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05-20-2022, 08:36 AM - 2 Likes   #46
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QuoteOriginally posted by BigMackCam Quote
It's possible, sure, but it's a lot of work even just for one lens, never mind the hundreds listed - and since PentaxForums is a privately-owned-and-run user community, not a profit-driven commercial venture, I can't imagine who here would be prepared - and equipped - to carry out that work for philanthropic motives alone...
...especially considering how much it costs to buy the equipment necessary to do accurate and repeatable lens resolution tests. Putting a camera on a consumer grade tripod and pointing it at a test target might give the impression of doing a lens test, but the reality is the person doing it is kidding themselves.
The best way to do a technical test on a lens is to do MTF measurements, and that is a very expensive way to do things.
The best way for a user to test a lens is to go out and take pictures. If you are after sharpness and the lens you are using satisfies that need, it's sharp enough, if it doesn't, then you have a decision to make.

05-20-2022, 09:16 AM   #47
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QuoteOriginally posted by Mikesul Quote
Although the OPs question was a bit nave and probably annoying to some it has prompted a very interesting discussion which I hope will continue a while longer.
Couldn't agree more, Mike. The OP's question was entirely valid, and I hope they too feel the discussion is worthwhile. I'm sure a lot of members reading this will learn something useful...
05-20-2022, 09:22 AM   #48
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QuoteOriginally posted by Wheatfield Quote
...especially considering how much it costs to buy the equipment necessary to do accurate and repeatable lens resolution tests. Putting a camera on a consumer grade tripod and pointing it at a test target might give the impression of doing a lens test, but the reality is the person doing it is kidding themselves.
The best way to do a technical test on a lens is to do MTF measurements, and that is a very expensive way to do things.
The best way for a user to test a lens is to go out and take pictures. If you are after sharpness and the lens you are using satisfies that need, it's sharp enough, if it doesn't, then you have a decision to make.
More than the difficulty of it, except for Roger Cicala, no one tests more than one copy of a lens. That means that you might have an outlier in either direction. Just because Optical Limits says 'x' lens is the sharpest, doesn't mean that your copy fits that bill.
05-20-2022, 09:31 AM   #49
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QuoteOriginally posted by Rondec Quote
More than the difficulty of it, except for Roger Cicala, no one tests more than one copy of a lens. That means that you might have an outlier in either direction. Just because Optical Limits says 'x' lens is the sharpest, doesn't mean that your copy fits that bill.
Absolutely true. How often have we read about people buying half a dozen copies of a lens and returning all but one of them? I recall in our brand, it was decentering that was the problem being countered by purchasing multiple copies and keeping the best one, but in a piece of equipment where a millionth of an inch can make the difference between excellent and merely good, it's really impossible to know if what you have is the best there is or also ran unless you can compare your results back to the factory MTF specs, which takes us back to needing a very expensive and specialized optical test bench in your climate controlled laboratory.

05-20-2022, 10:32 AM - 2 Likes   #50
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QuoteOriginally posted by Wheatfield Quote
Absolutely true. How often have we read about people buying half a dozen copies of a lens and returning all but one of them? I recall in our brand, it was decentering that was the problem being countered by purchasing multiple copies and keeping the best one, but in a piece of equipment where a millionth of an inch can make the difference between excellent and merely good, it's really impossible to know if what you have is the best there is or also ran unless you can compare your results back to the factory MTF specs, which takes us back to needing a very expensive and specialized optical test bench in your climate controlled laboratory.
I read that and thought how does that work? I buy one test it. Decide it is not good enough and demand a replacement. Next one may be better or worse. Have I made a mistake returning the first. Try again and again. It's like playing cards. But then the penny dropped. You meant buying half a dozen at one time!! Surely not. Personally I respect our struggling retailers too much to play that game. (Please don't bother mentioning Amazon as not struggling. I only ever buy lenses from small independents.)

