Gar! What is it with me and the decentered lenses?!

Outis · 03-31-2016, 02:10 PM

The last lens I bought was the 14mm Rokinon f/2.8. I had to go through three decentered copies of that lens before I found one that worked. That was a little annoying. (But yay for B&H's return policy!)

Now I went and got the Pentax 20-40mm Limited. The first copy I got was decentered. I exchanged it for another one, which is also decentered. So I'm going to have to exchange this one as well. Aaarrrggghhh. (But yay for Adorama's return policy!) I just want a lens that works!

Sorry, just needed to rant.

One3rdEV · 03-31-2016, 02:21 PM

With all the de-centered lenses circulating around in the retail / distribution pool - it seems to me that they need to get flushed out, and find their way back to the manufacturer.

FantasticMrFox · 03-31-2016, 02:22 PM - **1 Like**

Quality control does indeed seem to be slipping across the board (although I am lucky to not have a single decentered lens), and the problem is more prevalent with certain manufacturers (e.g. Samyang) and lenses (e.g. Pentax 16-85) than others, but it also appears that there are more and more people who conduct meticulous testing and are dissatisfied due to the smallest optical weaknesses that many others wouldn't even notice.

Technically every lens is decentered, because perfect optical centering on the microscopic level is impossible. There is a continuum of decentering from 'not-measurable' to 'discernible by my grandma', and personal perception of this varies.

With five decentered copies of two lenses, you are either incredibly unlucky, which is perfectly possible, or maybe simply a bit picky

Outis · 03-31-2016, 02:35 PM

Yeah. I considered the 'too picky' part, but I consulted with other forum members about the 14mm Rokinon and they agreed with me, and with the 20-40, it is obviously worse than my kit lens, which should not be the case. Bummer.

Dlanor Sekao · 03-31-2016, 02:52 PM

The Rokinon 14mm.....mehhhh.....lots are de-centered and its almost expected. But with the 20-40 I would be quite picky.

osv · 03-31-2016, 02:55 PM

Originally posted by Outis

The last lens I bought was the 14mm Rokinon f/2.8. I had to go through three decentered copies of that lens before I found one that worked.

you were lucky to find a good one, the first korean 14mm prime that i tried was way off, so i gave it up completely.

i went thru four copies of the korean 35/1.4 lenses before giving up... this was perhaps the worst of the bunch, at f/2: https://www.dropbox.com/s/0gxrx5uebxgstlk/DSC03353at2point0.JPG

fwiw, you should congratulate yourself for being a competent enough photographer to spot a defective lens, not everyone can do that.

**jatrax** · 03-31-2016, 03:14 PM

Originally posted by osv

not everyone can do that.

That must be me. I've never (that I know of) had a de-centered lens. And to be honest I don't see anything wrong with that picture. What am I missing?

**Digitalis** · 03-31-2016, 03:22 PM - **1 Like**

Originally posted by jatrax

I don't see anything wrong with that picture. What am I missing?

Take a closer look at the buildings near the left edge.

**jatrax** · 03-31-2016, 03:39 PM

Originally posted by Digitalis

Take a closer look at the buildings near the left edge.

Got it, thank you!

What causes that? And it appears to be only the left side, correct? Harder to see but it looks like the grass in the foreground has the same issue.

starjedi · 03-31-2016, 03:45 PM

Originally posted by Outis

The last lens I bought was the 14mm Rokinon f/2.8. I had to go through three decentered copies of that lens before I found one that worked. That was a little annoying. (But yay for B&H's return policy!)

Now I went and got the Pentax 20-40mm Limited. The first copy I got was decentered. I exchanged it for another one, which is also decentered. So I'm going to have to exchange this one as well. Aaarrrggghhh. (But yay for Adorama's return policy!) I just want a lens that works!

Sorry, just needed to rant.

My first copy of FA31 is heavily de-centered but it is still sharp at center...

tibbitts · 03-31-2016, 05:44 PM

I've had various brands/models of obviously decentered lenses, including Pentax. Part of the problem is probably that lens designs are generally more complex than in the past, and part of it is that we can test much more effectively and less expensively than was possible with film. But manufacturers have to realize that if they want us to keep buying newer, higher-resolution bodies, they're going to have to figure out how to make optics that can keep up.

osv · 03-31-2016, 08:50 PM

Originally posted by jatrax

Got it, thank you!

What causes that? And it appears to be only the left side, correct? Harder to see but it looks like the grass in the foreground has the same issue.

viewed at 100% size, right? it looked bad in that left foreground area to me as well.

the characteristics of this lens are that it's sharp on both edges, and the center, but a number of lenses do that, it's nothing special... on the right mid-field side, you can very faintly see the wavy donut focus field, it's on the left side as well, but obliterated by the defect: diglloyd - Understanding optics - Understanding Field Curvature

what really kills these lenses tho is random out-of-focus areas that come and go with aperture changes... they all looked sort of usable at f/1.4, but one click down and things got ugly, on all four copies.

i actually documented it with edited crops, but got so discouraged that i just put the whole project away.

Auzzie-Phoenix · 04-01-2016, 07:11 AM

Develop a new style of photography that requires lens decentering... then you're golden.

03-31-2016, 02:10 PM	#1
Outis Veteran Member Join Date: Apr 2014 Location: Cambridge, MA Posts: 935	Gar! What is it with me and the decentered lenses?! The last lens I bought was the 14mm Rokinon f/2.8. I had to go through three decentered copies of that lens before I found one that worked. That was a little annoying. (But yay for B&H's return policy!) Now I went and got the Pentax 20-40mm Limited. The first copy I got was decentered. I exchanged it for another one, which is also decentered. So I'm going to have to exchange this one as well. Aaarrrggghhh. (But yay for Adorama's return policy!) I just want a lens that works! Sorry, just needed to rant.

