[Brightcolours]

I give up. If everybody here is so sure about equivalent focus length and real focal length are the same, there's not much of a point discussing it. To me it remains different things.

You need to understand that the testing target remains the same size, and needs to fill the frame in a particular manner (the corner target needs to be in the corner, the border target in the border and the center target in the center). The test targets are about lines/line pairs per image height.

This makes that for 135 format "full frame" one shoots at a shorter distance to the test targets than with 1.6x crop APS-C, for instance, with the same focal length. 

 

So, for the MTF tests, equivalent focal lengths are which dictate the testing distance. I believe that the MTF targets used are designed for 51x the focal length for 135 format (35mm film photo format). So if one were to test a 6x9 MF camera + lens with these targets, one would use a 2.4x (crop factor compared to FF) shorter distance with the same focal length than "full frame" 135 format.

 

I have some old test targets which were designed for 101x the focal length distance, which would mean an even bigger required test distance, especially with APS-C or MFT.

And Markus, allow me to reply, Klaus was writing about nothing else than 200-500. NOT THE SAME AS 600mm, in no case. I don't know which lenses he checked in the past, I was just looking at the Canon section of PZ.

Again, Klaus meant that he had tested longer lenses (meaning: lenses with a longer focal length than PZ does now) before. He did not mean longer than this particular Tamron. Due to the current testing "facilities", it is difficult or impossible for the PZ members to test 600mm, let alone 600mm on APS-C, due to the required shooting distance.

 

By the way, the test target design has another limitation: one can not test lens resolution for a lens at different distances. So, wide angle lenses can't be MTF tested for infinity (which gives at times some skewed results, like with the Voigtländer 20mm f3.5 SL II for instance), and one can not test at macro distances so the MTF tests for macro lenses show how they perform as portrait lens and not as macro lens. And for instance, lenses like my Ultra Micro Nikkor 55mm f2 and the Canon MP-E 65mm f2.8 can't be tested at all.