Wary of this approach by some purchasers to lens buying I would never buy an "opened box" lens as I've always suspected it had been returned. Pity the retailer. I've bought numerous lenses over many years and only returned one. The replacement performed much the same. My mistake. I felt bad. I vowed then I would only ever return a lens if I was sure it was faulty as I don't buy into this poor quality control idea, believing that it's more a question of very fine tolerances. Sure a duff manufacturer could have huge tolerances, but Pentax don't do that.
05-20-2022, 11:21 AM   #51
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QuoteOriginally posted by BarryE Quote
I read that and thought how does that work? I buy one test it. Decide it is not good enough and demand a replacement. Next one may be better or worse. Have I made a mistake returning the first. Try again and again. It's like playing cards. But then the penny dropped. You meant buying half a dozen at one time!! Surely not. Personally I respect our struggling retailers too much to play that game. (Please don't bother mentioning Amazon as not struggling. I only ever buy lenses from small independents.)

Wary of this approach by some purchasers to lens buying I would never buy an "opened box" lens as I've always suspected it had been returned. Pity the retailer. I've bought numerous lenses over many years and only returned one. The replacement performed much the same. My mistake. I felt bad. I vowed then I would only ever return a lens if I was sure it was faulty as I don't buy into this poor quality control idea, believing that it's more a question of very fine tolerances. Sure a duff manufacturer could have huge tolerances, but Pentax don't do that.
From a few posts in these forums over the years, I've learned that some folks buy, try, use (often for several days or weeks) and return items even if there's nothing wrong with them - i.e. just because they don't like the item, or they've changed their mind. Like you, I couldn't do that to a retailer - but lest we be too critical, it actually seems to be part of the accepted mail-order shopping culture in some countries, such that it's not even considered unusual or commercially-unfriendly practice. Amazon Warehouse in the USA seems to be a business-within-a-business formed largely from that culture.

I'd have thought that kind of practice must inflate prices to some extent. The potential losses from returned, re-stocked then re-sold-at-discount items would have to be built in to a business' pricing model, or else it would become commercially unviable...

With all that said, I have absolutely no qualms in returning a lens (or any other product) that doesn't perform largely as intended and expected... and whilst I do my best to test any lens on the day I receive it - or, at latest, the day after - I once returned a lens after several days' use, as it wasn't immediately clear that the issue or "quirk" would negatively impact my shooting (it was the HD DA16-85, with what seems to be a relatively common issue of movement in the frame during AF operations). When I receive a new lens, I do some basic tests - checking any switches, making sure it focuses to infinity, confirming it can focus accurately within the AF fine adjustment limits of my K-3 and K-3II, and checking that all four quarters of the image are similar in terms of sharpness, both for close-up and distant scenes. It's not test-bench stuff... just basic tests to ensure the lens broadly does the job it was designed for

I've bought "open box" products before. Some have been fine, but with others it was clear why they were returned. If the price is right, warranty is good and returns are easy, I'll take the risk... but I set my expectations accordingly to avoid disappointment

Last edited by BigMackCam; 05-20-2022 at 09:18 PM.
05-20-2022, 12:36 PM   #52
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I acquired my first set of Pentax 67 lenses (late 55 mm f/4, late 90 mm f/2.8 and late 200 mm f/4) in 1991 and all three were excellent. Over the years, my arsenal grew to 13 lenses and all proved to be EXCELLENT. I started getting interested in 645 equipment 10 years ago and all camera bodies (645N, 645Z), 17 lenses and multiple accessories performed flawlessly, even beyond expectations.

I started getting DSLR K-mount digital cameras and lenses in 2007 (after 40 years of using Minolta film cameras and MD manual-focus lenses) and only two lenses proved to be subpar : a DA 18-55 mm f/3.5-5.6 II kit lens that was badly decentered and an FA J 75-300 mm zoom that was an absolute DUD. Apart from that, all the other 30 some K-mount lenses were perfect. I test all my lenses as soon as I receive them. Over time, you learn to use the potential of each lens to the best of its and your ability.

No use to lose sleep over that.


