Time for some education. Why was it a tu142 and not a fighter jet that Russia send?
Because the objective is not to use fighter radar to map f35 but rather obtaining high resolution images of f35 flying from all kind of cameras ( thermal ,image , infrared , passive tv and many more ).
Basically map all the surface with all it's irregularities go back home make a model with similar irregularities and measure it against fighter radars.
Science is not so simple that a two bit lense can stop data gathering.
Think again why is USA afraid to field it side by side to s400? So much so that they kicked out turkey from production and forsake order of 100+ jets worth 10s of billions? That right there tells you just how effective lurenburg lens is. Lol. Ask critical questions before believing everything.
Oh man, if it's only photo of F-35s that Russians want tge don't need Tu-142. They just attend airshows take photos all they can from static displays and from aerial demos of F-35s. Theu can use all kinds of camera including IR.
But what will the Russians learn from it? Nothing. The most important thing in fighters especially the F-35, are their radar signatures and electronic emmissions. You won't get these data from pictures.
You cannot get the radar profile of F-35 simply by analyzing photos or making a 3D model out of these photos. The F-35 uses not only shaping to evade radar, it uses exotic skin coating, EW, decoys, etc. In the IR spectrum it uses elaborate fuselage cooling, exhaust IR mitigation, etc.
Re, S-400. It's not a real threat to F-35. Even F-16, SH and F-15s operating with Growlers, MALD swarm, JASSM or AARGM can defeat it. Mix in B-2, F-22 and F-35 the no AD system will survive a full on onslaught by US and NATO air forces.
The only reason US has been targetting S-400 is to disrupt Russia's strategic political msneuvers. USAF and the Israeli Air Force have been flying in and out of Syria where Russian S-400 is active. So, sorry to burst your bubble.