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03-31-2016, 02:21 PM	#2
One3rdEV Senior Member Join Date: Mar 2013 Location: So-central, MI Posts: 285	With all the de-centered lenses circulating around in the retail / distribution pool - it seems to me that they need to get flushed out, and find their way back to the manufacturer.

03-31-2016, 02:22 PM - 1 Like	#3
FantasticMrFox Veteran Member Join Date: Oct 2014 Location: Munich Posts: 2,339	Quality control does indeed seem to be slipping across the board (although I am lucky to not have a single decentered lens), and the problem is more prevalent with certain manufacturers (e.g. Samyang) and lenses (e.g. Pentax 16-85) than others, but it also appears that there are more and more people who conduct meticulous testing and are dissatisfied due to the smallest optical weaknesses that many others wouldn't even notice. Technically every lens is decentered, because perfect optical centering on the microscopic level is impossible. There is a continuum of decentering from 'not-measurable' to 'discernible by my grandma', and personal perception of this varies. With five decentered copies of two lenses, you are either incredibly unlucky, which is perfectly possible, or maybe simply a bit picky

03-31-2016, 02:35 PM	#4
Outis Veteran Member Join Date: Apr 2014 Location: Cambridge, MA Posts: 935 Original Poster	Yeah. I considered the 'too picky' part, but I consulted with other forum members about the 14mm Rokinon and they agreed with me, and with the 20-40, it is obviously worse than my kit lens, which should not be the case. Bummer.

03-31-2016, 02:52 PM	#5
Dlanor Sekao Veteran Member Join Date: Jul 2013 Posts: 1,457	The Rokinon 14mm.....mehhhh.....lots are de-centered and its almost expected. But with the 20-40 I would be quite picky.

03-31-2016, 02:55 PM	#6
osv Veteran Member Join Date: Mar 2007 Location: So Cal Photos: Gallery Posts: 2,080	Originally posted by Outis The last lens I bought was the 14mm Rokinon f/2.8. I had to go through three decentered copies of that lens before I found one that worked. you were lucky to find a good one, the first korean 14mm prime that i tried was way off, so i gave it up completely. i went thru four copies of the korean 35/1.4 lenses before giving up... this was perhaps the worst of the bunch, at f/2: https://www.dropbox.com/s/0gxrx5uebxgstlk/DSC03353at2point0.JPG fwiw, you should congratulate yourself for being a competent enough photographer to spot a defective lens, not everyone can do that.

03-31-2016, 03:14 PM	#7
jatrax Site Supporter Join Date: May 2010 Location: Washington Cascades Photos: Gallery \| Albums Posts: 12,991	Originally posted by osv not everyone can do that. That must be me. I've never (that I know of) had a de-centered lens. And to be honest I don't see anything wrong with that picture. What am I missing?

03-31-2016, 03:22 PM - 1 Like	#8
Digitalis Site Supporter Join Date: Mar 2009 Location: Melbourne, Victoria Photos: Gallery Posts: 11,694	Originally posted by jatrax I don't see anything wrong with that picture. What am I missing? Take a closer look at the buildings near the left edge.

03-31-2016, 03:39 PM	#9
jatrax Site Supporter Join Date: May 2010 Location: Washington Cascades Photos: Gallery \| Albums Posts: 12,991	Originally posted by Digitalis Take a closer look at the buildings near the left edge. Got it, thank you! What causes that? And it appears to be only the left side, correct? Harder to see but it looks like the grass in the foreground has the same issue.

03-31-2016, 03:45 PM	#10
starjedi Veteran Member Join Date: Dec 2013 Location: New Jersey Posts: 932	Originally posted by Outis The last lens I bought was the 14mm Rokinon f/2.8. I had to go through three decentered copies of that lens before I found one that worked. That was a little annoying. (But yay for B&H's return policy!) Now I went and got the Pentax 20-40mm Limited. The first copy I got was decentered. I exchanged it for another one, which is also decentered. So I'm going to have to exchange this one as well. Aaarrrggghhh. (But yay for Adorama's return policy!) I just want a lens that works! Sorry, just needed to rant. My first copy of FA31 is heavily de-centered but it is still sharp at center...

03-31-2016, 05:44 PM	#11
tibbitts Pentaxian Join Date: Apr 2007 Location: Oklahoma USA Posts: 2,196	I've had various brands/models of obviously decentered lenses, including Pentax. Part of the problem is probably that lens designs are generally more complex than in the past, and part of it is that we can test much more effectively and less expensively than was possible with film. But manufacturers have to realize that if they want us to keep buying newer, higher-resolution bodies, they're going to have to figure out how to make optics that can keep up.

03-31-2016, 08:50 PM	#12
osv Veteran Member Join Date: Mar 2007 Location: So Cal Photos: Gallery Posts: 2,080	Originally posted by jatrax Got it, thank you! What causes that? And it appears to be only the left side, correct? Harder to see but it looks like the grass in the foreground has the same issue. viewed at 100% size, right? it looked bad in that left foreground area to me as well. the characteristics of this lens are that it's sharp on both edges, and the center, but a number of lenses do that, it's nothing special... on the right mid-field side, you can very faintly see the wavy donut focus field, it's on the left side as well, but obliterated by the defect: diglloyd - Understanding optics - Understanding Field Curvature what really kills these lenses tho is random out-of-focus areas that come and go with aperture changes... they all looked sort of usable at f/1.4, but one click down and things got ugly, on all four copies. i actually documented it with edited crops, but got so discouraged that i just put the whole project away.

04-01-2016, 07:11 AM	#13
Auzzie-Phoenix Veteran Member Join Date: Sep 2014 Photos: Albums Posts: 1,020	Develop a new style of photography that requires lens decentering... then you're golden.