Nikon Z 35/1.8 S - hard to find a well centered copy?

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quintana Regular Member • Posts: 447
Nikon Z 35/1.8 S - hard to find a well centered copy?

I have currently two copies of this lens. I bought one two weeks ago on the used market.

In multiple tests there were always one or two corners significantly softer than the others. Not really bad and most probably within Nikon‘s norm but definitely and easily visible at f/2 and still visible at f/4.

So I bought a second copy of this lens brand new to check if it is any better. Unfortunately it isn’t. There are still always 1-2 corners distinctively softer than the others and the extent is only ever so slightly better than the first copy.
Since I‘m testing on a not very demanding 24 MP body (Z5) I‘m a bit disappointed. I can live with some decentering in zoom lenses as they are more complex but with a prime lens that costs usually around 750 Euros (only now with instant rebates 100 Euros less) I find it not very satisfying.

My Z 24/1.8 is perfectly centered and even my 24-70/4 zoom lens is better centered at all focal lengths than both 35/1.8 lenses.

What are your experiences with centering of Z mount prime lenses and the 35mm in particular?

I really hope that my Z 85/1.8 that is currently back ordered will perform significantly better than the 35/1.8.

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gnet158 Veteran Member • Posts: 3,082
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?

Never thought about it, good to know.  Good luck finding a good copy.

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I got to get out and shoot more.

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kenw
kenw Veteran Member • Posts: 6,324
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?
8

When you say 1-2 corners are significantly softer I presume it is the same 1-2 corners that are softer on a particular copy of the lens?

It is really easy to make a mistake when testing a lens - especially wider aperture primes with shallow depth of field. It sounds like you've done a number of comparisons and shot similar tests with other lenses so I'm assuming your test setup is consistent and you are getting the same results over more than one test.

In the past weeks I've acquired the 35/1.8, 50/1.8 and 85/1.8.

The first 85/1.8 that I got had a quite soft corner showing a lot of astigmatism that still was noticeably soft compared to the other corners even at F/8. The box for the lens was visibly crushed (the actual retail box for the lens, not just the shipping box) so it is quite possible it had some sort of shipping damage along the way. The replace 85/1.8 was excellent.

The first and only 50/1.8 that I got was excellent right from the start.

The first 35/1.8 that I got had been shipped by Amazon in a padded envelope which was torn with a corner of the retail box inside sticking out. The retail box itself actually looked fine. This copy of the lens had a marginal corner that was still a bit ugly at F/4. Normally I would have probably considered it acceptable as typically for fast primes I expect the corners to be out of focus. In this case though I plan to use the lens for astrophotography so wide open wide field performance matters and I was also annoyed with Amazon for sending a $700 lens to me in padded envelope instead of a properly packed box.

The second 35/1.8 amazingly was also sent in a padded envelope by Amazon! It did test out just fine.

So in my case purchasing five Z primes I found one was quite obviously poor and one was marginal and three were amazingly good. The poor and the marginal one both showed signs of shipping damage in one way or another.

I usually do a quick test for symmetry and if something looks odd do a more sensitive test. In this case since I've been trapped in the house without travel by COVID for months and had nothing better to do I did the more sensitive test on all five lenses on my Z7. The test is described by Jim Kasson here:

https://blog.kasson.com/lens-screening-testing/

My version is slightly modified to allow me to do indoor testing at shorter ranges while still testing for a flat field.

Note this is an extremely sensitive test. Pretty much every lens will show some amount of asymmetry on a test this sensitive. It is a question of degree. Jim's blog has a nice catalog of images from various lenses he and others have tested in this way to give you an idea of what to expect.

I test at the widest aperture just to get the most sensitive measure but I assume that I'm going to see asymmetry almost for sure. I also tested the primes at F/4 to see if aberrations cleaned up as expected.

For reference here is the near perfect 50/1.8:

Z50/1.8S @ F/1.8

Z50/1.8S @ F/4

Here is the clearly poor Z85/1.8S that I received first. Note the upper right corner has really bad astigmatism that is still quite bad at F/4. In landscape/cityscape test shots there was still quite visible astigmatism giving a double-edge effect in that corner even at F/8.

