Vario Tessar 16-70mm Decentered?

[shadowman]

I just bought a new sony vario tessar 16-70mm lens from eBay. After reading up on this lens, I became concerned about the amount of decentering issue with this lens.

I printed a B&H Photo test sheet and decided to do a couple of test shots. Mounted my camera on tripod, disabled OSS, and shot the sheet with widest aperture on self timer.

My heart sank when I saw that the upper left corner was very soft compared to the upper right which was sharp.

Is it acceptable or shall I exchange it? I read that pretty much there are no perfect lens. But this is an expensive lens and I was expecting a bit more.

Thanks and please pardon my noobness.

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[Pieter]

Do make sure to shoot the test chart with the camera axis exactly perpendicular to the chart. Based on the keystone shape of the chart, you didn't shoot it perpendicular. Otherwise the focal plane is not aligned with the test chart and you get inaccurate decentering results.

[Chrissie]

@Pieter: you beat my by 15 minutes on this answer ?. (I was still researching ...). But of course you're spot-on with your diagnosis.

The poster did not align the camera well enough to make the judgement he did. (Top-left corner of the test chart is significantly closer to the sensor than the bottom right one).

How to improve:

DXO have a very good description on this kind of measurement:

Quote

Before shooting, we ensure that the camera sensor and target planes are parallel by using a mirror placed flush against the target. Perfect alignment is achieved when the reflected image of the lens appears at the center of the camera viewfinder.

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Image source: DXO

Edited January 13, 2020 by Chrissie

[shadowman]

Thank you both on the suggestions. That mirror suggestion sounds awesome. The challenge is for me to find a free mirror of that size to use.

Perhaps I can use the bathroom wall mirror, then aim my camera. I can use a frame to trace an outline for the centering and then attach the test sheet in the outline.

 

[Chrissie]

16 hours ago, shadowman said:

I printed a B&H Photo test sheet

 

2 hours ago, shadowman said:

Perhaps I can use the bathroom wall mirror, then aim my camera. I can use a frame to trace an outline for the centering and then attach the test sheet in the outline.

In that case, be sure to align the test sheet flush to the mirror, by at least taping all edges of the sheet to the mirror. In your 1st attempt, there are some warps clearly visible at the left edge. Since you're investigating a possible de-centering, it will not be the center area that you're worrying about. So you might as well cut out the center part of the test sheet liberally, to avoid a two-step approach. If you go that way, I'd also tape the inner edges of the cutout to the mirror.

Good luck, and please do keep us posted on your further progress.