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09-01-2008, 08:50 PM   #1
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DA* 16-50 testing

Sorry to beat a dead horse here..... I finally took the plunge and ordered this lens for my K10. I've read some horror stories about bad copies, (and yes, I've used the search function) but I haven't seen a clear explanation on how I can fully test my copy (when it arrives Wednesday) to make sure it's a good one. After spending that kind of $$, I'm much rather take a few hours and fully test the lens, rather than realize I have a problem down the road. I remember reading something about taking shots of a brick wall? Can somebody either explain how to do this, or link to an explanation they are already aware of. Thanks for your help......... jeff

09-01-2008, 09:02 PM   #2
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So, you're a gamblin' man? It is simple to test. Some people will say, "go out and take real pictures and be happy yada, yada" but the danger is that you won't see the problem many of us had until you take a picture of a group of people and the ones near the edges are fuzzy, and the lens is now out of warrantee. Pictures that show how great the DA16-50 is are usually shots of a center subject with bokeh all around. That will hide a whole class of problems that this lens has.

Go to aperture priority mode, and set 2.8. Then take a picture of something that is all in the same plane, that has some detail. This is why the brick wall is so common. Make sure you are not too close to the wall, and that the camera is perpendicular to it. Do this at each extreme in focal length (16 and 50) and somewhere in the middle as well. Compare the sharpness in the center, to the sharpness on the edges. Is it symmetric? If no, then you have a decentered lens. I have had that problem, but I have also had a copy that was symmetric but the edge focus was so bad around the edges that it would make you see double. My third copy was decentered again, and is on the table with the UPS tag on it waiting to go back.

Now of course the image at 2.8 is going to be softer than at smaller apertures, but it is the first place to start, and you will see decentering right away.

good luck!

Last edited by PentaxPoke; 09-01-2008 at 09:14 PM.
09-02-2008, 09:14 AM   #3
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QuoteOriginally posted by JCorwin Quote
Sorry to beat a dead horse here..... I finally took the plunge and ordered this lens for my K10. I've read some horror stories about bad copies, (and yes, I've used the search function) but I haven't seen a clear explanation on how I can fully test my copy (when it arrives Wednesday) to make sure it's a good one. After spending that kind of $$, I'm much rather take a few hours and fully test the lens, rather than realize I have a problem down the road. I remember reading something about taking shots of a brick wall? Can somebody either explain how to do this, or link to an explanation they are already aware of. Thanks for your help......... jeff
First, test you camera with one of the Front Focus/Back Focus test charts that you can find on the internet and follow those instructions. Before you do the following, you want to make sure that your camera/lens combination is focusing at the proper distance. If you have a K20D, adjust as/if needed.

I have performed the following tests both with a Brick Wall (outdoors) and with multiple typed print newspaper pages taped to a well lit wall (indoors). Outdoors I have used Blue Masking Tape to mark the center point and I've used a black felt pen marker to make a cross at the center of the newspaper. These center marks are what I align to use for focusing on. For outdoors, I have been about 10' distance from the wall, while indoors I have setup between 30" to 36" from the wall.

Mount your camera on a tripod and square it up compared to the wall. You do not want to be too far away from the wall, but you do want to have the bricks or newspaper fill the entire frame at the 16mm wide end. Use Aperture Priority mode, select Center Focus Point only, select Single AF, adjust White balance if necessary, set shutter to 2 second delay (or use remote release), select sensitivity of 100, 200, or 400 (max) ISO.

The DA*16-50 is marked at 16mm, 20mm, 28mm, 35mm, and 50mm. Take 2 test shots at each focal length with each apertures of f/2.8, f/4, f/5.6, f/8, and f/11. Inbetween each individual exposure, readjust the focus manually so that it is out of focus and that the camera will need to re-aquire focus for each exposure.

Then view your images on a computer monitor at both it's default size (where you can see the entire image on the screen) and at 100% (where you have to scroll around to see different portions). The key thing to look for is symmetry.

The border image quality of the DA*16-50 is not that great at 16mm @ f/2.8. By that I mean that there is a considerable amount of the image on the wide borders that will be considerably less sharp/blurred than the center. There will also be linear distortions quite noticeable at the wider end, but these are normal and will improve as the focal length increases.

However, as you increase the focal length, decrease the aperture, or both - you should see the border areas that are less sharp significantly be reduced to narrower bands. The amount of improvement (lack of sharpness and detail) on both the right and left should improve fairly uniformly on both the right and left sides. By 35mm and 50mm and f/5.6 or slower, the amount of border unsharpness as well as the percent of the image should be be quite reduced from when you started at 16mm and f/2.8. For the newspaper test, you should be able to discern/read the text across the full image (even wide at f/2.8). Also, the center should remain the sharpest portion of the image.

If the sharpest portion of the images is not or does not remain at the center, then your lens is decentered. If the boarder IQ on one side improves significantly (and as expected), but the other side retains a large portion of the border IQ that never improves anywhere close to the same as the other side - then your lens is decentered, or at least defective. Once again, the key thing to look for is symmetry in the IQ improvement - not perfect IQ from border to border, corner to corner.

Since I had one, I've also take test shots with my DA 18-55mm kit lens at about 20mm, 28mm, 35mm, and 50mm and f/5.6, f/8, amd f/11 for comparison and as a control. I do this to eliminate/reduce the effects that may be induced if the camera is not 100% squared to the wall. If there are IQ issues on one side of the DA*16-50mm images that are due to not being squared, then they should also be exhibited using the kit lens. If you have a good DA* lens, then at these comparable focal lengths and apertures, the DA*16-50 should clearly beat the kit lens in terms of sharpness, contrast, and clarity both at the center and on both sides.