Z85/1.8S bad copy - F/1.8

Z85/1.8S bad copy - F/4

Here is the replacement which is excellent (note when I tested this second copy the lighting on the target was a bit different and that's why the images appear just a bit brighter than on the first copy):

Z85/1.8S good copy - F/1.8

Z85/1.8S good copy - F/4

Here is the first copy of the Z35/1.8S that I received. Note the lower left corner. Really at F/1.8 I think that level of asymmetry is just fine. Notice though that it doesn't improve much in that corner at F/4. On a landscape/cityscape at F/8 that corner really wasn't too bad at all but my 14-30/4 actually did a better job which was a bit disappointing. Still I think this is marginally acceptable and it was really Amazon's insanely poor packing and visible shipping damage that pushed me to return it.

Z35/1.8S marginal copy - F/1.8

Z35/1.8S marginal copy - F/4

And here is the second copy of the Z35/1.8S which is much better. Note the upper central square has something a little odd going on. These Siemens star tests are extremely sensitive so we need to be reasonable with expectations. To me this copy is excellent overall and looks as such on my more "real world" landscape and cityscape test shots.

Z35/1.8S good copy - F/1.8

Z35/1.8S good copy - F/4

Hopefully that is helpful for you.

Again I want to stress that usually "bad copies" of a lens are down to bad testing of the lens. It sounds like from your post you have experience doing this so that probably doesn't apply to you.

Also again I want to stress just how sensitive the above Siemens star tests are at showing even tiny amounts of asymmetry that aren't really going to be visible on real world subjects. The two lenses I returned were returned because they did show obvious aberrations on real world subjects - the 85 especially. The first 35 was probably a keeper if I wasn't intending to use it for wide field astrophotography and if I wasn't additionally annoyed at Amazon for their ridiculous packing.

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JimKasson
JimKasson Forum Pro • Posts: 32,164
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?
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To Ken: Good job.

To the OP: please post images like the ones that Ken posted. Are the lenses decentered or tilted? You can tell be focusing on the target in the bad corner.

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Ernie Misner
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Re: Nikon Z 35/1.8 S - hard to find a well centered copy?
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" The first 35 was probably a keeper if I wasn't intending to use it for wide field astrophotography and if I wasn't additionally annoyed at Amazon for their ridiculous packing. "

Do you think it was actually Amazon that did the packing or the camera store where the lens came from? That seems so totally unacceptable. Here in the USA I usually order from B&H and hope they don't start doing that. Thanks for the informative tests and information. Good to see the link to Jim K's test info again as well.

I noticed where Jim said "the camera doesn't have to be perfectly square to the target" or something similar. That surprised me, did it you?

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1llusive
1llusive Veteran Member • Posts: 3,398
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?

Ernie Misner wrote:

" The first 35 was probably a keeper if I wasn't intending to use it for wide field astrophotography and if I wasn't additionally annoyed at Amazon for their ridiculous packing. "

Do you think it was actually Amazon that did the packing or the camera store where the lens came from? That seems so totally unacceptable. Here in the USA I usually order from B&H and hope they don't start doing that.

My Z 85 f/1.8 S was shipped from and sold by Amazon and also came in the yellow bubble envelope. I should do this test.

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OP quintana Regular Member • Posts: 447
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?

JimKasson wrote:

To the OP: please post images like the ones that Ken posted. Are the lenses decentered or tilted? You can tell be focusing on the target in the bad corner.

Currently I am not at home so I can not post the pictures at the moment because they are on my hard drive.

I don’t test my lenses indoors but like this: http://www.gletscherbruch.de/foto/test/dezentrierung/dezentrierung.html

It might not be as sophisticated as the test Ken did but still it should result in 4 corners with the same level of sharpness when the copy of the lens is perfect.

If I focus both not-so-perfect-copies of the Z 35/1.8 on the bad corner it gets as sharp as I would expect. This probably means that it’s tilted and not decentered, right? Until I read your answer I have to admit that I always thought that decentered and tilted mean the same.

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kenw
kenw Veteran Member • Posts: 6,324
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?
2

Ernie Misner wrote:

" The first 35 was probably a keeper if I wasn't intending to use it for wide field astrophotography and if I wasn't additionally annoyed at Amazon for their ridiculous packing. "

Do you think it was actually Amazon that did the packing or the camera store where the lens came from?

The lens was specifically sold by Amazon and not a 3rd party.  I'm pretty sure if it had been a camera store selling through Amazon they would have packed it differently!

That seems so totally unacceptable.

Agree.  When the second one came that way I tried to figure out how to get someone at Amazon to change whatever in their system is telling their packers to use envelopes.  It turns out this is essentially impossible for a purchaser to do.

And they are consistent.  Someone just this past week also posted about their Z35/1.8S coming from Amazon in a padded envelope.