Regards

05-20-2022, 03:10 PM - 1 Like   #53
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QuoteOriginally posted by BarryE Quote
I read that and thought how does that work? I buy one test it. Decide it is not good enough and demand a replacement. Next one may be better or worse. Have I made a mistake returning the first. Try again and again. It's like playing cards. But then the penny dropped. You meant buying half a dozen at one time!! Surely not. Personally I respect our struggling retailers too much to play that game. (Please don't bother mentioning Amazon as not struggling. I only ever buy lenses from small independents.)

Wary of this approach by some purchasers to lens buying I would never buy an "opened box" lens as I've always suspected it had been returned. Pity the retailer. I've bought numerous lenses over many years and only returned one. The replacement performed much the same. My mistake. I felt bad. I vowed then I would only ever return a lens if I was sure it was faulty as I don't buy into this poor quality control idea, believing that it's more a question of very fine tolerances. Sure a duff manufacturer could have huge tolerances, but Pentax don't do that.
I don't have a lot of of sympathy for Amazon, but yes I have read reports of people buying multiple copies of a lens using them all for a few days and cherry picking the best of the lot.
I read a guy on DPREVIEW whining that Amazon had fired him as a customer for doing it too many times.

Last edited by Wheatfield; 05-20-2022 at 07:02 PM.
05-24-2022, 05:17 AM - 4 Likes   #54
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QuoteOriginally posted by Digitalis Quote
You should have been there when I was doing my tests of the Pentax 67 800mm f/4 Takumar Vs the SMCP-M*67 800mm f/6.7 ED. To eliminate vibrations caused by domestic traffic I was working at night, but there was a freight train passing by several kilometers away that was causing enough vibrations to mess with the data. I called in a few favors, and ended up using a massive $200,000 air cushioned holography table to get clean data.
Imagine what I had to do to test the 150-450mm with 1.4 TC for Pentaxforums! Asked permission to use a subterran garage with a 65m line-of-sight, used the heaviest tripod I could gain access to, use flashes daisy-chained to trigger optically (I didn't have a remote with enough range at that time), use 10 seconds mirror lock-up with ES, and take many many shots to get a valid one. Rinse and repeat for all apertures, center/edge/corner. Fun times.

QuoteOriginally posted by BarryE Quote
Similarly, with em radiation and vibrations in the physics lab I worked in (lasers). At night. All lifts disabled in nearby buildings. Doors wedged open to stop them banging. Etc.. Worse thing was our kitchen area was out of bounds. That hurt the most. It is remarkable how far vibrations travel. Add that into the mix for the specifications for high resolution lenses testing
When the photonics university R&D lab was developed at Laval university where I did my PhD, they:

1-physically separated the building from the rest of the university, classes, offices, etc, even though there were connecting corridors
2-separated the elevator which was on its own concrete slab, separate from the rest
3-pur all the ventilation machinery on another building
4-braced the building with concrete "arms" extending as far as the building's length
5-study natural vibration frequencies of the ground, as well as that generated by cars on nearby streets, and account for those
6-create dirt walls to further dampen unexpected vibrations
7-build in the ground instead of in the air
8-use piping with varying diameters so that waves would not propagate as well

I must be missing a lot that I didn't know about. Fantastic building, in any case.
05-24-2022, 06:54 AM - 2 Likes   #55
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QuoteOriginally posted by bdery Quote
When the photonics university R&D lab was developed at Laval university where I did my PhD, they:

1-physically separated the building from the rest of the university, classes, offices, etc, even though there were connecting corridors
2-separated the elevator which was on its own concrete slab, separate from the rest
3-pur all the ventilation machinery on another building
4-braced the building with concrete "arms" extending as far as the building's length
5-study natural vibration frequencies of the ground, as well as that generated by cars on nearby streets, and account for those
6-create dirt walls to further dampen unexpected vibrations
7-build in the ground instead of in the air
8-use piping with varying diameters so that waves would not propagate as well

But what about gravitational waves? If one of those happened to hit the lens, distorting the corners by 10(-18)m, that tiny fraction of a single proton's worth of error would be enough for someone with two posts on the forum to declare it unusable and give it a one star rating.

