A77: why long lenses seem to be so out resolved?

Started 5 months ago | Discussions thread
VirtualMirage
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Re: A77: why long lenses seem to be so out resolved?
In reply to JimmyMelbourne, 5 months ago

I hate to say you are looking at it the wrong way, but you are.

You are claiming that long lenses on the A77 get out resolved when comparing to similar resolution sensors the competition uses, yet you are comparing different lenses. Apples and Oranges.

We will never know how a Sony 70-200 or 70-400 would perform on a Nikon or Canon, so you can't claim the issue is with the A77.  When you put the same lens on the lower resolution sensors, you don't see a dramatic increase in performance.  At best you will see equal performance and at worst poorer performance.  When a lower resolution sensor score the same with a lens as a higher resolution sensor, then you can conclude that the sensor is out resolving the lens and the lens is at its limitation.

You will be better off comparing the same lens across all sensors to get a better idea as to what to expect.  Unfortunately, it doesn't seem DxO accounts for possible poor manufacturing tolerances on lenses (a goody copy versus a bad copy).  One example of this is comparing the Sigma 24-70 across the Sony, Nikon, and Canon.  The Sony performs poorly compared to how it performs on Nikon and Canon, yet all three are identical lenses in design (same optical formula).  At the very least, you should see similar optical characteristics despite higher or lower resolutions.  An example would be corner sharpness and the transition from center to corner sharpness.

The Nikon and Sony sensors share the same crop, thus use the same portion of the lens, so they should exhibit similar characteristics.  When compared wide open, they don't in this respect.  The Canon is a tighter crop and users a smaller portion of the lens, 1.6x versus 1.5x.  So its characteristics should look like a slightly magnified version of the Nikon and Sony charts.  While it, too, varies a bit, it at least looks more similar to the Nikon in characteristics than the Sony does.  From all three, you could assume that the Nikon was using the best copy of the lens of the three, with the Canon taking a close second, and the Sony a distant third.  Even the vignetting isn't the same.  This is a sign that a copy that wasn't calibrated very well was used.

So to wrap it up, take the numbers with a grain of salt (especially when comparing different brands of lenses).  Manufacturing tolerances and the quality of the copy chosen can have an affect too.

P.S.

I would like to add that the Sony 70-400 doesn't perform as bad as you think against the competition.  The Nikon 80-400 scores about the same as it does.  Same goes for Canon's closest competing lens, the 100-400.

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Paul

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