I did find that 3rd parties that use "fulfilled by Amazon" (this is where Amazon does the packing for 3rd parties) were extremely frustrated by Amazon sending obviously delicate things in padded envelopes and then getting bad reviews from their customers for bad packing when they didn't have any control over it!  Long threads of 3rd party sellers describing strategies to navigate Amazon's system to get something obviously delicate like a crystal glass flagged as "ship in box only" after having a bunch destroyed in shipping.

Here in the USA I usually order from B&H and hope they don't start doing that.

Me too!  Once or twice I've had B&H or Adorama pack something with less padding then I'd like.  Like having the retail box sitting flat against the bottom and one side of the shipping box such that there is no actually shock protection from hits on those sides.  But nothing as silly as just a padded envelope!

Thanks for the informative tests and information. Good to see the link to Jim K's test info again as well.

I noticed where Jim said "the camera doesn't have to be perfectly square to the target" or something similar. That surprised me, did it you?

The idea behind Jim's test is that the target is shot from far away enough that DoF makes up for the fact that the you are essentially doing "focus and recompose" on the target.  That ends up being a lot of DoF and so you really don't need to be careful at all about keeping the target square - the effective recomposing distance change is far, far larger than what tilt of the target could cause.

That's the nice thing about Jim's test - it is nearly idiot proof!  Though Jim does give some amusing examples of where folks manage to rise to the occasion...

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rokoko
rokoko Senior Member • Posts: 2,072
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?

quintana wrote:

JimKasson wrote:

To the OP: please post images like the ones that Ken posted. Are the lenses decentered or tilted? You can tell be focusing on the target in the bad corner.

Currently I am not at home so I can not post the pictures at the moment because they are on my hard drive.

I don’t test my lenses indoors but like this: http://www.gletscherbruch.de/foto/test/dezentrierung/dezentrierung.html

It might not be as sophisticated as the test Ken did but still it should result in 4 corners with the same level of sharpness when the copy of the lens is perfect.

If I focus both not-so-perfect-copies of the Z 35/1.8 on the bad corner it gets as sharp as I would expect. This probably means that it’s tilted and not decentered, right? Until I read your answer I have to admit that I always thought that decentered and tilted mean the same.

https://www.lensrentals.com/blog/2012/05/testing-for-a-decentered-lens-an-old-technique-gets-a-makeover/

Hope this can help.

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JimKasson
JimKasson Forum Pro • Posts: 32,164
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?

quintana wrote:

JimKasson wrote:

To the OP: please post images like the ones that Ken posted. Are the lenses decentered or tilted? You can tell be focusing on the target in the bad corner.

Currently I am not at home so I can not post the pictures at the moment because they are on my hard drive.

I don’t test my lenses indoors but like this: http://www.gletscherbruch.de/foto/test/dezentrierung/dezentrierung.html

It might not be as sophisticated as the test Ken did but still it should result in 4 corners with the same level of sharpness when the copy of the lens is perfect.

If I focus both not-so-perfect-copies of the Z 35/1.8 on the bad corner it gets as sharp as I would expect. This probably means that it’s tilted and not decentered, right?

Right.

Until I read your answer I have to admit that I always thought that decentered and tilted mean the same.

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michaeladawson Forum Pro • Posts: 14,976
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?

kenw wrote:

Hopefully that is helpful for you.

Again I want to stress that usually "bad copies" of a lens are down to bad testing of the lens. It sounds like from your post you have experience doing this so that probably doesn't apply to you.

And yet 2 out of 5 lenses you sampled were "bad", 40%.  I've never tested my lenses.  But if 40% is par for the course I'd be hesitant to test my lenses now and find out I have to get rid of 40% of them.  I've seen many posts over the years where people say they needed even 3 copies of a lens to get a good one.

I never really know what to think about lens testing threads in these forums.  Auto-Focus Fine Tune is another one.  I was diligent and careful with my AF tuning with my DSLR cameras.  Every single lens I ever owned benefited from some degree of AFFT.  Sometimes it was just a small value like +/- 3.  Other times it was 5, 10, and in the worst cases it as much as 15.

Other people have reported the same.  Yet when the topic comes up many people report they have never had to fine tune a lens.  I don't know what to think of this.  Bad testing by those that report no AFFT needed?  Bad testing by those the say all their lenses benefit?

My response is not intended to doubt your testing.  The rigor with which you perform it leads me to believe it is probably accurate.  But what does that say about the state of manufacturing and quality controls?

