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Possible Canon 55-250 IS STM Decentering Issue

Started May 25, 2016 | Discussions thread
photonius Veteran Member • Posts: 6,895
Re: Possible Canon 55-250 IS STM Decentering Issue

skogsfaktor wrote:

So, i recently bought a new lens for my 7D, the Canon 55-250 IS STM. Since i am a bit pedantic with my equipment, i have been testing the lens all night. However, i have had a bit of a problem with determining if my lens has misaligned optics.

To test the issue i took a handheld photo of a nearby apartment building wall at a distance from my balcony(since i do not own a tripod). The photos were taken using a 250mm focal length, aperture of f/5.6(which is the largest), AV mode, spot AF(PDAF) and the center AF point. The camera was probably not parallel to the wall.

The photos below show the entire image and crops(not uniform) from all 4 corners, top to bottom, left to right.

The problem is that i don't know how to interpret the data. What is an acceptable difference in sharpness between the corners? It is evident that the top of the frame exhibits more chromatic aberration, with the left corner being the worst in terms of sharpness and CA. Is this difference just the result of the conditions in which the photograph was taken, or could it be that the lens has a decentering issue? Could/Would an exchanged lens perform better optically? Does this make a difference in real life shooting?

Any conclusions, tips or opinions would be of great help to me.

Looks quite ok. Serious decentering would look worse.

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