Some other tests that I have done: I use some woods across an open field to test for consistent and symmetric IQ across the FOV when focusing at infinity. The overall clarity of the leaves and branches should be fairly equivalent on both the left and right sides, if you have a good copy. Also, if you have a model/person available, take some half body shots - focusing on the eyes - in portrait/verticle position where some images are taken with the left side of the camera up and others with the left side of the camera up. A good copy should record equivalent sharpness and detail on the face regardless of which side of the camera was held on top.

GOOD LUCK!

Last edited by Imagination4; 09-02-2008 at 09:28 AM.
09-04-2008, 09:12 PM   #4
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Thank you both for the great information. I finally got the lens this evening after playing tag with the UPS man for a few days. With any luck, I'll be able to check it out thoroughly over the weekend. I've got my fingers crossed that it's a good one. If not, I bought it from Amazon, and they are great about returns.

09-04-2008, 09:37 PM   #5
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great info PentaxPoke and Imagination...i have no idea how to test it either...thanks
09-05-2008, 06:17 PM   #6
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Inflation - 4th time is the charm

On my 4th attempt at acquiring a DA* 16-50mm lens, I finally have a keeper. It passed the

1. (Indoors) newspaper taped on the wall,
2. (Outdoors) brick wall, and
3. (Outdoors) a 1 1/2 hour stroll through a nearby park with both prairie and wooded areas

IQ tests!

I'd really had given up after 3 bad copies, but the lure of the dust and weatherproofing finally swayed me to give it one more try. I guess in this case perseverance did pay off.
09-11-2008, 10:51 PM   #7
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holy crap.....I may have a good one on my first try. Brick wall tested OK, Need to do the newspaper test again to confirm my suspicions that inconsistant light/angles/ led to a few problems. Hopefully by the end of the weekend I can declare this a victory and really begin enjoying this lens.
09-11-2008, 11:04 PM   #8
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QuoteOriginally posted by JCorwin Quote
holy crap.....I may have a good one on my first try. Brick wall tested OK, Need to do the newspaper test again to confirm my suspicions that inconsistant light/angles/ led to a few problems. Hopefully by the end of the weekend I can declare this a victory and really begin enjoying this lens.

I hope you are correct, if so you will be one happy photographer. I too talk the plunge and an even deeper one for I purchsed from B&H USA and I'm in Australia.


This lens is great when you have a good one and it exceeds all my expectations, it is a perfect match for my DA 50-135.

I have found so far that this is my goto lens and seems to live on my camera.

One tip... remove the hood if you ever go from outdoors to indoors and use the camera's inbuilt flash for the wider angle shots at 16mm


enjoy this great lens



Neil

09-12-2008, 07:26 AM   #9
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Hi,
I'm kind of late to the dance.
Great description of the tests. I just like to add: if you 're using a newspaper and close enough to it, make sure that plane of the sensor as close to parallel to the paper as possible. Otherwise, you can get artificial de-centering.
My story with 16-50: first I started shooting and enjoyed the results, then I read all thoes horrible stories and started to test - after a few attempts found that the major poins are OK, then the SDM went to la-la land - I sent the lens to Pentax, they fixed it, now it works like a swiss clock, only silently.
Good luck
09-12-2008, 07:45 AM   #10
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Why not have it serviced?

Wouldn't it be easier to send the lens in for service (where it would be thoroughly tested) vs going through multiple copies?

I'm just curious about which is easier or faster.
09-12-2008, 07:06 PM   #11
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QuoteOriginally posted by alfdog Quote
Wouldn't it be easier to send the lens in for service (where it would be thoroughly tested) vs going through multiple copies?

I'm just curious about which is easier or faster.
Perhaps if Pentax service would be able to actually *FIX* the same lens sent in - then perhaps "Yes", or if not, then send a brand new lens that Pentax service had already checked out. However, (at least in the U.S.) Pentax may provide a refurbished item (if your original one cannot be repaired) in lieu of providing a new one or taking the full time of repairing your original one. This is actually common practice in the U.S. for a lot of consumer electronics, and seeing as how Pentax does not even include a copy of their warranty in the box, it is difficult to determine what their actual warranty entails - beyond the scope of TIME.

That said, here was my time line going thru 4 DA* 16-50 lenses.

1) Order 1st lens from Amazon.com. After determining that it was defective, I went thru Amazon's on-line process to arrange for a Return/Exchange.

2) My 2nd lens (the replacement from Amazon for #1) was actually shipped out from Amazon.com to me before they had fully processed my returned lens #1 - so in less than a week after arranging for an exchange I already had lens #2.

3) After determining that lens #2 was bad, I process an Amazon.com Return/Exchange on-line again, but they refused to send me a 3rd (a 2nd replacement lens) - so I ended up waiting about 1 week for Amazon to receive and process my 2nd returned lens.

I purchased my 3rd one locally from Calumet Photographic, determined that it was also defective within 2 days - so returned it 3 days after I had purchased it.

4) After the credit for my 3rd lens returned showed up on my credit card statement, I placed a new order for my 4th lens from Amazon.com again (which they processed and I had within 2 days). This 4th one ended up being good.

So I went thru 4 lenses in a little about 2 1/2 weeks, which compared to sending one in to Pentax service, at least insured that I was getting a NEW lens each time.
10-10-2008, 09:44 AM   #12
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Nice topic, thanks for the recap about the testing lens... i have ordered mine on my K10d, hope it will be OK.

I have one question, what is the filter did you put on your 16-50 (if any!), you can reply on my post here: https://www.pentaxforums.com/forums/pentax-camera-accessories/38986-best-filt...guys-have.html

thanks!
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