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JimKasson
JimKasson Forum Pro • Posts: 32,164
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?

quintana wrote:

JimKasson wrote:

To the OP: please post images like the ones that Ken posted. Are the lenses decentered or tilted? You can tell be focusing on the target in the bad corner.

Currently I am not at home so I can not post the pictures at the moment because they are on my hard drive.

I don’t test my lenses indoors

My test is not usually performed indoors. I've never used it indoors. The distances are usually far to large for that.

but like this: http://www.gletscherbruch.de/foto/test/dezentrierung/dezentrierung.html

It might not be as sophisticated as the test Ken did but still it should result in 4 corners with the same level of sharpness when the copy of the lens is perfect.

Sometimes.

I wrote this some time ago:

The Gletscherbruch test

This test uses one or more distant natural or man-made objects for the target. The lens is focused with the target in the center, then, without refocusing, the image is recomposed, placing the target in the corners and possibly at the center right/left/up/down locations.

The Gletscherbruch test has a lot to recommend it. It gets around the alignment issues of the full-frame flat-target tests. It has two main drawbacks.

  • Atmospheric effects. Here on earth, performing lens testing at great distances puts a lot of air between you and your target. That air is subject to thermally-created changes in density that cause time-varying bending of light rays that result in uncontrolled and unpredictable blurring of images. When performing Gletscherbruch testing in unpopulated areas in still early-morning air, this can be dealt with for all but the longest lenses, but at other times of the day or in cities with unseen, and often unsuspected, heat sources, it can be a problem even at moderately short focal lengths. The time-varying nature makes it especially tricky when you’re looking for differences in the image sharpness at the four corners of the frame. Sometimes the blurring caused by the atmosphere can be greater than that of the lens and camera, making it impossible to see small lens defects.
  • Inappropriate target. This is the same problem that you have with found flat targets. They have the wrong spatial-frequency makeup and they aren’t repeatable. You can’t spot focusing errors by inspection of the captures. You can’t read out sharpness in any way that’s describable to others. You don’t know what the images are supposed to look like with any specificity.

If I focus both not-so-perfect-copies of the Z 35/1.8 on the bad corner it gets as sharp as I would expect. This probably means that it’s tilted and not decentered, right? Until I read your answer I have to admit that I always thought that decentered and tilted mean the same.

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Dan DeLion Contributing Member • Posts: 887
Quick - Dirty - and Meaningless

quintana wrote:

JimKasson wrote:

To the OP: please post images like the ones that Ken posted. Are the lenses decentered or tilted? You can tell be focusing on the target in the bad corner.

Currently I am not at home so I can not post the pictures at the moment because they are on my hard drive.

I don’t test my lenses indoors but like this: http://www.gletscherbruch.de/foto/test/dezentrierung/dezentrierung.html

It might not be as sophisticated as the test Ken did but still it should result in 4 corners with the same level of sharpness when the copy of the lens is perfect.

If I focus both not-so-perfect-copies of the Z 35/1.8 on the bad corner it gets as sharp as I would expect. This probably means that it’s tilted and not decentered, right? Until I read your answer I have to admit that I always thought that decentered and tilted mean the same.

The Gletscherbruch test you describe is meaningless.  You are shooting through miles of moving, dirty air with thermals all over the place.  Quick and dirty tests are the reason Nikon Repair has a stamp reading "IN SPEC."

I've bought over 75 pro Nikkors (F's and Z's) with no returns and no problems.  Somehow tests, like you describe, show so many faults and problems and so many returns.  Think about it!

Happy New Year - Dan

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kenw
kenw Veteran Member • Posts: 6,324
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?
1

michaeladawson wrote:

kenw wrote:

Hopefully that is helpful for you.

Again I want to stress that usually "bad copies" of a lens are down to bad testing of the lens. It sounds like from your post you have experience doing this so that probably doesn't apply to you.

And yet 2 out of 5 lenses you sampled were "bad", 40%. I've never tested my lenses. But if 40% is par for the course I'd be hesitant to test my lenses now and find out I have to get rid of 40% of them.

This was definitely anomalous.  I've tested probably 60 lenses over the years, mixture of "consumer" and "pro" grade.  These were really the only "pro" grade lenses I've ever considered poor enough to exchange, and both quite probably were exposed to shipping damage.

Also we can look at the various review sites who have over the years tested probably a few hundred lenses from different manufacturers and usually mention if they had to try a second copy.  Doesn't really happen very often to them it seems and they of course should really notice!