(ish)
05-24-2022, 10:51 AM   #56
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QuoteOriginally posted by Dartmoor Dave Quote
that tiny fraction of a single proton's worth of error would be enough for someone with two posts on the forum to declare it unusable and give it a one star rating.
You clearly haven't read many user reviews I wouldn't be surprised if the average score of all lenses is above 8.
05-24-2022, 03:23 PM - 2 Likes   #57
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QuoteOriginally posted by Dartmoor Dave Quote
But what about gravitational waves? If one of those happened to hit the lens, distorting the corners by 10(-18)m, that tiny fraction of a single proton's worth of error would be enough for someone with two posts on the forum to declare it unusable and give it a one star rating.
Fortunately the kind events that cause large gravitational waves of sufficient magnitude to cause that degree of deflection are relatively rare*, so that cuts down on the excuses reviewers can use.Though, they can always fall back on the old excuse of "that darned butterfly on the other side of the earth with its wings flapping everywhere" and there there is this old excuse when we re-test old lenses:



*well at least from what we can detect our currently primitive gravitational astronomy.

Last edited by Digitalis; 05-26-2022 at 06:53 PM.
05-24-2022, 05:10 PM - 1 Like   #58
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QuoteOriginally posted by dkpentax Quote
isn't it possible to determine the lines per inch that the full size K-1 and APS-C K-3 sensors can achieve, then measure every lens of some kind of lens bench, and determine the real resolving power at all the different combinations of aperture and position across the image plane.
I hear you about how terrible sample images can be - unrepresentative, and depending on the subject, skills of the photographer, and camera and postprocessing used.

IMATEST software will approximate your dream, but there's still a lot of user error possible. It needs a picture, and a JPG has been sharpened, and we live in a day and age where RAWs are baked, too.

The *industry standard* is the MTF chart, that's what the camera companies all go by. You can see below the one for the FA35. (People who say that the FA35 is sharp across the frame but the DA35 isn't, need to see below, that's simply not true!).



Various camera companies do disclose MTF charts, and Pentax certainly do for selected lenses.
05-24-2022, 11:00 PM - 1 Like   #59
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QuoteOriginally posted by clackers Quote
Various camera companies do disclose MTF charts, and Pentax certainly do for selected lenses.
So far as I'm aware, most of the MTF data provided by lens manufacturers is calculated - i.e. theoretical - rather than measured. It's still useful, of course, if you want to understand something of the intended "best case" performance in terms of resolution... but, as per the well-worn saying, "actual results may vary"

Last edited by BigMackCam; 05-24-2022 at 11:55 PM.
05-25-2022, 12:30 AM - 2 Likes   #60
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QuoteOriginally posted by bdery Quote
Imagine what I had to do to test the 150-450mm with 1.4 TC for Pentaxforums! Asked permission to use a subterran garage with a 65m line-of-sight, used the heaviest tripod I could gain access to, use flashes daisy-chained to trigger optically (I didn't have a remote with enough range at that time), use 10 seconds mirror lock-up with ES, and take many many shots to get a valid one. Rinse and repeat for all apertures, center/edge/corner. Fun times.



When the photonics university R&D lab was developed at Laval university where I did my PhD, they:

1-physically separated the building from the rest of the university, classes, offices, etc, even though there were connecting corridors
2-separated the elevator which was on its own concrete slab, separate from the rest
3-pur all the ventilation machinery on another building
4-braced the building with concrete "arms" extending as far as the building's length
5-study natural vibration frequencies of the ground, as well as that generated by cars on nearby streets, and account for those
6-create dirt walls to further dampen unexpected vibrations
7-build in the ground instead of in the air
8-use piping with varying diameters so that waves would not propagate as well

I must be missing a lot that I didn't know about. Fantastic building, in any case.
One of my friends (he was in DNA nanotech) worked in the same building I did. Standard Cold-War era East German shoebox.

He was extremely angry at my Chinese colleagues working regularly until 23:00, because it meant that he had to delay AFM measurements to midnight, otherwise the vacuum pump vibrations in the floor below would mess up the imaging.
It got to the point that I was texting him when my colleagues left for dinner, so he could sneak in an hour or two in between
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