have puzzling results. I've shot few interior shots, and at f8 on a tripod/ES/remote shutter - image is sharp throughout the frame, incredible amounts of detail, much better results than same rooms with my Rokinon 14 2.8
But, I also drove around looking for shots outside (we had thick fog today, so a lot of cool shots were presenting themselves) - and I definitely see edge blurriness, even at f8. I was thinking - could it be due to sensor stabilization by any chance? Center looks sharp, but edges aren't. I'm trying to figure out if it's decentering (maybe my interior shots are sharp in corners because the of the working distance?) that shows at further distance? Unfortunately weather didn't allow me to setup a tripod somewhere and test it, although I was less worried about getting wet than with my Rokinon) Samples below (slightly processed and not in full res, but should be big enough to see edge detail). Hope someone can help me figure out if I got a good copy or a dud) I don't have enough experience with UWA's to decide I guess.

PS: It kind of seems that if I hold the camera almost perpendicular to ground, I don't have the edge/corner softness, but if I tilt it up/down, then I do, feels a bit like tilt-shift effect-ish, although of course not as extreme. Could I be because of the curved front element, and extremely wide angle?

Interior sample, on tripod, ES, remote control, f8 - corners/edges are sharp:
Room_201_1.jpg - Google Drive

Outdoors shot that shows the edge/corner softness - f8, hand-held, 1/8 with IBIS on, center seems sharp:
Fog4.jpg - Google Drive

Outdoors, f8, 1/10, hand-held, IBIS on, edge/corners seem sharp:
Fog2.jpg - Google Drive

Ourdoors, f8, 1/8, hand-held, IBIS on, right bottom corner and left upper corners are soft, rest seems sharp:
Fog6.jpg - Google Drive
12-05-2017, 07:01 PM   #12
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Anyone?) I'd like to figure this out before my return and exchange window runs out with Adorama
12-06-2017, 12:07 AM   #13
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Round 2
OK, to me, it just looks like the foregrounds are out of focus because they're way, way in front of the focus plane. Like on the road shot, it's clear the focal point is on the road, about a 1/3 the way down from the center of the picture. Any closer than that will be getting out of focus.
Wide angle lenses don't have any greater depth of field than any other lens. Need to stop down even more if you want such a huge focal range. Try f/16, or try taking a similar shot where you focus on a very close object in the corner of the frame - I bet that will look sharp - because the brick wall shot seems to confirm that the lens is very sharp.
12-06-2017, 12:45 AM   #14
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QuoteOriginally posted by awscreo Quote
It's hard to do the test that PF posted in guides - the one where you place the object into each corner of the image and comparing it - with such wide fov.
What is the issue?

Go outside with a tripod and do the four shots. Yes, obviously you need to turn the camera quite a bit from corner to corner, but that can not be any issue.

I would not want to rely on any other test scenery - especially not a flat one like the brick wall with a wide angle lens.
12-06-2017, 09:12 AM   #15
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I think the lens is not right, I've just shot a bunch of shots in the field, object was in focus at infinity, f8-16, hand held with and without ibis, with the main subject being somewhere in the middle of the focal plane etc. The left side is consistently softer, quite a bit softer. Its there at all apertures, especially prevalent at f8-11 I think. I'll do two more tests today and I think I'll be sending the lens back.

---------- Post added 12-06-17 at 09:38 AM ----------

Could a lens be decentered only at the edge, but not as much at the corner. It's weird, I've never seen it like this, not with my Rokinon 14, nor with the Samyang 10 2.8 I had for crop. It's like the right quarter of the Pic is blurred where it shouldn't be, the object in focus (edge of a field) goes across the frame at about equal distance to the camera at both edges of the frame..
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