I've seen many posts over the years where people say they needed even 3 copies of a lens to get a good one.

In general I discount these as people with unreasonable expectations in most cases.

However, over the years there appear to have been certain lenses that especially near introduction had some sort of systematic assembly error in which both multiple review sites and forum members find a similar problem on many copies (e.g. the Olympus 12/2 suffered from a whole bunch with quite noticeable tilt right at introduction).  So I it does happen in unusual circumstances that you might actually get multiple "bad" lenses in a row.

I never really know what to think about lens testing threads in these forums.

I start by assuming the test methodology was probably bad and then often can help the poster test more appropriately.  In this case it appears the OP was using a sound test.

Auto-Focus Fine Tune is another one. I was diligent and careful with my AF tuning with my DSLR cameras. Every single lens I ever owned benefited from some degree of AFFT. Sometimes it was just a small value like +/- 3. Other times it was 5, 10, and in the worst cases it as much as 15.

Other people have reported the same. Yet when the topic comes up many people report they have never had to fine tune a lens. I don't know what to think of this. Bad testing by those that report no AFFT needed? Bad testing by those the say all their lenses benefit?

Probably different standards and different ways of using the lens would be my best guess!

I think a good example of that would be something like the Samyang/Rokinon 135/2 which is a hit both with the portrait photography crowd and the astro crowd.  The astro crowd finds a lot more "bad" copies because every photo they take of the sky near wide open is essentially a very sensitive test for "decentering".  Meanwhile the portrait crowd is going to say all their lenses are just fine because of course the corners and edges of all their photos are out of focus anyway.

My response is not intended to doubt your testing. The rigor with which you perform it leads me to believe it is probably accurate. But what does that say about the state of manufacturing and quality controls?

In my particular case it probably says more about the state and quality of shippers and packers!  Both of the "bad" lenses appeared to be exposed to likely shipping damage.  Certainly it is also possible they were bad from the factory, but given I could see evidence of shipping damage on the packaging it really makes it hard to point the finger at the manufacturer.

Roger Cicala at LensRentals has written on this extensively in blog posts over the years.  The answer mostly seems to be that quality controls are quite good but there is always a small chance of getting a "bad" lens for whatever reason and this is true for any manufacturer.  He has also pointed out over and over again that a significant fraction of "I have a bad lens" posts are really down to "I have unreasonable expectations" or "I have no ability to test a lens properly".

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kenw
kenw Veteran Member • Posts: 6,324
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?
1

quintana wrote:

JimKasson wrote:

To the OP: please post images like the ones that Ken posted. Are the lenses decentered or tilted? You can tell be focusing on the target in the bad corner.

Currently I am not at home so I can not post the pictures at the moment because they are on my hard drive.

I don’t test my lenses indoors but like this: http://www.gletscherbruch.de/foto/test/dezentrierung/dezentrierung.html

It might not be as sophisticated as the test Ken did but still it should result in 4 corners with the same level of sharpness when the copy of the lens is perfect.

I use a test like that myself as a quick screening.  For normal to wide angle lenses like the 35/1.8 it is a pretty good quick check.  Often if this kind of test looks good then I don't bother doing the more careful Siemens star test.  If this kind of test looks poor then I start doing more testing to be sure.

As others already pointed out this kind of test can definitely be problematic with longer focal length lenses because you start to see atmospheric effects instead of lens effects!  Even then though if your shutter speed is high enough (say about 1/250) the atmospheric effects result in small scale distortions rather than the blurriness and smearing of lens aberrations.  So if you are familiar with how things should look from experience you can still use this kind of test on long focal length lenses to detect obvious asymmetry but it is far from ideal.

My typical procedure is to use something like the Gletscherbruch test first and if it doesn't look good then I do more careful and controlled testing.  Whenever a lens test looks bad I usually assume the problem is with me or the test first.  It is too easy to make mistakes and so demonstrated repeatability of the results using more than one method is a good practice before declaring anything "bad".

If I focus both not-so-perfect-copies of the Z 35/1.8 on the bad corner it gets as sharp as I would expect. This probably means that it’s tilted and not decentered, right? Until I read your answer I have to admit that I always thought that decentered and tilted mean the same.

That does suggest that it is likely "tilt" but isn't conclusive.  As Jim pointed out though the target might not be appropriate for really showing what is going on.  For example if the target has detail in only one dimension you might not detect astigmatism.  If look at my tests you'll see that one axis of the star looks great while in the other everything is falling apart.

