[Klaus]

Impressive ...

http://www.opticallimits.com/fuji_x/783-fuji1855f284

... albeit somewhat decentered (again).

[frank]

I often hear the word "decentered". I wonder how boring a (moderately) decentered lens is in a real world? (I have no experience with a decentered lens---maybe I used a decentered lens but I didn't know.)



Frank

[Klaus]

[quote name='Frank' timestamp='1359972698' post='21746']

I often hear the word "decentered". I wonder how boring a (moderately) decentered lens is in a real world? (I have no experience with a decentered lens---maybe I used a decentered lens but I didn't know.)



Frank

[/quote]



Well, if so you're a happy camper.



Seriously there're three types of decentering effects:

- unsymmetrical sharpness distribution - this is also the case with the Fuji lens

- loss of contrast at large apertures

- a combination of both

[bherman01545]

Hello;



I recently registered on your site but have enjoyed the tests/reviews and the overall site in general for quite a while. I own a Fuji X-E! and several lenses - one of them being the Fujinon XF 18-55mm f/2.8-4 R LM OIS lens.



I followed your instructions on how to test for decentering etc. Opened the lens to maximum aperture, used a tripod, manual focus etc. and enlarged the image in Live View. The inner-most edges were uniform when in and out of focus, (so that's good, right?) After that is when I got confused.



You stated "if you want to do it correctly - do it with a tripod and taske a picture with Live View AF". Would I then expect the resulting image to be sharp? When I performed the test with Live View AF and viewed it on the screen at 100%, I saw what appeared to be some artifacts and CA on the edges.



It certainly looked better to me when manually focusing and enlarging the image under magnification using Live View on the LCD prior to taking the picture.



Am I missing something?



Thanks



Brad

[Klaus]

The comment with the tripod relates more to the idea of having a more controlled setup.

Lateral CA should not be visible in the image center. However, you may spot bokeh fringing in slightly defocused images which looks a similar except for the defocused base.

[bherman01545]

[quote name='Klaus' timestamp='1360097458' post='21802']

The comment with the tripod relates more to the idea of having a more controlled setup.

Lateral CA should not be visible in the image center. However, you may spot bokeh fringing in slightly defocused images which looks a similar except for the defocused base.

[/quote]



Thanks Klaus. So, I guess what I am asking is if the focus test is crisp and clear, do I have a good copy?





Brad

[Klaus]

[quote name='bherman01545' timestamp='1360097813' post='21803']

Thanks Klaus. So, I guess what I am asking is if the focus test is crisp and clear, do I have a good copy?





Brad

[/quote]



If the slightly defocused image is symmetrical the chances are good that the copy is fine. A slightly defocused image is actually a easier indicator than using a perfectly focused image.



However, you could still have an issue at the image sides.

Make it a 70% indication.



The tested Fuji was in the remaining rest. I did an immediate check after the purchase. However, I discovered the problem then later in the detailed analysis.



If you want to make sure do a classic "brick wall" test on top - also at max. aperture.

[frank]

Do other Fuji lenses (18mm, 35mm, 60mm) suffer decentering problems too?

[Klaus]

The first sample of the 35mm was decentered. The 2nd was fine.

The tested (...) 14mm sample was fine as well.

[bherman01545]

I just picked up a Zeiss Siemens Star Test Chart to check for lens focus and decentering. Well, I just ordered it. I'm assuming that it is just a piece of paper or thin cardboard, right? If so, can it be laminated in plastic without any effect on it's quality or use?

 

Thanks

 

Brad