# Opinion about decentred lens element



## mistaspeedy (Mar 4, 2018)

I just bought a 40mm F2.8 STM pancake lens, and it seems to have a decentred lens element. You can take a look at a random test image I took here:
https://i.imgur.com/UVbTG7M.jpg

The image was taken at F5.6. As you can see, the left side and middle look like they are in focus (from the closest water to the background. However, on the right side, from near to far, nothing is in focus besides maybe the extreme close right bottom corner.

The whole reason I bought the lens was because my main zoom lens also has a decentred element ( Tamron 28-75 F2.8 ), and I will have to wait until about April 17 to take it to the service center in Cologne.

I guess I have to take it back to the store (bought it new).

1) How often are you guys getting decentred elements?
2) What do you think of the above image, is this proof enough of the problem?
3) Could the lens mount be to blame?
Several more images exhibit the same issue to varying degrees.


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## Valvebounce (Mar 4, 2018)

Hi mistaspeedy. 
My guess, you will need shots of a test chart or very similar target and possibly a shot of your setup to prove that you were shooting square and perpendicular to your target, then you will need a salesperson that comprehends “decentered” and how your test proves decentering! 
In my humble opinion your shot is not proof of decentering, unknown distances and focal point do not allow for proof of concept. 
Good luck. 

Cheers, Graham.


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## Mt Spokane Photography (Mar 4, 2018)

There is a simple and easily done test, no need to align everything perfectly.

Check this out.

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

Here is a link to some printable targets

http://blog.kasson.com/lens-screening-testing/printable-siemens-star-targets/


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## mistaspeedy (Mar 4, 2018)

I will see what I will do about it or not... I was 'on the edge' between various lens purchase decisions, so I might just trade it in and get another (different) lens.


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## Valvebounce (Mar 4, 2018)

Hi Mt Spokane. 
I was trying to remember that test but could not quickly find it late last night, I thought it all still had to be well aligned! I still think the biggest problem might be getting a member of staff that understands! 

Cheers, Graham. 



Mt Spokane Photography said:


> There is a simple and easily done test, no need to align everything perfectly.
> 
> Check this out.
> 
> ...


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## mistaspeedy (Mar 4, 2018)

I returned the 40mm F2.8 STM lens as a trade-in for some other piece of photography equipment (full price).

Since I have to upgrade both my camera body AND lens lineup, I took the plunge and went with a camera body.

The store just happened to have a used Canon 6D sitting there with only 600-700 clicks on it.

I believe you will all agree it is a massive upgrade from my 1D mark II 

I will let you know my impressions once I actually get to test the thing properly.


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## Mt Spokane Photography (Mar 4, 2018)

mistaspeedy said:


> I returned the 40mm F2.8 STM lens as a trade-in for some other piece of photography equipment (full price).
> 
> Since I have to upgrade both my camera body AND lens lineup, I took the plunge and went with a camera body.
> 
> ...



Printing out the star chart and testing your lenses is a good idea, or for ~$30, just buying a Zeiss Siemans Star Target to use whenever a lens is dropped or seems to have sharpness issues can come in handy.


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## mistaspeedy (Mar 5, 2018)

I will do some testing with my lenses to see how they perform. I suspect something with my Tamron. On a full frame sensor, any misalignment is going to show.

For now, I'm getting used to the 6D which feels just right for now.


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