But yes, in the forums "decentered" has become the way many refer to any sort of asymmetry in aberrations even though strictly the lens might not have any "decentered" elements in it.

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michaeladawson Forum Pro • Posts: 14,976
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?

Thanks for the detailed reply Ken.

I am of the type that demands a high level of perfection.  That's why I think it's a good thing that I don't start testing my lenses for decentering and tilt.

I am quite confident of my AFFT testing.  But I've backed off a little.  Now I really only bother to test a lens if I notice that photos aren't coming out as sharp as I think they should.  It was really getting to be a hassle to retest every lens every time I got a new camera body.  So I stopped.

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Mike Dawson

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JimKasson
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Re: Nikon Z 35/1.8 S - hard to find a well centered copy?
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kenw wrote:

But yes, in the forums "decentered" has become the way many refer to any sort of asymmetry in aberrations even though strictly the lens might not have any "decentered" elements in it.

I think Roger likened this to saying that your car is out of gas whenever it won't start.

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kenw
kenw Veteran Member • Posts: 6,324
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?

JimKasson wrote:

kenw wrote:

But yes, in the forums "decentered" has become the way many refer to any sort of asymmetry in aberrations even though strictly the lens might not have any "decentered" elements in it.

I think Roger likened this to saying that your car is out of gas whenever it won't start.

LOL, that's perfect.  I love Roger's way with words.

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Ken W
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 kenw's gear list:kenw's gear list
Panasonic Lumix DMC-GM1 Olympus E-M5 II Nikon Z7 Nikon Z 14-30mm F4 Nikon Z 24-200mm F4-6.3 VR +37 more
1llusive
1llusive Veteran Member • Posts: 3,398
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?

kenw wrote:

Probably different standards and different ways of using the lens would be my best guess!

I think a good example of that would be something like the Samyang/Rokinon 135/2 which is a hit both with the portrait photography crowd and the astro crowd. The astro crowd finds a lot more "bad" copies because every photo they take of the sky near wide open is essentially a very sensitive test for "decentering". Meanwhile the portrait crowd is going to say all their lenses are just fine because of course the corners and edges of all their photos are out of focus anyway.

As you mention in your other post, beyond any reasonable distance you start to get blurring from the air. So while a shot of a star field seems to be an ideal test, I think shutter speeds need to be very short and I think several images need to be taken and analyzed to be sure you aren't knocking a lens corner when it's just the atmosphere.

 1llusive's gear list:1llusive's gear list
Nikon Z6 II Sigma 100-400mm F5-6.3 Nikon Z 24-70mm F4 Nikon Z 85mm F1.8 +1 more
kenw
kenw Veteran Member • Posts: 6,324
Re: Nikon Z 35/1.8 S - hard to find a well centered copy?

1llusive wrote:

kenw wrote:

Probably different standards and different ways of using the lens would be my best guess!

I think a good example of that would be something like the Samyang/Rokinon 135/2 which is a hit both with the portrait photography crowd and the astro crowd. The astro crowd finds a lot more "bad" copies because every photo they take of the sky near wide open is essentially a very sensitive test for "decentering". Meanwhile the portrait crowd is going to say all their lenses are just fine because of course the corners and edges of all their photos are out of focus anyway.

As you mention in your other post, beyond any reasonable distance you start to get blurring from the air. So while a shot of a star field seems to be an ideal test, I think shutter speeds need to be very short and I think several images need to be taken and analyzed to be sure you aren't knocking a lens corner when it's just the atmosphere.

Pointing up into the sky and pointing along the surface of the earth have dramatically different seeing profiles (along the surface of the earth is far, far, far worse).  So while 100mm is often problematic pointing at a distant terrestrial target it is not often an issue pointing up at the zenith.  But still, seeing varies *a lot* from night to night and the location you shoot an astro photo also impacts your local seeing a lot as well.

On a Z7 with a 100mm lens a pixel has about a 9 arcsecond angle of view (unless I screwed up the math).  Seeing limits of 9 arcseconds at zenith are incredibly bad and are actually beyond the lowest seeing rating of typical scales used to grade astronomical seeing.  So it sure seems like down around 135mm a star field near zenith is a perfectly reasonable test target?  Or did I make a mistake somewhere?

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Ken W
See profile for equipment list

 kenw's gear list:kenw's gear list
Panasonic Lumix DMC-GM1 Olympus E-M5 II Nikon Z7 Nikon Z 14-30mm F4 Nikon Z 24-200mm F4-6.3 VR +37 more
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