Nikon Z 24-200 f/4-6.3 compared to Canon RF 70-200 f/4

Started 8 months ago | Discussions thread
peripheralfocus Veteran Member • Posts: 4,907
a little more on cross-system comparisons
3

starbase218 wrote:

You can’t compare across systems, even if the sensors are the same resolution.

It's true that all tests that are based on a captured digital image cannot be definitively compared from one system to another, and the same is true even within a single system if different cameras are used, for reasons shown in this thread. This includes all tests that are conducted with Imatest, which uses a captured digital image for analysis and thus is testing the whole imaging chain that was used (camera + lens + any software enhancements). Since the large majority of all current lens testing sites use an Imatest system, this means most lens tests on the Internet are not suitable for cross-system comparisons.

It's also true that you cannot definitively compare, across brands, the MTF charts that manufacturers publish for their lenses. These are not computed from a digital image, and theoretically refer to the lens only, but the methods used to calculate those MTF curves differ from company to company -- i.e. if Sigma took a Canon lens and computed its MTF using their process, they likely would produce a somewhat different result than Canon gets with their own process.

All that said, it is possible to measure lens MTF "in air" -- i.e. without using a camera or digital image -- and if that is done carefully using the same equipment and procedure, then you can get very solid comparisons from one system to another, if a sufficient number of samples is tested. Almost nobody does this. (LensRentals does a form of it, but even they are only testing at one focus distance, which is a significant limitation.)

Bottom line is that there are no definitively reliable lens tests publicly available (with the partial exception of LensRentals), so if you want to know what's really going on with a specific lens model, you have to read lots of tests and aggregate them into what is at best a tentative conclusion. I also place a lot of value in the subjective reports of people whose opinions I've found to be trustworthy. I just accept that there is no single number or test anywhere that gives me a completely reliable picture.

Ultimately, we have to make lens decisions based on imperfect knowledge, but that, of course, is something we humans are forced to do all the time.

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